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A Study on Biodegradable Foam of Poly (butylene succinate) (PBS)The Relationship among Branching Factor, Rheological Properties and Processability of Direct Extrusion Gas Foaming for PBS
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Imaizumi, Mitsuhiro / Fujihira, Ryutaro / Suzuki, Jun / Yoshikawa, Katsuyuki / Ishioka, Ryoji /Takahashi, Masaoki
Aliphatic polyesters as biodegradable plastics have been studied and their commercial applications are growing progressively. Processability to be applied to conventional forming methods must be an important factor to extend the applicability of biodegradable plastics. It has been known that long chain branching contributes excellent processability of polyethylene and polypropylene. For aliphatic polyesters the introduction of long chain branching (LCB) is expected to improve their processability. In this study the molecular structure, viscoelastic properties of the melts and processability for direct extrusion gas foaming were investigated for branched poly (butylene succinate) (PBS-B) which was copolymerized with multifunctional monomer and linear poly (butylene succinate) (PBS-L). It was found that the PBS-B showed a broad distribution of molecular weights and existing of LCBs in a molecule. Furthermore, the PBS-B had longer relaxation time components in dynamic viscoelasticity and showed strain hardening in the elongational viscosity measurement, while PBS-L did not show such characteristics.
The processability of direct extrusion gas foaming for PBS-B was thereby drastically improved, e.g. we were able to obtain biodegradable foamed sheet products having densities from 30 to 250 kg/m3 and thicknesses from 0.5 to 3 mm, while PBS-L did not show such good processability. In addition, these foamed sheets were stable in the atmosphere for 2 years, but biodegradable in hot compost or in moist soil under aerobic conditions where a large number of microorganisms ware present.
Key words: Poly (butylene succinate) (PBS) / BIONOLLE / Long chain branching (LCB) / Processability / GPC-MALLS / Dynamic viscoelasticity measurement / Uniaxial extensional flow measurement / Melt tension / Direct extrusion gas foaming / HCFC-22¥HCFC-142b mixed gas / HFC-134a