TABLE OF CONTENTS See also preceding Section 4.4.2 relating to ethylene-vinyl alcohol copolymers.
These polymers are produced by a more or less complete hydrolysis of polyvinyl acetate.
The properties depend greatly on the degree of hydrolysis. The major interest of this family and, at the same time, the main disadvantage, is its solubility in water, which is:
proportional to the degree of hydrolysis
inversely proportional to the degree of polymerization.
In addition to their water solubility, PVALs are appreciated for their good mechanical properties in the dry state, resistance to common solvents, barrier effect in dry atmospheres, possibility of food contact for suitable grades, biodegradability.
On the other hand, the water solubility and high moisture absorption are an obstacle to their development in engineering applications. PVALs must often be protected with other polymers. The cost is in the range for engineering polymers.
Stresses at yield can be from 40 MPa up to 50 MPa with elongations at break varying from 100% to more than 200%. Density is about 1.23 1.30g/cm 3 and coefficients of thermal expansion are roughly 7 8 10~ 5/ C.
PVAL can be plasticized and processed by casting, dipping, injection, extrusion.
The main engineering applications, possibly in combination with other polymers, are, for example:
films for packing chemicals, fertilizers, herbicides, disinfectants, dyes, colorants, scalers, cosmetics
release films for composite moulding
solvent-resistant tubes and pipes
membranes for pumps carrying petroleum or chemical products
binders for ferrite cores
Trade names examples:...
