Foam High temperature
Foam High temperature resistant PLA foams Scientists based at Crown Research Institute Scion in New Zealand have developed PLA foams with high dimensional stability at elevated temperatures. The research was led by Jean-Phillippe Garancher and Alan Fernyhough for the Biopolymer Network (BPN) Ltd, a research company with a keen interest in development and commercialisation of biofoams. One of the major limitations of PLA foams in some applications is its poor dimensional stability (leading to squashing, deformation and collapse) when exposed to conditions above 60°C. This temperature corresponds to PLA’s glass transition temperature (Tg). Above its Tg, PLA softens and is therefore unable to sustain loads, leading to distortion of the moulded foam articles. One of the ways to overcome this issue is to promote the crystallisation of PLA. Crystals will provide a rigid structure to PLA products used at elevated temperatures. Increased crystallisation can be achieved using additives such as nucleating agents or controlling the monomer isomer composition in PLA (making it more pure in one isomeric form). If sufficiently crystallised, PLA is able to bear loads at temperatures significantly above its Tg. These approaches are not always compatible with a particle foaming process as crystalline regions in the PLA tend to restrict both blowing agent uptake and the polymer expansion. Garancher demonstrated that highly crystalline grades of PLA could be successfully foamed and moulded to low densities. He achieved this by refining an already existing particle foaming process developed by BPN, which used sub-critical CO 2 and commercially-available predominantly amorphous PLA to produce mouldable particle foams. This proprietary method involves absorption of CO 2 by PLA followed by pre-expansion and then moulding similar to that used by the EPS industry. The trick to using crystalline grades of PLA is adjusting the CO 2 impregnation parameters (the subject of an additional patent application). The method was successful using commercial grades of PLA, with the grade of PLA selected depending on the final foam properties desired. Using off-the-shelf material, expanded PLA (EPLA) was produced with a high level of crystallinity, simultaneously with low density and fine cellular structure. These foams showed significantly higher dimensional stability at elevated temperatures compared with their amorphous alternatives. This work provides an opening for EPLA to be used as a substitute for EPS and other polymer foams in a much wider range of applications where stability in higher temperature conditions is important, such as specialised sporting goods and packaging applications. In earlier work, EPLA had been shown to have thermal insulation properties and mechanical properties comparable to EPS at given density values. As BPN moves closer to commercialising its foam technology, it has built a PLA foam pilot plant in Nelson, New Zealand. The plant will be used to fine-tune the production of PLA foam articles on EPS moulding equipment and to put PLA foam products in to the cold chain packaging marketplace. 28 bioplastics MAGAZINE [01/13] Vol. 8
Foam By Paul Charteris Science Communicator Scion Rotorua, New Zealand Research to produce environmentally friendly packaging options is a priority for the New Zealand fresh seafood industry which seeks to maintain a leadership position in the international market place. The pilot plant consists of three machines: one for impregnation of the PLA beads, one to pre-foam the impregnated beads and another to produce moulded foam products. The impregnation machine performs the impregnation on a set cycle utilising CO 2 as the blowing agent, which is a BPN proprietary process. The machine cycle allows excellent recovery of CO 2 to minimise foam production costs. The beads are then foamed in the pre-foamer and transferred directly to the moulding machine. A small semi-automatic moulding machine is being used, with three moulds operational – a fish box, a fish box lid and a small block mould. After only a few weeks of operation, a number of low density fish boxes and lids have been produced. Moulding is being further optimised in early 2013 to achieve lower densities concurrently with large volume trials through a commercial plant. Based on early results, a number of New Zealand EPS moulders are keen to trial this process. This research was funded by New Zealand’s Ministry for Science and Innovation from its BPLY 0801 programme. Garancher and Fernyhough’s paper: Crystallinity effects in polylactic acid-based foams was published in Journal of Cellular Plastics September 2012 vol. 48 no. 5 387-397. Info: Scion Scion is a New Zealand Government–owned Crown Research Institute that undertakes research, science and technology development in forestry, wood products, biomaterials and bioenergy. Scion‘s work contributes to beneficial economic, environmental and social outcomes for New Zealand. Formerly the NZ Forest Research Institute, Scion employs approximately 340 people and has its head office in Rotorua. Biopolymer Network Ltd The Biopolymer Network Ltd (BPN) is a New Zealand research company dedicated to creating technologies to convert primary production outputs into a wide range of high performance, bio-based products. BPN research is focused on creating products using renewable, natural materials instead of petrochemicals. Biopolymer Network Ltd has, and continues to develop, its portfolio of intellectual property in biopolymers, specialty chemicals, bio-composites, bio-foams and moulded structures. With key partners these products are being taken into the market place. The Biopolymer Network‘s research base is built from three of New Zealand‘s largest and leading research organisations, AgResearch, Plant and Food Research and Scion. This provides us with world leading scientific expertise and the largest focused research effort in this area in New Zealand. www.scionresearch.com www.biopolymernetwork.com bioplastics MAGAZINE [01/13] Vol. 8 29
