Structure And Properties Of Poly(Glycolide-co-L-lactide) Fibers During Drawing Process

Poly(glycolide-co-L-lactide) (PGLA) is an important and valuable material with excellent biodegradability and bioadaptability. In this paper, as-spun PGLA fibers with 92/8 molar ratio of glycolide to L-lactide was used as the raw materials for studing the relationship between drawing conditions, including drawing temperature, deformation rate and drawing ratio and the properties of drawing fibers. The molecular mechanism of the structural formation and the relationship between the structure and properties was described. And the PGLA fiber with excellent mechanical properties was produced. The conclusions are as following:1) In order to obtain the key structure parameter of amorphous orientation function of poly(glycolide-co-L-lactide) fibers, the intrinsic transverse moduli in the amorphous region and the crystalline region were determined in a technology of sonic propagation speed based on two-phase model. They were E_t,c⁰=9.35 GPa and E_t,am⁰=3.21GPa respectively. Their correctness was proved by thermo-shrinkages of different drawing PGLA fibers.2) When drawing ratios were enhanced, the crystallinity and the amorphous orientation function were increased. Elongations at break were reduced from 160% to 40% linearly, whereas the Young's modulus and the tenacity at break were increased linearly. When the drawing ratio was higher than 7, the strain induced crystallization was developed obviously, the increase rate of the crystallinity and the amorphous orientation function became larger and a turning point was observed. The same phenomenon was discovered for the Young's modulus.3) The increase of drawing temperature would promote the disorientation of molecular chains obviously and decrease the value of the amorphous orientation function, which made strain-induced process become more difficult and therefore crystallinity and Young's modulus were decreased. When the temperature was further increased, the obvious flow drawing was observed and the disorientation of global chain orientation happened dramatically. For the drawing sample at 90℃, the elongation at break was 1.98%, tenacity at break was 0.6cN/dtex, which were very closed to that of undrawn fibers.4) Within the range of deformation rate of 0.39-3.02s-1, the Young's modulus was increased 18% and the elongation at break and the tenacity were decreased by 37% and 24% respectively as deformation rate increase. At the same time crystallinity and the amorphous orientation function were increased. When the deformation rate was higher than 1.52s-1, the X-ray diffraction peak of crystallites appeared and the strain induced crystallinity increased apparently, which prevented disorientation of molecular chains at certain degree, therefore the amorphous orientation function became larger.5) The molecular chains of PGLA showed higher flexibility. In order to get PGLA fibers with improved initial moduli, the structure with higher orientation and the more perfect crystallite structure were necessary. Not only a more perfect crystallite structure, but also preferable high chain orientation in the amorphous region and preferable regularity of macromolecule were needed for fibers with high tenacities.6) Based on the study of the relationship between the structure and properties and processing conditions mentioned above, new PGLA fibers with excellent properties were produced in our laboratory, which tenacity and Young's modulus were 5.5cN/dtex and 83.3cN/dtex respectively and elongation at break was 15.3%.This is a foundational research for controlling the condensed structure of PGLA fibers, and has come into play controlling and improving the mechanical properties of PGLA fibers.