Effect of a Small Amount of Thermoplastic Starch Blend on the Mechanical Recycling of Conventional Plastics
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ORIGINAL PAPER
Effect of a Small Amount of Thermoplastic Starch Blend on the Mechanical Recycling of Conventional Plastics Dan Åkesson1 · Gauthaman Kuzhanthaivelu1 · Martin Bohlén2 Accepted: 14 October 2020 © The Author(s) 2020
Abstract The usage of bioplastics could increase in the future which may cause contamination of the waste streams of conventional plastics. The objective of this study was to investigate if a small amount of biopolymer contaminating conventional polymers would significantly affect mechanical and thermal properties. A starch-based plastic was first compounded by blending plasticised starch with PLA (polylactic acid). This polymer blend was subsequently compounded with HDPE (high density polyethylene), PP (polypropylene) or PET (polyethylene terephthalate) at 0%, 1% and 5% of the biopolymer. The compounds were characterised by tensile tests, Charpy impact tests, DSC (differential scanning calorimetry) and FESEM (field emission scanning electron microscopy). Tests showed that PE and PP were not significantly affected in terms of tensile strength and modulus but the elongation at break showed a strong reduction. PET was, on the other hand, incompatible with the starchbased plastic. Already at 1% contamination, PET had lost most of its impact strength. Keywords Bioplastics · Contamination · Mechanical recycling
Background Mechanical recycling is often regarded as the preferred method of recycling thermoplastics [1]. As most thermoplastics are not blendable, the most critical step for successful mechanical recycling is the sorting. Considering that there are many different thermoplastics on the market and that these plastics also occur in different colours and with or without different fillers, sorting is obviously rather complicated. A potential problem is that new plastics emerge on the market which evidently further complicates the sorting. Biopolymers are very attractive as they can be both renewable and biodegradable and have been studied quite intensively over the years. Biopolymers such as polyhydroxyalkanoates (PHA), thermoplastic starch (TPS) and polylactic acid (PLA) are already on the market although currently used in small volumes.
* Dan Åkesson [email protected] 1
Swedish Centre of Resource Recovery, University of Borås, 501 90 Borås, Sweden
Rise Research Institutes of Sweden, Molndal, Sweden
2
However, the introduction of bioplastics on the market is not unproblematic. While mechanical recycling for plastics such as high-density polyethylene (HDPE) and polyethylene terephthalate (PET) is already established, bioplastics that are biodegradable may have different properties than petrobased polymers and if volumes increase this could further complicate the sorting process and disturb current recycling regimes [2]. Even if advanced separation techniques are deployed, some plastics will inevitably be missorted and biodegradable plastics may end up in the waste streams of recycled plastics. These plastics may be sensitive to thermal and hydrolytic degradation but the knowl
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