LDPE Recycling

Recycling of LDPE packaging in the U.S. is primarily directed at stretch wrap, collected from businesses, and at merchandise sacks, collected from consumers through drop off sites located at stores. There is little collection of plastic bags at 

Recycling of plastic bags and film (which are mostly LDPE/LLDPE and HDPE) is more widespread. The study by Moore Recycling Associates showed that over 90% of the U.S. population has access to plastic collection programs for plastic bags within a 10 mile radius, and over 70% to plastic film recycling [12]. 

The major market for recycled film in the U.S. in 2011 was the manufacture of plastic lumber, 55% of the total. Film and sheet applications totaled 16%, with various other applications comprising the remaining 29%. The export market is also very important, accounting for over 40% of the total recycled film [13]. 

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Greenhouses with simple walls LDPE, EVA, PVC, multilayer LDPE/EVA, LDPE/recyclate. 

Altliough LDPE is the primary constituent of plastic in MSW, little film plastics (LDPE) recycling is done. Little data is available on post-consuiner collection of LDPE. When LDPE is collected in recycling, it can be expected to comprise 25% by weight of the plastics collected. 

Figure 12.22 Trends in LDPE recycling in the United States. ...

Generally, non-pressurized pipes contain carbon black (CB) as a pigment. However, CB may have a negative effect on the thermo-oxidation of polyolefins. The influence of CB on the long term thermal behavior of irrigation pipes (for vineyards in Cap Province, South Africa) based on LLDPE/LDPE recyclate is shown in Figure 21. 

In 1994 in the U.S., recycled PET, HDPE, LDPE, and PS had a 16—46% cost advantage (4). This cost advantage largely disappeared by 1996. Bureau of Labor Statistics data indicate U.S. plastics prices in mid-1997 are seven percent below those of mid-1995 after being more than ten percent less in 1996... 

Phenolics are consumed at roughly half the volume of PVC, and all other plastics are consumed in low volume quantities, mosdy in single apphcation niches, unlike workhorse resins such as PVC, phenoHc, urea—melamine, and polyurethane. More expensive engineering resins have a very limited role in the building materials sector except where specific value-added properties for a premium are justified. Except for the potential role of recycled engineering plastics in certain appHcations, the competitive nature of this market and the emphasis placed on end use economics indicates that commodity plastics will continue to dominate in consumption. The apphcation content of each resin type is noted in Table 2. Comparative prices can be seen in Table 5. The most dynamic growth among important sector resins has been seen with phenoHc, acryUc, polyurethane, LLDPE/LDPE, PVC, and polystyrene. 

The two forms of polyethylene differ slightly in density. Linear polyethylene is referred to in the recycling business as /ligh-density polyethylene, represented by the symbol HDPE 2 on the bottom of a plastic bottle. The corresponding symbol for branched polyethylene is LDPE 4, indicating low-density polyethylene. (The smaller the number, the easier it is to recycle.)... 

Dow ABS Nylon 6/6 Polycarbonate Polyethylene, HDPE, LDPE, LLDPE, ULDPE Polypropylene HPPP, CPPP Polystyrene HIPS, GPPS, Recycled, Advanced Styrenic Resin SAN Polyurethane Elastomers Polyolefin Plastomer PC/ABS Crystalline Polymer ABS/TPU... 

To separate any ethylene from the LDPE in the autoclave effluent, the pressure is let down in successive vessels and the ethylene flashes off (vaporizes). It is recycled to the compressors. The LDPE in a molten (hot liquid) state is cooled, extruded, pelletized, dried, and bagged. 

The compression ratio for pellet feedstocks typically ranges from about 1.8 for PMMA resins [2] to 4.5 for LDPE resins [3], although many exceptions are practiced. Compression ratios for several common resins are reported by Giles, Wagner, and Mount [2]. If high levels of a low-density recycle stream are added back into the feed hopper, then the compression ratio and compression rate will need to be increased as follows ... 

There have been more efforts to use blends such as Nova Chemicals Arcel (an ethylene styrene interpolymer in bead form) to create a more durable foam than EPS. EPP can be moulded into complex shapes, with the steam bonding of the beads (291). These packaging foams compete with polyolefin film products such as Jiffy foam (bubblewrap) and macrobubbles made by heat sealing 150 mm lengths of tubular LDPE film. As it is difficult or costly to recycle such foam products, in some countries there is a move towards biodegradable starch foams and moulded paperboard. 

Since about 1990 plastics recycling has been a growing and developing business. It is here to stay in one form or another. Collection and separation are the main problems. PET and HDPE by far are the main plastics that are most easily recycled. These two polymers are used as containers and easily reprocessed. Plastic films (especially LDPE) have a potential for recycling increases, but this form of plastic material is not as easily collected and stored. 

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%. 

Identify what the bottles are made of from the following recycling codes found on their bottoms (a) 4 with the letters LDPE (b) 6 with the letters PS (c) 5 with the letters PP. 

J. Pospfsil, I. Forteln, D. Micheilkovei, Z. Kruli , and M. Slouf, Mechanism of reactive compatibilisation of a blend of recycled LDPE/HIPS using an EPDM/SB/aromatic diamine co-additive system, Polym. Degrad. Stab., 90(2) 244-249, November 2005. 

The most difficult recyclates are the MSW, which usually consists of more or less dirty plastics of various types and sources. According to one report [15] the plastic portion of MSW contains typically 50% PE (mainly low density polyethylene, LDPE), 8-14% polypropylene (PP), 15% polystyrene (PS), 10% polyvinylchloride (PVC) and 5% polyethylene terephthalate (PET), and 5% other polymers, while the hard packaging fraction consists of approx. 60% of PP and HDPE [16]. 

Diblock copolymers, especially those containing a block chemically identical to one of the blend components, are more effective than triblocks or graft copolymers. Thermodynamic calculations indicate that efficient compat-ibilisation can be achieved with multiblock copolymers [47], potentially for heterogeneous mixed blends. Miscibility of particular segments of the copolymer in one of the phases of the bend is required. Compatibilisers for blends consisting of mixtures of polyolefins are of major interest for recyclates. Random poly(ethylene-co-propylene) is an effective compatibiliser for LDPE-PP, HDPE-PP or LLDPE-PP blends. The impact performance of PE-PP was improved by the addition of very low density PE or elastomeric poly(styrene-block-(ethylene-co-butylene-l)-block styrene) triblock copolymers (SEBS) [52]. 

LDPE from three different points in recycling plant... 

Table 2 Example of low molecular weight compounds identified in recycled LDPE at three ...

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