Mechanical Properties of Biocomposites

The superior mechanical properties of biocomposites with appropriate alkali-treated natural fibers are ascribed to the increased fiber-matrix adhesion on removing the natural and artificial impurities, thereby forming roughened surfaces. As described earher, alkali treatment may lead to fiber fibrillation, resulting in the increase surface area contactable with the polymer. Such surface roughness and increased aspect ratio by fibrillation offer better natural fiber-polymer matrix bonds [4]. In another paper [143], the effect of the addition of silane-treated- and untreated talc as filler on the mechanical properties of PLA/recycled newspaper cellulose fiber/talc hybrid composites was evaluated. 

Thomas et al. [144] studied extensively the effect of fiber surface modification on the mechanical properties of sisal/UPE composites fabricated by RTM. Alkali, 

4 How Does the Suiface Treatment Influence the Properties of Biocomposites 1159 

It was found that alkali and silane treatments also increased the tensile and flexural strength of PLA/ramie composites, exhibiting that alkali treatment (5 wt%, 3h) is more effective than silane treatment (APS and GPS, 24h) [145]. Oxygen plasma treatment of jute fibers improved the tensile and flexural properties of jute/HDPE composites, showing that radio frequency (RE) plasma treatment was more effective than low frequency (LE) plasma treatment up to 60 W [139]. Oligomeric siloxane treatment after alkali treatment of jute fibers resulted in an additional increase in both tensile and flexural strengths of JEP and JUP composites, compared with either alkali or silane treatment alone, resulting from the increase of fiber-matrix adhesion by surface treatment, as mentioned earlier [53]. 

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The results of mechanical properties (presented later in this section) showed that up to 20 phr, the biofillers showed superior strength and elongation behavior than CB, cellulose being the best. After 30 phr the mechanical properties of biocomposites deteriorated because of the poor compatibility of hydrophilic biopolymers with hydrophobic natural rubber(results not shown). While increasing quantity of CB in composites leads to constant increase in the mechanical properties. Scanning electron micrographs revealed presence of polymer-filler adhesion in case of biocomposites at 20 phr. 

Figure 17.6 shows the tensile mechanical properties of biocomposites based on different fillers (LCPq i, LCFo o.i, and LCFo.i-i) with different content (from 0 to 30 wt%). Stress-strain evolutions show that PBAT is at room temperature a ductile material with a high elongation at break (ei,), more than 200%. This is consistent with Tg and Tf values. 

Oil Absorption Behavior and Its Effects on Mechanical Properties of Biocomposites... 

The chemical and/or physical interaction between the silane-treated natural fibers and the polymer matrix is an important factor for improving the mechanical properties of biocomposites. Physical mixing of silane-treated natural fibers with thermoplastic resins can enhance the fiber-matrix interaction through in-termolecular entanglement or acid-base interaction [56]. In this case, limited improvement in the mechanical properties may be expected. The mechanical properties may be marginally increased by the increased wettability and the uniform dispersion of silane-treated natural fibers into the thermoplastic matrices [71]. The molecular chains may be interdiffused into the natural fiber surfaces, forming a (semi)interpenetrating polymer network [65, 72]. 

The energy and frequency of UV radiation are smaller than those of X-rays but greater than those of visible light UV energy, which ranges from approximately 200-400 nm, can also be used to modify the natural fiber surfaces [113]. UV treatment may lead to an increase of the polarity of the fiber surfaces. As a result, the wettability of the fibers can be increased and the interfacial and mechanical properties of biocomposites can be increased. 

T. 0. Eom, G.N. Ramaswamy, B.M. Gatewood, Alternative Agricultural Fibers Comparison of Mechanical Properties of BioComposites Made via Poiymer Extrusion and Nonwoven Fiber Processes, Abstract, Textile Chemist and Colorist, 30(8) (1998), p. 47. 

The mechanical properties of biocomposites depend on a number of factors. Firstly, these are the quantity and type of fiber added to the material, but the type and amount of plasticizers and the production temperature are also important parameters [14]. One of the parameters with a dominating influence on the mechanical properties of biocomposites is the quantity of both natural fiber and plasticizer [3, 4, 6]. It has been observed that the addition of fiber enhances the mechanical strength. The addition of extra plasticizer causes a decUne in the maximum sample stress. 

Amaral, M., Lopes, M.A., Silva, R.F., Santos, J.D., Densification route and mechanical properties of Si3N4-bioglass biocomposites, Biomaterials, 23, 2002, 857-862. 

Torres, F.G., Arroyo, O.H., Gomez, C. Processing and mechanical properties of natural fiber reinforced thermoplastic starch biocomposites. J. thermoplast. compos, mater. 20,... 

The effect of four surface treatments of industrial hemp fibers on mechanical and thermal properties of biocomposites was studied. The treatments done were Alkali treatment, silane treatment, an UP matrix treatment, and a treatment with acrylonitrile of the hemp materials has been studied. 

Shen, L., Yang, H., Ying, J., Qiao, F, and Peng, M. (2009) Preparation and mechanical properties of carbon fiber reinforced hydroxyapatite/polylactide biocomposites. J. Mater. Sci. - Mater. Med., 20 (11), 2259-2265. 

Hyun SL, Donghwan C (2008) Effect of natural fiber surface treatments on the interfacial and mechanical properties of henequen/polypropylene biocomposites. Macromol Res 16 411 17... 

Yang HS, Wolcott MP, Kim HS, Kim S, Kim HI (2007) Effect of different compatibilizing agents on the mechanical properties of lignocellulosic material filled polyethylene biocomposites. Compos Struct 79 369-375... 

Lu Y, Weng L, Cao X (2005) Biocomposites of plasticized starch reinforced with cellulose crystallites fromcottonseed linter. Macromol Biosci 5 1101-1107 Lu Y, Weng L, Cao X (2006) Morphological, thermal and mechanical properties of ramie crystallites-reinforced plasticized starch biocomposites. Carbohydr Polym 63 198-204 Malainine ME, Mahrouz M, Dufi esne A (2005) Thermoplastic nanocomposites based on cellulose microfibrils from Opuntia ficus-indica parenchyma cell. Compos Sci Technol 65 1520-1526 Mangalam AP, Simonsen J, Benight AS (2009) Cellulose/DNA hybrid nanomaterials. Biomacromolecules 10 497-504... 

Chapters 15-18 focus on the weathering/mechanical study of lignocellulosic fiber-reinforced polymer composites. The effect of different environmental conditions on the physico-chemical and mechanical properties of the polymer composites is discussed in detail in these chapters. Chapter 15 mainly focuses on the effect of weathering conditions on the properties of lignocellulosic polymer composites. Most of the focus of this chapter is the effect of UV radiation on different properties of composites. Chapter 16 describes the effect of layering pattern on the physical, mechanical and acoustic properties of luffa/coir fiber-reinforced epoxy novolac hybrid composites, and Chapter 17 summarizes the fracture mechanism of wood plastic composites. Chapter 18 focuses on the mechanical behavior of biocomposites xmder different environmental conditions. 

Y. Lu, L. Weng, and X. Cao, Morphological, thermal and mechanical properties of ramie crystallites—Reinforced plasticized starch biocomposites. Carbohydr. Polym. 63, 198-204 (2006). 

M. Khalid, A. Salmiaton, T.G. Chuah, C.T. Ratnam, and S.Y.T. Choong, Effect of MAPP and TMPTA as compatibilizer on the mechanical properties of cellulose and oil palm fiber empty fruit bunch-polypropylene biocomposites. Compos. Interfaces 15, 251-262 (2008)... 

S. Shinoj, R. Visvanathan, S. Panigrahi, and N. Varadharaju, Dynamic mechanical properties of oil palm fibre (OPF)-linear low density polyethylene (LLDPE) biocomposites and study of fibre-matrix interactions. Biosyst. Eng. 109,99-107 (2011). 

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