From Science & Research
From Science & Research A B C Fig 1: Biofibers (A) Soy hull; (B) Switchgrass and (C) Miscanthus Bio-Composites Flexural strength (MPa) 70 56 42 28 14 0 Influence of biofibers and their hybrids on the mechanical properties of a PHBV/PLA Blend Flexural strength A B C D E Fig. 2: Flexural strength and modulus of PHBV/PLA and its composites A: PHBV/PLA B: PHBV/PLA +30% soy hull C: PHBV/PLA +30% switchgrass D: PHBV/PLA +30% miscanthus E: PHBV/PLA +30% hybrid Flexural modulus 6 4.5 3 1.5 0 Flexural modulus (GPa) Soy hull, switchgrass and miscanthus (Fig.1) are cheap and widely available biofibers. Soy hull is obtained from soy beans during the extraction of oil and used as animal feed or discarded as waste. Both miscanthus and switchgrass are perennial biofibers mainly treated as energy crops. These products contain cellulose based fibers which have the potential to be used as reinforcement in composites. Utilization of these under-valued local biofibers with biobased polymers may strengthen the economy of farmers and reduce the emission of hazardous materials to the environment compared e.g. to biofiber/carbon fiber/glass fiber reinforced petroleum based composites [1]. The aim of the work described here was the use of fibers, which are cheaper than traditional agricultural fibers like flax, hemp and jute fibers etc, with bioplastics to make cost efficient sustainable composites. Also there is always a great concern about the supply chain for industrial production of green composites, for example when biofibers are temporarily not available in necessary qualities and quantities [2]. Since these fibers have different chemical compositions, it is hypothesized that the performance of hybrids (made by combining all these fibers in equal proportion) in composites is an average of all used biofibers and it helps to maintain the continuity of the supply chain. Recently the authors studied the mechanical performance of green composites fabricated from above mentioned biofibers and their hybrids with a blend of the biopolymers polyhydroxybutyrate-co-valerate (PHBV: 60 % by weight) and polylactide (PLA: 40 % by weight) [3]. It was observed that the fibers have comparatively lower density (1.4 g/cm 3 ) over the traditional fibers like glass fibers (2.5 g/cm 3 ) and carbon fibers (1.7 g/cm 3 ), etc., which gives the composites an advantage particularly in automotive industry in terms of lightweight design and thus subsequently in increasing fuel efficiency. 28 bioplastics MAGAZINE [04/13] Vol. 8
From Science & Research by Malaya R.Nanda 1,2 , Manjusri Misra 2 , Amar K. Mohanty 2 1 Institute for Chemicals and Fuels from Alternative Resources (ICFAR), Department of Chemical and Biochemical Engineering, Western University, London, Otario, Canada 2 Bioproducts Discovery and Development Centre (BDDC), Department of Plant Agriculture, University of Guelph, Guelph, Ontario, Canada a b Different fibers were successfully incorporated to the PHBV/PLA matrix. Although the addition of fibers reduces the tensile strength a significant improvement in elastic modulus was observed. The mechanical performance of the fibers and their hybrid is given in Fig. 2. It was observed that the properties of the hybrid is an average of other fibers. c d Scanning electron microscope (SEM) images of the composites are given in Fig. 3 where fiber fractures, debonding of fibers and fiber pullout were observed. The gap between fiber and matrix indicated the poor adhesion between the two which may have caused the poor strength of the composites [4]. The hybrid composite showed acceptable heat deflection temperature (HDT B @ 0.45 MPa: 103 ± 1˚C). The hydrophilic nature of the biofibers is mainly responsible for the high moisture absorption of the composites [5]. One of the major advantage of using PHBV/PLA blend as matrix is that the blend has a balanced stiffness, toughness and an acceptable heat deflection temperature which is collectively not found in either of the biopolymer [6]. The future plan includes further improvement in the properties of PHBV/PLA based composites by surface modification of the fibers or by using compatibilization chemistry and its comparison with respective polypropylene (PP)- composites. The engineered composites are renewable, biodegradable and have better cost versus mechanical performance over the traditional petroleum based composites. These composites demonstrated the potential to substitute petrobased composites in some of the applications particularly in automotive industries. Acknowledgements: The authors appreciate the financial support provided by the Hannam Soy bean Utilization fund- 2008 (HSUF) for this project. Fig. 3: Scanning electron microscope images of (a) PHBV/ PLA+30% soy hull (b) PHBV/PLA+30% switchgrass (c) PHBV/ PLA+30% miscanthus (d) PHBV/PLA+30% hybrid composites References: [1] S.V. Joshi, L. T. Drazl, A.K. Mohanty, S. Arora, Are natural fiber composites environmentally superior to glass fiber composites . Composites, Part A. 2005, 35, 371-376. [2] C. Nyambo, A.K.Mohanty, M. Misra, Polylactidebased renewable green composites from agricultural residues and their hybrids. Biomacromolecules, 2010, 11, 1654-1660. [3] M.R. Nanda,M. Misra, and A.K. Mohanty, Performance evaluation of biofibers and their hybrids as reinforcements in bioplastic composites. Macromol. Mater. Eng. doi: 10.1002/mame.201200112 [4] P.V. Joseph, G. Mathew, K. Joseph, G. Groeninckx, S. Thomas, Dynamic mechanical properties of short sisal fibre reinforced polypropylene composites Composites(A). 2003,34, 275-290 [5] S. M. Zabihzadeh, Water uptake and flexural properties of natural filler/HDPE composites. Bio Resources. 2010, 5, 316-323 [6] M.R.Nanda, M. Misra,A.K. Mohanty, Mechanical performance of soy-hull-reinforced bioplastic green composites: A comparison with polypropylene composites. Macromol. Mater. Eng. 2012, 297, 184- 194. bioplastics MAGAZINE [04/13] Vol. 8 29
