学位論文内容の要旨

著者

１．

俞 颖

論文題目

Processing and Mechanical Characterization of Cellulose Based Composites
２．

論文要旨

The appropriate specific mechanical properties, biodegradability and cost-effective of
natural fibers have made them as attractive alternatives to synthetic fibers used inpolymer composites. Natural fiber reinforced composites are considered to be very
promising materials in numerous engineering applications especially in automotive
sectors. However, the hydrophilic nature, high moisture absorption and low mechanicalproperties of natural fibers were reported negatively affects the performance of thecomposites. In addition, the characteristics of natural fibers will also cause different
problems in different manufacture process. In order to improve the properties of thenatural fiber composites, settle the optimal manufacturing condition for different
molding processes, researches on the processing and mechanical characterization ofnatural composites have been presented in this thesis which mainly consists of two parts.
The first part was focused on recycled jute woven fabric reinforced unsaturated
polyester composite molded by hand lay-up molding process. While the second part was
researches on wood particle reinforced polypropylene composite molded by injection
molding process.
In chapter 2, as a primal investigation, the effect of moisture contents of the recycled
jute woven fabric on the mechanical properties of the composites was discussed. It isfound that the mechanical properties of composite decrease with the decrease of themoisture due to the decrease of the tensile strength of jute fiber itself although betterinterface property can be obtained by deeply dried jute fabric reinforced composite.
On the other hand, in chapter 3, the hydrothermal aging performance of recycled jute

woven fabric reinforced composite was evaluated and comparison of the weight changemechanism between glass fiber reinforced composite and natural fiber reinforced
composite was also discussed. It was found that with a comparatively long immersion
times, there was no obvious differences of water absorption and weight loss behavior
and bending properties of the composites with two different moisture contents.
Therefore, it is considered it may be not necessary to perform dry process on recycled
jute woven fabric before hand lay-up molding process. This conclusion is helpful tolessen the energy consumption during processing and increased the molding
effectiveness. While compared to glass fiber, since jute fiber is easily to absorb water byitself and some compositions will also possible to dissolve in water, it will therefore
lead to high weight gain (Mg), weight loss (Ml) and higher decrease of the mechanicalproperty. After clarifying the water absorption mechanism of jute reinforced composites,
the detail compositions of Ml can be calculated. The corresponding model is consideredalso suitable for other natural fiber reinforced composite.
In addition, in order to extend the application of the jute composites, the effects of thelaminated structures of recycled jute woven fabric hybrid with glass woven fabric wereinvestigated in chapter 4, the hybrid structure with glass layer can increase the impact
resistance of the composite not only due to the higher strength of the glass fiber but also,
the glass layer can increase the damage area of the composite during impact. And theposition of the glass layer result in variations in the impact behavior of composites.
When the glass layer was at the bottom of the dropped impacted surface, the composite
exhibited highest impact energy than those glass layers on top or middle.
In chapter 5, the effect of filler content on the physical and mechanical properties of thewood/PP composites and the comparison between talc/PP and wood/PP has been carriedout. It could be concluded using wood/PP in the automotives instead of talc/PP isreasonable and could lead to a high fuel economy due to the composite’s low weight aswell as the low thermal conductivity. However, wood particles aggregated at a highwood content and consequently lead to a decrease of the mechanical properties.
Therefore, in chapter 6, proper molding conditions and effect of additives wereproposed to solve the feeding problem of the wood particle due to the low bulk density

and enhance the interfacial adhesion property and distribution condition. Pre-molding
process (dry-blending and compounding) and the effect of adding the additives(maleated polypropylene (MAPP) and crystalline polyalpha olefin (CPAO)) on themechanical properties of the wood/PP composites were discussed firstly. Results
showed the mechanical properties of the wood/PP composites molded throughcompounding process are better than the ones molded by direct dry-blending process
because the less voids contents and the distribution of the wood particle in the PP matrix
was well improved. The optimal MAPP content in this research is determined at 2wt%
which could best improve the properties of composite because of the improvement of
the interfacial adhesion property. While incorporating CPAO could improve the woodparticle distribution condition and consequently lead to the increasing of thecomposite’s property. In addition, other technique approaches such as the effect ofcompounding screw geometry and perform twice compounding process before injection
molding at high wood content were also discussed. Result showed by using weakextruder screw, the color of cellulose/PP will be lighter and compared to the ones withstrong extruder screw, the mechanical properties won’t decrease so much. While byperforming twice compounding process, the feeding difficulty could be solved as wellas keep comparable high mechanical properties.
In chapter 7, the hybridization effect of wood particle with glass short fiber wasdiscussed and the elastic modulus of hybrid composites was predicted by using the ruleof hybrid mixtures (RoHM) equation and classical lamination theory (CLT) and theaccuracy of the two estimation models has been discussed. It could be concluded thatwith appropriate material design, it is possible to get hybrid material with comparable
high mechanical properties with high green degree. While to better predict the elastic
modulus of the hybrid composite, the interaction between glass short fiber and woodparticle and the reinforcing effect including fiber orientation factor, fiber length
distribution factor, particle dispersion factor, and particle aspect ratio factor and so onneed to be considered in the prediction model.
This research showed the potential of molding recycled jute woven fabric reinforced
unsaturated polyester composite by hand lay-up process without dry process on thefabric in advance and developed a suitable calculation method to analyze the detailcompositions of Ml after hydrothermal aging test of natural fiber reinforced composite.
In addition, it also presents the proper molding conditions and optimal additive agent’s
content for injection high wood particle content reinforced polypropylene composite.
And the elastic modulus of glass short fiber/wood particle/PP composite could be
predicted by appropriate modifying of the RoHM prediction model.