Influence of small rubber particles on the environmental stress cracking of high impact polystyrene

Abstract

This article exploits the influence of rubber particle size (RPS) and rubber crosslinking on environmental stress cracking resistance (ESCR) of high impact polystyrene (HIPS), with special interest on the influence of small rubber particles fraction. Three commercial HIPS of high ESCR were selected and four batches of HIPS were prepared in-house, including samples based on high cis and very high viscosity polybutadiene (PB). Their morphologies were analyzed by low angle laser light scattering, optical microscopy, and transmission electron microscopy, and the samples were submitted to flexural ESCR tests with fatty agents. The ESCR to sunflower oil was found to increase with the reduction of the rubber particles fraction smaller than 1-2 micron. Results have also confirmed that an increase in RPS is the key parameter to promote ESCR, although there is limit for RPS to be effective on ESCR improvement. The reduction of small rubber particles fraction in HIPS was achieved by using a high cis PB, that promotes low grafting efficiency of polystyrene onto PB backbone because of the low content of 1,2 vinyl isomer. Besides the ESCR improvements, HIPS with high cis PB showed higher elastic modulus and impact resistance than HIPS containing medium cis PB, which is desired for thickness reduction in food packaging and refrigeration cabinets.

Environmental stress cracking: A review

“…Impact polystyrene and ABS are among the major commercially available products in this classification. It has been well‐recognized in the literature that rubber impact modification (particularly in the case of polystyrene) leads to improved ESCR [47, 80, 103, 112–118]. This was illustrated in a comparison of the case of a blend of polystyrene with a high rubber content polystyrene where the stress required for failure with exposure to heptane increased by more than an order of magnitude with increasing high rubber content PS concentration during constant stress loading [103].…”

Polymerization of butadiene under the action of lithium containing initiating system

“…2,8,9) and reduction in the content of the initiating system c is (experiment nos. 2, 10, 11) in the polymerization lead to an increase in molecular weights of the polymer while maintaining the polydispersity index.…”

“…The emergence of new applications of plastics, such as pharmaceuticals, medicine and food industry [8,9], puts forward a number of specifi c requirements to polybutadienes: preset microstructure and molecular characteristics, lack of residual hydrocarbons and gel fraction, low metal content and reduced coloration. So, investigations of synthesis of polybutadienes with lithium-containing catalysts are relevant also to the present time [10,11].…”

Environmental stress cracking (ESC) resistance of polycarbonate/SiO2 nanocomposites in different media

“…The stress‐cracking resistance drops when the stress agents have a smaller molecular size and a less bulky molecular structure. This results in rapid diffusion of the ESC agent into the polymer and accordingly promotes premature ESC failure . In this logic, filled plastics, in particular, nanocomposites should support the absorption of the solvent due to the enormous internal interfaces between the filler and the plastic matrix and thus reduce the stress‐cracking resistance of the polymer.…”