Civil Engineering Reference
In-Depth Information
poly(hydroxyoctanoate). h ey claimed that specii c polymer-i ller interactions and
geometrical constraint due to the particle size of the latex need to be considered to
account for the mechanical reinforcement ef ect of cellulose whiskers.
However, the dispersion in organic media of ered a huge challenge. One of the
drawbacks in using polar surface cellulose whiskers is that they cannot be uniformly
dispersed in non-polar media such as organic solvents or monomers. Many method-
ologies have been adopted by researchers to improve the dispensability of cellulose in
non-polar media. h e use of surfactants with the aim of obtaining a stable suspension
of cellulose nanocrystals in organic media is a procedure used by dif erent authors as
discussed earlier. Bonini
et al.
dispersed the surfactant-coated whisker in toluene by
mixing it with cellulose whisker in aqueous suspensions. At er freeze-drying of these
suspensions, the surfactant-coated whisker could be dispersed in cyclohexane. By sur-
face acetylation, stable suspension of cellulose whiskers with degree of substitutions of
0.75 could be obtained in acetone, but not in solvents of lower polarity (Yuan
et al.
). In
2002, Bonini
et al.
[97] described a procedure based on their previous patented experi-
ments. Marchessault
et al.
[98] described an interesting method in which the nano-
crystal suspension of tunicin whiskers was mixed with the surfactant and freeze dried
to obtain pellets. h e pellets were then dispersed in toluene and the excess surfactant
eliminated by centrifugation and redispersion in toluene. h is procedure can be used to
prepare nanocomposites by dispersing the suspension of coated whiskers in a polymer
solution in toluene. Nanocomposites with a high level of dispersion were obtained due
to the use of the surfactant. Ljungberg
et al.
[85] reported that the mechanical behavior
in the nonlinear range was increased, especially the tensile strength of the nanocompos-
ites compared to the neat matrix. Moreover, elongation at break remained unchanged.
A similar study was performed using the same surfactant to prepare nanocomposites
with isotactic polypropylene. A mat formation followed by resin immersion and cur-
ing by UV light was used by Iwamoto
et al.
to make optically transparent composites
reinforced with plant i ber-based cellulose microi brils [45]. Another mat method was
used to make PF resin composite using hot press with high pressures [99]. A method of
i ltration mats followed by compression molding was also used [100]. Mirta Aranguren
and coworkers expanded these options by producing a stable cellulose nanowhisker
suspension in dimethylformamide to be subsequently incorporated in dif erent poly-
urethane (PU) matrices. Dufresne's group [87, 89] adopted another method of freeze
drying the initial aqueous suspension of the nanowhiskers, which then can be further
redispersed in DMF.
h e dispersion of i bers in polymer latex to prepare composite has been reported
for poly(ß-hydroxyoctanoate) (PHO) [101, 102], polyvinylchloride (PVC) [103],
waterborne epoxy [104] and polyvinyl acetate (PVAc) [94]. Most of the works focus on
the use of non-polar, non-water-sensitive polymers, while keeping an aqueous media
for the processing of the i lms to preserve the dispersion of the nanoparticles. In their
pioneering work, Favier
et al.
[94] adopted the technique of solvent casting using a
synthetic latex obtained by the copolymerization between styrene (35 wt%) and butyl-
acrylate (65 wt%) (poly(S-co-BuA)). Nanowhiskers were dispersed in the latex and
evaporated. h e nanocomposite i lms were obtained by water evaporation and particle
coalescence at room temperature, that is at a temperature higher than Tg of poly(S-co-
BuA), around 0°C.
