Surface treated banana fiber reinforced poly (lactic acid) nanocomposites for disposable applications
Graphical abstract
Introduction
Biodegradable composites and nanocomposites of polylactic acid (PLA) have been extensively studied by several researchers for past two decades. Wollerdorfer and Bader (1998) have reported preparation and characterization of composites from l-Polylactide and natural fiber (Wollerdorfer and Bader, 1998). The author has been prepared biocomposites by melt blending method and reported improved mechanical performance for PLA matrix. Sinha et al. (2002), Pluta et al. (2002), Mohanty et al. (2000), etc, have been also identified significance of PLA as its nanocomposites and natural fiber reinforced composites for different end use applications (Sinha et al., 2002; Pluta et al., 2002; Mohanty et al., 2000). PLA is known for good mechanical properties, transparency and biodegradability characteristics. However, it is also known for poor processability and brittleness nature. As a result, majority of the studies on PLA were concentrated on the modification of these drawbacks.
Natural fiber reinforced PLA biocomposites are one of the much discussed area of research among the material scientists in recent years. Jute, banana, bamboo, pineapple leaf etc. are the most commonly using natural fiber as reinforcement within the PLA matrix (Oksman et al., 2003; Luo and Netravali, 1999; Okubo and Fujii, 2002). However, poor interfacial interaction in between the matrix and natural fiber is a pondering subject for material scientists in this area.
Surface modification of natural fiber is a method to improve the interfacial interaction between the matrix PLA and natural fiber. Kalaprasad et al. (1997) has reported various chemical modifications of natural fiber which provides better interface within the biocomposites (Kalaprasad et al., 1997).
Sometimes, surface modifications of natural fiber alone may not promote the properties biocomposites to the required level for end use applications. This may be due to the larger interstitial voids created within the biocomposites during the reinforcement of natural fiber. Such voids can accelerate premature breakage during mechanical testing. In such cases intercalation/exfoliation of organically modified layered silicates within the biocomposite system can be a good method to regain/boost the performance characteristics of the biocomposite. Biswal et al. (2009), has reported a similar study with improved mechanical and thermal properties of pineapple leaf fiber reinforced polypropylene nanocomposites (Biswal et al., 2009).
In the view of above observations, current study has been attempted to prepare and characterise BF and cloisite 30B (C30B) reinforced bionanocomposites using PLA matrix. BF was chemically modified using coupling agents like 3-Aminopropyltriethoxysilane (APS) and [bis-(3-triethoxysilylpropyl) tetrasulfane] (Si69) and also mercerized using NaOH to enhance the compatibility with the matrix. Susequently, PLA/BF biocomposites have been prepared by melt mixing method. Further, organically modified layered nanosilicate, cloisite 30B (C30B) has been reinforced within the PLA/BF biocomposites with optimized composition. The biocomposites and bionanocomposites were characterized by mechanical, thermal, morphological and flammability studies.
Section snippets
Materials
Poly-lactic acid (PLA 4042 D), obtained from M/s Nature Works LLC, was used as base matrix with a molecular weight around (Mw) 165,000 g/mol. Banana fiber (Musa sepentium) obtained from M/s Tripura Mushroom Growers welfare Society, Tripura, India, with a density of 1.35 g/cc was used as reinforcement material. Surface modifiers, 3-aminopropyltriethoxysilane (APS), a product of M/s Evonic Degussa (China) Co. Ltd supplied by Aroma Chemical Agencies (India) Pvt. Ltd. and bis-(3-triethoxy silyl
Surface modification of banana fiber (BF)
Banana fibers, in the form of bundles were cut into a length of 13–15 cm, and scoured in mild detergent solution at 60 °C for about 2 h to remove dust and other impurities. Finally, the fibers were washed in distilled water and dried in air for 2 days. Detergent washed fiber is denoted as ‘UBF’ within the whole study.
Mercerization or NaOH treatment
Mercerization of the fibers was carried out by immersing the fibers in 1N sodium hydroxide (NaOH) solution for 1 h at room temperature. Then the fiber washed with distilled water
Confirmation of surface treatments of banana fiber using FT-IR
Fig. 1 shows FT-IR spectra of untreated and chemically modified BF. The expected changes by surface modifications using NaOH and silane coupling agents are given in Fig. 2a. As the main components of natural fiber are cellulose, hemicelluloses and lignin, the observed FT-IR spectra of untreated and all the treated BF featured mainly of these components. Peak in the region of 1030–1150 cm-1 is primarily due to C–O–C and C–O stretching in the cellulose, lignin and their glycoside linkages.
Conclusion
Eco-friendly biodegradable cutlery has been prepared successfully using optimised composition of surface treated BF reinforced bionanocomposite. Mechanical, thermal and flammability study has been proved that the newly developed material has better or comparable properties with petroleum based polymers. Surface treatments of banana fiber have been proved to be acceptable way of enhancing the interfacial interaction in between PLA and BF. In addition, the newly added functionalities, especially
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