Recycling of poly(ethylene terephthalate) as polymer‐polymer composites

Abstract

Microfibrillar reinforced composites (MFC) comprising an isotropic matrix from a lower melting polymer reinforced by microfibrils of a higher melting polymer were manufactured under industrially relevant conditions and processed via injection molding. Low density polyethylene (LDPE) (matrix) and recycled poly(ethylene terephthalate) (PET) (reinforcing material) from bottles were melt blended (in 30/70 and 50/50 PET/LDPE wt ratio) and extruded, followed by continuous drawing, pelletizing and injection molding of dogbone samples. Samples of each stage of MFC manufacturing and processing were characterized by means of scanning electron microscopy (SEM), wide‐angle X‐ray scattering (WAXS), dynamic mechanical thermal analysis (DMTA), and mechanical testing. SEM and WAXS showed that the extruded blend is isotropic but becomes highly oriented after drawing, being converted into a polymer‐polymer composite upon injection molding at temperatures below the melting temperature of PET. This MFC is characterized by an isotropic LDPE matrix reinforced by randomly distributed PET microfibrils, as concluded from the WAXS patterns and SEM observations. The MFC dogbone samples show impressive mechanical properties—the elastic modulus is about 10 times higher than that of LDPE and about three times higher than reinforced LDPE with glass spheres, approaching the modulus of LDPE reinforced with 30 wt% short‐glass fibers (GF). The tensile strength is at least two times higher than that of LDPE or of reinforced LDPE with glass spheres, approaching that of reinforced LDPE with 30 wt% GF. The impact strength of LDPE increases by 50% after reinforcement with PET. It is concluded that: (i) the MFC approach can be applied in industrially relevant conditions using various blend partners, and (ii) the MFC concept represents an attractive alternative for recycling of PET as well as other polymers.

Preparation, structural development, and mechanical properties of microfibrillar composite materials based on polyethylene/polyamide 6 oriented blends

“…If they are chopped into pellets, the precursors can be reprocessed by a second extrusion process or by injection molding at a temperature below the melting point of the reinforcing phase. This alternative was reported for the first time by Monticciolo et al 15 and was applied later by Pesneau et al, 16 Evstatiev et al, 17 and Li et al 18,19 with different polymer blends. In terms of composition, among the MFCs containing polyolefins, the most studied are the poly(ethylene terephthalate)-reinforced HDPE, 20 polypropylene (PP), 14,21,22 and low-density polyyethylene.…”

Effect of microfiber reinforcement on the morphology, electrical, and mechanical properties of the polyethylene/poly(ethylene terephthalate)/carbon nanotube composites

“…The average diameters of the microfibers in the 80/20/0.5 microfiber and 50/50/0.5 microfiber systems are around 8 and 4 lm, respectively. Microfiber reinforced composites are generally molded at a lower temperature than the melting temperature of the microfiber phase, to preserve the microfiber structure and perform the transformation of the composite into isotropic material reinforced with the microfibers [30,31]. Figure 8a and b show that the microfiber structure is protected in the composites which were molded at 2108C.…”

Preparation and Properties of Novel <i>In Situ</i> Composite Materials Based on Polyethylene-Polyamide Oriented Blends

“…In doing so, the oriented crystalline structure of the latter is preserved, thus forming the reinforcing elements of the NPC. To carry out the NPC preparation at an industrial scale, continuous setups are used where polymer blending, forming and cold drawing of the initial strands is performed in a twin-screw extruder coupled with one or more stretching haul-off units [5,6]. The isotropization stage is performed by either compression or injection molding techniques.…”