Hello and welcome to a new blog post. Today we are going to discuss how to turn thermoplastics carbon negative in an effective way.
In previous posts I presented to you the Global Warming Potential (GWP) of different plastics vs. their density as well as the GWP values of thermoplastics compared to their different thermal properties and transitions: Tg, heat capacity (Cp), short term temperature exposure (HDT) and long term temperature exposure (UL Yellow Card).
Among the materials and chemicals, thermoplastics have already a low GWP value. Gasses such as methane (CH4) have an estimated GWP of 27-30 over 100 years, and the average cement has a GWP of 600-800 kg CO2 eq / ton. Most thermoplastics are in the range of 2 -8 kg CO2 eq / ton.
Is it possible to have carbon negative thermoplastics?
Yes, by using specific functional fillers which are able to lock in more carbon dioxide than they release in a later stage. In the following we discuss two filler examples: biochar and hemp. In general, after the pyrolysis of biomass, biochar is the lightweight black residue and it consists out of carbon and ashes.
Biochar
Seth Kane [2] and his team demonstrated that carbon-neutral composite materials can be produced by adding biochar. They evaluated it over a cradle-to-gate life cycle assessment. Biochar was added as a filler in recycled HDPE (rHDPE), virgin HDPE, bio-based polylactic acid (PLA), and polyhydroxybutyrate (PHB). In general, biochar fillers lock carbon in a stable form and this in a permanent way. Key results were that 40 w% biochar filler is sufficient for rHDPE to reach 0 kg CO2 equivalent. PLA requires 50 w% biochar filler to be considered 0 kg CO2 equivalent. And HDPE needs 52 w% to reach carbon neutrality (Figure 1). Furthermore they found out that biochar increases the tensile strength of rHDPE by 45%, and stiffness by 126%. Also the flexural storage modulus could be improved by 79% however all over the compound was more brittle. They concluded that adding biochar linearly reduced the GWP potential of the examined plastics by up to 3.3 kg CO2 equivalent per kg of material compound.
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| Figure 1: Overview polymers with biochar filler to reach 0 kg CO2 eq. GWP |
Hemp
In a similar situation we have hemp as a filler. It can be used with PP as base polymer in Automotive applications (door panels, seat backs paneling, bumpers, spoilers). Apart from cost and weight reduction, using hemp additives reduces the carbon footprint too. Industrial hemp additive manufacturer Heartland [4] demonstrated a carbon footprint reduction of virgin plastics by as much as 44%.
Conclusions
Biochar and hemp used as fillers in thermoplastics are an effective way to reduce the carbon footprint. Together with recycling of thermoplastics (including fillers, and compounds) as well as other mitigation strategies such as bio-based plastics, usage of renewable energy in plastics manufacturing will reinforce the advantage of plastics over other so-called green materials in the long run.
Greetings and #findoutaboutplastics
Herwig
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Literature:
[1] https://www.madeofair.com/
[2] https://www.sciencedirect.com/science/article/pii/S2666682022000226#sec0007
[3] https://www.sciencedirect.com/science/article/pii/S0959652620338956
[4] https://www.businesswire.com/news/home/20220124005281/en/Heartland-and-Ravago-Develop-Products-to-Reduce-the-Carbon-Footprint-of-Plastic
[5] https://www.researchgate.net/figure/Global-warming-potential-GWP-range-for-cementitious-Environmental-Product-Declarations_fig3_341943113
[6] https://www.findoutaboutplastics.com/2022/02/design-data-for-plastics-engineering.html
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