The Influence of Branching Agent Concentration and Geometry on the Non-Isothermal Crystallization Behavior of Branched Poly(ethylene terephthalate)

• Main Author: Krohe, Christopher W. A.
• Language: EN
• Published: Lehigh University 2017
• Subjects: Polymer chemistry|Materials science|Plastics
• Online Access: http://pqdtopen.proquest.com/#viewpdf?dispub=10250067

<p> Poly(ethylene terephthalate) (PET) is a semi-crystalline polymer that has mechanical and thermal properties suitable for many applications. The rate of crystallization in manufacturing environments influences the final physical, mechanical, and optical properties of PET. Many industrial PET processes occur under dynamic or non-isothermal conditions and in the melt phase. The final material properties are influenced by the size, dimension, and distribution of crystallites and morphology that develop upon cooling from the melt. PET films of varying thickness for optical applications require clarity and transparency. One way achieving clarity and transparency in PET films is to limit or inhibit the quiescent crystallization, while not completely eliminating useful strain-induced crystals. The crystallization behavior of PET is influenced by many things including molecular weight, catalyst remnants, nucleating additives, and the addition of linear and multifunctional comonomers (i.e. branching agents). Branching agents have been reported to inhibit the crystallization of PET. It is of interest to study the effects of branching agents on branched PET (BPET). </p><p> In this investigation the influence of branching agent concentration and geometry on the non-isothermal crystallization behavior and kinetics of BPET was studied. To study the influence of branching agent concentration and geometry, two structural isomers of benzenetricarboxylic acid (<i> n</i>=3) were used at concentrations of 0.10, 0.25, 0.50, and 1.00 mol% (with respect to purified terephthalic acid). The branching agents used were 1,3,5-benzenetricarboxylic acid (trimesic acid, TMA) and 1,2,4-benzenetricarboxylic acid (trimellitic acid, TMLA). TMA and TMLA were used to study the influence of branching agent geometry because TMA is planar and TMLA is non-planar. Two different series of BPET were made to evaluate the influence of catalyst remnants and process on the non-isothermal crystallization behavior of BPET. The Jeziorny-modified Avrami model, the Ozawa model, and the Mo model were applied to study the effects of the branching agent concentration and geometry on the non-isothermal crystallization kinetics of BPET at various cooling rates (5, 10, 20, 50 &deg;C/min). </p><p> The results from the study showed that equivalent amounts of TMA and TMLA produced different non-isothermal crystallization results even though the molecular weight and catalyst concentration remained approximately constant. Increasing branching agent content did not produce a systematic decrease in the crystallization peak temperatures <i>T</i>c. The Mo model was successful in characterizing the non-isothermal crystallization behavior and kinetics of BPET. The crystallization rate was inhibited at concentration of 0.25 and 0.50 mol% TMA and 0.50 and 1.00 mol% TMLA. However, the crystallization rate was enhanced at 0.10 and 1.00 mol% TMA and 0.10 and 0.25 mol% TMLA. It is thought that at small concentrations of the branching agents, regardless of geometry, the branching agents act as nucleating agents. At other branching agent concentrations it is thought that the branching agent geometry influenced the non-isothermal crystallization behavior.</p>