Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – At least one aryl ring which is part of a fused or bridged...
Patent
1999-02-01
2000-09-12
Warzel, Mark L.
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
At least one aryl ring which is part of a fused or bridged...
524306, 524310, 524315, 524317, 524320, 524321, 524449, 524451, 524442, 524599, 524601, 523124, 528272, 528354, C08K 509
Patent
active
061179280
DESCRIPTION:
BRIEF SUMMARY
This application is the national phase under 35 U.S.C. .sctn.371 of prior PCT International Application No. PCT/FI97/00143 which has an International filing date of Mar. 4, 1997 which designated the United States of America, the entire contents of which are hereby incorporated by reference.
The invention relates to polylactide films with improved mechanical properties. The invention relates in particular to the use of plasticizers to improve mechanical properties.
Polylactide, i.e. polylactic acid, which is usually prepared from lactic acid dimer, i.e. lactide, has already for years been used for medical purposes, for example in the manufacture of surgical sutures, for degradable bone nails, and for controlled release of drugs. The use of polymers for packaging materials and for other bulk products has so far been limited by the high price of polymers and their susceptibility to breaking down during technical processing. It has not been economically profitable to produce and treat in a manner intended for medical applications a polymer intended for bulk products.
In recent years, interest in biodegradable polymers, i.e. biopolymers, has greatly increased, and many companies have made efforts to launch on the market packaging materials, hygiene products, sacks and films for agricultural purposes, and sacks for waste. In particular, various films have gained importance.
The manufacture of films, in particular film blowing, by no means constitutes simple technology, and so far commercial biopolymers have not been successful in this area. The mechanical and optical properties of film and, for example, its sensitivity to moisture, vary widely.
Polylactides, or condensation polymers which are based on lactic acid, are for many reasons a very attractive group of biopolymers. Their principal degradation product, lactic acid, is a product common in nature, it is not toxic and is used widely in the food and pharmaceutical industries. A high molecular weight polymer can be produced by ring-opening polymerization from lactic acid dimer, lactide. Lactic acid is optically active, and thus its dimer appears in four different forms: L,L-lactide; D,D-lactide; L,D-lactide (mesolactide); and a racemic mixture of L,L- and D,D-lactides. By polymerizing these either as pure compounds or at different blend proportions, polymers are obtained which have different stereochemical structures affecting their resilience and crystallinity and, consequently, also their mechanical and thermal properties. The obtained polymers are usually hard and optically clear, but not as such usable, owing to certain problems.
Upon forming, polylactide is in equilibrium with its monomer, lactide. This has sometimes been deemed to be advantageous, since monomers and oligomers may act as plasticizers of the polymer, but it also leads to rapid hydrolysis and causes problems of adhesion in the processing of the polymer. Furthermore, the presence of the monomer lowers thermal stability during melt processing. In general the residual lactide must be removed from the polymer. An acceptable lactide content is below 2%, preferably below 1%. Various removal methods, such as evaporation, have been disclosed.
The breaking down of polymers during processing can be reduced by the removal of the residual lactide, the maintenance of the water content at a low level (below 200 ppm) or by the addition of commercial stabilizers (WO 94/07941, Cargill). In terms of film blowing, an advantageous method is to mix certain peroxides with the polymer, whereby the melt strength of the polymer will be sufficient for film blowing (FI945964, FI945264, Neste).
Polylactide has excellent optical properties and a high tensile strength, but it is rigid and brittle, and its elongation values are low, as are its tearing strength and bursting strength (dart-drop). Attempts have been made to plasticize the films by using various plasticizers. Battelle's -patent publication WO 92/04493 mentions leaving monomers and oligomers in the polymer for plasticizing purposes. Cargill, WO 94/07941, has
REFERENCES:
patent: 3636956 (1972-01-01), Schneider et al.
patent: 5180765 (1993-01-01), Sinclair
patent: 5403897 (1995-04-01), Ebato et al.
Hiltunen Elina
Selin Johan-Fredrik
Skog Maria
Neste Oy
Warzel Mark L.
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