Plasticized sponge material and method of making same

Patented Dec. 29, 1953

2,664,367

UNITED STATES PATENT OFFICE

2,664,367

PLASTICIZED SPONGE MATERIAL AND METHOD OF MAKING SAME

Christopher Lumley Wilson, Columbus, Ohio No Drawing. Application September 19,1949, Serial No. 116,643

Claims. (Cl. 117—138.8)

This invention relates to a sponge material comprising partially formalized polyvinyl alcohol, and relates particularly to such a sponge material having incorporated therein a plasticizer to maintain the sponge in a soft and resilient condition.

Sponge and expanded materials comprising partially formalized polyvinyl alcohol and their preparation are described in my copending application Serial No. 29,657, filed May 27, 1943, and now Patent No. 2,609,347, which is a continuation-in-part of my prior copending application Serial No. 769,537, filed August 19, 1947, now abandoned. These sponge materials are prepared by reacting the formaldehyde with polyvinyl alcohol so that only a portion of the hydroxyl groups of the alcohol enters into the reaction. Preferably the solution of the materials is expanded as by beating air into the solution and the reaction is then permitted to proceed so that a solid is formed containing openings formerly occupied by the bubbles of ail’ or other gas. In the preferred procedure, an acid catalyst is employed in order to speed up the reaction.

As further set forth in the above mentioned Patent 2,609,347, the sponge materials described therein are made by a process comprising providing an aqueous solution of formaldehyde, polyvinyl alcohol containing less than 10% residual hydrolyzable material in the molecule,. an acid catalyst in which the acid functional group is inorganic and having a dissociation constant of at least 10-³ and a froth-stabilizing wetting agent soluble in and substantially stable to said solution; forming a substantially stable and homogeneous froth with said solution stabilized with the wetting agent; reacting the polyvinyl alcohol and the formaldehyde in the solution thereby causing gellation and solidification of the froth with the production of interconnected pores simultaneously with the progression of the reaction, the froth being formed prior to appreciable reaction between the polyvinyl alcohol and the formaldehyde; and stopping the reaction when approximately 35-80% of the hydroxyl groups of the polyvinyl alcohol have been reacted, with the , formaldehyde.

Sponge materials prepared in the above manner are soft and resilient when they contain appreciable amounts of witter. When the sponge materials become dry, however, they shrink to a i certain extent and become hard and rigid. They are immediately softened as soon as water is reintroduced into the sponge material. Although this re-wetting of the sponge material immediately changes it from a rigid solid to a resilient 55 elastic material and the drying out of the material causes no deleterious effects, the dry sponge material does not have as pleasing an appearance to the prospective purchaser.

I have discovered that the sponge material may be maintained soft and resilient if a plasticizer is incorporated therewith. These plasticizers are polyethylene glycols and polyalkanolamines and may be introduced by soaking the sponge material in either the heated plasticizer or in an aqueous solution of the plasticizer. After soaking in the liquid, the excess liquid, is removed. These plasticizers, which are preferably liquid at ordinary room tempei’atures, maintain the sponge material in a soft, resilient condition.

One of the features of this invention is to provide a method of making a soft, resilient sponge material comprising providing a partially formalized polyvinyl alcohol sponge and soaking the sponge in a liquid including a member of the class consisting of polyethylene glycols and polyalkanolamines; another feature of this invention is the provision of a partially formalized polyvinyl alcohol sponge material containing as a plasticizer a member of the class consisting of polyethylene glycols and polyalkanolamines. Other features and advantages of the invention will become apparent from the following description and the accompanying claims.

The plasticizers of this invention, may be introduced into the Sponge material either in the form of a solution or as substantially anhydrous liquids. When a solution is used an aqueous solution is preferred in which the sponge is soaked so as to absorb the maximum amount of solution and then the excess solution is removed. When the plasticizers are added in substantially anhydrous form, the liquid plasticizer is heated and the sponge is immersed in the heated plasticizer for from a few seconds to several hours depending upon the temperature employed. The sponge is then removed from the plasticizer and the excess plasticizer is removed.

Among the suitable plasticizers that have been discovered are diethylene glycol, triethylene glycol, tetraethylene glycol, polyethylene glycol having a molecular weight of about 200, other polyethylene glycols having molecular weights of more than 200, triethanolamine and methyl diethanolamine. The plasticizers may be used alone or in combinations of two or more. When the substantially anhydrous plasticizer is employed, the liquid plasticizer is preferably heated at a temperature between about 37° to 100° C. At the higher temperatures care must be used

3,664,367 that the sponge is not immersed for too long a time, as ordinarily only a few seconds is required at the high temperatures. A temperature of about 50° C. is preferred.

Any amount of plasticizer desired may be used so long as a plasticizing effect is achieved. In general, the sponge should contain approximately 50% of the anhydrous plasticizer by weight of the dry sponge material. In actual practice, it has been found that excellent results have been achieved when at least 30% of the plasticizer is employed by weight of the dry sponge material. Ordinarily not more than about 100 % is required, but in some instances it may be advisable to use more. Under conditions of high humidity, the minimum amount may be reduced below 30%. For example, 20% is satisfactory if the relative humidity of the atmosphere surrounding the sponge is at least 85-90%.

The following examples illustrate methods of practicing this invention:

Example 1 grams of dry sponge material, prepared as described in my prior Patent No. 2,609,347, were soaked in a solution of 150 parts by weight of triethylene glycol and 35 parts of water. The sponge material was then centrifuged in a 5 inch basket at 5,000 R. P. M. to remove the excess liquid. The sponge material retained about 6 grains of the solution and remained flexible in the atmosphere.

Example 2

A. partially formalized polyvinyl alcohol sponge made according to the above application was soaked overnight in triethylene glycol at 50° C. At the end of this time, the excess plasticizer was removed by squeezing the sponge. This sponge remained soft and flexible when exposed to air at room temperature.

Example 3

A portion of the sponge material was soaked in a 30% by weight aqueous solution of triethanolamine. After the excess solution had been removed by squeezing, the sponge remained soft when exposed to air at room temperature. The sponge was found to contain 60% triethanolamine, calculated as anhydrous amine and based on the weight of the dry sponge.

Example 4

A portion of the sponge material was soaked in a 30% by weight aqueous solution of methyl diethanolamine. After the excess solution had been removed by squeezing, the sponge remained soft when exposed to air at room temperature. The sponge was found to contain 60% methyl diethanolamine, calculated as anhydrous amine and based on the weight of the dry sponge.

Of the plasticizers described herein, the polyethylene glycols are preferred, and especially triethylene glycol. Diethylene glycol, triethylene glycol, tetraethylene glycol and other polyethylene glycols having a molecular weight of at least 200 may be employed. It is preferred, however, that the polyethylene glycol contain not more than 8 ethylene groups in the molecule.

Polyhydric alcohol plasticizers for partially formalized polyvinyl alcohol sponges are disclosed and claimed generally in my copending application Serial No. 116,642, filed September 19,1949.

Having described my invention as related to various embodiments of the same, it is my intention that the invention be not limited by any of the details of description unless otherwise specified, but rather be construed broadly within its spirit and scope as set out in the accompanying claims.