From Science & Research
From Science & Research Fig. 1: (from left): Soy hull | PHBV | PLA | PHBV-PLA-soy hull composites Composites based on soybean hull Soybean hull is one of the most widely available field crop residues obtained during the extraction of soy bean oil. Normally it is discarded as waste or used as animal feed after enrichment. The low cost, and with high fiber content, soy hull and its utilization in green composites has the potential to create extra revenue for the farmers. Using soy hull might be another way of making affordable injection molded biocomposites with specific desired mechanical properties. Recent studies performed by the authors have focussed on the fabrication of green composites from a blend of bioplastics, polyhydroxybutyrate-co-valarate (PHBV: 70 % by weight) and polylactide (PLA: 30 % by weight) reinforced with soy hull (Fig. 1) [1]. It was observed that the composites have a low density compared to the composites reinforced with traditional fibers (carbon and glass) [2]. The hydrophilic nature of biofibers adversely affects its compatibility with the hydrophobic polymeric matrices. Also, there is a concern of agglomeration of biofibers in the biopolymer as the fiber loading increases which may lead to the poor dispersion of biofiber in the matrix phase resulting in the reduction of mechanical performance of the Flexural strength (MPa) 70 56 42 28 14 0 Flexural strength Impact strength A B C D E Fig. 2: A: Neat PP B:PP+30% soy hull C: PHBV/PLA(70:30) D: PHBV/ PLA+30% soy hull E: mPHBV/PLA+30% soy hull Impact strength (J/M) material. Different surface treatment techniques for fibers and compatibilizers have been reported to increase the fiber matrix adhesion [3]. In this work, an isocyanate terminated compatibilizer, Krasol, has been used to improve the physico-mechanical properties of the green composites. The mechanical performance of the composites were compared with the corresponding polypropylene based composites and are given in Fig. 2. From the figure it is clear that incorporation of soy hull reduced the strength of the composite which is common in case of biocomposites and is attributed to the poor adhesion between the fiber and matrices. However, a significant enhancement in the flexural strength (20%) and impact strength (35%) of the modified composite (mPHBV/ PLA/ soy hull) over corresponding unmodified composites were observed by using 10 PHR of the compatibilizer in the PHBV/PLA/soy hull composites. No enhancement in the heat deflection temperature (HDT) and stiffness of the modified composites were observed. Scanning electron microscopy (SEM) images given in Fig. 3 showed the covering of fibers by polymeric matrices in modified composites. Less evidence of fiber fracture and pull out in the modified composites than in the unmodified composites suggesting a strong fiber matrix adhesion. One of the major advantages of using PHBV and PLA polymers is that they are 100% biodegradable and recyclable [4]. The biodegradation of PHBV and PLA is influenced by several factors like moisture level, temperature and pH. Since the fibers are hydrophilic they tend to absorb moisture which helps in the hydrolysis of the ester group present in the biopolymers to form oligomers [5]. These oligomers are easily degraded by micro-organisms hence have the ability to uplift the land fill shortages. Based on the observed properties of the modified green composites, some prototype materials, like storage bins and leaf rakes etc., were fabricated and are presented in Figure 4. It was found that that the composite can easily be coated with a pigment to give a desired color. Acknowledgements: The authors appreciate the financial support provided by the Hannam Soy Bean Utilization fund- 2008 (HSUF) for this project. 20 bioplastics MAGAZINE [04/14] Vol. 9
Fig. 3: SEM images of A) PHBV-PLA/30 wt% soy hull B) m PHBV-PLA+30 wt% soy hull biopolymere. ROHSTOFFE – TECHNOLOGIEN – PRODUKTE 4. Kooperationsforum mit Fachausstellung By: Malaya Nanda, Sandeep Ahankari Saswata Sahoo, Manjusri Misra, Amar Mohanty University of Guelph Guelph, Ontario, Canada [1] M. R. Nanda, M. Misra, and A.K. Mohanty. Mechanical performance of soy hull reinforced bioplastic green composites: A comparison with polypropylene composites. Macromol. Mater. Eng. 2012, 297,184-194. [2] M. R. Nanda, M. Misra, and A.K. Mohanty. Performance evaluation of biofibers and their hybrids as reinforcements in bioplastic composites. Macromol.Mater.Eng.2013, 298, 779-788. [3] M. Avella, G. Bogoeva-Gaceva, A. Buzarovska, M. E. Errico, G. Gentile, A. Grozdanov, Poly(lactic acid)-based biocomposites reinforced with kenaf fibers J. Appl. Polym. Sci. 2008, 108, 3542-3551. [4] M. R. Nanda, M. Misra, A. K. Mohanty, The effects of process engineering on the performance of PLA and PHBV blends Macromol. Mater. Eng., 2011, 296, 719-728. [5] C.Nyambo, A.K. Mohanty, M.Misra, Polylactide-based renewablegreen composites from agricultural residues and their hybrids. Biomacromolecules, 2010,11,1654-1660 BILDNACHWEIS Clairant GmbH Joseph-von-Fraunhofer-Halle Straubing, 21. Oktober 2014 ANMELDUNG www.bayern-innovativ.de/biopolymere2014 KOMPETENZFELD material. Netzwerk LifeScience Fig. 4: Leaf rake, Storage bin bioplastics MAGAZINE [04/14] Vol. 9 21
