Polylactic acid (PLA) is a bio-based polymer made by using starch as the raw material. The advantages of PLA include high strength, high modulus and biodegradability, but its drawbacks of low heat resistance, brittleness, and high cost limit its applications. Making heat resistant PLA foam sheet is one of major goals for PLA researchers because the foam has good toughness and low cost.

The foam sheet can be easily thermoformed into short life packaging stuff such as food containers. The short life stuff is the ideal application for PLA since this stuff is very

Fig.1 Food Containers

hard to be recycled or reused. But the low melt strength of PLA renders it difficult to make foam, especially foam sheet. Although there were some reports on making PLA foam sheet, it was not broadly used due to its low heat resistance. The L, D-PLA stereocomplex can be made foam sheet, but its price is too high to be widely used. The most economical approach is to make heat resistant foam sheet directly from regular PLLA.

Prof. Jin Zhu’s group of the Ningbo Institute of Materials Technology and Engineering (NIMTE), the Chinese Academy of Sciences (CAS), and the Guangzhou Bio-plus Materials Technology Co., Ltd. (www.bio-plus.cn) have solved both the issues of low melt strength and low heat resistance of PLA. The heat distortion temperature of PLA has been improved to 120oC from 55oC of regular PLLA. The heat resistant PLA foam sheet was successfully obtained through a commercial foaming extruder by using butane or CO2 as the foaming agent. The foam sheet has been thermoformed into a variety of food containers such as plates, cups, boxes, and so on (Fig.1). The foaming ratio is more than 15 times.

The thermoformed containers can stand the temperature more than 100oC. It can replace the stuff made by polystyrene foam and paper. Several companies are now working on making the commercial products. The real heat resistant PLA foam products will come soon.

The group and their partner are seeking worldwide cooperation with plastic processing companies to manufacture various products based on this PLA  foam sheet.

Professor Jin Zhu jzhu@nimte.ac.cn

Research Gruop Url : http://english.nimte.cas.cn/rh/rd/bp

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