Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Treating polymer containing material or treating a solid...
Reexamination Certificate
1999-08-13
2001-02-13
Truong, Duc (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Treating polymer containing material or treating a solid...
C528S354000, C528S490000, C528S501000, C528S503000, C521S045000
Reexamination Certificate
active
06187901
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to the removal of lactide from polylactide by ensuring effective material transfer during evaporation and relates to the recovery of lactide from the process for the preparation of polylactide.
DISCUSSION OF RELATED ART
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 use of polymers of lactic acid in these applications has so far been limited by the high price of the polymers and their susceptibility to breaking down during technical processing.
Polyhydroxy acids can be prepared by polycondensation reactions, which are typical in the preparation of polyesters, or by ring-opening polymerization from cyclic lactones. Polyhydroxy acids are thermoplastic polyesters which resemble many conventional polymers.
Polylactides, or condensation polymers based on lactic acid, are for many reasons especially attractive, since 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 best be produced by ring-opening polymerization from the dilactone, also called 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 bright.
The ring-opening polymerization of cyclic lactones of hydroxy acids, such as lactide, glycolide, epsilon-caprolactone, etc., constitutes technology known per se. The polymerization processes known are various, some examples being U.S. Pat. No. 5,378,801 relating to extrusion polymerization, patent publication EP 0 664 309-A relating to two-step polymerization, and patent publication EP 0 499 747-A describing polymerization in a mixing reactor.
REFERENCES:
patent: 5378801 (1995-01-01), Reichert et al.
patent: 0499747A2 (1991-12-01), None
patent: 0664309A2 (1995-07-01), None
patent: 0755956A2 (1997-01-01), None
Kaariainen Kari
Katsaras Nikitas
Koskinen Jukka
Selin Johan-Fredrik
Birch & Stewart Kolasch & Birch, LLP
Fortum Oil and Gas OY
Truong Duc
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