Structural Foams of Biobased Isosorbide-Containing Copolycarbonate

Abstract

Isosorbide-containing copolycarbonate (Bio-PC) is a partly biobased alternative to conventional bisphenol A (BPA) based polycarbonate (PC). Conventional PC is widely used in polymer processing technologies including thermoplastic foaming such as foam injection molding. At present, no detailed data is available concerning the foam injection molding behavior and foam properties of Bio-PC. This contribution provides first results on injection-molded foams based on isosorbide-containing PC. The structural foams were produced by using an endothermic chemical blowing agent (CBA) masterbatch and the low pressure foam injection molding method. The influence of weight reduction and blowing agent concentration on general foam properties such as density, morphology, and mechanical properties was studied. The test specimens consist of a foam core in the center and compact symmetrical shell layers on the sides. The thickness of the foam core increases with increasing weight reduction irrespective of the CBA concentration. The specific (mechanical) bending properties are significantly improved and the specific tensile properties can almost be maintained while reducing the density of the injection-molded parts.

Microphase Separation: Enabling Isosorbide-Based Polycarbonates with Improved Property Profile

“…41 From the results in Table 1, it is clear that samples S3−S5 meet these requirements. Since the refractive index of the isosorbidepolycarbonate is 1.50 and sufficiently different from the 1.475 reported for dimer fatty acids, 29,42 the observed transparency must either be caused by complete miscibility or microphase separation into very small domains. If complete miscibility were the cause of the transparency, the measured T g would be expected to be around 114 °C (estimated by the Flory−Fox equation using the following literature values: T g = −15 °C for C 36 44 and T g = 169 °C for the isosorbide homopolymer (S2)).…”

“…The isosorbide homopolymer has previously been produced in melt transcarbonation processes using diphenyl carbonate (DPC) as reported by Dhara et al Long reaction times and temperatures exceeding 270 °C were required and resulted in relatively low molecular weights (∼16 kg/mol); copolymers have been proposed to overcome thermal instability issues due to β-hydrogen elimination (see Figure ), − ,− as already mentioned in the Introduction.…”

“…Thermomechanical properties have been improved by the copolymerization of isosorbide with a range of (non-bio-based) aromatic comonomers, − but in addition to having a reduced overall bio-content, these copolymers do not have improved flow and processing properties. Improved processability, transparency, and flow have been achieved by the introduction of certain soft blocks, incorporating C 2 –C 12 linear diols − ,, or cyclic aliphatic monomers such as 1,4-cyclohexanedimethanol, − but thus far, this approach invariably has resulted in reduced glass transition temperatures.…”