Polyolefin Composite Pellets

Another innovation in the 1990s involved compounding thermoplastic polymers and cellulosic materials along with other ingredients into a feedstock in the form of durable, easy to transport, and durable pellets. 

994 [112] describes a WPC material produced as feedstock pellets in a twin screw extruder, and comprising wood flour (about 20-80%) and polyethylene (80-20%) as a preferred plastic. 

612 [80, 82] and 6,210,792 [113] (all—by Andersen Corporation) disclose a wood-plastic composition manufactured as feedstock pellets comprising PVC and wood fiber. 

368 [114] describes plastic cellulosic composite pellets comprising 20-60% by weight of polyethylene, polypropylene or polystyrene, 40-80% of cellulosic fiber (jute, kenaf, sisal, bamboo, rice hulls, corn husks, wood fiber, and wood flour) with an aspect ratio of between 2 and 20 and a trace of mineral coating (talc) dispersed on the surface of the pellet. 

863 [115] (by Crane Plastics Company, Timber-Tech) discloses a wood-plastic composition manufactured as feedstock pellets comprising 55-90% cellulosic material such as wood flour and wood fiber, 10-40% of polyolefin such as HDPE, LDPE, and polypropylene, and 0-35% total of additive(s), such as lubricants and inorganic fillers, such as talc and mica. 

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Cellulose-polyolefin composite pellets, 89 Cellulosic reinforced plastic composite, 89 Center point load, or concentrated load (3-pt load), 244, 252, 264 CertainTeed Corporation, 58, 79, 90 Cesa-mix 8468, 174 Cesa-mix 8611, 174 Chain breaking antioxidants, 526 Chain reaction, 526 Charpy impact resistance, 73 Chemark UV-234, 535 Chemark UV-326, 535 Chemical composition of fillers, 125, 133-154... 

Since this t)q)e of mixer cannot generate any appreciable discharge pressure necessary to extrude file material, it is often combined wifii an extruder for pelletizing. The ctmtinuous internal mixer is employed in applications involving polyolefin homogenization, PVC compounding as well as in the preparation of low filler loaded polyolefin composites. 

The building and construction industry commonly uses polyolefin microcomposite and nanocomposite as reinforcement materials to enhance the physical properties (tensile strength, modulus, and damping) of POCs. There are many current and future applications of POCs in constmction including walling, roofing, outdoor furniture, and timber. These composites can be molded into sheets, frames, pellets, structural shapes, and others [77]. 

There are compositional differences between polymers, especially between polyvinyl chloride and chlorinated polyvinyl chloride, which are more susceptible to degradation in processing and require higher levels of processing stabilizers, and polyolefins, which must be stabilized for processing stability as well as for protection into the service environments. There are also differences in material handling as PVC is converted from reactor flake product, whereas CPVC, PE, PP, and other materials are converted from pelletized compounds. 

These products are typically incorporated into the final formulation as additives at levels of a few percent. They are proprietary combinations of additives, which, with appropriate compositional adjustments, allow for a wide range of storage, use, and degradation times, depending on the end use and the enviroiunent. Polyolefin pellets, which have been compounded with these additives, are processed on conventional equipment at normal speeds. 

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