Study The Effect Of Ppzn On Crystallization Behaviors And Mechanical Properties Of Poly(L-Lactic Acid)

Poly(L-lactic acid) is a biodegradable polymer materials, which is expectedto become an alternative to petroleum based polymers. It has broad applicationprospects. PLLA has many excellent properties, but the material itself has manydisadvantags, such as brittleness, low heat-resistance and low crystallinity, which areseriously restricted to its promotion and application in various fields. These defectsrelate to the low crystallinity of PLLA. Currently, researchers are trying to find methodto modify PLLA, among which adding nucleating agent is a method easy to achive.Theose studies show that many materials can be used as a nucleating agent for PLLA,but widely conducted are not more. Thus searching a cheap and efficient nucleatingagent for PLLA is a meaningful research.In this paper, we synthesized phosphate nucleating agent (PPZn) by a simplemethod, and yields higher. First we investigated the effect of several nucleating agents(PPZn, PEG, PCL, Talc) on the crystallization behavior of PLLA by DSC and POM.The results showed that the crystallization effect of PPZn is most prominent, resultingin the small spherulites as well as the dramatically reducd crystallization time. We thenstudied the relationship between the non-isothermal and isothermal crystallizationbehavior of PLLA and PPZn content. Adding5%PPZn in PLLA during thenon-isothermal cold crystallization process, the crystallization temperature comparedwith a pure sample dropped to110℃, reduced by about18℃and the crystallinityincreased about107%up to27%. The crystallization properties of PLLA furtherincreased with increasing PPZn concentration. We also did the corresponding FT-IRexperiments which proved that the crystal form of poly (lactic-acid) during the non-isothermal melt crystallization processing was not affected by PPZn, but theremay exist interactions between PLLA and PPZn, which could accelerate the PLLAcrystallization rate. And then the isothermal crystallization kinetics of PLLA/PPZnsystems were calculated by the Avrami equation. Finally, we studied the effect ofnucleating agents on the mechanical properties of PLLA. The results show that PPZnweakened the mechanical properties of PLLA, but it could improve heat resistance.Wethen added the nucleating agents and plasticizers PEG and other additives compoundsin PLLA to improve its weakened mechanical properties. Results showed that highmolecular weight PEG in5%-10%can greatly improve the elongation break of PLLA,while reduceds its tensile strength. Found that it does not exist a synergy betweenPPZn and PEG. PPZn and additives will produce the negative effects weakening themechanical properties and heat resistance of PLLA.