Degradable Polyethylene-like Materials

Abstract

Long-chain aliphatic polyesters obtained from plant oil-based monomers constitute a renewa- ble alternative to conventional, petrochemical-based HDPE. The in-chain ester groups are potential ‘breaking points’ and facilitate solvolysis of the polymer chain to the underlying mon- omer building blocks. In this work, the utilization of the in-chain ester groups for closed-loop chemical recycling and enabling non-persistency of HDPE-like polyesters in the environment is explored. In the first section of this work, the closed-loop chemical recycling of long-chain aliphatic poly- esters is investigated through the example of polyester-18,18 (PE-18,18). PE-18,18 is sub- jected to an alcoholysis process to allow for quantitative recovery of the underlying long-chain aliphatic monomers. The re-polymerization of the obtained building blocks to regain PE-18,18 with properties akin to the virgin material is probed. With regard to the separation from waste streams, the chemical recycling of PE-18,18 is additionally extended to the separation of the polymer from its blends with HDPE, polyolefin contaminations, and colorants by depolymeri- zation. As an advanced processing technique for HDPE-like polyesters, fused deposition mod- eling (FDM) is tested. Long-chain aliphatic polyesters due to their high crystallinity and hydrophobicity are stable to- wards hydrolysis. In the second section of this work, melt blending with small amounts of acid releasing long-chain aliphatic poly(H-phosphonate)s is investigated as an approach to render PE-18,18 amenable to hydrolytic degradation under environmentally relevant condi- tions. Due to their cost efficiency, short-chain diols offer themselves as substitutes for their long- chain congeners in the synthesis of HDPE-like polyesters. In the third section of this work, the material properties of the short-chain diol analogues (C2 – C12 diols) of bio-based PE-18,18 and PE-12,12, producible from a complementary petrochemical feedstock, are investigated. A particular emphasis is placed on PE-2,18, of which the synthesis is optimized with regards to a desirably high molecular weight and concomitant HDPE-like mechanical properties. The ef- fect of the chain length of the diol component on the materials’ biodegradability is investigated by means of respirometric tests under industrial and home composting conditions (measured according to standard ISO 14855). Polyolefin waxes, produced on a scale of hundred thousand tons per year, are employed as auxiliaries in numerous products and production processes. The HDPE-like crystalline struc- ture of long-chain aliphatic polyesters encouraged the exploration of wax materials based on their monomer building blocks. In the last section of this work, waxes based on the repeat unit motifs of PE-12,12 and PE-2,18, namely waxes linear ester (WLE)-12,12 and WLE-2,18, re- spectively, are investigated.