Thermoplastics recycling

Recycling of HDPE. Polyolefins, including HDPE, are the second most widely recycled thermoplastic materials after PET (110). A significant fraction of articles made from HDPE (mostly bottles, containers, and film) are collected from consumers, sorted, cleaned, and reprocessed (110—113). Processing of post-consumer HDPE includes the same operations as those used for virgin resins blow mol ding, injection molding, and extmsion. 

Metal derivatives (Ti, Zn, Cd, Sn, Sb, Pb) and bromine from additives in recycled thermoplasts from consumer electronic waste were determined by dissolving the samples in an organic solvent, followed by TXRF analysis [56], The procedure proved considerably less time-consuming than conventional digestion of the polymer matrix. Results were validated independently by INAA. 

The ability to make PE with properties that fall outside these limitations would lead to a tremendous expansion of uses for this polymer, for example replacing flexible polyvinylchloride (f-PVC), which cannot be incinerated or recycled, thermoplastic polyurethanes (TPUs), or thermoplastic vulcanates (TPVs). 

Some plastic producers market recycled thermoplastics such as polyamides. Table 7.5 (after BASF) shows examples of properties for recycled and virgin polyamides. 

Total recycled thermoplastic resin production almost tripled between 1990 and 1995 and is well over 1 billion lb per year. The percentage breakdown of the amount for recycling is the following HDPE (especially bottles), 35% PET (soft drink bottles), 34% PP (auto battery cases), 14% LDPE (film), 9% PS (packaging), 3% PVC, 0.5% other, 4%. 

Many polymers, such as cellulose and HDPE, are linear polymers considering long, continuous, covalently bonded atoms. Others may be branched or cross-linked. Both linear polymers and those with branching are generally thermoplastics that can be remolded by application of heat and pressure. Others that are cross-linked are thermosets that cannot be remolded by application of heat and pressure. Both groups of polymers can be recycled, but it is easier to recycle thermoplastic materials. 

Polymers are often divided according to whether they can be melted and reshaped through application of heat and pressure. These materials are called thermoplastics. The second general classification comprises compounds that decompose before they can be melted or reshaped. These polymers are called thermosets. While both thermoset and thermoplastic polymers can be recycled, thermoplastic recycling is easier and more widespread because thermoplastic materials can be reshaped simply by application of heat and pressure. 

Okamura, M., Kaniwa, T., and Kamata, A., Recyclable Thermoplastic Resin Compositions Containing Cyclic Inulooligosaccharides with Good Mechanical Properties and Chemical and Heat-Resistance, Japanese Patent 09048876, 1997. 

This patented process allows virgin or recycled thermoplastics such as PP, PC/ABS, etc. to thermally bond with the backing of multilayer PP based fabrics providing good elasticity. This one step molding technique provides a low cost approach for in-mold fabric lamination that range from simple to complex shapes. 

Blends of recycled thermoplastics recovered from domestic and commercial waste, and comprising PE and/or PP, PS, PVC, and < 10 wt% of other thermoplastics, were compatibilized and impact modified by incorporation of 3-20 wt% SBS. The blends were re-stabilized against light and thermo-oxidative degradation by addition of pentaerythritol ester and phosphite [Pauquet et al., 1994]. 

A ZIA O/OTHERS any other plastics that do not fall into any of the above categories, e.g. melamine-formaldehyde, often used in plastic plates and cups or mixtures of recycled thermoplastics... 

Starting in the 1980 s, a number of governmental recycling policies created a demand for recycled thermoplastic olefin (TPO) for post-consumer applications. Since polystyrenes and TPOs are not miscible, polystyrene-TPO diblock copolymers are being developed to reduce the interfacial tension in PS/TPO blends. TPOs are tough materials with low stififiiess properties. If blended with polystyrene, they improve the toughness of polystyrenes. If compatibilized, the properties of PS/TPO should be similar to styrene-hydrogenated polybutadiene rubbers. 

The use of natural fiber reinforcements in recycled thermoplastic polymers has generated considerable research interest due to the increasing environmental threat created by the high consumption rate of petroleum-based plastics. Therefore, there is a growing interest in the development of green, environmentally-friendly composites for agro-based structural materials. Apart from this, the renewed interests in recyclability and environmental sustainability have also arisen in the last few years. The best possible way to develop such composites are to incorporate natural fibers into recycled... 

These materials differ from mineral-filled composites [23]. PWC based on recycled thermoplastics and their blends are of special interest because the desired compositions with the required service performance could be developed. 

The reinforcing fibers in composites offer unique properties but create complications in recycling. Thermoplastic composites have the potential of primary and secondary recycling since the reprocessing of waste can result in a prodnct with the same or comparable properties, whereas thermoset... 

The thermal stability of pure HDPE, PET/HDPE conventional composite and MRC with different exposure times was measured by means of the VST data listed in Table 12.4. The addition of PET leads to an increase in VST due to the rigidity of the PET phase. Moreover, the VST of PET/HDPE MRCs is much higher than that of PET/HDPE conventional composite. In particular , after 360 h exposure, it is 92,7°C for MRCs, but 88.9°C for conventional composite. This is associated with the formation of the three-dimensional PET microfibrils network, which is beneficial for improving the thermal deformation resistance of the HDPE matrix, thus enhancing the VST of PET/HDPE MRCs. On extending the exposure time, the VST of PET/HDPE MRCs increases, while it decreases for pure HDPE and PET/HDPE conventional composite. These results indicate that the application of MRCs concept has promising potential to recycle thermoplastic polymers. 

The materials used in this work were two recycled thermoplastics (PET and PP) and a virgin elastomer. PET has been obtained from a separate collection of post-consumer bottles and has an average intrinsic viscosity of about 0.7 dl/g. 

R. Schaaf, Recycling Thermoplastic Wastes , VDl-Verlag, Uusseldorf, 1979, p. 153. 

PALAP. PALAP (Patterned Prepreg Layup Process) is a process that was developed by a consortium consisting of the Japanese firms Denso, Wako Corporation, Airex, Kyosha, Noda Screen, and O.K. Print. Originally, the process started with copper-clad laminates (CCL), but now utilizes thermoplastics like PEEK resins (polyether-ether ketone) or a new plastic called PAL-CLAD. M L-CLAD is characterized by the electrical properties and heat resistance of BIAC, a recyclable thermoplastic resin film produced by Japan Gore-Tex, Inc. 

M. Karabulut in Production and Characterization of Nanocomposite Materials from Recycled Thermoplastics, Middle East Technical University,... 

Heat stabilizers can also play a role in recycling thermoplastics, when material is again subjected to heat. Some stabilizer systems introduced into the original compound retain their effectiveness through subsequent re-processing, but there may be a need to restabilize waste plastics for more efficient recycling. 

Guo HF, Merrington, A. Effects of compatibil-izers and additives on recycled thermoplastics. Annual recycling conference proceedings 1996. 

Liu X, et al. Using experimental interpolymers to upgrade mechanical properties of recycled thermoplastics. Global plastics environmental conference proceedings 2003. 

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