Method for the defibration respectively decorticating of bast fiber plants

The invention relates to a process for the de-fibering or de-wooding of bast fiber plants, such as flax hemp, kenaf and jute.

Renewable raw materials are becoming increasingly popular because they not only conserve existing resources, but also make a contribution to reducing the CO2 known as greenhouse gases. Some processes for textile fiber production are known which aim to obtain fibers that are as long as possible. For flax these can have a length of approx. 500 - 1000 mm, for hemp also 1000 - 2000 mm. Traditionally, the bast fiber plants used are roasted before the fibers are extracted, often called deforestation. Such a roasting process degrades or at least weakens the pectin layer that connects fibers and wood. The degradation takes place either enzymatically by roasting bacteria or chemically. The following systems are known in particular: river roast, pond roast, basin roast and dew roast, the latter being the most imperfect.

The main area of ​​application for this material, which is preferably produced as long fiber, is the production of textiles. At Jute, the focus is on the production of sacks and fabrics for the non-clothing sector.

To a lesser extent, the defibering / de-worting is carried out without a previous roasting process. However, this results in a more uneven fiber, which is also coarser and less supple.

In conventional processes, the straw of the bast fiber family is broken. The purpose of these crushers is to break the woody core of the straw into small pieces, which are then thrown out of the long fibers in wings or turbines by a kind of centrifugal movement.

In recent times, mobile fiber removal and de-wooding machines have also been developed that harvest the fibers and seeds for oil production directly on the fields, as well as broken wooden parts of the bast fiber stems, which are deemed worthless <img file="EP0744477A2_D0001.tif" /><img file="EP0744477A2_D0001.tif" />Called shives ", but heedlessly left it there.

All in all, the effort involved in obtaining a long fiber is very considerable, although such a long fiber is often not required for technical purposes, and in most cases cannot even be used. This effort to obtain fibers therefore means costs that are unacceptable for the purpose of technical use.

The object of the invention is to provide a process for the de-fiberizing or de-wooding of bast fiber plants, which supplies material for technical purposes, not necessarily for textile further processing, the process itself being supposed to work more economically, more effectively and largely automated than the known processes for the production of long fibers.

This object is achieved according to the invention from the features of the characterizing part of the main claim.

The first process step of pre-comminuting the bast fiber straw to the desired fiber or stack length has proven to be particularly advantageous. On the one hand, the straw is sheared to a uniform length and, on the other hand, it is converted into a bulk material in order to be able to better automate the further process path in order to minimize the costs. Furthermore, this pre-shredding creates the prerequisite for the fact that in the further process path in fast-running or rotating machines no wrapping around rotating or stationary machine parts can occur. If the straw and straw material were not cut into such high-speed rotating machines, the bast fiber strands would wrap around tools, shafts or axes and lead to increased friction until the machine comes to a standstill or is destroyed or, if heated, may lead to a fire.

For the pre-shredding, machines are provided according to the invention which can ensure a uniform or fairly uniform length of the straw sections, in particular choppers such as rotor, disc or sickle choppers or, in the case of crops pressed into bales or round bale cutting mills, which are also called granulators in the plastics industry, furthermore Quar cutter, as they are common in veneer paper processing.

The defibering in the second process step advantageously takes place in a high-speed rotating mill, in which the defibering / de-wooding takes place by shear, friction, impact and impact. These are fast rotating machines, as are already known in the wood and plastics industry. In the wood industry they are mainly used as chip breakers, in the plastics industry they are used for the production of granules and powders. In modified form in the pharmaceutical industry and food technology, they are mainly used for the production of powders.

These mills are also ideal for removing the fibers of the pre-shredded material from the wooden components. This releases the high-strength, tough, flexible fiber from the brittle, inflexible, woody core and the woody parts are broken up in shells of different sizes depending on the speed of the machine and the mold material. In this way, even with unroasted material, a fineness and suppleness of the fibers is achieved, which is roughly equivalent to that of roasted material when using conventional fiber removal technologies. The fiber material obtained, on the other hand, is far superior to the so-called green tow from unroasted straw using conventional technologies in terms of fineness and smoothness. The separated wooden parts, however, have a particle size, which they qualify very well as a raw material for the production of panels and thermal insulation materials, especially for bulk insulation.

The subsequent separation of fibers and shives can advantageously be carried out with the aid of sieves and / or sifters, the fibers also being able to simultaneously classify and fractionate length and remove oversize particles, dust and foreign bodies. Furthermore, a silo and metering device can be connected upstream between the first and the second method step. If, however, a roasting process is to be provided, this can be carried out immediately before the second process step.

The short fibers produced, with their new geometry, with a preferred length between 2 and 50 mm, longer fibers up to about 100 mm are also conceivable, forge ahead into new technical fields of application in which synthetic fibers predominate to this day, so that a total of one big comeback of the bast fiber family can be expected. These fibers, which previously played a major role in the textile and clothing sector, are now used in much larger areas, such as reinforcing fibers that are incorporated into plastics, as short fibers that are processed into nonwovens and felts, and as short fibers that processed into thermoformable mats for the production of molded parts or as short fibers, which are used for the production of thermal insulation materials for the building industry.

Further advantageous embodiments of the invention result from the subclaims.