Polyethylene Composites Reinforced by Kenaf Fiber Modified by Silane by roq91753

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									             Polyethylene Composites Reinforced by Kenaf Fiber
             Modified by Silane Grafted Low Density Polyethylene
                           Yajuan TIAN, and Shin-ichi KURODA†

                     Gunma University, Graduate School of Engineering
                                 Kiryu, Gunma , Japan
                                skuroda@gunma-u.ac.jp

Introduction
        The use of natural fibers as reinforcements and fillers in natural-fiber/thermoplastic
composites has become more commonplace in recent years as they have many advantageous
attributes, such as low density, low cost, high specific strength and modulus, relative non-
abrasiveness, and biodegrability. Kenaf bast fiber has high potential as a reinforcing fiber in
thermoplastic composites because of its superior toughness and high aspect ratio in
comparison with other fibers. A single fiber of kenaf can have a modulus as high as 11-60
GPa1).
        The main disadvantages of natural fibers in composites include incompatibility
between hydrophilic natural fibers and hydrophobic polymers and potential moisture
absorption of the fibers. To improve the compatibility with hydrophobic thermoplastics,
many efforts for the surface treatment of natural fiber have been done2-4), such as maleated
polyolefin (1-3wt%) treatment, silane coupling, silane coupling together with maleated
polyolefin treatment, esterification and etherification etc.. Some improvements have been
achieved to some extent by these methods.
        As we have successfully prepared a new polymeric coupling agent, i.e. silane grafted
LDPE with relative higher graft yield by photo-grafting technique in our former studies and
very strong adhesive strength to glass plate has been achieved5), it’s expectable that this
polymeric coupling agent will bring good properties for natural fiber/hydrophobic
thermoplastics composites.
        In this study, by using low molecular weight vinyl silane coupling agent and this
polymeric coupling agent for the surface treatment of kenaf fiber, kenaf fiber/LLDPE
composites were prepared and their properties were studied.

Experimental
        Methacryloxypropyltriethoxysilane and 3-methacryloxypropyltriethoxysilane grafted
LDPE (Si-g-LDPE, graft yield 10%-20%) prepared through photo-grafting technique in our
lab were used for the surface treatment of kenaf fiber. Si-g-LDPE were first dissolved in
xylene at 80℃ to form a solution, then kenaf fiber were added. After 1 h immersion and the
following drying, they were subjected to soxhlet extraction with xylene for 24 h and then
dried at room temperature in a vacuum oven. Some other kenaf fiber were treated by 3-
methacryloxypropyltriethoxysilane by the same procedure. The surfaces of kenaf fibers
before and after modification were analyzed by X-ray photoelectron spectra.
        LLDPE/kenaf fiber composites were prepared by hot pressing technique. LLDPE
power (60wt%), Sumilizer (0.3wt%) and kenaf fiber (40wt%) were mixed together, then they
were poured into the mold already preheated to 200℃ and molded at 15MPa. After the
following cooling down to room temperature, they were taken out of the mold and
composites were prepared. Dynamic mechanical property of LLDPE/kenaf composite were
measured by a viscous-elastic device (TOYOSEIKI), and water absorbency were detected by
immersing the corresponding composites in water at room temperature for 12 h and
calculating the weight percentage increased.
Results and discussion
        Figure 1 shows the kinetic mechanical behavior of LDPE and the composites
reinforced by kenaf fiber without pretreatment, modified by Si-g-LDPE and modified by low
molecular weight silane. Modulus of LDPE dropped very quickly with temperature
increasing, while modulus of composites decreased slowly. All the composites showed a high
modulus at room temperature, among which composites filled with Si-g-LDPE modified
kenaf has the highest modulus. On the plot of modulus (imaginary part) against temperature,
the peak appeared around -24°C for LDPE, which was assigned as the relaxation of the
amorphous part of LDPE caused by branching, shifted to a higher temperature after filled
with kenaf fiber, and the absolute value decreased. This suggests good interaction exist
between kenaf fiber and LDPE.
            3.5
     3500000000                                                               180000000
                                                                                   0.1
        Modulus (GPa) (real part)




                                                                               Modulus (GPa) (imaginary part)
            3.0
     3000000000                                                               160000000
                                                                                   8
                                                                              140000000
                                                                                   0.1
            2.5
     2500000000                                                                                                                                   a
                                                                                                                                                  9-1
                                                                         a
                                                                         9月1日      6
                                                                              120000000
                                                                                                                                                  b
                                                                                                                                                  24-1
            2.0
     2000000000                                                          b         0.1
                                                                         24-1 100000000                                                           c
                                                                                                                                                  7-3
            1.5
     1500000000                                                          c         4
                                                                         7月3日 80000000                                                            d
                                                                                                                                                  LDPE
                                                                         d         0.1
                                                                               60000000
            1.0
     1000000000                                                          LDPE
                                                                                   2
                                                                               40000000
            0.5
      500000000                                                                    0.1
                                                                               20000000
                                    0 0                                            0 0

                                       -200   -100    0     100    200                                          -200   -100    0      100   200
                                                 Temperature (℃)                                                         Temperature (℃)

Figure 1. Temperature dependence ofdynamic mechanical property of kenaf fiber/LLDPE composite.
           a--- Pretreated by Si-g-LDPE; b--- Pretreated by silane; c--- Without pretreatment; d---LDPE

        Table 1 shows the water absorbency of PE/kenaf fibe composites. Composite using
Si-g-LDPE treated kenaf fiber has lower water absorbency compared with composite using
untreated kenaf fiber. Water absorbency contributes to hydrogen bonding of hydroxyl groups
on kenaf fiber with water. Lower water absorbency means difficult accessibility of water to
fiber, which in turn means better interaction of fiber with matrix.

                                                Table 1. Water absorbency of PE/kenaf fiber composites
                                                     Kenaf fiber                                                Water absorbency (%)
                                               Without pretreatment                                                     3.95
                                                Pretreated by silane                                                    3.39
                                              Pretreated by Si-g LOPE                                                   1.74

Conclusion
       3-methacryloxypropyltriethoxysilane photo-grafted LDPE is a very effective coupling
agent for kenaf fiber/LLDPE composites. Good interactions between kenaf fiber and LLDPE
matrix has been established by this polymeric coupling agent. Improved mechanical property
and water absorbency has been achieved for kenaf fiber/LLDPE composite.

References
1. Shinji, O., Mechanics of Materials, 40, 446-452 (2008).
2. Mohanty, A. K.; Drzal, L. T.; Misra, M. Journal of Adhesion Science and Technology, 16, 999 (2002).
3. Gassan, J., Applied Science and Manufacturing, 33A, 369 (2002)
4. Baiardo, M., Frisoni, G., Scandola, M., Licciardello, A., Journal of Applied Polymer Science, 3, 38 (2002).
5. Tian, Y.J., Kuroda, S., to be submitted.
   Main Body of Text Times New Roman 12 pt The talk will present novel results relating to
the pioneering work of Staudinger. 1 References superscript; total abstract length maximum 2
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1
    Staudinger, H. Nature 1944, 30, 605-643. Citation Style 'Macromolecules'

								
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