Compositions: coating or plastic – Coating or plastic compositions – Carbohydrate or derivative containing
Reexamination Certificate
2000-03-20
2003-05-20
Brunsman, David (Department: 1755)
Compositions: coating or plastic
Coating or plastic compositions
Carbohydrate or derivative containing
C106S215300
Reexamination Certificate
active
06565640
ABSTRACT:
The invention relates to compositions which comprise starch and/or modified starch and plasticizers and also, if desired, other additives, and which can be processed to give shaped articles, in particular to give shaped biodegradable articles, and to the use of the compositions for producing shaped articles.
Constantly increasing awareness of the environment, together with continuing increases in the strictness of regulations relating to waste disposal or recycling, have led to a marked increase in efforts to use biodegradable materials for producing shaped articles. In addition to this, ever increasing efforts are being made to use, wherever possible, materials based on renewable raw materials rather than those based on mineral oil. In many cases substances from natural sources are also less physiologically hazardous.
Starch and modified starch, alone or else mixed with other polymers, in particular with biopolymers, are renewable raw materials of constantly increasing importance, especially for producing shaped articles, such as foils or films. There are many problems here for processors. For successful shaping of starch, modified starch or else mixtures with other polymers, very intimate mixing, i.e. homogenization, of the components is required, in particular if the materials are to be processed thermoplastically. It is also important that during shaping the mixture has been sufficiently plasticized, in order to avoid having to accept excessively high shaping temperatures and the associated decomposition of the components. The shaped articles, furthermore, should not only have good biodegradability but also have a very homogeneous internal structure and good mechanical properties, such as strength and elasticity. In particular, a requirement for most applications is that brittleness and abrasion are very low. The plasticizer should also be environmentally friendly, i.e. biodegradable and physiologically nonhazardous.
There is a wide variety of known molding compositions which are based on starch, comprise plasticizer and can be processed to give shaped articles.
U.S. Pat. No. 3,312,560, for example, describes how amylose, with diglycerol as plasticizer, can be used to produce foils from aqueous solutions, via coagulation. In the presence of a certain amount of water the diglycerol-plasticized amylose can also be processed by extrusion to give foils. However, the method is restricted to the processing of amylose or of mixtures of amylose with low contents of amylopectin and, respectively, of chemically modified amylose. A further disadvantage is that diglycerol first has to be synthesized.
EP-A2-0 609 983 describes starch having at least two sugar alcohols of mono- or disaccharides as a plasticizer, and also describes water-containing compositions from which biodegradable articles can be produced, also with concomitant use of emulsifiers. Prior-art plasticizers mentioned in this text for starch products include low-molecular-weight propylene glycol, sorbitol, mannitol and polyvinyl alcohol. The compositions may initially be processed to give pelletized material, using an extruder, and this may subsequently be further processed to give shaped articles, e.g. by injection molding. A disadvantage of the process described there is the use of the emulsifier, which shows a tendency to migrate to the surface, as well as known chemical effects such as low thermal stability. The process is relatively complicated and attended by additional costs. In addition, the blending of at least two sugar alcohols with the amount of water stated there makes the shaped articles susceptible to fracture.
Thermoplastic mixtures of starch with other polymers, such as proteins, have been described, for example, in WO-A1-93/19125. Crosslinking, e.g. by aldehydes, is first required here. The plasticizers recommended comprise especially polyhydroxy compounds and various esters. Due to the crosslinking step the products obtained have only a very narrow processing range. The reaction is very sensitive and susceptible to problems, and processability is therefore reduced.
WO 90/05161 describes what are known as fatty-acid-based lubricants (fats, lecithins, fatty acids). These compounds, which also have free carboxyl groups, facilitate the processing procedure, but have the disadvantage of being unable on their own to plastify starch sufficiently.
U.S. Pat. No. 5,397,834 describes biodegradable thermoplastic compositions built up on the basis of proteins and aldehyde starch, where aldehyde starch and proteins have been crosslinked with one another. The compositions may comprise antioxidants, inter alia from 0.001 to 1% of ascorbic acid, preferably in the form of ascorbylpalmitate, as well as plasticizers, lubricants and extenders.
Although there is a wide variety of known compositions which comprise starch or, respectively, modified starch and plasticizers, and of known processes for producing shaped articles from compositions of this type, there is a need for compositions of this type which offer advantages over products of the prior art.
It is therefore an object of the invention to provide compositions which comprise starch and/or modified starch and plasticizers, can be prepared simply and cost-effectively, have good homogeneity, and even in a mixture with other polymers, in particular with biopolymers, such as proteins, are very homogeneous, and have good thermoplastic processability, are physiologically nonhazardous and biodegradable, and can advantageously be processed to give shaped articles which are useful in industry, and have good homogeneity and good mechanical properties, such as excellent flexibility, and in which the plasticizer has little or no tendency to migrate.
This object is achieved by compositions comprising starch and/or modified starch and plasticizers for producing shaped articles, in particular shaped biodegradable articles, wherein the compositions comprise at least one polymer based on starch and/or on modified starch and, as plasticizers, polyhydroxycarboxylic acids derived from aldoses and/or from ketoses or comprise lactones of these acids except ascorbic acid in amounts of up to 1% by weight, based on the solids in the compositions, and also, if desired, comprise other polymers, in particular biopolymers and additives, such as extenders, lubricants, mold-release agents, dyes, water and the like.
Other advantageous embodiments of the novel compositions are wherein the plasticizer is a polyhydroxycarboxylic acid derived from pentose and hexose, or a lactone of said polyhydroxycarboxylic acid derived from pentose and hexose. The plasticizer can also be a sugar acid or lacione of said sugar acid; an aldonic acid or a lactone of said aldonic acid; an uronic acid or a lactone of said uronic acid or a gluconic acid or gluconolactone or a mixture thereof. The plasticizer is preferably present in an amount from 2 to 30% by weight. The composition can contain destructured starch, hydrolytically degraded starch, chemically modified starch, canonically or anionically modified starch. The composition further comprises proteins as other polymers. The composition preferably has a pH set at from 6 to 10, preferably 8 to 10. The composition can further comprise an additional plasticizer. The composition can comprise a total of from 3 to 50% by weight of the plasticizer. The composition according to the invention can be used as a shaped article. The composition according to the invention can be used for the production of the following:
a packaging for food or drink,
a sausage casing,
a packaging for pharmaceutical products,
a shaped articles for the controlled release of active substances and
a temporary protective coating for a technical device. The invention further relates to a process for preparing a composition which comprises mixing and homogenizing starch and/or modified starch and plasticizers and optionally other polymers and additives, wherein said plasticizers are polyhydroxycarboxylic acids derived from aldoses and/or from ketoses, or using lactones of these acids. The process pref
Bengs Holger
Grande Jürgen
Brunsman David
Celanese Ventures GmbH
Connolly Bove & Lodge & Hutz LLP
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