Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Cellular products or processes of preparing a cellular...
Patent
1996-06-27
1998-01-06
Foelak, Morton
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Cellular products or processes of preparing a cellular...
106122, 521 79, 521 81, 264 53, C08J 904
Patent
active
057055360
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a process for producing a substantially biologically degradable polymer foam, a process for the production of a polymer mixture suitable for the production of the biologically degradable polymer foam, a biologically degradable polymer foam and uses of the biologically degradable polymer foam.
The production of foamed polymers is a known process and is effected either mechanically without pressure or by means of foam-forming agents or else by sudden expansion of gases, expansion agents, or solvents which, at higher pressures, produce an inflation pressure in the plastic or liquid polymer composition.
Such polymer foams have the most varied uses in, among other things, packaging, thermal insulation, acoustic insulation, construction and many fields of use of daily life. As is generally the case with polymers or plastics, disposal or degradability constitutes an important factor also in the case of foamed materials, particularly if the foamed materials have a high strength and compressing is not readily possible.
For this reason, a number of foamed substances of so-called biologically degradable polymers are known such as, for instance, starch foamed materials, in connection with which, starting from, for instance, native or so-called disaggregated starch, such a foamed material is produced by means of an expansion agent. Thus for almost a century a sponge made from starch has been known which is produced in the manner that a boiled starch paste is cooled to temperatures below the freezing point and the water then removed from the sponge mass by thawing.
In Federal Republic of Germany 23 04 736, a process for the production of a foamed material is described in which carbohydrates or polysaccharides in granulated, compacted or coarsely crystalline form are heated until dry in a tunnel furnace for 10-40 minutes at 200.degree. to 400.degree. C. with the addition of small amounts of organic or inorganic acids or acid salts. Due to the pyrolysis of the carbohydrate material which takes place, inflation occurs, whereby a carbonated foam material is obtained.
In Federal Republic of Germany 32 06 751, a relatively rigid foam is obtained by an extrusion process in which heating of the starch material is effected already in an extruder due to the shearing forces and the pressure, inflation and foaming of the emerging gelating starch taking place due to the development of gas upon the reaction of expansion agent additives with simultaneous solidification of the starch paste. As expansion agent additives, calcium carbonate and phosphoric acid are described, whereby carbon dioxide is produced.
WO 91/02023 describes a starch foam containing starch and ethylene acrylic copolymer which is obtained by adding an expansion agent such as sodium bicarbonate in the presence of a polymeric acid. Once again, carbon dioxide is the expansion gas.
In WO 91/18048, a nucleating agent is applied to granules of starch. The nucleating agent is decomposed by heat, whereupon the development of the foam commences. As nucleating agent, carbonates enter into consideration, so that once again carbon dioxide is the responsible expansion agent.
Starch foam can however also be produced in the manner, for instance, that powdered starch is mixed with water, this mass is extruded and upon the extrusion the starch is inflated by the steam which is produced.
All such starch foams of this type which have been described are, as a rule, partially or completely biologically degradable, in which connection, of course, the degradability can be negatively influenced by the addition of synthetic additives or plastic additives. Furthermore, it has been found that by the introduction of water as expansion agent or by the use of carbon dioxide as expansion gas, a foaming of the starch can be effected, but a non-uniform cell structure is established which, in its turn, requires additional additives. Furthermore, the required percentage of expansion agent or water necessary to produce the corresponding steam is very high and amounts u
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patent: 5360586 (1994-11-01), Wyatt et al.
patent: 5589518 (1996-12-01), Bastioli et al.
patent: 5602188 (1997-02-01), Nakanishi
Bio-Tec Biologische Naturverpackungen GmbH
Foelak Morton
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