Supramolecular polymer additives to improve the crystallization behavior and optical properties of polybutylene terephthalate and polyamides

The use of additives to enhance the processability and end properties is one of the main measures to enlarge the property profile of commercial thermoplastic polymers. The physico chemical properties of semi crystalline polymers depend to a large extend on the crystal structure and spherulite size, which can be controlled by nucleating agents. These additives can increase the crystallization temperature and thus reduce cycle times during melt processing, affect the physical properties and can in some cases improve the optical properties (clarity and haze). This thesis describes the use of supramolecular nucleating agents to increase the polymer crystallization behavior and to improve the optical properties of polybutylene terephthalate and polyamides. In the first chapter the influence of the molecular structure of 1,3,5-benzenetrisamides on the nucleation behavior of polybutylene terephthalate was investigated. In order to explore structure property relations, 43 derivatives were screened with regard to their nucleation ability of PBT. For promising compounds the additive dissolution and crystallization behavior in the polymer melt and crystallization temperature of the polymer were investigated. It was revealed that certain 1,3,5- benzenetrisamides are capable to nucleate PBT. They can act as supramolecular polymer additives, are soluble in the PBT melt under the processing conditions and upon cooling self assemble into fine fibrillar supramolecular nano objects inducing the nucleation of PBT. It was found that particularly the trisamide derivatives based on the 1,3,5 triaminobenzene core are much better soluble than the derivatives based on the 1,3,5-benzenetricarboxylic acid core and 2,4,6-trimethyl-1,3,5-trisaminobenzene core. As a result additives featuring too good solubility do not self-assemble prior to the polymer crystallization and hence do not induce nucleation. This demonstrates that the nucleation efficiency strongly depends on the individual chemical structure of the additives and slight structural changes have large impact. In addition for the first time it was possible to visualize the supramolecular structures within the PBT matrix by selectively hydrolyzing PBT. The morphology of the formed supramolecular nano objects is determined by cooling rate and additive concentration. Faster cooling and lower additive concentrations leads to the formation of needle like structures with smaller lateral dimensions and a narrower size distribution. In the second chapter a new class of supramolecular nucleating agents on the structural motif of 1,4- cyclohexane bisureas was synthesized specifically for semi crystalline polyamides. The bisureas are temperature stable enough to be applied in high melting polyamides. In total, 29 derivatives were synthesized and investigated with respect to their nucleation and clarification behavior in PA6. The chemical structure of the additives was systematically varied by changing the conformation of the central unit and the length and degree of branching within the peripheral substituents. Bisureas based on the trans conformation of 1,4- cyclohexane are capable to efficiently nucleate the alpha form of PA6 even at concentrations below 200 ppm, with extremely high nucleation efficiencies of around 90 %. In addition, selected derivatives were found to distinctly improve the optical properties haze and clarity, as well as the laser transparency, in injection molded samples. This is the first time semi crystalline polyamides were clarified. The most efficient clarifiers for PA6 were found to decrease the values for haze from nearly 100 % (1.1 mm thick samples) for neat PA6 to 19 % and 11 % at a concentration of 1.5 wt%. By varying the peripheral substituents of the trans-bisureas interesting structure property relations could be revealed. The investigated derivatives with longer flexible substituents were efficient nucleating agents for PA6, but displayed only modest improvements in optical properties. Short, highly branched substituents, preferably in alpha position to the urea groups, were found to be a key segment for the clarification of PA6. Additionally we demonstrated that the process conditions, namely cooling rate and mold thickness, strongly determine the final optical properties. The use of trans-1,4-cyclohexane bisureas could also be expanded to other semi crystalline polyamide homo- and copolymers. For the first time the concept of supramolecular nucleating and clarifiying agents was sucessfully transferred to semi crystalline polyamides. With the new class of compounds it could be demonstrated that trans-1,4-cyclohexane bisurea derivatives are capable to increase the crystallization behavior and improve the optical properties, particularly the haze values, remarkably.

Level thesis:degree_level

thesis.doctoral

Grantor dc:publisher

Universität Bayreuth

Year

2012

Author dc:creator

• Richter, Florian

Contributors dc:contributor

• Schmidt, Hans-Werner

Repository record source_url

https://epub.uni-bayreuth.de/id/eprint/135/

OAI identifier oai:identifier

oai:epub.uni-bayreuth.de:135