Closing the Loop for Plasticized PVC Waste Via Mechanical and Solvent-based Recycling

Poly Vinyl Chloride (PVC) is one of the oldest thermoplastics. Several additives are added to PVC to make it suitable for a specific application. The addition of additives makes it both very versatile and difficult to recycle. Different regulations are put in place by the European Chemicals Agency (ECHA), which restrict the use of harmful additives, often referred to as legacy additives. In plasticized PVC (P-PVC) applications, legacy additives such as bis(2-ethylhexyl) phthalate (DEHP) have been widely used in the past, which hinders the mechanical recycling of such waste. This thesis therefore explores two complementary strategies to close the loop for P-PVC waste: reusing post-industrial P-PVC waste through mechanical recycling and reformulation and selectively removing DEHP from P-PVC waste using solvent-based recycling (SBR), followed by re-compounding with a safer plasticizer. In the first part, heterogeneous P-PVC waste was mechanically recycled with slight adjustments in the formulations to achieve desired flexibility. It is important to understand whether recycled P-PVC with a certain level of flexibility, measured in terms of Shore-A, can replace virgin P-PVC with the same flexibility. To investigate the properties of post-industrial recycled P-PVC granules and its possibility of replacement of virgin P-PVC, virgin and recycled samples with close Shore-A and density values are comprehensively compared for chemical, mechanical, thermal and rheological properties. FT-IR and EDS analyses confirmed the absence of legacy additives. For processability, samples were tested with a plastographer and melt flow index (MFI), recycled samples revealed higher MFI values and lower torque because of reduced viscosity due to repeated processing and possible loss of molecular weight. Thermal Gravimetric Analysis (TGA) confirmed that recycled material degrades above processing temperature similar to virgin material. In tensile testing, recycled material showed a similar stress-strain curve in the beginning of the stretch with lower yield strength and (%)Elongation. A recyclate with suitable properties was selected and incorporated at 30 wt.% into the inner layer of a spiral pool hose prototype. The prototype met the key mechanical and functional standards. The second part is focused on Solvent-based recycling (SBR) or dissolution precipitation, to remove unwanted substances from PVC. According to this method, a suitable solvent is used to dissolve the polymer which is then precipitated with a non-solvent. The precipitated polymer is recovered while the organic additives remain in the liquid phase. In this study, SBR was applied to PVC samples containing DEHP (≥30 wt.%) as a plasticizer. Hansen Solubility Parameters were used to select solvent and non-solvent for PVC. Conductor-like Screening Model for Real Solvents (COSMO-RS) was used to predict the relative solubility of DEHP in different solvent and anti-solvent mixtures, which is validated experimentally. Gas Chromatography-Mass Spectrometry (GC-MS) analysis was carried out to confirm DEHP removal and a residual content below the legal limit of <0.1 wt.% after three dissolution precipitation cycles. The recovered PVC powder was then thoroughly characterized in comparison wiyh virgin PVC K70 resin for K-value, apparent density, true density and morphology. The recycled PVC powder revealed an almost unchanged K-value and true density. Although the apparent density was significantly reduced, further confirmed by scanning Electron microscope (SEM) images having low particle size. Further, recycled PVC powder was reformulated with Bis(2-ethylhexyl) terephthalate (DOTP) and necessary additives. The recycled P-PVC was comprehensively evaluated in comparison to virgin P-PVC, with a similar formulation, in terms of chemical, morphological, thermal and mechanical properties.