Abstract
Plastics recycling remains a challenge due to the relatively low quality of the recycled material, since most of the developed recycling processes cannot deal with the additives present in the plastic matrix, so the recycled products end up in lower-grade applications. The application of volatile organic solvents for additives removal is the preferred choice. In this study, pretreatment of plastic packaging waste to remove additives using biosolvents was investigated. The plastic waste used was high-density polyethylene (HDPE) with blue and orange colorants (pigment and/or dye). The first step was to identify the type of colorants present in the HDPE, and we found that both plastics presented only one colorant that was actually a pigment. Then, limonene, a renewable solvent, was used to solubilize HDPE. After HDPE dissolution, a wide range of alcohols (mono-, di-, and tri-alcohols) was evaluated as antisolvents in order to selectively precipitate the polymer and maximize its purity. The use of limonene as solvent for plastic dissolution, in combination with poly-alcohols with an intermediate alkyl chain length and a large number of hydroxyl (OH) groups, was found to work best as an antisolvent (1,2,3-propanetriol and 1,2,4-butanetriol), leading to a removal of up to 94% and 100% of the blue and orange pigments, respectively. Finally, three cycles of extraction were carried out, proving the capability of the solvent and antisolvent to be recovered and reused, ensuring the economic viability and sustainability of the process. This pretreatment provides a secondary source of raw materials and revenue for the recycling process, which may lead to an increase in the quality of recycled polymers, contributing to the development of an economical and sustainable recycling process.
Highlights
Biosolvents derived from renewable sources were shown to be efficient in the removal of colorants from plastic packaging waste by solvent extraction
We found that the removal of pigments was more efficient when using limonene as solvent for the plastic dissolution and alcohols with an intermediate alkyl chain and multiple OH groups as the antisolvent
The pigment removal was most effective for the tri-alcohols (1,2,3-propanetriol and 1,2,4-butanetriol), removing up to 94% and 100% of the blue and orange pigments, respectively, showing the potential of these biosolvents to remove the additives from plastic waste, which could be used in the development of a more sustainable plastic waste recycling process
Summary
Plastics (polymers) are widespread in most activities and our daily lives. In 2018, the global polymer production reached 360 Mt, which is anticipated to rise four-fold by 2050 [1]. Of this total, 61.8 Mt was consumed in the European Union (EU), with packaging being the most significant use, representing 40% of this value [2]. Plastics have a short life cycle, generating large amounts of waste with high prevalence in the environment due to their lower biodegradability, becoming one of the imminent environmental concerns of the. The European Commission is encouraging plastic waste recycling through the implementation of the Circular Economy Package, aiming to recycle 50% of the plastic
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