THESIS - ROC CH ... - FINAL - resubmission.pdf - University of Guelph

The effects of fiber addition did not reveal large differences in mechanical strength. At
such low fiber additions, the cellulose fibers may not be able to impact material strength in a
dramatic way. The most notable difference was with the addition of fiber at 0.25% w/w fiber/SPI.
Both SNF and SMF at this concentration exhibited similar positive effects on tensile strength at
all 3 levels of RH. The positive results are comparable at 43 and 58% RH. However, one
notable difference was observed at the highest RH of 84% where SMF loading at 0.25% w/w
SMF/SPI out-performed the rest of the specimens. A difference of about 1.5 MPa was increased
over the control. This could indicate that SPI films with low loadings of cellulose fibers might be
less hydrophilic. On the other hand, the water holding capacity might be lessened due to an
increase in crystalline cellulose fractions which are less susceptible to hydration. Water uptake
of SPI/cellulose hybrid films have been shown to lessen with increased cellulose content (Wang
et al. 2006). Nonetheless, this shows the potential of strong interaction between cellulose and
SPI. Due to high protein chain mobility with increased water content, low interfacial adhesion
should result in a greater decrease of tensile strength. However, the opposite of this was true
for SMF0.25. Furthermore, negative effects were not significantly observed when fiber content
was increased at high RH. Tensile strength was only affected by more fiber addition at 43% RH.
These findings might indicate that the effect on tensile strength was more related to the
dispersion of cellulose than with interfacial interaction. Since higher fiber content was seen to
form aggregated clumps, inadequate dispersion of fiber could increase micro-sized defects
causing discontinuity of the protein matrix. As witnessed through the SEM data, high fiber
loading did exhibit more, smaller defects at the fracture surface. The presence of larger
aggregates also corresponds with a decrease in surface area for interaction. In the presence of
a plasticizer such as water, maintaining tensile strength would heavily rely on the interfacial
adhesion between filler and polymer. As such, negligible effects on tensile strength at high
relative humidity with higher defects in the films may highlight the excellent interaction between
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