The two reactive systems using cellulosic fiber reinforcement emphasiz
ed in this article are twin screw extrusion maleation of polypropylene
(PP) and structural reaction injection molding (SRIM). Both simultane
ous and sequential compounding of sweet gum wood fiber (WF) with malea
tion were studied. Similar PP/WF mechanical properties are observed fo
r simultaneous and sequential compounding. However, the melt viscosity
of the simultaneous compounding and maleation deceases initially comp
ared to neat polypropylene, whereas the sequential process does not ha
ve an initial decrease. After the initial response, the melt viscosity
and shear thinning characteristics in both systems increase with WF c
ontent compared to their respective low WF behavior. The cellulosic re
inforcement in the SRIM studies include: cheesecloth; and nonwoven mat
s formed separately from fiber bundles of sugar cane rind, kenaf, and
sweet gum wood. In the SRIM system the modulus and tensile strength of
the neat polyurea/urethane increases with cellulose content, independ
ent of cellulosic source; the modulus doubles with only 4% cellulose,
and the tensile strength doubles with only 7% cellulose. However, the
elongation to break decreases from 300 to 30% with only 4% cellulose.
Cellulose is as reactive with isocyanate in SRIM as are the commercial
polyols. (C) 1996 John Wiley & Sons, Inc.