SMI: Wood - Polymer Composites

Wood Polymer Composites with Specialty Minerals Talcs

Wood polymer composites (WPCs) have exhibited incredible growth rates as their benefits as alternative decking materials become better known to builders and homeowners. The potential to reduce upkeep while maintaining a new, finished appearance for long periods of time has allowed this revolutionary class of building materials to sustain growth while commanding a price premium over conventionally treated wood.

WPCs typically appear in three forms, differentiated by the polymer base in use. These forms are PE composites, PP composites, and PVC composites.

The PE, or polyethylene-based, composites have generated the largest market share in the U.S. decking market, currently about 80 percent. Compounding and extrusion is straightforward and performance is more than adequate for most applications. This resin preference historically stems from the large recycle stream that has been available to the growing industry. Recently, virgin resin has been used to support the double-digit growth rates.

PP, or polypropylene, composites have about 10 percent market share in the U.S. but show a lot of promise for the future given the pricing trends of PP resin and the superior flexural modulus properties of PP composites.

PVC composites comprise the remaining 10 percent of the U.S. market and are something of a wild card. They have not grown as quickly in decking as their polyolefinic cousins but do show significant promise as profile components in handrails and related applications.

Talcs in Wood Polymer Composites
As in other polyolefinic reinforcement applications (automotive, appliance), talcs have demonstrated good compounding characteristics and excellent performance in raising flexural modulus (i.e., stiffness). Likewise, in WPCs, talc has found acceptance as a stiffening additive for decking and other applications. Several years ago, Specialty Minerals Inc. (SMI) introduced Talcron^® MP 45-26 talc as a true reinforcement filler for PE-based WPCs. Talcron^® MP 45-26 talc is easy to handle and compounds well in the WPCs’ extrusion process. WPCs’ formulations containing Talcron^® MP 45-26 talcs exhibit improved flexural modulus.

Click on a product name to download the technical data sheet for the product.

Specialty Minerals Min-Flex^® WPCs Reinforcement for Wood Polymer Composites
SMI was the first supplier to introduce modified-talcs specifically designed for the unique characteristics of WPCs. Unlike conventional talcs that work well in polyolefins because of their hydrophobic surface character (which matches well with the hydrophobic character of polyolefins), SMI's modified-talcs, trade-named Min-Flex^® WPC reinforcments, work especially well in wood polymer composite formulations because of their mixed hydrophobic/hydrophilic nature. In WPCs, the polymer part of the formulation is hydrophobic and the wood flour portion (up to 60 percent by weight) is hydrophilic. Min-Flex^® WPCs reinforcements also have this mixed or dual character and exhibit excellent dispersion and flexural modulus development in WPCs, along with reduced external lubricant demand compared to other mineral fillers.

Extrusion trials at the University of Maine have demonstrated the dramatic boost in flexural modulus that Min-Flex^® WPC reinforcements impart to highly wood flour-filled composites as well as the excellent extrusion behavior of these formulations. Compared to mineral fillers like calcium carbonate, Min-Flex^® WPC reinforcements also exhibit reduced external lubricant demand.

Click here to download the technical data sheet for the Min-Flex^® WPC reinforcement minerals.

Non-Wood Flour WPCs
To produce even higher performance wood polymere composites, the industry is working to develop non-wood flour-containing WPCs. Click here to read more about this development.

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