Enclosure for protecting contents from external humidity

(54) Title: METHOD FOR SELECTING ONE (57) Summary:

RESIN-SORBED COMPOSITION,

MANUFACTURING ARTICLE, AND, MULTIPLE LAYER BARRIER STRUCTURE (30) Unionist Priority: 3/29/2007 us 60/908841, 3/30/2007 US 60/909247 (73) Holder (s): Multisorb Technologies, Inc.

(72) Inventor (s): Samuel A. Incorvia, Stanislav E. Solovyov, Thomas Powers (74) Attorney (s): Momsen, Leonardos & CIA.

(86) International Order: pct us2008004055 of 03/28/2008 (87) International Publication: wo 2008 / i2i32ide 09/10/2008

<img file="BRPI0809503A2_D0001.tif" />

"METHOD FOR SELECTING A SINK COMPOSITION CONNECTED TO RESIN, MANUFACTURING ARTICLE, AND, MULTIPLE LAYER BARRIER STRUCTURE"

FIELD OF THE INVENTION

The invention largely relates to packaging materials, more specifically to composite adsorptive barriers for packaging applications, and even more particularly to a method for selecting the materials and composition of them for adsorptive composite barriers for packaging applications.

BACKGROUND OF THE INVENTION

Polymer-based composites loaded with inorganic particulates have long been used to improve the mechanical properties of thermoplastic and thermoset polymers. Composites loaded with moisture absorbers have also been proposed for the purpose of preparing desiccant coatings and other internal parts of thermoplastic containers and controlling moisture in such containers, for example, United States patent No. 6,130,263. Multiple applications in the packaging of electronic, automotive, pharmaceutical, diagnostic and food products require very low humidity levels within the packaging or encapsulated enclosed area to protect moisture sensitive products or components from exposure to environmental humidity. Progressively, automotive electronics and electronics change with the use of metal mold foundations for casings and components for the use of thermoplastics. This transition is fueled by the need to reduce weight and cost in an ever-increasing competitive environment. As a result of the rapid pace of development of these applications, the process of selecting thermoplastic resins often does not take into account the water vapor transport properties of such resins that directly impact the service life of components or devices.

In conjunction with this trend is the miniaturization of components or devices that leave little or no space for bounded sorbents that result in inadequate or no protection from moisture whatsoever. Currently, the selection and use of thermoplastics that have the best passive moisture barrier characteristics often do not achieve the objective of providing protection from ingress of moisture during the desired service life of the component or device. To date, delimited areas of this type have essentially failed to achieve the objective of providing sufficient performance in terms of preventing the ingress of moisture.

Several US patents focus on improving moisture transport in the desiccant-loaded composite in order to accelerate the desiccant effect of such composites by quickly removing moisture from inside the package, especially when used as an interior part of the container. See, for example, United States patents Nos. 5,911,937; 6,130,263; 6,194,079; and 6,214,255. The devices are unsuitable for many of the described needs, as they do not work to prevent moisture ingress, but merely absorb moisture after it has entered an enclosed area during packaging operations, during the service life of a device or after opening the resealable containers.

Since all plastic materials are permeable to atmospheric gases and water vapor, plastics are unable to provide a moisture-free environment within any packaging or enclosed area made from it for significant periods of time. Until now, the control of permeated moisture, that is, moisture that has already entered a defined area, has been the main motivation for developing composites that absorb moisture. An alternative approach to removing moisture that has already permeated a package is to improve the moisture barrier properties of the polymeric packaging material itself. The dispersion of a water absorber in a thermoplastic polymer resin allows the creation of a composite that acts as an active barrier for permeation of water vapor. Active barriers intercept and remove moisture that diffuses through the barrier by physical and / or chemical means. Such barriers allow the reduction or complete elimination of moisture permeation in the packaging for significant durations of time. See, for example, United States patent applications Nos. 11 / 040,471; 11 / 335,108; and 11 / 635,750, whose applications are incorporated herein by reference in their entirety.

In composite barriers filled with moisture-adsorbing additives, the sorbent additives distributed in the polymeric matrix can cause a significant delay, known in technology as a diffusive delay time of a barrier layer, before moisture begins to penetrate a package, which it is often several orders of magnitude greater than the delay observed in barriers made of pure resins. Although the calculation of the delay time for pure resins and composite resin / sorbent barriers is described in the DETAILED DESCRIPTION OF THE INVENTION below, it should be understood that these shells are well known in the art. These delay time calculations were used as a determinant of the failure of the bounded area. In other words, once the delay time is reached, it is assumed that the enclosed area did not work, since it is assumed that the unimpeded moisture permeation crosses the barrier to continue thereafter. On the contrary, it has been observed that this assumption is incorrect for certain types of sorbent materials and barrier compositions. For example, for a period of time after the delay time has been reached, an enclosed area can be kept below a relative humidity of 10-50% and, as long as the contents of the enclosed area are not deteriorated and / or damaged by such relative humidity levels, the enclosed area has not merely failed to achieve the delay time. Thus, it is advantageous to understand how a delimited area works after reaching the delay time.

As they can be derived from the variety of devices and methods aimed at producing moisture-adsorbing polymers used both to provide an active barrier and to absorb existing moisture from a defined area, many means have been contemplated to achieve the desired purpose, that is, protection of a component sensitive to moisture from degradation, thus extending the component's service life. So far, choices between material selection and mixing ratios have been required and, as described, such determinations have been made without fully understanding their effects. Thus, there is a longstanding need for a method for selecting polymer resins, sorbents and mixing ratios to achieve specific designs and performance targets. There is still a longstanding need for a medium to accurately predict the effects of the polymer resin, sorbent and mixing ratio of these selections. In view of the foregoing, the present invention allows for better moisture barrier properties of packaging articles rather than merely understanding its moisture sorption rate. In addition, the moisture barrier of the present invention provides effective barrier characteristics at the point of ingress of moisture, thereby preventing or minimizing moisture permeation, rather than providing the removal of moisture after it reaches the interior of a defined area.

SUMMARY OF THE INVENTION

The present invention broadly comprises a method for selecting a sorbent composition bound to the appropriate resin that can be used at least to prepare, in part, a bounded area to protect contents from external moisture, wherein the bounded area has an internal top volume V , a thickness L and a surface area A, the enclosed area surrounded by an environment having an external relative humidity h_safd_The which is a fraction of a saturated water vapor density p_sat in an air at temperature T, the internal volume having a maximum internal relative humidity which means an end point of moisture barrier protection, the method comprising the steps of: a) selecting a plurality of resins, a plurality of particulate sorbents and a plurality of reasons between them to form a plurality of composites and a plurality of composite layer thickness, wherein each resin of the plurality of resins has a vapor diffusivity of effective water D_m and a water vapor solubility coefficient S_m, and each composite of the plurality of composites has a volume fraction of the resin φ_ιη and a fraction of volume of the cp sorbent_d ; b) calculating a plurality of failure times for the plurality of composites and the plurality of composite layers, where each failure time of the plurality of failure times is based on when an internal relative humidity h_eneach composite of the plurality of composites is equal to the maximum internal relative humidity; c) determine which of the plurality of failure times is greater; and, d) selecting a composite from the plurality of composites and a thickness of the composite layer based on the result of step (c). It was also understood that the thickness range of a composite layer comprising a bounded area is often affected by other design considerations of the bounded area, for example, mechanical and electrical properties, weight, material and manufacturing costs. In this way, the selection of an ideal composite in step (d) can be made to satisfy the wall thickness restriction of the specific delimited area.

In some embodiments, each particulate sorbent of the plurality of particulate sorbents is stoichiometric and irreversible with respect to the amount of water vapor absorbed and each composite of the plurality of composites has a stoichiometric coefficient μ, an initial mass concentration Ro and a concentration C_output of water vapor dissolved on an external surface of the bounded area or a composite layer, the evolution of the internal relative humidity after a delay time t_LR is calculated according to the equation:

^ input (0 = output

- exp / λ &lt;í&gt;_ms_ms_mAtt

LR

L (p_satV + - &lt;f&gt;_ms_mAL

A * where:

t is a time to reach the internal relative humidity h_m; and,

ÍLRt is the delay time of the area delimited with the thickness L. In these modalities, the delay time is calculated according to the equation:

Z.² = - (1 + 3Ψ) m

in which exit

Although in other embodiments, each particulate sorbent of the plurality of particulate sorbents is reversible with respect to water vapor adsorption and has a water vapor sorption isotherm, said water vapor isotherm is linear having a vapor solubility coefficient constant water S_d and a pseudo stoichiometric coefficient μ that describes the amount of water adsorbed in maximum equilibrium per unit weight of sorbent in contact with saturated water vapor, and each composite of the plurality of composites has an initial mass concentration R &lt;&gt; of said sorbent and a C concentration_sawater vapor dissolved on an external surface, the evolution of the internal relative humidity after a delay time t_LL is calculated according to the equation:

rv ^ inbound outbound - exp

Φ_ηΑ_η2_ίηΑ (ί - t_LL)

up „v + F„ al

2. 7 where: t is a time to reach the internal relative humidity “inlet t_LL is the delay time of the bounded area having the thickness L; and,

Sef = 0_ms_m+ 0_ds_d

In these modalities, the delay time is calculated according to the equation:

jjt_LL = - (ΐ + ΨΛ ^

6£&gt;

m where:

ψ_ c

exit

In still other modalities, each particulate sorbent of the plurality of particulate sorbents has a water vapor sorption isotherm, the water vapor sorption isotherm is a double sorption mode with a gap saturation constant C_max, a Langmuir affinity constant b, and the internal volume has an initial internal relative humidity h_andntrada, o&gt; ^The evolution of internal relative humidity after a delay time t_Ln is calculated according to the equation:

Ln ^ Entry β ajl + bh ^)

In 1 ^ Entry \ + bh ^linput _tQ

I_n ^ output h - h input input - ln (l + Z&gt; A) l + bh ^Thei^The-j ⁺ I_n Latda Enter, where:

t is a time to reach the internal relative humidity h_entrada;

t_LD is the delay time of the bounded area having the thickness L; ^βι = ^^çmaxà;

^ατ.

AL ^The4 = Psa,^V ; ^and&gt;

T m mm

In these modalities, the delay time is calculated according to the equation:

t

LD ~

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<img file="BRPI0809503A2_D0003.tif" />

V

D² + ^ - (l + y) ln (l + n 9_ms_my L2 where:

y = bh_output.

In still other embodiments, the sorbent composition bound to the resin is formed with the help of a copulating agent or a compatibilizing agent, wherein the copulating agent or compatibilizing agent is chemically compatible with each resin of the plurality of resins and improves adhesion or copulation of the sorbent particles with each resin from the plurality of resins. In some of these modalities, the copulating or compatibilizing agent is selected from the group consisting of reactive and non-reactive agents, while in some of these modalities, the compatibilizing agent is selected from the group consisting of a metal, a metal oxide, a acrylate, stearate, block copolymer, maleate, epoxy, silane, titanate, organometallic binder and mixtures thereof. In still other modalities, the resin-bound sorbent composition is composed of a twin screw extruder.

The present invention broadly comprises an article of manufacture constructed of a resin-bound sorbent composition, wherein the resin-bound sorbent composition is made according to the method described above. In some embodiments, the resin-bound sorbent composition includes from about two weight percent (2 weight%) to about fifty five weight weight (55% weight) sorbent and about forty five weight percent (45% by weight) to about ninety-eight percent by weight (98% by weight) of resin, while in other modalities, the resin-bound sorbent composition includes from about twenty-five percent by weight (25% by weight) to about fifty-five percent by weight (55% by weight) sorbent and about forty-five percent by weight (45% by weight) to about seventy-five percent by weight (75% by weight) of resin, and still in other modalities, the sorbent composition bound to the resin includes from about thirty-five percent by weight (35% by weight) to about forty-two percent by weight (42% by weight) sorbent and about fifty-eight percent by weight (58 % by weight) to about sixty-five weight percent (65% by weight) of resin. In still other embodiments, the resin-bound sorbent composition includes a resin and a particulate sorbent and essentially all particles of the particulate sorbent are separated by the resin matrix.

The present invention also broadly comprises a multilayer barrier structure having at least one layer, wherein at least one layer includes a resin sorbent composition made according to the method described above.

It is a general objective of the present invention to provide a method for selecting the resin, sorbent and ratio between them for the construction of an active sorbent barrier bound to the resin.

It is another general objective of the present invention to maximize the useful life of a defined area based on the characteristics of the active barrier of the defined area and the requirements of the contents included in it.

These and other objectives and advantages of the present invention will be readily apparent from the following description of the preferred embodiments of the invention and the accompanying drawings and claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The nature and mode of operation of the present invention will now be more fully described in the following detailed description of the invention with the figures in the accompanying drawings, in which:

Figure 1 is a graph of a water vapor pressure profile in a passive membrane for reference permeation conditions (solid line) and steady state conditions (dotted line);

Figure 2 is a graph of a reference time delay on a passive membrane;

Figure 3 is a graph of water vapor isotherms typical of molecular sieve and silica gel;

Figure 4 is a graph of model forms of water sorption isotherms;

Figure 5A is a graph of water sorption isotherms for polypropylene and various sorbent materials;

Figure 5B is a graph of permeation dynamics through a composite barrier comprising polypropylene resin and various sorbent materials;

Figure 6A is a graph of water sorption isotherms for high density polyethylene and various sorbent materials;

Figure 6B is a graph of permeation dynamics through a composite barrier comprising high density polyethylene resin and various sorbent materials;

Figure 7A is a graph of water sorption isotherms for polyethylene terephthalate and various sorbent materials;

Figure 7B is a graph of permeation dynamics through a composite barrier comprising polyethylene terephthalate resin and various sorbent materials;

Figure 8 A is a graph of water sorption isotherms for nylon and various sorbent materials;

Figure 8B is a graph of permeation dynamics through a composite barrier comprising nylon resin and various sorbent materials; and

Figure 9 is a cross-sectional view of a typical resin sorbent composite formed according to the method of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

In the beginning, it should be noted that equal numbers of the drawing in the different views of the drawing identify identical, or functionally similar, structural elements of the invention. Although the present invention is described with respect to what is currently considered to be the preferred aspect, it is understood that the claimed invention is not limited to the aspects described.

Furthermore, it is understood that this invention is not limited to the particular methodology, materials and modifications described and as such can certainly vary. It is also understood that the terminology used here is for the purpose of describing particular aspects only and is not intended to limit the scope of the present invention, which is limited only by the appended claims.

Unless otherwise defined, all technical and scientific terms used herein have the meaning commonly understood by one versed in the technology to which this invention belongs. It should be noted that the term "delimited area" is synonymous with terms such as "packaging", "container", etc., and such terms can be used regardless of the form that appears in the specification and claims. Although any methods, devices or materials similar or equivalent to those described herein can be used in the practice or testing of the invention, the preferred methods, devices, and materials are now described.

Unlike closed desiccants and internal desiccant layers designed for rapid removal of trapped moisture within a package / area enclosed after sealing, as described above, the desiccant barrier composites of the present invention are designed to primarily prevent moisture permeation through of the packaging article, that is, the defined area, for the longest possible period of time. The removal of moisture from the inner packaging is also observed during the use of such barrier structures, although the rate of such removal can be quite slow, and the improvement of the sorption rate within the enclosed area does not form a part of the present invention. In order to reduce the moisture permeation rate through a polymer based composite packaging / bounded area, for example, a bounded resin sorbent bounded area, and delaying the achievement of a steady state permeation pattern across the thickness of the barrier wall, the present invention uses the method described below to select composite materials, ratios between them and charge incorporation procedures.

As described above, polymeric composites loaded with moisture adsorptive loads can serve as effective long-term moisture barriers in packaging applications. The transient performance of such barriers is described in terms of diffusive delay time and effective transient permeation rates in an environment contained after the delay time. Although the calculation of diffusive delay times is well known in the technology, the determination of effective transient permeation rates has so far not been completed. Analytical results for irreversible stoichiometric absorbers, as well as Fickian-mode (linear) and double water sorption isotherms of polymer matrices and fillers are described hereafter and serve as a model for transient permeation and moisture-increasing kinetics data inside a sealed package. Critical composite barrier design features and ways to improve the performance of the transient barrier are also discussed here.

The performance of polymeric barriers permeable to gas and water vapor permeation is routinely characterized by transport properties of two stable states: the steady state transmission rate (permeability), TR^SS , and the reference delay time tL. TR^SS is the permeation flow through a unit A barrier area normalized to the Ap gas pressure difference in separate environments. The flow rate of water vapor permeation is expressed in units of mois per square meter per second (mol / (ms) or grams per square meter per second (g / (ms)), although the flow rate of gas permeants is expressed in units of millis per square meter per second per Pascals (mol / (m² s Pa)) or in units of cubic centimeters at standard temperature and pressure per square meters per second per Pascals (cm (STP) / (ms Pa)). Alternatively, for water vapor transport, permeability is often expressed in units of grams per square meter per day by difference in relative humidity (g / (m day AUR)), in a difference in temperature and specific relative humidity (AUR ), that is, the difference in relative humidity on the opposite sides of the barrier membrane was maintained at the same fixed temperature. The time delay can be determined as a response time to a sudden change in external relative humidity for any initial conditions on the membrane or, in other words, an asymptomatic delay before establishing a steady state permeation flow pattern. The reference delay time of the degassed barrier membrane initially with water vapor pressure downstream maintained at zero is commonly reported as the delay heat in time tL. (See figure 1). As shown in figure 1, an initial reference water vapor pressure profile is presented for a passive membrane by the solid line and for a steady state permeation condition by the dotted line.

It should be noted that after the delay in time the relative humidity in the contained environment will increase continuously, eventually reaching equilibrium with the external environment. Since the temperature in the external environment can vary with the season and during cycles of day14 at night, there is always a potential for condensation of water vapor within the volume contained by a drop in temperature. As described above, condensation can cause corrosion of encapsulated electronic components, shortening of electronic circuits and other undesirable effects. A desiccant polymeric structure selected and / or optimized in accordance with the present invention acts as a long-term barrier to moisture permeation and thus dramatically increases the service life of a packaged device.

As previously presented, the present invention comprises several steps to determine and select the polymer resin, sorbent material and ideal ratio. First, non-intumescent polymeric barriers were discussed, that is, examples of resins that do not allow water condensation in the matrix and that can be considered with the present invention. Although the polymer barriers do not include sorbent material, the barriers still absorb moisture in the manner described below. In the following embodiments, a uniformly thick solid polymer barrier membrane is considered. Bonding conditions on an inner membrane surface, that is, inside a package, are fixed at a relative humidity h_enand an outer membrane surface, that is, outside the packaging, is fixed at a relative humidity h_leavesd_The. It should be noted that h_input is equivalent to the ratio of the density of water vapor inside the package at temperature T, that is, p_m, and the density of saturated water vapor at temperature T, that is, p_sat, while h_exit is equivalent to the ratio between the water vapor density outside the packaging at temperature T, that is, p_saída&gt; e Psai- Additionally, each membrane corresponds to a fixed partial pressure of water vapor of p_enep track_sarespectively with respect to a saturated water vapor pressure p_salt at a specified temperature T.

(χ 100%) «- (x100%) // &lt;« V) Psat V '(1) exit (T) =

Psatd) ^ (O (x 100%) (2)

Subsequently, temperature-dependent saturation vapor density p_sai (T) is used to determine the amount of water m_m in the package having an internal top volume V.

m_ent_frogh-input Psat V (3)

It should be noted that the internal top volume V means any volume in a package or enclosed area that is not filled with components, materials or any objects contained in the package.

Analogous to a solubility coefficient S of non-condensing gases in polymers, the water vapor solubility coefficient S_min polymeric matrices can be expressed as a mass m_w of water dissolved in a polymer per unit volume V_ena dry polymer matrix (initially neglecting the swelling of hydrophilic polymers) at an external relative humidity (RH) of 100% at a given temperature T. The water vapor solubility coefficient S_m is expressed in units of grams per cubic meter by a relative humidity of one hundred percent (g / (m³ (100% RH)).

S (T) = - * V_m \ QWoUR (4)

So the C concentration_m of water dissolved in a non-intumescent polymer matrix with Fickian sorption (linear), in equilibrium with the external humidity h_leavesd_The (T), is linearly proportional to the external humidity h_output . The C concentration_m is expressed in units of grams per cubic meter (g / m).

Ç_m (H_sai_gives) S_mH_exit (5)

Alternatively, the amount of water dissolved in a non-swelling polymer matrix can be calculated on a weight gain basis W_ent_frogin a polymer matrix having a specific gravity p_m. Weight gain base W_thenis expressed in units of grams of water per gram of polymer (g (water) / g (polymer)).

ψ _ exit β}

P_m

Using water vapor diffusivity D_{goes into}of (T) in the polymer matrix given in square meters per second (m / s), the water vapor permeability P_m (T) of the polymer can be calculated. The permeability of water vapor P_m (T) is expressed in units of millimeters of gram per square meter per second for a relative humidity of one hundred percent ((g 'mm) / (m²* s' 100 ° / oUR)).

P_m= D_ms_m (7)

In equation (7) above, 100% RH refers to the difference in relative humidity AUR on opposite sides of the permeation barrier, that is, 100% RH at the outer interface and 0% RH at the inner interface. This difference in relative humidity serves as a driving force for diffusing water vapor through the barrier.

The rate of transmission of steady-state water vapor WVTR through a unit area of ​​the barrier with a uniform thickness L in a water vapor pressure difference unit Δρ (Τ), corresponding to the 100% relative humidity difference , is expressed in equation (8) below. The WVTR water vapor transmission rate is expressed in units of grams per square meter per second for a relative humidity of one hundred percent (g / (m² 's' 100% UR)) WVTR (T) =

P_m(T) _ D_ms_m (8) ss

The steady-state material flow J_O of water vapor through a unit area of ​​the barrier with a uniform thickness L and a difference in relative humidity Ah through it is expressed in equation oo (9) below, steady state material flow J_O is expressed in units of grams per square meter per second (g / (m² ' s)).

- Jf (T, ΔΑ) = ΔΑ = ^D”^s”^Ah (9)

The water vapor concentration in the C balance_m in the material can potentially depend non-linearly on the vapor pressure in the adjacent gas phase through a non-linear sorption isotherm C_m (p) or at a relative humidity h at a fixed temperature such as C_m (H). This sorption behavior is discussed earlier.

The reference delay time t_L refers to the asymptomatic delay before the steady state solute concentration profile C^SS(Q is established on a membrane initially degassed with a downstream water vapor pressure kept at zero, that is, input = 0. An example of the reference time delay for a passive polymeric membrane with linear sorption is shown in figure 2.

For arbitrary initial condition &lt;3ο (ξ) = C (Ç, t = 0) for the concentration of the solute through the thickness of the membrane L with dimensionless coordinate ξ - x / L = [0., 1] through the thickness and the Fixed connection conditions Centered ⁼ C (0) = 0 and exhaustion ⁼ C (l)&gt; 0 on the inner surface and the outer surface connections, respectively, the delay time is obtained, for example, using the Frisch method. Frisch HL, J Phys. Chem. 61, 93-95 (1957). The delay time tL calculated according to Frisch is described in equation (10) below.

», = 7 ^ - (ío) exit 0

In equation (10), D_input, is the diffusivity coefficient of the permeant in the barrier material and the origin of the x coordinate is located on the inner surface of the membrane (see figure 1). For the membrane initially degassed with C_O (ξ) = 0 and Fickian sorption with S_m, = const, the steady state vapor concentration in the membrane is calculated according to equation (11)

C »fe) = ic ^, = (11)

The integration equation (10) in view of equation (11) yields equation (12), thus resulting in the delay in the reference time t_L.

⁽¹²⁾

For homogeneous barrier material, it does not matter whether the concentration of the solute in the material is expressed in grams per cubic centimeters (g / cm³) or as a weight gained in grams per gram (g / g), since these properties are linearly related to each other through the density of the polymer matrix p_m according to equations (5) and (6) above, and cancel each other out.

After the time delay, that is, t_L , the weight gain of water vapor (m_entrada) ^ηθ volume contained V is accompanied by the steam gain (m_B) in the polymer matrix of the barrier. Thus, the weight gain of water vapor in the contained volume is calculated according to equation (13).

= (13) dt dt

Alternatively, water vapor weight gain can be calculated using equations (3) and (9) above. Thus, the weight gain of water vapor can be determined using equation (14).

τ / dh_entrac]_The _ _mA, \ 1 ç »AT dhenlrada

CT, ~ _r output ⁿ entryJ

j. τ v òaiua cmraaa / &lt;-&gt; m ί.

dt L 2 dt (14)

The Vi coefficient in equation (14) appears due to the outside humidity h_output be fixed while h_enthat is, the humidity in the defined area, is evolving. Rearranging equation (14) gives equation (15).

TZ I 1 Ο A r I ^ h_{goes into}da f / m S m A (jf

P ^₊-S.AL = ¹ exit '^ entry, (15)

The result of integrating equation (15) is equation (16).

f Λ ^ entry '(0 = h_exit - ΔΑ₀ exp £ | Psa7 + ^ S_mAL t

(16)

In view of the previous equations, for an initially dry contained environment with h_entread (θ) ⁼ θ, that is, the volume in the bounded area, the evolution of relative humidity within the approximate by equation (17).

bounded area or packaging is

0, for / &lt;t_L , (') = - exp

V + Is_mAL 2 for t&gt; i_L (17)

In summary, during the time period before reaching the delay time t_L there is no moisture in the enclosed area, while during the time period after the delay time t_L the evolution of humidity in the defined area is reached and calculated according to the second equation in (17).

Then, composite barriers, that is, barriers comprising both resin and sorbent, were discussed. When a membrane contains a dispersed particulate additive that can absorb the diffusion permeant, three different situations are possible: (1) the additive catalytically removes the unlimited amount of permeant (reacting with it and consuming it or converting it into other species without depletion of the additive's absorption capacity); (2) the additive irreversibly absorbs the permeant to a certain stoichiometric amount (usually chemical reaction or chemosorption); or, (3) the additive reversibly immobilizes the permeant by means of physical adsorption. The performance of the catalytically reactive and reactive stoichiometric barriers, that is, the performance through the delay time, was analyzed elsewhere. Siegel RA and Cussler EX., J Membr. Know. 229, 3341 (2004). and Solovyov SE, J. Phys. Chem. B 108, 15618-15630 (2004). The time delay in the barriers containing reversible adsorptive loads (desiccants in the case of water vapor) was obtained by double-sorption isotherms commonly observed from such adsorbents dispersed in a polymer matrix with Fickian (linear) sorption. Paul DR and Kemp DR,

J Polim. ScL, Symp. 41, 79-93 (1973). The present invention allows the prediction and optimization of the performance of such composite barriers after the time delay when the vapor permeation increases the vapor pressure in the contained environment downstream, that is, the environment in a defined area.

Water vapor cannot be removed catalytically under conditions close to the environment, that is, no known additives can irreversibly remove an unlimited amount of water vapor, thus, only irreversible and reversible linear stoichiometric sorption adsorbents dispersed in the matrices polymeric as fine particulates (powders) are considered here.

First, irreversible stoichiometric absorbers are considered. The commonly observed double sorption behavior can give rise to two distinct sorption patterns: (1) rapid saturation at low RH values ​​and (2) quasi-linear sorption over a wider range of UR (gap filling process) ) followed by asymptomatic saturation (common dissolution in the matrix). The former is represented by molecular sieves (MS) that occur synthetically and naturally, and the latter by silica gel (SG) desiccants, as shown in figure 3. The permeation dynamics with MS sorption isotherm are closely approximated by irreversible stoichiometric chemical reaction that removes a predetermined amount of water before being deactivated, that is, DM saturation approximately above 20% RH. This characteristic is shown in figure 4 as a stoichiometric absorbent. This aspect is especially relevant when the driving force for diffusion is represented by a fixed external UR, which is much greater than the saturation point MS and a zero percent UR downstream, that is, a zero percent UR in the bounded area .

The reference delay time t_LR in the permeation barriers containing a chemically irreversible reactive absorber of diffusion gases and vapors with an initial mass concentration profile Ro (ξ) through the thickness of the barrier L and a stoichiometric coefficient μ in grams of water per gram of absorbent (g / g) is found as a sum of the reference delay time t, the matrix polymer barrier and the steady state delay time t_R due to the stoichiometric reaction of the solute with the dispersed additive. Siegel RA and Cussler EL, J Membr. Know. 229, 33-41 (2004). The reference delay time t_LR is described by equation (18).

= &lt;L + '«

67) DC_{exit 0}^J_(lg)

For uniform reactive additive loading across the thickness of the Ro barrier (ξ) = const, the expression for the delay time is simplified for equation (19).

L² L²

--H '

6D μΚ L²

2D C_out! 6D (1 + 3Ψ) (19)

The dimensionless Ψ complex is called the relative reactive capacity of the barrier material and is described by equation (20).

(20) exit

For polymers with Fickian sorption, the water concentration in the upstream membrane bond, that is, the outer surface of the bounded area, can be expressed by means of the constant solubility coefficient S_m as in equation (5).

For desiccant adsorbent with volume fraction &lt;p_d and the apparent particle density p_d dispersed in a polymer matrix with the volume fraction (p_m and the density p_m , where (p_d + q&gt;_m = 1, the concentration of desiccant mass in the uniformly filled composite material having a volume V_ç is described by equation (21).

R, = = &lt;fbPu (21)

A modified form of equation (11) takes into account the fact that the solubility of water vapor in both the matrix and in the dispersed irreversible absorbent contributes to the concentration of the water mass at steady state in the composite material. Equation (22) is the modified form of equation (11).

(22)

Wj is the saturation capacity of stoichiometric desiccant type MS, that is, the weight of water adsorbed per unit weight of desiccant pe_d is the apparent density of a desiccant particle, that is, the mass of the desiccant particle divided by the volume excluded by the particle in a polymer matrix. However, water immobilized in the adsorbent does not contribute to steady-state flow. For the reference conditions, the time delay is calculated according to equation (23).

L²

Gr

Φηι mm rm m output oj (l = _n . 5, —J (1 - ξίΦΧΚΧί + wXpM^DffPm^sm^Hs_aida o (23)

L² Φ_ά W_dPd 'Z &amp; m Φγη S output 6ída) (1 + 3Ψ)

Equation (23) is a mass fraction equivalent of the result of equation (20); however, in this example, Ψ is described by equation (24).

P _ P ^ o _ Φα W_dPd (24)

B mP output Φαί aposaida

If q&gt; d is the volume fraction of adsorbent, that is, desiccant, loaded in the polymeric matrix, and f &lt;j is the weight fraction of the adsorbent, then these fractions can be interconverted according to equations (25) and (26 ).

&lt;t&gt; d = - / - (25)

Λ + - (ΐ-Λ)

Λ = - (26) ^ + Υΐ- ^)

Pd

If a perfect depression exists in the downstream membrane after the delay time, then the rate of incoming solute is proportional to the permeability TR^SS of inactivated composite material with effective diffusivity D_ç and solubility coefficient S_ç- The effective flow J_O represents the rate of permeation of the solute through the membrane connection downstream. It should be noted that a “perfect depression” means that the downstream membrane, or in other words, the volume in the bounded area, is maintained at zero percent (0%) RH, including during periods of moisture ingress through the material barrier.

- Λ (0 = TR ^SS (P_exit - P_input (0) = {p exit - Pentrado (O) (27)

Equation (27) assumes that the internal pressure p_m it changes slowly and the pseudo-stable state flow is established through the barrier. This is usually the case for enclosed packaging areas that encapsulate a total volume much larger than the volume of packaging material used, which is a standard design objective for any packaging. When the adsorbent is impermeable to water vapor, that is, it does not act as a water diffusion path and the adsorbent does not significantly affect the mobility of the water molecule in the matrix, so equation (27) is modified to become equation ( 28).

-j {t) ^^mD^Sm{H_exit-H_enirada(tj) (28)

Using equations (23) and (28), and taking into account the reduced volume fraction of the polymer matrix available for diffusion, due to the presence of adsorbent particles, the evolution of moisture inside the package, that is, the enclosed area, is expressed by equation (29).

entry (0 = (29) - exp

P &lt;tAAL&gt; to t&gt; t_LR

In summary, during the time period before reaching the delay time t_LR there is no humidity in the enclosed area, whereas during the time period after the delay time ile is reached, the humidity in the enclosed area is calculated according to the second equation in (29).

For RH levels below desiccant saturation humidity h_sai, the desiccant sorption isotherm is often linear: Cd {h &lt;h_salt) = Sjh, and the previous saturation vapor pressure p_sai of the internal surface of the desiccant are close to being saturated and the Fickian dissolution is often insignificant: Cd (h&gt; h_leaves) ~ Sdh_salt = const. These sorption modes are analyzed and discussed above.

Below the desiccant saturation vapor pressure, the effective solubility coefficient of the composite material can be defined on a volumetric concentration basis and is calculated according to equations (30) and (31).

Ç_ç = S_eJh (30)

s_andf - φπ4, η Ί^- φΑΕ ^ ρ ^ (31)

Referência reference delay time t_LL in a composite barrier having a linearly dispersed adsorbent in it is calculated according to equation (32).

(32) h_L= -Aj (id^ç'^sç)-^ço0) k =

DáSh nt · mmsr I? Φ S +4&gt;, S. r, ί O - ξ) ξ · S_efH_s^ ”/ -— [(ξ-ξ²) άξ ³ D_ φ ^ ^Jo ^ J&gt; nm sfridsi Q _Τ²ίφ ^ Ύξ² ^³VL² r L · &amp; Λ «A ³J₀^6ZA ^ aJ 6ώΛ φ ^

Α^{(ι + ψα}+

It should be noted that t_LL, that is, equation (32), is approximately three times smaller than t_LR, that is, equation (23) when the relative adsorption capacity of the barrier Ψ »1 and external humidity h_output is close to 100%.

After the delay time t_LL, the accumulation of water vapor in the internal top volume V, that is, the empty volume in the bounded area, is described by a mass balance analogue of equation (14), equation (33) below.

_P = ρ Α (33) dt 2 dt

Equation (33) can be rearranged as shown in equation (34) below.

(34)

Solving equation (34) for h_eriresults in equation (35), where Ah₀ = h_output - H_enand the difference in initial relative humidity through the barrier.

^Hand_ntrOdA0 = \ aida ~ ^exP τ m mm i | pjA-s, ai (35)

In view of the above, the approximate combined solution for the growth of the internal pressure to the initial reference conditions results in equation (36) having the value t_LL provided by equation (32) and the value S_andf provided by equation (31).

0, for t &lt;t_LL (^) - exp _mA (t LL) for t&gt;

(36)

s_and/AL k 2

In summary, during the time period before reaching the delay time there is no moisture in the enclosed area, while during the time period after the delay time t_LL is reached, the humidity in the bounded area is calculated according to the second equation in (36).

As described above, many sorbents can also behave as double reversible adsorbents with Fickian (mass dissolution) and Langmuir (saturation gap) sorption behavior. Double-mode Sd (h) sorption isotherms (DS) from common desiccants can be incorporated into the effective solubility coefficient of the polymer composite loaded with desiccant with Cc = S_andf (T) h according to equations (37), (38) and (39).

= (37) + ά / ζ

s_ef(h) = + $_ds_d(h) (38)

Ç_ç(h) = S_ef (h) h = 0_ms_mh + 0_d ffyh (39) \ + bh

The parameter C_max it is the so-called gap saturation constant in Langmuir mode sorption.

The phenomenological Langmuir affinity constant b is correlated with the ratio of the solute sorption and desorption rate constants in the Langmuir mode. The effective sorption isotherm combines the Fickian mode sorption of the polymer matrix and the dual sorption of the desiccant.

Õ Tld reference delay time with the desiccant double sorption isotherm is found in equation (10). Paul DR and Kemp DR, J

Polim. Scl, Symp. 41, 79-93 (1973).

t_lD = -f- f &lt;1 - ξ) [c “(£) - C„ = (40) ^L\ í₁₊^Ç^^{b 6} I ..2

]) &lt;Pm ^smy

Unlike the previous Ψ, y is shown in equation (41) below.

y bh_said_The (41)

Unlike equation (33), the change in the effective solubility coefficient S_andf (h_enbarrier) during a change in internal humidity h_entraction cannot be underestimated due to the non-linearity of the sorption isotherm and this change has to be differentiated to obtain permeation dynamics. In this example, the mass balance within the fixed container volume V is expressed by equation (42), (43) or, equivalently (44).

dt input _ l ^ output Fl input) - ALL 2 dt (42)

P-^{v +}f \ ^^s~⁺^ v _² V_ (1 + fc / i, ^) h - fa '* exit ^rt input

Λ dh.

kD.SA mmm

The.

(l + dh output '* input dt dt (43) (44)

The coefficients of equation (44) are included below in (45) equation (45).

^The2 ⁼ Φπι ^ ιη '

AL ^α'= Ύ' «4 = P_Sat^V', φ D _m SA τ mmm

Solving equation (45) results in equation (46) and subsequently equation (47) for the integration constant, obtained from the known initial condition h_ino for relative humidity inside the package.

33 ^ 34) (l + bhggjja) 1 nfhgajja-hgnradaf-aiaj 11ΐ (1 + bh_saij_The) / ln (1 + bh_{en; ra}j_The) ^ 5 (1 + bhout) = t + const = t + const

34CÍ3 1 π (1 + bh_entratj_Theo) - (â], 13 + 34) (1 + bh_leaves(ja) Jn (b_saj ^_The-H_antraf3_The) -3j331 n (l + bh_sa;_Ç[_The) / 1 π (1 + bh_entracj_TheO)

2 ^ 5 (1 + bítsaida) (46) (47)

Although the UR in the defined area remains equal to zero percent (0%) before reaching the index calculated by equation (40), the evolution of the hentral UR (t) inside the package after t_LD is an implicit function expressed as t (h_entrada)₅ that is, equation (48).

t = t,_n+ a_s(l + bh, ^ j ln l ^{+ bh}i »l + bh

-ln Igrida erUrada.Q l + bh ..

l + bh ..

(48)

Thus, different from the previous equations, to calculate the humidity value in the bounded area h_input based on time t, a plurality of h_enare used to determine a plurality of times t. Subsequently, the relationship between h_entr et can be plotted or analyzed using other methods.

In view of the previous analysis, the following examples of resin and sorbent composites show how the present invention is used to optimize formulations of adsorptive composite barriers through the selection of such materials and the ratios between them. In the first example, the resin used is polypropylene (PP) (see figures 5A and 5B), while in the second example, high density polyethylene (HDPE) is the resin (see figures 6A and 6B). In the third example, the resin used is polyethylene terefitalate (PET) (see figures 7A and 7B), and the fourth example uses a hygroscopic polyamide resin nylon 6.6 (see figures 8A and 8B). Each example compares the performance of each respective resin in combination with stoichiometric, linear and double adsorbents, where double-mode adsorbents are modeled as having both a weakly non-linear sorption isotherm, that is, close to a linear adsorbent, and a strongly nonlinear sorption isotherm, that is, close to a stoichiometric adsorbent.

In the examples below, the stoichiometric or irreversible chemical adsorbent considered is calcium oxide (CaO), while the linear adsorbent considered is silica gel at zero to sixty percent (0 - 60%) relative humidity, the adsorbent mode strong double sorption adsorption is molecular sieve, and the weak double sorption mode adsorbent considered is a mixture of molecular sieve and silica gel. It should be understood that other sorbents that are well known in the art can also be considered in the development of the method of the present invention, and such sorbents are in the spirit and scope of the claimed invention. In addition, although only polypropylene, high density polyethylene, polyethylene terephthalate and nylon are discussed below, it should be noted that the method of the present invention can be used considering any appropriate resin / polymer and such resin / polymers are in the spirit and scope of the claimed invention.

In addition, all sorption isotherms were adjusted to correspond to the same twenty-six percent by weight (26% by weight) of final moisture sorption capacity in one hundred percent (100%) of relative humidity to facilitate comparison between cases . Actual isotherms differ in the final capacity shown in figure 3. Additionally, it should be noted that, although each composition described below comprises forty percent by weight (40% by weight) of sorbent, the volumetric loading values ​​are each different due to differences in the density of the resin.

Example 1 - Polypropylene and various sorbents Table 1 - characteristics of polypropylene and sorbents used in calculations

<td>Variable</td><td>Value</td><td>Units</td>

<td>relative external humidity (h_sagoing)</td><td> 80%</td><td></td>

<td>initial internal relative humidity (hentry, o)</td><td> 0%</td><td></td>

<td>barrier surface area (A)</td><td>6.00 x 10⁴</td><td>m²</td>

<td>barrier thickness (L)</td><td>1.00 x 10 '³</td><td>m</td>

<td>diffusivity (D or D_m)</td><td>1.00 x 10 '¹²</td><td>m²/s</td>

<td>permeability (P)</td><td>5.00 χ 10 '¹⁰</td><td>gm / (m²s 100% RH)</td>

<td>loading fraction of desiccant weight (0_d)</td><td> 0,4</td><td></td>

<td>desiccant density (pd)</td><td> 2,0</td><td>g / cm³</td>

<td>matrix or resin density (p_m)</td><td> 0,90</td><td>O g / cm</td>

<td>saturation capacity of the desiccant (W_d)</td><td> 0,26</td><td>g / g / 100% RH</td>

<td>weak DS mode of gap saturation constant (Cmax)</td><td> 0,52</td><td>g / g / 100% RH</td>

<td>strong DS mode of the gap saturation constant (C_max)</td><td> 0,27</td><td>g / g / 100% RH</td>

<td>weak DS mode of the Langmuir affinity constant (b)</td><td> 1</td><td></td>

<td>strong DS mode of the Langmuir affinity constant (b)</td><td> 30</td><td></td>

<td>internal top volume (V)</td><td>1.00 x 10 '⁶</td><td>m³</td>

<td>density of saturated steam at 20 ° C (Psat)</td><td> 17,3</td><td>g / m³/ 100% RH</td>

<td>saturated vapor pressure at 20 ° C (p_sat)</td><td> 1208</td><td>Pan</td>

As can be seen in figure 5B, delay times vary from about twenty four (24) months to about seventy-two (72) months, and internal relative humidity levels increase according to the resin / sorbent composition. Thus, if an internal relative humidity of sixty percent (60%) is considered the point of failure, failure times vary from about seventy-six (76) months to about one hundred and eight (108) months.

Example 2 - High density polyethylene and various sorbents

Table 2 - characteristics of high density polyethylene and sorbents used in calculations

<td>Variable</td><td>Value</td><td>Units</td>

<td>relative external humidity (h_leaves-d_The)</td><td> 80%</td><td></td>

<td>initial internal relative humidity (he_ntrada, o)</td><td> 0%</td><td></td>

<td>barrier surface area (A)</td><td>6.00 χ 10^-4</td><td>m²</td>

<td>barrier thickness (L)</td><td>1.00 x 10 '³</td><td>m</td>

<td>diffusivity (D or D_m)</td><td>5.50 x 10 ~¹³</td><td>m²/s</td>

<td>permeability (P)</td><td>2.80 χ 10 '¹⁰</td><td>gm / (m²s 100% RH)</td>

<td>loading fraction of desiccant weight (0f)</td><td> 0,4</td><td></td>

<td>desiccant density (p_d)</td><td> 2,0</td><td>g / cm³</td>

<td>matrix or resin density (p_m)</td><td> 0,96</td><td>-2 g / cm</td>

<td>saturation capacity of the desiccant (W_d)</td><td> 0,26</td><td>g / g / 100% RH</td>

<td>weak DS mode of the constant of gap saturation (C_max)</td><td> 0,52</td><td>g / g / 100% RH</td>

<td>strong DS mode of the gap saturation (C_badx)</td><td> 0,27</td><td>g / g / 100% RH</td>

<td>weak DS mode of the constant of Langmuir affinity (b)</td><td> 1</td><td></td>

<td>strong DS mode of the affinity constant from Langmuir (b)</td><td> 30</td><td></td>

<td>internal top volume (V)</td><td>1.00 x IO '⁶</td><td>m³</td>

<td>density of saturated steam at 20 ° C (Psat)</td><td> 17,3</td><td>g / m³/ 100% RH</td>

<td>saturated vapor pressure at 20 ° C (p_sat)</td><td> 2308</td><td>Pan</td>

As can be seen in figure 6B, delay times vary from about forty-eight (48) months to about one hundred and forty-four (144) months, and internal relative humidity levels increase according to the resin / sorbent composition. . Thus, if an internal relative humidity of sixty percent (60%) is considered the point of failure, failure times vary from about one hundred and forty-four (144) months to about two hundred and seven (207) months.

Example 3 - Polyethylene terephthalate and various sorbents

Table 3 - characteristics of polyethylene terephthalate and sorbents used in calculations

<td>Variable</td><td>Value</td><td>Units</td>

<td>relative external humidity (h_leavesd_The)</td><td> 80%</td><td></td>

<td>initial internal relative humidity (he_ntrada, 0)</td><td> 0%</td><td></td>

<td>barrier surface area (A)</td><td>6.00 x 10 '⁴</td><td>2 m</td>

<td>barrier thickness (L)</td><td>1.00 x 10 '³</td><td>m</td>

<td>diffusivity (D or D_m)</td><td>2.00 χ IO '¹²</td><td>m²/s</td>

<td>permeability (P)</td><td>3.00 χ IO '⁹</td><td>gm / (m²s 100% RH)</td>

<td>weight loading fraction of the desiccant (0a)</td><td> 0,4</td><td></td>

<td>desiccant density (pa)</td><td> 2,0</td><td>1 g / cm³</td>

<td>matrix or resin density (p_m)</td><td> 1,3</td><td>g / cm³</td>

<td>saturation capacity of the desiccant (W_d)</td><td> 0,26</td><td>g / g / 100% RH</td>

<td>weak DS mode of the constant of gap saturation (C_max)</td><td> 0,52</td><td>g / g / 100% RH</td>

<td>strong DS mode of the gap saturation (C_max)</td><td> 0,27</td><td>g / g / 100% RH</td>

<td>weak DS mode of the constant of Langmuir affinity (b)</td><td> 1</td><td></td>

<td>strong DS mode of the affinity constant from Langmuir (b)</td><td> 30</td><td></td>

<td>internal top volume (V)</td><td>1.00 x 10 '⁶</td><td>m³</td>

<td>density of saturated steam at 20 ° C (Psat)</td><td> 17,3</td><td>g / m³/ 100% RH</td>

<td>saturated vapor pressure at 20 ° C (p_sat)</td><td> 2308</td><td>Pan</td>

As can be seen in figure 7B, delay times vary from about six (6) months to about eighteen (18) months, and levels of internal relative humidity increase according to the resin / sorbent composition. Thus, if an internal relative humidity of sixty percent (60%) is considered the point of failure, failure times vary from about nineteen and a half months (19 1/2) months to about twenty six (26) months.

Example 4 - Nylon and various sorbents

Table 4 - characteristics of nylon and sorbents used in calculations

<td>Variable</td><td>Value</td><td>Units</td>

<td>relative external humidity (h_sagoing)</td><td> 80%</td><td></td>

<td>initial internal relative humidity (he_ntrada, o)</td><td> 0%</td><td></td>

<td>barrier surface area (A)</td><td>6.00 x 10^-4</td><td>m²</td>

<td>barrier thickness (L)</td><td>1.00 x IO '³</td><td>m</td>

<td>diffusivity (D or D_m)</td><td>2.40 x 10 '^1J</td><td>m²/s</td>

<td>permeability (P)</td><td>1.24 x IO '⁸</td><td>gm / (m²s 100% RH)</td>

<td>loading fraction of desiccant weight (0d)</td><td> 0,4</td><td></td>

<td>desiccant density (pd)</td><td> 2,0</td><td>g / cm³</td>

<td>matrix or resin density (p_frog)</td><td> 1,14</td><td>g / cm³</td>

<td>saturation capacity of the desiccant (W_d)</td><td> 0,26</td><td>g / g / 100% RH</td>

<td>weak DS mode of the gap saturation constant (C_badx)</td><td> 0,52</td><td>g / g / 100% RH</td>

<td>strong DS mode of the gap saturation constant (C_max)</td><td> 0,27</td><td>g / g / 100% RH</td>

<td>weak DS mode of the Langmuir affinity constant (b)</td><td> 1</td><td></td>

<td>strong DS mode of the Langmuir affinity constant (b)</td><td> 30</td><td></td>

<td>internal top volume (V)</td><td>1.00 x 10 '⁶</td><td>m³</td>

<td>density of saturated steam at 20 ° C (Psat)</td><td> 17,3</td><td>g / m³/ 100% RH</td>

<td>saturated vapor pressure at 20 ° C (p_sat)</td><td> 2308</td><td>Pan</td>

As can be seen in figure 8B, delay times vary from about two (2) months to about four (4) months, and internal relative humidity levels increase according to the resin / sorbent composition. Thus, if an internal relative humidity of sixty percent (60%) is considered the point of failure, failure times vary from about five and a half months (5 1/2) to about seven (7) months.

The results presented demonstrate that linear and weakly non-linear adsorbents, while providing a shorter delay time, can potentially result in a longer service life of packaged components. For example, such linear adsorbents can provide a much longer time to reach 60% RH inside the container than stoichiometric and strongly nonlinear adsorbents (dual mode) with the same saturation capacity and loading of the fraction of weight in a composite barrier, from as shown in figures 5A to 8B. In view of the above, one skilled in the art can determine which resin in a group of resins, whose sorbent in a group of sorbents, and whose ratio between them will provide the required characteristic, for example, rigidity, hardness, weight, compatibility of the material , etc., while maintaining a relative humidity at an acceptable level or below it in a defined area constructed of the resin / sorbent composite for the desired time. Thus, part of the costs can be minimized and part of the performance can be maximized.

In view of the above, it is believed that the methods of the present invention show that preferred resins for such active barriers include passive polymer matrices of high moisture barrier, for example, polyolefins, such as polypropylene and polyethylene or, in other words, polymers with inherently low water vapor permeability. It has been observed that desiccant materials, such as chemical adsorbents, for example, silica gels and molecular sieves, and chemical adsorbents, for example, calcium oxide, should be prepared as fine powders with particle sizes of approximately one micron (1 pm) ) at approximately fifty microns (50 pm) before dispersion in a polymer matrix during preparation of the compound. Smaller particle sizes of sorbent particles have been shown to reduce the likelihood of water molecules diverting these particles during the diffusion of moisture through a composite barrier in the same sorbent charge. View Solovyov

SE, J Phys. Chem. B 110, 17977-17986 (2006). The resulting effect is to reduce transient permeation rates through such composites to zero or close to zero.

The previous results were obtained based on the assumption that the particulate desiccant is well dispersed in the polymer matrix without agglomeration and that it does not provide easy paths for diffusion of moisture in the polymer matrix, such as channels, voids, pores, and entrapped particle compartments interconnected. It was observed that the dispersion of the desiccant particles has to be carried out during the preparation stage of the molten compound to prevent particle agglomeration in the composite, provide sufficient separation between nearby particles and create a contiguous matrix polymer phase in a composite. The techniques of single and twin screw extrusion were observed to be more suitable for preparing molten compost. It was also observed that in a preferred embodiment, the volumetric load of the desiccant in the composite should be limited to levels below twenty five to thirty percent by volume (25-30% by volume) to prevent agglomeration and particle-to-particle contact mentioned above. At desiccant charge levels below 25-30 vol%, discrete desiccant particles do not touch each other and therefore cannot facilitate the transport of moisture between them. Thus, moisture transport occurs mainly through the contiguous polymer matrix and is thus controlled by the water vapor transport properties of the matrix polymer. However, it should be noted that the desiccant volumetric load is chosen as the maximum possible load in the previously described constraint, in order to achieve the maximum moisture adsorption capacity of the composite, and the high volumetric load also serves to prevent water molecules bypass the desiccant particles during diffusion through the composite barrier.

An example of a polymer matrix like this is shown in figure 9. The polymer matrix 20 comprises contiguous resin 22 and sorbent particles 24. As can be seen in the figure, each individual sorbent particle 24 is separated from each other particle 24 by resin 22. Matrix 20 includes outer surface 26 and inner surface 28. Water vapor adjacent to outer surface 26 enters matrix 20, for example according to the unidirectional arrow 30. Before saturation of the sorbent particles 24, the water vapor can, for example, progress in the matrix 20 according to the unidirectional arrows 32 and such vapor is eventually absorbed by the sorbent particles 24. Subsequent to the saturation of the sorbent particles 24, the water vapor can progress through the matrix 20 according to the unidirectional arrow 34, or according to the unidirectional arrow 36 whose water vapor is absorbed by the sorbent particle 38 and subsequently released from particle 38 according to the unidirectional arrow 40. Any water molecule, i.e. water vapor, that reaches the inner surface 28 can leave the matrix 20, for example according to the unidirectional arrow 42.

Particle dispersion and essential separation media in the matrix, such as mixing and compound preparation procedures, details of polymer preparation and desiccant for compound preparation, feeding and processing conditions during compound preparation, potential use of compatibilizing agents and processing aids to stabilize highly loaded composite morphologies, etc., also form part of this invention. It was observed that microscopic interfacial clearances and defects between the desiccant particles and polymer matrix that commonly arise from the thermodynamic incompatibility of the resin and the dispersed desiccant particles are preferably reduced or eliminated through the use of suitable compatibilizing agents in the resin-sorbent composite; however, it should be noted that only the minimum adequate amount of compatibilizing agent is used in order to prevent agglomeration and minimize other interactions of the compatibilized desiccant particles, such as formation of microchannels that connect particles, and to essentially prevent the formation of pores, holes and micro-cracks in the composite during cooling. Α microfracture formation in the contiguous polymer phase is often observed in highly charged polymer composites upon cooling as a result of the non-uniform shrinkage of the polymer limited by the charged sorbent particles and such defects can lead to a significant increase in moisture permeation rates across of the composite. Thus, the choice of suitable controlled and compatible cooling regimes allows the reduction of the formation of such microfractures in manufactured parts of the sorbent composites bonded to the resin of the present invention. The selection of processing aids and additives to achieve the desired particle dispersion in a composite is responsible for the fact that such additives must not promote or facilitate the diffusion of moisture around the desiccant particles and from one particle to the other, for example , along the compatible interfaces and through the overlapping connection layers around each particle, on the contrary, it only serves to stabilize the morphology of the composite and to prevent the blockage of moisture permeation for the particles. As such, compatibilizing agents are chosen to provide wet vapor permeability close to or identical to that of the polymer matrix.

Generally, sorbents that are used and functional in this invention are those that mechanically bind to the resin without special additives, such as molecular sieve, as previously discussed. Still according to the present invention, others can be induced to bind to the resin through the use of a suitable additive, that is, they bind with the help of a copulating or compatibilizing agent. In addition to the molecular sieve, other representative sorbents that are used in the compositions of the invention include silica gel, activated carbon, activated alumina, clay, other natural zeolites and combinations thereof. Sorbents that have been observed to work with copulating or compatibilizing agents include such members as activated carbon and alumina.

Additives that work as compatibilizers fall into two categories, namely those that bind with resin or sorbent, and those that have some affinity with both resin and sorbent, and act as solid-state surfactants. Reactive copulating agents include such classes as maleates, epoxies and silanes. More specifically, reactive copulating agents include such representative examples as grafted polymers of maleic anhydride used in amounts ranging from about 2 to about 5% by weight. In particular, they can include such representative examples as maleic anhydride grafted with polypropylene or ABS resins, the latter being used as copulating agents with styrenic polymers. Similarly, silanes with several functional groups attached can be used.

The present invention also contemplates the use of the so-called non-reactive compatibilizing agents that bind to the sorbent and resin. This comprises such representative examples as metals (for example, zinc or sodium), metal oxides, organometallic binders, acrylates, stearates and copolymer blocks, for example, zinc stearate, sodium stearate in a range of about 0.01 to about 0.2% by weight based on the sorbent. The true level is driven by the surface area, which in turn is proportional to the particle size. For a molecular sieve with an average particle size of 10 pm, 100 ppm of aluminum stearate should be a typical starting level for compatibility with a polyamide resin. With both reactive and non-reactive copulating / compatibilizing agents, it is believed that their incorporation into the resin matrix does not create phase bonds.

The sorbent composition bound to the resins can be prepared according to the present invention using thermoplastic compound preparation techniques generally familiar to those skilled in the art. Molecular sieve, a preferred sorbent, can be incorporated into the resin, for example, polyamide, polyolefin, or the like, feeding the sorbent into a powder form together with beads of the chosen resin in a plastic extruder with good mixing characteristics. Although single screw extruders can be used to compose a resin and sorbent, a mixture of resin and sorbent usually needs to be doubly composed in order to produce a suitable resin-bound sorbent material. Even after double compounding, re-agglomeration and phase separation sometimes occur during further processing. It was observed that sorbent materials bonded to the resin composed with twin screw extrusion equipment with extensive return mixture are necessary to achieve near complete dispersion of the sorbent and to develop the superior mechanical and physical characteristics that are an objective of this invention. In other words, sorbent materials bonded to the resin formed by means of a twin screw extruder show little or no sorbent migration in the resin matrix and, thus, these sorbent materials bonded to the resin maintain a homogeneous appearance. In this way, compounding with a twin screw extruder is typically used to form sorbent materials bonded to the resin of the present invention, since the resin is melted and the sorbent mixed thoroughly. It is usually advantageous for the resin to be heated above its melting point, as determined by DSC (differential scanning calorimetry) before the sorbent is added. That is, when preparing the sorbents linked to the resin of the invention, the temperature must be increased to the point where all crystallinity is lost, in order to achieve complete miscibility of the sorbent in the molten resin. For example, DuPonfs Zytel® 101 polyamide resin can be heated above 262 ° C. The extruded resin is cooled and then cut into pellets or granules. Because the compost is formed at elevated temperatures, the sorbent does not adsorb moisture during this processing period, but retains its adsorption capacity when molded in a part of the component and installed in a work environment.

An additional advantage realized with the resin-bound sorbent system, in which the resin and sorbent are closely linked, is that gram by gram it is more effective than adsorbent systems that employ a bloated adsorbent, that is, adsorbent capacity per volume unit. According to previous methods in which bags were used to place the sorbent in a container, the sorbent required effervescence to prevent entry into the refrigerator chain, for example. This required the sorbent to be bound in a binder resin, typically 15% by weight of binder, such as in the form of a powder. Thus, when 40 grams of a commercially prepared sorbent were placed in a bag, in reality only 34 grams of sorbent were introduced into the system (with 6 grams of binder). In contrast, the sorbents bonded to the resin of the present invention do not require any additional binder resin because the sorbent is placed directly on the molding resin, from which the components are manufactured. Advantageously, with the present invention, no intermediate binding resin is required, allowing for greater sorbent loading factors than would otherwise be achieved with the usual bloated sorbents.

It should be noted that the duration of the lowest rates of water vapor permeation through the described composite barriers, both absorbent and chemically reactive, is determined by the so-called barrier delay time. For chemical absorbents, the delay time depends on the stoichiometric reactive capacity of the barrier material. For physical absorbers, the delay time is controlled by the ability to adsorb moisture from the used desiccant, its charged fraction, and the shape of its water vapor sorption isotherm. Unlike chemical absorbents whose reactive capacity has to be completely depleted through the thickness of the barrier before the barrier begins to "leak", physical absorbents are not completely saturated when permeation proceeds through the barrier loaded with them. The composite structure continues to function as an absorbent barrier even after the transport of steady-state water vapor is established through the barrier. As such it reduces the rate of water vapor accumulation in the package due to a need to saturate a fraction of the additional sorbent, as the moisture level inside the package increases.

It has been observed that the methods of the present invention provide a means of creating highly charged polymer composites which, due to the high levels of desiccant loading, present significantly reduced bowing and shrinkage upon cooling and thus provide a means for producing thicker structural parts in narrow manufacturing tolerances. Such composites can be used as structural molding resins for the manufacture of rigid single-layer packaging and encapsulation articles in a variety of applications. In addition, modified degrees of impact of the described composites can be prepared by adding to the resin-sorbent matrix a dispersed elastomeric phase, for example, thermoplastic rubber, having low moisture permeability. In addition, the method of the present invention can be used to create resin-sorbent composites that can form a high moisture barrier coating on the outside of a packaging article in order to extend its useful service life, that is, the duration of barrier improvement.

It should be noted that prior to the present invention, packaging and / or delimited areas did not work based on the calculation of the delay time alone. However, most content in such delimited areas can withstand internal relative humidity levels above zero percent (0%), in fact some content can still support levels of relative humidity in excess of sixty percent (60%). Thus, assuming that the enclosed area has been breached, once the delay time has been reached, longer periods of time where the contents still remain secure have been lost, resulting in reduced service life forecasts or alternative enclosed area projects at a higher cost. . In view of the foregoing, the present invention provides a means of accurately determining the increase in internal relative humidity in such delimited areas for longer periods of time. As a tech expert acknowledges, it is not practical to merely test such areas enclosed in high humidity levels because the test can take years and there are no reasonable methods of accelerating such testing. In this way, the method of the present invention provides information regarding the performance of such delimited areas without the need for prolonged, impractical testing.

The method of the present invention provides a means of determining, from a group of resins and sorbents, which compositions of resins and sorbents will meet the design requirements, for example, ingress of moisture into a defined area made from such compositions and part of general cost. The method includes the steps of: a) selecting a plurality of resins, a plurality of sorbents and a plurality of reasons among them to form a plurality of composites; b) calculating a plurality of failure times for the plurality of composites, where each failure time of the plurality of failure times is based on when an internal relative humidity h_input of each composite of the plurality of composites is equal to the maximum internal relative humidity (see previous discussion regarding the various methods of calculating the internal relative humidity); c) determine which plurality of failure times is greater; and, d) selecting a composite from the plurality of composites based on the result of step (c). Performing the previous method, a sorbent composition bonded to the resin can be selected that most closely matches the design requirements of the defined area.

Thus, it is observed that the objectives of the present invention are efficiently achieved, although modifications and alterations of the invention may be readily apparent to those skilled in the technology, whose modifications are intended to be in the spirit and scope of the claimed invention. It is also understood that the above description is illustrative of the present invention and is not to be considered as limiting. In this way, other embodiments of the present invention are possible without departing from the spirit and scope of the present invention.