THE POTENTIAL FOR USING ALKALINE-HYDROLYSIS TO STUDY THE FINE-STRUCTURE OF FIBERS MANUFACTURED FROM A THERMOTROPIC LIQUID-CRYSTALLINE COPOLYESTER

The possibility of utilizing alkaline hydrolysis for studying changes in the properties of thermotropic liquid crystalline copolyester fibre s is evaluated. The copolyester fibre manufactured from 4-hydroxybenzo ic acid (HBA) and 2-hydroxy 6-naphthoic acid (HNA) in a molar ratio of 73/27 HBA/HNA was hydrolysed at 21-degrees-C with 2.5 M NaOH, 0.1% ce tyltrimethylammonium bromide solution. After hydrolysis the shape of t he HBA/HNA fibre cross-section changed from round to polygonal, unlike the cross-section of poly(ethylene terephthalate) fibre which does no t change in shape after a similar treatment, Although heat treatment m arkedly increased the tenacity of HBA/HNA fibre, the tenacity fell ste adily with increasing weight loss by hydrolysis. In contrast, the tena city of the non-heat-treated fibre remained constant up to a weight lo ss of 58%, indicating that hydrolysis was occurring at the fibre perip hery and leaving its core unaffected. For both the heat-treated and no n-heat-treated products the initial modulus of the fibres fell progres sively with increasing weight loss. Significant change in brittleness did not appear to occur when either form of HBA/HNA fibre was hydrolys ed to a weight loss of 38%.