Preparation of Low-Density Microcellular Foams from Recycled PET Modified by Solid State Polymerization and Chain Extension

Abstract

Recycled polyethylene-terephthalate (RPET) bottle regrinds were physically foamed after two types of industrially feasible molecular weight increasing processes. Intrinsic viscosity (IV) of initial waste (0.71 dl/g) increased both after reactive extrusion carried out using a multifunctional epoxy-based chain extender (0.74 dl/g) and after solid state polycondensation (SSP) (0.78 dl/g), while capillary rheometry revealed higher degree of branching in the chain extended PET material. Despite the relatively low IV values (below 0.80 dl/g), physical foaming, a mild and cost efficient way, was successful in both cases, uniform microcellular foam structures with void fractions ranging between 75 and 83% were achieved. During the experiments morphology change in the materials was tracked by differential scanning calorimetry (DSC) besides recording IV values. The IV drop during foaming was between 0.03-0.10 depending on the pre-processing technology. Structure of 2 foams produced from the two different modified RPET materials was compared with each other based on scanning electron microscopic imaging (SEM) of cryogenic fracture surfaces.The average cell diameters were measured to be 213 and 360 µm in the case of chain extended and SSP-modified materials, respectively.

Future trends of plastic bottle recycling: Compatibilization of PET and PLA

“…The chain extenders, through their reactive functional groups, reconnect the degraded polymer chain segments, thereby increasing melt strength. For polyesters, many researchers [42][43][44][45][46] use the Joncryl ADR 4368 (BASF) multifunctional epoxy-based styrene-acrylic oligomer to compensate for degradation and/or increase molecular weight. However, nowadays it is also used as a reactive compatibilizer due to its reactive epoxy functional group [43,[47][48][49][50].…”

Chemical recycling of polyesters

“…For this reason, the use of various types of commercially available ChEx can be safely considered an effective method of constructive chemical recycling of polyesters. The properties of granules obtained in the presence of ChEx can be further improved using the SSP technology [52,53].…”

Rheological/thermal properties of poly(ethylene terephthalate) modified by chain extenders of pyromellitic dianhydride and pentaerythritol

“…Polyethylene terephthalate (PET) is an engineering plastic, which is a semi‐crystalline thermoplastic polymer 1–4 with high mechanical properties, appropriate thermal and chemical resistance, and ease of processing. Its proper price has caused it to be used in a variety of applications, such as food and beverage packages, films, fibers, tapes and batteries 5–8 . Along with the advantages of PET, this polymer has also several handicaps.…”

“…Its proper price has caused it to be used in a variety of applications, such as food and beverage packages, films, fibers, tapes and batteries. [5][6][7][8] Along with the advantages of PET, this polymer has also several handicaps. In fact, the linear structure, low molecular weight, narrow molecular weight range, and low crystallization rate, have caused PET to be restricted in processes such as blow molding, film-blowing, foaming and molding.…”