**7. Conclusion**

Due to the growing competition in producing cost-effective products, in addition to the excreted environmental limitations, natural fibers have recently become attractive to researchers because of their advantages over conventional mineral fillers. However, several limitations must be overcome in order to exploit the full potential of natural fibres. The incompatibility between natural fiber and polymer matrix is a major problem for interfacial adhesion between these two component materials, which is of critical importance for the mechanical properties of the composite. In the present chapter, we focused on the natural fiber-thermoplastic composites and its worldwide application markets, reviewed some influence factors on the injection molding process to produce the natural fibers thermoplastic compound and introduced some research on interfacial adhesion strength between natural fibers and thermoplastic matrix and then reported the effect of various chemical modifications of wood fiber on the interfacial strength of wood polypropylene injection molded composites. The results showed that, at first, chemical modification of natural fiber is necessary and respectively silane and alkaline treatment of wood flour improved interfacial adhesion and so increased the mechanical performance of these composites. Secondly, simultaneous use of chemical modification and coupling agent on the properties had synergic effect. Thirdly, however, adhesion factor is a good way for understanding interfacial behavior of WPCs, further evidences of improved matrix–filler interactions is observed by SEM. Finally, future areas of interest should be focused on developing new coupling agents and new class of natural fiber modification such as enzymatic treatment.

#### **8. References**

246 Some Critical Issues for Injection Molding

It is also clear from the SEM images in Fig. 23a that the wood fibers in unmodified sample are pulled out easily and some holes are noticed around the fibers which imply that there are weak interactions between the filler and polymer. As it can be seen in Fig. 23e, there is a better polymer-filler adhesion with the silane treatment than in the composite prepared with untreated wood flour, which implies an increase in the thickness of the interface between the particles and polymers. In samples undergone alkali treatment (Fig. 23b), fibers removed from pp matrix and broken, but not the isolated fibrils were observed, which means that the interactions between the phases are not strong enough. Similar trend is also observed for samples containing acrylic acid (Fig. 23c) and benzoyl (Fig. 23d) treated fibers. As in the case of adhesion factor, the best encapsulation of wood fibers with polymer matrix can be seen in samples with silane treatment. This explanation is similar to that of adhesion factor results.

Fig. 23. SEM Micrographs of modified wood polymer composites with: (b) alkali, (c) acrylic

Due to the growing competition in producing cost-effective products, in addition to the excreted environmental limitations, natural fibers have recently become attractive to researchers because of their advantages over conventional mineral fillers. However, several limitations must be overcome in order to exploit the full potential of natural fibres. The incompatibility between natural fiber and polymer matrix is a major problem for interfacial adhesion between these two component materials, which is of critical importance for the mechanical properties of the composite. In the present chapter, we focused on the natural fiber-thermoplastic composites and its worldwide application markets, reviewed some influence factors on the injection molding process to produce the natural fibers thermoplastic compound and introduced some research on interfacial adhesion strength between natural fibers and thermoplastic matrix and then reported the effect of various chemical modifications of wood fiber on the interfacial strength of wood polypropylene injection molded composites. The results showed that, at first, chemical modification of natural fiber is necessary and respectively silane and alkaline treatment of wood flour improved interfacial adhesion and so increased the mechanical performance of these composites. Secondly, simultaneous use of chemical modification and coupling agent on the properties had synergic effect. Thirdly, however, adhesion factor is a good way for understanding interfacial behavior of WPCs, further evidences of improved matrix–filler interactions is observed by SEM. Finally, future areas of interest should be focused on developing new coupling agents and new class of natural fiber modification such as

acid, (d) benzoyl chloride, (e) silane, and (a) unmodified samples.

**6.6 Surface morphology** 

**7. Conclusion** 

enzymatic treatment.

(2010). Demand for wood-plastic composite and plastic lumber to reach \$5.3 billion in 2013, In:, *Centre Magazine*, March 2010, Available from:

 <http://www.centremagazine.com/news/demand-for-wood-plastic-compositeand-plastic-lumber-to-reach-5-3-billion-in-2013/1000369238/>


Thermoplastic Matrix Reinforced with Natural Fibers: A Study on Interfacial Behavior 249

Kubat, J.; Rigdahl, J. & Welander, M. (1990). Characterization of interfacial interactions in

Larsson-Brelid, P.; Walinder, M.E.P.; Westin, M. & Rowell, R.M. (2008). Ecobuild- a center

Li, Y.; Mai, Y.W. & Ye, I. (2000). Sisal fibre and its composites: a review of recent

Li, Q. & Matuana, L.M. (2003). Foam extrusion of high density polyethylene/wood-flour

Liu, L.; Yu, J.; Cheng, L. & Qu, W. (2009). Mechanical properties of poly(butylene succinate)

Lu, J. & Drazel, L.T. (2010). Microfibrillated cellulose/cellulose acetate composites: Effect of

Maiti, S.N.; Subbaro, R. & Ibrahim, M.N. (2004). Effect of wood fibers on the rheological

Mathew, L.; Joseph, K.U. & Joseph, R. (2004). Isora fibres and their composites with natural

Mohanty, A.K.; Misra, M. & Drzal, L.T. (2001). Surface modifications of natural fibers and

Mooney, C.; Stolle-Smits, T.; Schols, H. & de Jong, E. (2001). Analysis of retted and non

Mukherjee, A.; Ganguly, P.K. & Sur, D. (1993). Structural mechanics of jute: the effects of

Oksman, K.; Lindberg, H. & Holmgren, A. (1998). The nature and location of SEBS-MA

Oksman, K. & Selin, J.F. (2004). Plastics and composites from polylactic acid. In: *Natural* 

Olesen, P.O. and Plackett, D.V. (1999). Perspectives on the Performance of Natural Plant

*Science*, Vol.69, No.1, (July 1998), pp. 201-209, ISSN 0021-8995

Kluwer Academic Publishers, ISBN 1-4020-7643-6, Boston

*for the Future*, pp. 1-7, Copenhagen Denmark, 27-28 May 1999

Vol.88, No.14, (June 2003), pp. 3139–3150, ISSN 0021-8995

(January 2010), pp. 153-161, ISSN 0887-6266

No.1, (January 2004), pp. 644-650, ISSN 0021-8995

Vol.8, No.5, (October 2001), pp. 313-343, ISSN 0927-6440

No.2- 3, (August 2001), pp. 205-216, ISSN 0168-1656

ISSN 0021-8995

2037–2055, ISSN 0266-3538

337–34, ISSN 1477-7606

pp. 348–353, ISSN 0040-5000

1542-1406

835X

high density polyethylene filled with glass spheres using dynamicmechanical analysis. *Journal of Applied Polymer Science*, Vol.39, No.7, (April 1990), pp.1527-1539,

for development of fully biobased material systems and furniture applications. *Molecular Crystals & Liquid Crystals*, Vol.484, No.1, (April 2008), pp. 623- 630, ISSN

developments. *Composites Science and Technology*, Vol.60, No.11, (August 2000), pp.

composites using chemical foaming agents. *Journal of Applied Polymer Science*,

(PBS) biocomposites reinforced with surface modified jute fibre. *Composites Part A: Applied Science and Manufacturing*, Vol.40, No.5, (May 2009), pp. 669-674, ISSN 1359-

surface treatment. *Journal of Polymer Science Part B: Polymer Physics*, Vol.48, No.2,

properties of i-PP/wood fiber composites. *Journal of Applied Polymer Science*, Vol.91,

rubber*. Progress in rubber, plastics and recycling technology*, Vol.20, No.4, (- 2004), pp.

performance of the resulting biocomposites: An overview. *Composite Interfaces,* 

retted flax fibers by chemical and enzymatic means. *Journal of Biotechnology*, Vol.89,

hemicellulose or lignin removal. *Journal of the Textile Institute*, Vol.84, No.3, (-1993),

compatibilizer in polyethylene- wood flour composites. *Journal of Applied Polymer* 

*fibers, plastics and composites*, Wallenberger, F.T. & Weston, N. (Eds), pp. 149-166,

Fibres, *Proceedings of Natural Fibres Performance Forum Plant Fibre Products-Essentials* 


Eckert, C. (2000). Opportunities for natural fibers in plastic composites, *Proceedings of the* 

Farsi, M. (2010). Wood–plastic composites: influence of wood flour chemical modification on

Gassan J. & Gutowski V.S. (2000). Effects of corona discharge and UV treatment on the

George, J.; Bhagawan, S.S. & Thomas, S. (1999). Effect of Strain Rate and Temperature on the

Hristov, V.N.; Krumova, M.; Vasileva, S. & Michler, G.H*.J.* (2004). Modified polypropylene

Huda, M.S.; Drzal, L.T.; Mohanty, A.K. & Misra, M. (2008). Effect of fiber surface treatments

Jahn, A.; Schroder, M.W.; Futing, M.; Schenzel, K. & Diepenbrock, W. (2002).

John, M.J.; Francis, B.; Varughese, K.T. & Thomas, S. (2008). Effect of chemical modification

*Manufacturing,*Vol.39, No.2, (February 2008 ), pp. 352-363, ISSN 1359-835X Joseph, K.; Mattoso, L.H.C.; Toledo, R.D.; Thomas, S., de Carvalho, L.H.; Pothen, L.; Kala, S.

Kandachar, P.V. (2000). Designing with natural fibre composites, *Proceedings of the* 

Kim, H.S.; Yang, H.S.; Kim, H.J.; Lee, B.J. & Hwang, T.S. (2005)*.* Thermal properties of agro-

Kokot, S. & Stewart, S. (1995). An Exploratory Study of Mercerized Cotton Fabrics by DRIFT

*Calorimetry*, Vol.81, No.2, (July 2005), pp. 299-306, ISSN 1388-6150

*Africa*, pp. 187–202, Arusha Tanzania, September 2000

1995), pp. 643-651, ISSN 0040-5175

No.24, (December 2010), pp. 3587–3592, ISSN 0731-6844

No.15, (November 2000), pp. 2857-2863, ISSN 0266-3538

Canada, May 25-26, 2000

0892-7057

0021-8995

ISSN 0266-3538

4604, ISSN 0022-2461

Brazil

*Conference on Progress in Woodfibre-plastic Composites*, University of Toronto,

the mechanical performance. *Journal of Reinforced Plastics and Composites*, Vol.29,

properties of jute-fibre epoxy composites, *Composites Science and Technology*, Vol.60,

Tensile Failure of Pineapple Fiber Reinforced Polyethylene Composites. *Journal of Thermoplastic Composite Materials*, Vol.12, No.6, (November 1999), pp. 443-446, ISSN

wood flour composites. II. Fracture, deformation, and mechanical properties. *Journal of Applied Polymer Science*, Vol.92, No.2, (April 2004), pp. 1286–1292, ISSN

on the properties of laminated biocomposites from poly(lacticacid) (PLA and kenaf fibers. *Composites Science and Technology*, Vol.68, No.2, (February 2008), pp. 424-432,

Characterization of alkali treated flax fibres by means of FT Raman spectroscopy and environmental scanning electron microscopy. *Spectrochimica Acta Part A: Mol Biomol Spectrosc,* Vol.58, No.10, (August 2002), pp. 2271-2279, ISSN 1386-1425 Jain, S.; Kumar, R. & Jindal, U.C. (1992). Mechanical behaviour of bamboo and bamboo

composite. *Journal of Materials Science,* Vol.27, No.17, (September 1992), pp. 4598-

on properties of hybrid fiber biocomposites. *Composites Part A: Applied Science and* 

& James, B. (2000). Natural fiber reinforced thermoplastic composites. In: *Natural Polymers and Agrofibers Composites*, Frollini, E.; Leao, A.L. & Mattoso, L.H.C. (Eds), 159-201, Embrapa Instrumentacao Agropecuaria, ISBN 858646306X, San Carlos,

*International Workshop on the Development of natural Polymers and Composites in East* 

flour-filled biodegradable polymer bio-composites. *Journal of Thermal Analysis and* 

Spectroscopy and Chemometrics. *Textile Research Journal*, Vol.65, No.11, (November


**11** 

 *USA* 

**Properties of Injection Molded High Density** 

 *Department of Chemical Engineering and Materials Science, East Lansing, Michigan,* 

This book chapter investigated the potential of using exfoliated graphene nanoplatelets, GNP, as the multifunctional reinforcement in high density polyethylene (HDPE) matrix. HDPE/GNP nanocomposites were fabricated by the conventional compounding method of melt-extrusion followed with injection molding. The mechanical properties, crystallization behaviors, thermal stability, thermal conductivity, and electrical conductivity of the resulting HDPE/GNP nanocomposites were evaluated as a function of GNP concentration. Results showed that HDPE/GNP nanocomposites exhibit equivalent flexural modulus and strength to HDPE composites filled with other commercial reinforcements such as carbon fibers (CF), carbon black (CB) and glass fibers (GF). But they have superior impact strength. By investigating the crystallization behavior of HDPE/GNP nanocomposites, it was found that GNP is a good nucleating agent at low loading levels and as a result can significantly increase crystallization temperature and crystallinity of HDPE. At high GNP loadings, however, the close proximity of GNP particles retards the crystallization process. The thermal stability and thermal conductivity of HDPE/GNP nanocomposites were significantly enhanced as a function of GNP concentration due to the excellent thermal properties of GNP. Meanwhile, results indicated that the percolation threshold of these nanocomposites prepared by the conventional melt - extrusion and injection molding is relatively high at around 10-15 vol% GNP loading. The high percolation threshold is mainly due to the sever GNP aggregation and platelets alignment during the processing conditions as verified by the morphology. To enhance their electrical conductivity and lower the percolation threshold, a wax coating method was introduced in this study which is proved to be efficient in improving the dispersion of GNP in HDPE which is responsible for the

better electrical and mechanical properties in the resulting nanocomposites.

Polymeric nanocomposites have attracted research interest both in industry and in academia in recent years, they can be found useful in many applications such as electromagnetic interference (EMI) shielding devices, low power rechargeable batteries, electronic devices, light emitting diodes (LEDs), gas sensors, super capacitors and photovoltaic cells (Hussain et al., 2006; Vaia, 2003). Polymeric nanocomposites have represented a radical alternative to

**1. Introduction** 

**Polyethylene Nanocomposites Filled with** 

*Michigan State University, Composite Materials and Structures Center,* 

**Exfoliated Graphene Nanoplatelets** 

Xian Jiang and Lawrence T. Drzal

