Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
2001-06-06
2004-05-04
Sergent, Rabon (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
C523S124000, C523S128000, C524S051000, C524S425000, C524S436000
Reexamination Certificate
active
06730724
ABSTRACT:
The present invention relates to biodegradeable compositions comprising starch and polysaccharide esters, suitable for producing moulded articles which can decompose rapidly during composting.
It is reported in the literature that thin cellulose acetate films are rapidly degradable; however, the time required for the biodegradation of thick films or of articles with thick walls is extremely long. For example, two months are required to degrade less than 60% of a thick film.
The problem to be solved in the case of compositions containing starch and cellulose esters consists of the provision of compositions having good biodegradability which are suitable for the production of shaped articles having an adequate capacity to decompose during composting.
Compositions comprising starch and cellulose esters which have improved compatibility between the polymeric components but which do not have adequate biodegradability are described in the patent literature.
For example EP-A0 722 980 describes compositions in which the starch and the cellulose ester are rendered more compatible with one another with the use of specific phase compatibilising agents which are selected from various classes of polymeric substances, and which—in addition to improving compatibility—also have the effect of improving biodegradability by virtue of the high level of dispersion conferred on the starch in the cellulose-ester matrix.
However, articles produced from the compositions still have too low a decomposition rate during composting.
It has now surprisingly been found that it is possible considerably to increase the biodegradability of articles produced from compositions comprising partially or completely destructurised and/or complexed starch and polysaccharide esters, preferably cellulose esters, and consequently their ability to decompose during composting.
The decomposition times for the articles produced can be reduced to less than two months in standard composting conditions.
The subject matter of the invention is defined by the appended claims.
The compositions of the present invention comprising starch and a polysaccharide ester and preferably a cellulose ester or a starch ester are characterized by a microstructure in which the ester constitutes the matrix and the fraction of destructurised and/or dispersed starch constitutes the dispersed phase, with a numeric mean dimension of the domains or dispersed particles preferably of less than 1 &mgr;m, more preferably less than 0.5 &mgr;m; the compositions contain an additive which can increase and maintain at values of 4 or more the pH of a solution obtained by immersing granules or pellets of the composition in water at ambient temperature for 1 hour with the use of a water:granules (or pellets) ratio of 10:1 by weight.
The term “partially” referred to destructurised or complexed starch is used to contemplate the possible presence of a portion of native crystalline starch up to 30% by wt. with respect to the starting starch content.
The additive, which has the above-mentioned capability to control the pH, has the effect of considerably increasing biodegradability of the compositions by neutralising the acid resulting from hydrolysis of the cellulose ester in composting conditions. Any substance available insoluble in water and having the above-mentioned capability may be a suitable additive.
Examples of additives are carbonates and hydroxides of alka-line-earth metals such as CaCO
3
, MgCO
3
, Mg(OH)
3
. CaCO
3
is the preferred additive.
The compositions comprise starch and the polysaccharide ester plasticised with a plasticizer in a quantity of from 10 to 40% by weight referred to the polysaccharide ester, in a ratio by weight of from 1:0.6 to 1:18, preferably from 1:2 to 2:3.
The pH regulating additive is present in a quantity of from 0.5 to 30%, preferably from 5 to 20%, by weight relative to the weight of the starch and of the plasticized polysaccharide ester.
Quantities greater than 30% by weight may be used without any significant further improvement.
Too large a quantity of additive may have an adverse effect on the mechanical properties of the compositions.
In addition to the plasticizer for the polysaccharide ester phase, the compositions may also comprise a plasticizer for the starch phase, used in a quantity of from 0.5 to 50% by weight, relative to the weight of the starch.
To permit the production of a finely dispersed microstructure as indicated above, further polymeric additives belonging to the following classes may be used:
a) polymers compatible with polysaccharide esters and/or starch, to which aliphatic or polyhydroxylated chains containing from 4 to 40 carbon atoms are grafted,
b) copolymers of hydroxy-acids and/or diamines with 2-24 carbon atoms with aliphatic or aromatic diisocyanates or with epoxy compounds or anhydrides,
c) copolymers of aliphatic polyesters, polyamides, polyureas or polyalkylene glycols with aliphatic or aromatic disocyanates,
d) polymers compatible with polysaccharide esters and/or starch to which polyols soluble in starch or polymers capable of complexing starch are grafted, and
e) polymers capable of complexing starch, such as ethylene/vinyl alcohol or ethylene/acrylic acid copolymers, aliphatic polyesters and polyamides.
The additives of type a) are preferably obtained by grafting aliphatic chains derived from vegetable or animal fats such as oleic, lauric, myristic, palmitic, stearic, linoleic, arucic and ricinoleic acids having terminal groups such as carboxyl groups, esters or salts to facilitate the grafting of the chains.
Examples of polymers compatible with the cellulose esters are:
cellulose esters with various degrees of substitution (DS),
starch esters with various DS values, such as acetates,
starch esters with various DS values, such as products of the reaction of starch with ethyelene or propylene glycol,
partially hydrolysed polyvinyl acetate,
aliphatic polyesters and aliphatic/aromatic copolyesters.
The number of grafted chains is between 0.1 and 100, preferably from 0.2 to 50, more preferably from 0.3 and 20 grafted chains per 100 monomeric units in the polymeric chain.
Examples of additives of type b) and type c) are the copolymers which can be produced from aliphatic polyesters such as polycaprolactones and polyethylene succinates.
Block copolymers between polycaprolactons and an aromatic or aliphatic diisocyanate, such as a caprolactone-urethane co-polymer marketed by Goodrich with the trademark Estane, grade 54351 is representative of the copolymers of class b).
The additives are present in quantities of from 0.1 to 20% by weight, preferably from 0.5 to 10%, relative to the sum of the weight of the starch and of the plasticised polysaccharide ester.
In addition to the components indicated above, the compositions of the invention may contain synthetic polymers in a quantity up to 30% by weight, preferably less than 10%, of polyvinyl alcohol, polyvinyl, acetate, thermoplastic polyesters such as polycaprolactone, copolymers of caprolactone with isocyanates, polymers of lactic acid, polyethylene or polybutylene and, in general, polyalkylene adipate, sebacate, and azelate.
The starch which is used to prepare the composition is a natural starch extracted from various plants such as maize, wheat, potato, tapioca and cereal starch. The term starch also includes starches with a high amylopectine content (“waxy” starches), starches with a high amylose content, chemically and physically modified starches, starches in which the type and concentration of the cations associated with phosphate groups are modified, starch ethoxylate, starch acetates, cationic starches, hydrolysed starches, oxidised and cross-linked starches.
The final composition contains starch which is partially or completely destructurised and/or complexed. As destructurised starch is intended starch which has lost its granular structure (that means absence of Maltese crosses which is visible by optional microscopy in polarised light with magnification in the range of 250-700 ×).
As complexed starch is intended starch showing
Bastioli Catia
Innocenti Francesco Degli
Lombi Roberto
Nicolini Matteo
Tosin Maurizio
Bryan Cave LLP
Novamont S.p.A.
Rajguru U. K.
Sergent Rabon
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