Polyvinyl alcohol composition and film

Abstract

A method of preparing a plasticised particulate polyvinyl alcohol (PVA) composition is provided, comprising: mixing, in a mixer, at a mixer speed and for a time sufficient that the mixture attains a temperature of at least 50° C.: particulate PVA resin in an amount from 80% to 90% by weight of the mixture; and plasticiser in an amount from 10% to 20% by weight of the mixture, wherein at least a portion of the plasticiser is water; monitoring the apparent viscosity of the mixture during mixing and continuing mixing until the apparent viscosity of the mixture has peaked to a maximum and dropped off to a substantially constant level, thereby to obtain a plasticised particulate mixture having a moisture content in the range from 7% to 14%; preferably adding an anti-caking agent in an amount from 0.05% to 0.5% by weight of the plasticised particulate mixture, and continuing mixing until the anti-caking agent is blended to the plasticised particulate mixture; and stopping mixing, and removing the mixture from the mixer, wherein the mixture temperature is kept below 100° C. at all times during mixing. The properties of the plasticised particulate composition are such that it can be processed, by extrusion and blowing, to a film having advantageous characteristics in terms of structure and properties. Accordingly, also provided is a PVA film characterised in that, when viewed using polarising light microscopy, it has a nonuniform texture consisting of distinct short range areas, e.g. 10 to 500 micrometers, each short range area showing anisotropic orientation within its area, each short range area being oriented isotropically.

1 - 22 . (canceled)  
   
   
       23 . A PVA film produced by a method comprising: 
 mixing, in a mixer, at a mixer speed and for a time sufficient that the mixture attains a temperature of at least 50° C.:    particulate PVA resin in an amount from 80% to 90% by weight of the mixture; and    plasticizer in an amount from 10% to 20% by weight of the mixture, wherein at least a portion of the plasticiser is water;    monitoring the apparent viscosity of the mixture during mixing and continuing mixing until the apparent viscosity of the mixture has peaked to a maximum and dropped off to a substantially constant level, to obtain a plasticised particulate mixture having a moisture content in the range from 7% to 14%;    stopping mixing, and removing the mixture from the mixer,    wherein the mixture temperature is kept below 100° C. at all times during mixing; and    processing the plasticized particulate PVA composition to a film through a temperature zone of at least 185° C.,    wherein the film is free of residual methanol.    
   
   
       24 . A PVA film comprising a PVA resin in an amount from 80% to 90% by weight and plasticizer in an amount from 10% to 20% by weight, wherein, when viewed using polarising light microscopy, the film has a nonuniform texture consisting of distinct short range areas, each short range area showing anisotropic orientation within its area (as evidenced by a uniform colour when viewed using polarising light microscopy), each short range area being oriented isotropically (as evidenced by different areas having different colours when viewed using polarising light microscopy).  
   
   
       25 . The PVA film of  claim 24  wherein the short range areas are 10 to 500 micrometers in length and width across the film.