|Abstract or Summary
- Sclereids are sclerenchyma cells having thick lignified
secondary walls. Douglas-fir sclereids, also called bast fibers,
are long (1 mm in length), sharply pointed, spindle-shaped fibers
of a red-brown color. Sclereids from Douglas-fir bark and nine
other western coniferous species were examined for their morphology.
The external surface characteristics of sclereids isolated from
Douglas-fir bark by mechanical disk refining (F858 Fiber and Steam
Refined Fiber) and chemical treatment through digesting in Kraft
liquor (WEF-313, 606, and 900) were studied with both light and
scanning electron microscopy.
For these ten western coniferous species studied, only Douglas-fir
sclereids can be an adequate plastic reinforcing agent. There
are two reasons for this: 1) Sclereids in Douglas-fir bark differentiate
individually and usually not in groups. Individual
sclereids can be separated because of this arrangement, while the
sclereids from nine other conifers studied were in groups. 2) The
Douglas-fir sclereid has sufficient length and stiffness, while the
sclereids from nine other conifers studied do not.
WEF is a chemically treated Douglas-fir bark fiber. It has a
clean surface and has been used as a reinforcing fiber in the plastics
industry and gave satisfactory results to improve impact
strength of plastic. However, the cost and inconvenience in production
of WEF has limited the market. An acceptable quality bast
fiber produced through mechanical processing is needed.
Both F858 Fiber and Steam Refined Fiber are mechanically
processed fibers; but, E858 Fiber has a surface heavily encrusted
with surrounding parenchyma fragments and extractives, and often
several sclereids are still together in a group. The Steam Refined
Fiber is well separated and free of parenchyma fragments on its
surface like the WEF fiber, but the Steam Refined Fiber appears to
have a smoother surface than much of WEF fiber.
The comparison of surface cleanliness among F858 Fiber, WEF,
and Steam Refined Fiber indicates that steam pressurized disk
refining has accomplished the objective of producing bark sclereids
with clean surfaces, and, therefore, Steam Refined Fiber would
appear acceptable for reinforcement of plastics.