| 摘要 |
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.
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