Plastic lumber properties

ASTM D 6109, Standard Test Methods for Flexural Properties of Unreinforced and Reinforced Plastic Lumbers ... 

The reason for the adapted ASTM procedure is that plastic lumber (and WPC products) is generally nonuniform through the cross section, and small cut specimens sometimes give large variations in compressive (and other) properties. 

PVC is one of the lowest-cost commodity resins, used extensively today due to its excellent chemical and mechanical properties. However, the thermal decomposition temperature of PVC is close to its processing temperature, and hence use of proper heat stabilisers during its processing is essential. In addition, PVC-wood composites (plastic lumber) discolour with time during outdoor use, and this can be improved by use of proper thermal stabilisers [16]. 

Mixed recycled plastic lumber bridge decks, boat docks, doors, floors, furniture, windows, fences, pallets, etc. are product examples in service. Plastic lumber would be maintenance-free for at least half a century, as opposed to 15 years for treated wood and 5 yeare for untreated wood. Extensive use is made in applying plastics in wood to improve their structural and decorative properties. 

In 1999, the Plastic Lumber Trade Association reported that RPL was growing at a 30 percent annual rate. Growth of plastic lumber was been fueled by growing knowledge about performance properties of the material and how they relate to composition, as well as by the develcmment of performance standards such as the standard test methods developed by ASTM. By 2005, nine ASTM test methods for RPL had been established, along with two standards for plastic/fiber composites. However, growth of plastic lum-her has slowed, and the Association has not placed an annual report on their web site since 2002. 

Higher melting point plastics such as PET become a filler if used in plastic lumber production. The physical properties of plastic lumber have been shown to improve significantly with the addition of PS to mixtures. 

Table 2.2 Mechanical Properties of Plastic Lumber Profiles (Phillips, et al., 1989, Carrier, 1989]...

Polymerix, a company which produces plastic lumber directly intended to confute with chemically treated outdoor grade lumber, has established a wash/clean process to obtain higher quality plastic with less foreign matter for input to fabrication. The result of material cleaning and ptuiial sepmation prior to use is a product with mechanictil properties... 

Wood fiber - recycled plastic composite lumber is a relatively new development and is similar to PS addition to plastic lumber because the potential exists for improved mechanical properties and dimensional stabilities. Wood fiber addition can serve as an excellent reinforcement for plastics, and wood fibers are abundant, lightweight, nonabrasive, nonhazardous and inexpensive. An effort is being made to examine the incorporation of treated and untreated aspen fibers into recycled HDPE milk bottles [Yam et al., 1990]. The work has shown tensile strength and Izod impact strength below that of HDPE alone when aspen fiber is added. Tensile modulus and flexural modulus are increased significantly above HDPE alone with the addition of wood fiber. Dispersion of the fiber in the resin has been reported as a dominating factor in the process thus far. 

In recent years, the diversity of properties of plastic lumber produced from different mixes of materials, by different processes, has resulted in calls for development of standards. In late 1997, the American Society for Testing and Materials (ASTM) issued five new test methods for plastic lumber intended to help establish a benchmark for minimum plastic lumber performance. The standards include tests for compressive properties, flexural properties, bulk density and specific gravity, compressive and flexural creep and creep rupture, and tests for performance of mechanical fasteners. ... 

The American Society for Testing Materials (ASTM) established structural and property standards for plastic lumber, ASTM D6662, in 2001 [52]. 

There are ontlets for mixed plastics, but because of the heterogeneous composition of the raw materials they are limited to the production of large components. This is so that contaminants and any material that has not melted and mixed will not have a great effect on the overall strength. Often products of this type find outlets as plastic lumber or concrete replacement products such as park tables, slabs or benches, where the non-rotting properties of plastics can be utilised. 

The 2-imino-4-thiazolines may be used as ultraviolet-light stabilizers of polyolefin compositions (1026). 2-Aminothiazole improves adhesive properties of wood to wood glue (271). Cbmpound 428 exhibits antioxidant properties (Scheme 242) (1027). Ammonium N-(2-thiazolyl)dithio-carbamate (429) is a bactericide and fungicide used in industrial products such as lumber, paint, plastics, and textiles (1037). Compound 430 is reported (1038) to form an excellent volume of foam coating in aluminum pans when ignited with propane. 

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