Laboratory Tests on Fungal Resistance and Hardness of Bagasse RMP Fiber/PP Composite

Transcription

1 Laboratory Tests on Fungal Resistance and Hardness of Bagasse RMP Fiber/PP Composite Seyyed Khalil Hosseini Hashemi Department of Wood Protection and Modification, Islamic Azad University, Karaj Branch, Karaj, Iran Mahdi Modirzare Department of Wood Science and Technology, Islamic Azad University, Karaj branch, Karaj, Iran Vahid-Reza Safdari Department of Wood Anatomy and Dendrochronology, Islamic Azad University, Karaj branch, Karaj, Iran Abstract To evaluate the effect of fungal decay on the fungal resistance and hardness of natural composites, a bagasse RMP fiber/polypropylene composite made-up in vitro by flat press method was sampled. Weight loss and hardness strength were determined after incubation with white and brown rot fungi for 8, 12, and 16 weeks. Results indicated that the white rot fungus caused more weight loss than the brown rot fungus, where weight loss values at 12 th and 16 th weeks after incubation was significant at 5 percent level. Hardness strength declined after incubation with fungi. The brown rot fungus generally caused a greater reduction in hardness strength than did the white rot fungus. Fungal decay had no significant influence on hardness strength for 8, 12, and 16 weeks. The weight loss and hardness strength of samples after incubation only with white rot fungus and only with brown rot fungus for 8, 12, and 16 weeks, was significant at 5 percent level. Keywords fungal decay, weight loss, hardness, bagasse RMP fiber thermoplastic composite, flat press Paper WS-32 1 of 6

2 Introduction Plant fibers from agriculture crops are renewable materials which have potential for creating green products and replacing synthetic materials which have potential for creating composites panel (Khalil et al. 2001). Bagasse as one of natural fibers is a biomass remaining after sugar cane stalks are crushed to extract their juice. Bagasse is also one of the most important non-wood lignocellulosic raw materials which are available for papermaking mills in Iran. Annually 4.3 million tones of bagasse approximately are produced in Iran that is mainly centered in the southwestern province of Khuzestan (Najafi et al. 2009). Bagasse nonwoven materials are also biodegradable and environmentally friendly, and, therefore are more attractive to industries either in replacement for synthetic materials or in use as reinforcement materials for a polymer matrix. During the last few decades, much effort has been devoted to increasing the utilization of bagasse. However, large quantities of this raw material are still left unused or burnt. A relatively simple possibility is to use bagasse as reinforcing filler for thermoplastics. Bagasse-based thermoplastic composites can replace wood in applications such as furniture and interior panels (Monteiro et al. 1998). Natural fibers reinforced with polymer composites have gained more interest because of their biodegradable, less expensive, light weight, easy processing, high specific modulus and also environmentally appeal. Rowell et al. (1998) in a preliminary 12-week soil block test, were found that never wet, oven dried 30 percent aspen fiber/70 percent PP specimens had less than 0.25 percent weight loss with G. trabeum and no weight loss using C. versicolor. Although there has been considerable research devoted on the weight loss and mechanical properties of bagasse/thermoplastic composites (Zabihzadeh et al. 2009), but there are few report about effect of exposure time on the weight loss and hardness strength of natural fiber/thermoplastic composites. Zabihzadeh et al. (2009) investigated influence of fungal decay on the weight loss, flexural modulus, flexural strength, and unnotched impact strength properties of a commercial extruded bagasse/pp composite and reported that brown rot fungus caused more weight loss than the white rot fungus. Modulus of rupture and modulus of elasticity declined after incubation with fungi. The brown rot fungus generally caused a greater reduction in flexural strength than did the white rot fungus. Fungal decay had no significant influence on unnotched impact strength. The objective of this study is to evaluate the influence of exposure time of fungal decay on the weight loss and hardness strength of a bagasse RMP fiber /thermoplastic composite. Experimental Material and Methods Bagasse refiner mechanical pulp (RMP) fiber/polypropylene composite made using a laboratory hot press was used for this Study. The composite was made with 38% polypropylene, 60% bagasse fiber and 2% MAPP by weight. Malt extract agar was used at a concentration of 48 g/l Paper WS-32 2 of 6

3 as the culture medium. Purified turkeytail (Trametes versicolor) and wet rot (Coniophora puteana) fungi were used in this study as the biological degradation agents. Fungi culture The purified turkeytail and wet rot fungi were transferred to Petri dishes containing malt extract agar under sterile hood using sterile pincers. The dishes were kept at 25ºC for one week until the culture medium was fully covered by the fungi. The cultured fungi were transferred into Kolle dishes containing the culture medium that were incubated for two weeks at 25ºC. Fungal inoculation and incubation of WPC Specimens The composite specimens were mounted over two 3-mm platforms and placed in the Kolle dishes. The dishes containing the fungi and the composite specimens were stored in an incubator for 8, 12, and 16 weeks at 25ºC and 75% relative humidity. Weight Loss Dry weights of the specimens were measured after 24 h at 105 ± 2ºC and weight losses were calculated using the following formula: Weight Loss (%) = (M b M a )/M b 100 Where M b and M a denote the oven-dry weights prior to and after incubation with fungi, respectively. Hardness Strength Hardness strength tests were performed according to ASTM D-2240 specification. In this test necessary force for immerse of needle into the composite specimens were determined by Sanatum apparatus. Each test was run in five replicate and the average values are reported. Results and Discussion Weight Loss The biodegradability of polypropylene is very limited (Zabihzadeh et al. 2009). Besides wood and plastic, additives in WPC are possible food sources for fungi. Therefore, calculation of weight loss was based on bagasse filler because this represents the predominant fungal food source in the composite. Turkeytail and wet rot fungi caused weight losses in Table 1. Table 1. Effect of fungal decay on the weight loss of a RMP bagasse fiber/pp composite. Exposoure Time (h) Composite Brown-rotted White-rotted Weight loss (%) 8 weeks Ave Weight loss (%) 12 weeks Ave Weight loss (%) 16 weeks Ave Paper WS-32 3 of 6

4 The possible reason for this was thought to be that the fungi could not get access to the fiber due to the plastic coating around it (Rowell et al. 1998) and more or less weight loss of samples exposed to brown and white rot fungi in an incubator after 8, 12, and 16 weeks could be difference in decay mechanism. One of the distinguishing biochemical features of white rot fungi is that some of them such as Trametes versicolor reduce both lignin and holocellulose simultaneously, but in brown rot fungi reduce hollocellulose because many of them produce oxalic acid (Betch-Anderson, 1988 and Illman et al. 1988). Oxalic acid is an agent by which brown rot fungi hydrolyze hemicelluloses and increase the accessibility of cellulose to decay enzymes and yield water-soluble sugars leaving only a lignin skeleton (Nemli, 2006). Because in this composite polypropylene content was very higher than bagasse fiber content, hence in the longer exposure time white rot fungus depolymerize the more lignin and less holocellulose than brown rot fungus and its action is directed towards the whole cellulose microfibrils, whereas white rot ones produce a gradual decrease in the average of the degree polymerization carbohydrates and attack the surfaces of the microfibrils (Kleman-layer et al. 1992, Green and Highley, 1995). Hardness Strength The mean values from Table 2 have been shown that significant difference was found between the hardness strength of samples prior to and after incubation with the fungi for 8, 12, and 16 weeks. Also no significant difference was found between the hardness strength of samples after incubation with the brown and white rot fungi, but significant difference was found between the hardness strength of samples after incubation only with the white rot fungus and only with the brown rot fungus for 8, 12, and 16 weeks. Hardness strength losses caused by Turkeytail and wet rot fungi and hardness strength of control samples were summarized in Table 2. Table 2. Effect of fungal decay on the hardness strength of a RMP bagasse fiber/pp composite. Exposoure Time (h) Composite Control Brown-rotted White-rotted Hardness strength (Shore D) 8 weeks Ave Hardness strength (Shore D) 12 weeks Ave Hardness strength (Shore D) 16 weeks Ave In decayed samples, only bagasse was degraded by the fungi, whereas the polymer remains undigested. Therefore, the hardness strength of the whole system was affected fungal decay appreciably. A high standard deviation is observed, which is owing to the fact that the fungi only deteriorated the all points in the specimens that have been more accessible. This is probably owing to the fact that generally hardness strength of polymer drastically decreases when lignocellulosic fiber is added to the system (Karimi et al. 2007). Paper WS-32 4 of 6

5 Conclusions This work investigated the effect of fungal decay on weight loss and hardness strength of a bagasse RMP fiber/polypropylene composite. The mechanical test result is showed that hardness strength decreased after incubation with turkeytail and wet rot fungi. The hardness strength of specimens at 8 th, 12 th, and 16 th weeks after incubation with brown rot fungus was reduced approximately by 9.27%, 14.14%, and 14.69% and with white rot fungus was reduced approximately by 9.21%, 13.21, and 15.66, respectively. The hardness strength was affected by fungal decay. Turkeytail and wet rot fungi caused a weight loss of specimens at 8 th, 12 th, and 16 th weeks after incubation with brown rot fungus was determined approximately by 3.29%, 5.12%, and 5.67% and with white rot fungus was determined approximately by 3.15%, 6.32, and 7.15, respectively. References ASTM D Standard Test Method for Rubber Property-Durometer Hardness. Betch-Anderson, J Production and Neutralization of Oxalic Acid Produced by the Dry Rot Fungus and Other Brown Rot Fungi. IRG/WP/1330. Green, F., and Highley, T The Long Road to Understanding Brown Rot Decay, p. 18, Int. Res. Group on Wood Press, Stockholm. Illman, B.L., Meinholtz, D.C., and Highly, T. L Generation of Hydroxyl Radical by Brown Rot Fungus, Postia Placenta. IRG/WP/ Karimi, A.N., Tajvidi, M., and Pourabbasi, S Effect of Compatibilizer on the Natural Durability of Wood Flour/High Density Polyethylene Composites against Rainbow Fungus (Coriolus versicolor). Polymer Composites. 28(3): Kleman-layer, K., Agosin, E., Conner, A., and Kirk, K Changes in Molecular Size Distribution of Cellulose during Attack by Rot and Brown Rot Fungi. Applied Environmental Microbiology. 58(4): Khalil, HPSA., Ismail, H., Rozman, H.D., and Ahmad M.N The effect of acetylation on interfacial shear strength between plant fibres and various matrices. Europ Polym. Monteiro, S.N., Rodriquez, R.J.S., and De Souza, M.V Sugar cane bagasse waste reinforcement in low cost composites. Advanced performance material. 5(3): Najafi, G., Ghobadian, B., Tavakoli, T., and Yusaf, T Potential of bioethanol production from agriculture wastes in Iran. Renewable and Sustainable Energy. 13 (6/7): Paper WS-32 5 of 6

6 Nemli, G., Gezer, E. D., Yildis, S., Temiz, A. and Aydin, A Evaluation of the Mechanical, Physical Properties and Decay Resistance of Particleboard Made from Particles Impregnated with Pinus brutia Bark Extractives. Bioresource Technology. 97: Rowell, R.M., Caulfield, D.F., Chen, G., Ellis, W.D., Jacobson, R.E., Lange, S.E., Schumann, R., Sanadi, A.R., Balatinecz, J.J., and Sain, M Recent advances in agro-fiber/thermoplastic composites. In: Second International Symp. on Natural Polymers and Composites. Atibaia, SP, Brazil. pp Zabihzadeh, S.M., Hosseini Hashemi, S.K., Mehregan Nikoo, H., and Sepidehdam, S.M.J Influence of Fungal Decay on Physico-mechanical Properties of a Commercial Extruded Bagasse/PP Composite. Journal of Reinforced Plastics and Composite. doi, / Paper WS-32 6 of 6