Patent CA-1339026-C (CA)
Inventor: SINCLAIR RICHARD G
IPC: C08L33/04
Filed: 1989-08-04
Granted: 1997-03-25
Abstract: A first embodiment  providing  for environmentally biodegradable compositions of L-lactide,  D-lactide,  meso D,L-lactide,  and racemic D,L-lactide which are suitable for pliable films and other packaging applications   conventionally   served   by   polyethylene   and   other thermoplastics, are prepared by polymerizing L-lactide, D-lactide, D,L-lactide or mixtures thereof using a catalyst at controlled conditions to allow the polymer in the composition to be plasticized by unreacted lactide monomer.  A copolymer prepared from about 80 parts by weight L-lactide, 20 parts by weight D,L-lactide and containing approximately 20 percent lactide is a thermoplastic with properties similar to a low density  polyethylene  except  that the lactide copolymer is slowly biodegradable in the environment.  Copolymers having properties similar to other known polymers may be prepared by varying the amount of plasticizer in the polymer,  the ratios of D-lactide,  L-lactide,  and D,L-lactide and process conditions.   Fillers and subsequent treatment are also used to modify properties.     A second embodiment providing for an environmentally biodegradable polymer, composition and process for a polymer and a composition.  The biodegradable polymer comprises polymerized lactic acid units of the structure              I   where n is an integer between 75 and 10,000 and the alpha carbon is a mixture of L- and D-configurations with a preponderance of either D- or L-units, wherein the polymer is prepared from L-lactide or D-lactide, at 85 to 95 parts by weight,  and D,L-lactide at 15 to 5 parts by weight, where the unoriented polymer has a tensile strength of at least 5000 psi  and tangent modulus of at least 200,000 psi  and dispersed plasticizer of 0.1 - 5 weight percent and the polymer is suitable for replacement of polystyrene.     The environmentally biodegradable composition  further comprises blends of a physical mixture of polymerized lactic acid units of the formula I, where n is an integer between 75 and 10,000 and the alpha carbon is a mixture of L- and D-configurations with a preponderance of either D- or L-units,  and a lactide homopolymer of D-lactide or L-lactide, wherein the unoriented composition has a tensile strength of at least 5,000 psi and a tangent modulus of at least 200,000 psi and dispersed plasticizer. A  third  embodiment  provides  for  an  environmentally  degradable composition comprising blends of a physical mixture of polylactic acid, and a polymer selected from the group consisting of the polymers of ethylene terephthalate,  a polymer or copolymer of styrene, ethylene, propylene,  vinyl  chloride,  vinyl  acetate,  alkyl  methacrylate,  alkyl acrylate, and physical mixtures thereof.     A fourth embodiment provides for an environmentally degradable composition comprising blends of a physical mixture of a polylactic acid, where the polylactic acid is about 50 to 99 weight percent of the composition,  and  a  blend  compatible  polymer,  such  as  a  segmented polyester, that provides improved impact resistance to the polylactic acid.