Polymeric Composites with Rice Hulls for Extrusion - Introduction to Polymeric Composites with Rice Hulls - page 122

on the basis of lesser polymer content being available for foaming. Clariant Additive
Masterbatches offers a range of CFA, which include endothermic, exothermic and
endo-exothermic blends for most polymer fibre blends, which are ideal for composites
with fibre content <50%. Foamasol CFA as marketed by Bergen International are
particularly for decorative mouldings such as siding trim boards, railings, spa panels
and interior facades, where loss of physical properties from foaming are not an issue.
Typical weight reductions for foamed composites are ≈30-35%.
10.2.5 Countering Mould and Mildew
Mould, mildew and stains on some outdoor composites (e.g., decking) needs the
attention of the manufacturers to consider using antifungal biocides that protect the
polymer content and maintain its surface appearance, or which preserve the fibre
component from decay and also reduce moisture absorption. Many additives will
carry out both functions. Unlike in normal WPC, PCRH provide a natural surface
barrier to counter these effects due to silica. However, producers may opt to use
additional additives to combat these problems.
Weathering and UV radiation have been known to degrade the surface of WPC
within a few weeks of exposure. Constant weathering and water absorption affect
the surface and colour fading is also probable. Also, moisture can lead to a loss
in mechanical properties and provide a more favourable localised environment
for fungal growth. Ciba Specialty Chemicals offers Irgaguard F3000, said to be a
broadly effective fungicide for fibre composites. Another product, Developmental
EB 43-25, combines with Irgaguard F3000 to provide a broad-spectrum fungicide
that can eliminate or reduce stains due to interactions of iron, tannin and moisture.
US Borax offers Borogard ZB zinc borate as a preservative for composites. It has
broad-spectrum activity against wood-destroying organisms, plus heat, UV stability,
as well as resistance to leaching and weathering. New developments for treating
natural wood also have great potential for treating wood flour or rice hull flour in
composites to prevent colour changes.
10.2.6 Fillers
Fillers are a normal part of most plastic compounding. For polymer composites, fillers
such as calcium carbonate (fine powder) or talc can be used. The degree of filling
will depend greatly on the end application. In general, a 15-20% use of a filler in a
composite mix could be considered feasible. If talc is used (acting as a lubricant), it
could also increase the throughput during extrusion of the compounded composite
mix. If rice hulls are heated beyond the ashes phase, the mass will produce tiny