Thermoplastic polyvinyl alcohol (PVOH) is emerging as a new material to meet the demands of various safety/environmental related applications, as well as specialty water soluble applications. Specific applications include water soluble and biodegradable films and bottles for packaging pesticides, herbicides, detergents and the like. Additional applications include water soluble fibers for woven structures which can be safely disposed of in water, hospital bags for containing clothing for safe delivery to laundry sources without human contact, and water soluble containers for disposal of shipboard wastes which are biodegradable. Designed multilayered films for environmentally acceptable destruction comprising interlayers of PVOH and exterior layers of polyolefins offer properties for yard waste disposal in compostable applications.
U.S. Pat. No. 5,051,222 discloses a method for making thermoplastic (melt extrudable) PVOH compositions which comprises, providing sufficient energy to a PVOH which is at least partially crystalline to both melt the PVOH and substantially eliminate the crystallinity in the PVOH melt while simultaneously removing energy from the PVOH melt at a rate sufficient to avoid decomposition of the PVOH. The melt is then extruded, preferably into a strand, rapidly cooled and cut into pellets for subsequent thermoprocessing into the desired product or article.
Thermoplastic PVOH, generally, has excellent toughness at high relative humidity due to plasticization by adsorbed water. At low to intermediate relative humidity, thermoplastic PVOH compositions have limited toughness. At lower temperature, these compositions also exhibited lower toughness than desired. In order to alleviate this problem, one solution has been to modify thermoplastic PVOH compositions with the addition of more plasticizer. Plasticizer migration can yield additional problems related to the surface characteristics of extruded or injection molded objects. Thermoplastic polyurethane addition to thermoplastic PVOH yields impact modification to alleviate the toughness deficiency. (See U.S. Pat. No. 5,028,648). However, thermoplastic polyurethane addition yields crosslinking of the PVOH under conditions of high time or temperature exposure. An impact modifier which yields impact modification along with melt stability with thermoplastic PVOH is desired.
Polymer blends comprising PVOH are noted in many patents. The blends involve thermoplastic PVOH with polyolefins, polyamides, natural polymers, other water soluble polymers and in a few cases polyesters. The need to improve the impact strength of PVOH is noted in several of these references.
U.S. Pat. No. 4,611,019 discloses that the addition of small amounts (0.5 to 4.5 wt %) of selected polyamides or polyesters to plasticized melt extrudable PVOH homopolymer yields compositions with lower permeability to oxygen and other gases. The degree of hydrolysis for the PVOH is taught as greater than 95%. Plasticizers from 7 to 15 wt % are desired. These plasticizers include: aromatic sulfonamides, N,N-dimethylamides of fatty acids, polyols, alkylene carbonates, aromatic phosphates and phosphites, aromatic sulfonates and alkyl pyrrolidones. The polyesters noted are: poly(butylene terephthalate), poly(ethylene terephthalate) and polyether-polyester block copolymers.
U.S. Pat. No. 4,608,187 discloses that rubbery inclusions into cast PVOH films can be used to improve toughness. The rubbery inclusions noted, include polysiloxane, poly(ethylene oxide), neoprene, polyisoprene, natural rubber, styrene-butadiene copolymers, acrylates, poly(isobutylene) and poly(vinylidene chloride).
J56118439-A discloses the addition of a styrene-diene block copolymer to an ethylene-vinyl alcohol (EVOH) copolymer to improve impact strength.
U.S. Pat. No. 4,600,746 discloses blends of PVOH with a polyolefin or an ethylene-ester copolymer with groups capable of reacting with the hydroxyl of the PVOH for use as barrier polymers. Ethylene-acrylic acid copolymers, ethylene-methacrylic acid ionomers, and maleic anhydride grafted polyolefins are noted in blends with PVOH as melt processible alloys.
U.S. Pat. No. 4,824,725 discloses a blend of PVOH and a sulfonate containing polyester for use as a hydrophilic coating for a transparent base drafting film.
J01308455-A discloses a blend of an EVOH copolymer and a polyester amide or a polyether ester amide for use as a gas impermeable polymer.
EP350,224-A discloses a blend of poly(butylene terephthalate) and an EVOH copolymer has good gas barrier properties for food packaging applications.
J63304043 discloses a blend of a thermoplastic polyester [poly(ethylene terephthalate) or poly(butylene terephthalate)], an EVOH copolymer and a maleic anhydride modified styrene/olefin block copolymer.
"Handbook of Thermoplastic Elastomers," ed. by B. M. Walker and C. P. Rader, Chp. 6, p. 181, Van Nostrand Reinhold Co., New York, 1988, discusses polyester-polyether block copolymers as thermoplastic elastomers.
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