Fabrication of high-performance poly(vinyl alcohol) tubes via stable melt extrusion by reversible crosslinking of boric acid

The unique intermolecular interactions of poly(vinyl alcohol) (PVA) endow it with excellent barrier properties to oxygen and nonpolar hydrocarbon organic solvents, thus having potential applications in the fields of oil and gas transmission. In view of the difficulties in thermal processing of PVA and based on the molecular complexation technology established by our research group, the melt extrusion of PVA tubes was achieved. To improve the extrusion stability of PVA tubes, boric acid (BA), which could form reversible crosslinking with PVA, was further introduced, and the influences of BA content on the interactions between BA and PVA, the thermal processability of PVA, as well as the mechanical properties and gasoline barrier properties of PVA tubes were systematically studied. The results showed that BA could form both chemical and physical crosslinking with PVA, so controlled the violent evaporation of water, one of plasticizers with low boiling point, and at the same time ensured the good thermal processing of PVA, lastly realizing the stable melt extrusion of PVA tubes. With the increase of BA content, the crystallinity of PVA decreased, but the glass transition temperature, mechanical properties, thermal dimensional stability, as well as water resistance of PVA tubes increased. The gasoline barrier of PVA tubes reached the best at the BA content of 0.10 wt%, that is, 0.97 g mm/m(2) day.