Biodegradable, liquid impervious multilayer film compositions

Claims

What is claimed is:

1. A biodegradable liquid-impervious multilayer film comprising:

a first polymer film layer and a second polymer film layer joined to said first layer; said polymer film layers comprising a thermoplastic polymer capable of forming a film by a melt process, said thermoplastic polymer being selected from the group consisting of:

(a) moisture sensitive polymers selected from the first group consisting of interpenetrated networks of destructurized starch, mixtures of destructurized starch, thermoplastic polyvinyl alcohol compositions, hydroxypropyl cellulose, and mixtures thereof;

(b) thermally sensitive polymers selected from the group consisting of polycaprolactone, other aliphatic polyesters having melting points below about 65.degree. C. or Vicat softening points of 45.degree. C. or less, and mixtures thereof;

(c) mechanically limited polymers selected from the group consisting of cellulose esters, cellulose ester blends with polycaprolactone, cellulose ester blends with polyhydroxybutyrate/valerate copolymers, and mixtures thereof;

(d) poly(alpha-hydroxy alkanoates);

(e) hydrolytically cleavable aromatic/aliphatic polyester copolymers selected from the group consisting of copolymers of polyethylene terephthalate and polybutylene terephthalate, wherein the aliphatic fraction of said copolymer is derived from the group consisting of oxalates, malonates, succinates, glutarates, adipates, pimelates, suberates, azelates, sebacates, nonanedioates, glycolates, and mixtures thereof;

(f) oxidized ethylene/carbon monoxide copolymers;

(g) aliphatic polyesters having melting temperatures or glass transition temperatures above 65.degree. C.; and

(h) thermoplastic, biodegradable elastomers selected from the group consisting of polycaprolactone/diene block copolymers and aliphatic polyester urethanes;

said first and second polymer film layers comprising different polymers;

said multilayer film having:

a machine direction (MD) tensile modulus from about 6.895.times.10.sup.8 dynes/sq. cm. to 6.895.times.10.sup.9 dynes/sq. cm. (10,000 to about 100,000 lbs./sq. in.);

a MD tear strength of at least 70 grams per 25.4 microns of thickness;

a cross machine direction (CD) tear strength of at least 70 grams per 25.4 microns of thickness;

an impact strength of at least 12 centimeters as measured by falling ball drop;

a moisture transpod rate less than about 0.0012 grams per square centimeter per 16 hours;

a modulus at 60.degree. C. of at least 5.52.times.10.sup.7 dynes/sq. cm. (800 lbs./sq. in.); and

a thickness from about 12 microns to about 75 microns.

2. The multilayer film of claim 1 wherein said poly(alpha-hydroxy alkanoate) is selected from the group consisting of polyhydroxybutyrate, polyhydroxybutyrate/valerate copolymers, and mixtures thereof.

3. The multilayer film of claim 1 wherein said oxidized ethylene/carbon monoxide copolymer is derived from ethylene/carbon monoxide copolymers containing 0.5 to 20 weight percent carbon monoxide.

4. The multilayer film of claim 1 wherein the multilayer film additionally comprises a third polymer film layer joined to said second layer such that the multilayer film comprises a center core layer forme