EFFECT OF SURFACE POLARITY OF CELLULOSE NANOFIBERS ON THE MECHANICAL - PDF document

18 TH INTERNATIONAL CONFERENCE ON COMPOSITE MATERIALS EFFECT OF SURFACE POLARITY OF CELLULOSE NANOFIBERS ON THE MECHANICAL PERFORMANCE OF STARCH BASED COMPOSITE Jitendra.K.Pandey, Hitoshi Takagi* Advanced Material Division, Institute of Technology and Science, The University of Tokushima, Tokushima-770-8506, Japan. Hitoshi Takagi: takagi@me.tokushima-u.ac.jp 1. Introduction Cellulose nano-crystals can be created Nano-reinforcement of polymer is gaining a by mechanical analysis and chemical treatments deliberate interest not only due to tremendous or both together. The cellulose micro-fibrils are alteration of mechanical properties but also due constituted by crystalline and amorphous to probability of reduction in weight of resulting regions. The amorphous regions are randomly composites in order to enhance fuel efficiency oriented in spaghetti like arrangement leading to by producing light weight automobile parts [1]. a lower density in these non-crystalline regions Therefore, several nano-fillers and their effect [3,7, 8]. The hydronium ions can penetrate the on different properties of polymers have been cellulose chains in the amorphous domains studied in order to optimize the cost promoting the hydrolytic cleavage of the performance ratio [2]. Recently, a renaissance in glycosidic bonds and finally releasing individual crystallites.[4,9,]. The different treatments of the use of nano filler from natural resources is taking place mainly to introduce eco-friendly these hydrolysed crystallites, such as character in resulting composites [3]. mechanical dispersion or ultrasonification, Cellulose has traditionally been used to develop permit the dispersion of the aggregates and biodegradable polymer composites and recently finally produce colloidal suspensions. Cellulose it was observed that the composites, prepared by nano-crystals have been used as fillers in many reinforcement of polymers through nano- polymer matrices, such as silk fibroin, cellulose crystalline cellulose can exhibit remarkable acetate butyrated, starch, polylactic acid, improvement in many polymer matrixes at very polyvinyl alcohol, and other plastics [7]. low filler concentrations in comparison of their However, the extraction of nano-fibers required neat host matrix. [4]. to balance the drawbacks, such as time- consuming preparation, low yield, and Plant cell wall is a complex structure, hydrophilicity, prior to industrial applications [4, comprises of different macromolecules such as 8]. cellulose, lignin, hemi-cellulose, pectin etc. During the biosynthesis of cellulose in plant a Surface charges on the nano-fillers are continuous and controlled deposition of highly significant in term of adhesion with microfibrils occur that finally dictate the matrix and therefore, interest is increasing [8] to mechanical properties of plants by adjusting evaluate the interactions of cellulose nano-fibers hierarchy and orientation [5]. It has been found with matrix as these interaction profiles that these microfibrils are highly crystalline in determine the final properties of the products. In nature and have modulus around 157 GPa which the present work we aimed to evaluate the effect is similar to engineering polymer like Kevlar [6]. of surface charges of cellulose nano filler on the

mechanical properties of biodegradable resin. allowed to digest in 64% H 2 SO 4 for 25 minute at 45 0 C. The product was washed several time The biodegradable resin was a blend of poly caprolactone) and corn starch. Chemical with deionized water and subjected to structures of biodegradable resin components sonication for 20 minutes and sample was are depicted in Figure 1. Two types of cellulose designated as Charged Nano Fiber (CNF). The nanofibers were employed to reinforce the biodegradable aliphatic polyester (Randy CP- biopolymer, i) with charged surface, prepared 300) was obtained from Miyoshi Oil & Fat Co., by acid hydrolysis of crystalline cellulose and ii) Ltd (Nagoya, Japan) which is hydrophilic with neutral surfaces, those were extracted polyester and a blend of polycaprolactone and merely by mechanical processes without using cornstarch. The biodegradable polymer has density 1.17 g/cm 3 , Tensile strength 10.1 MPa, any chemical treatment. The comparison of tensile strength and elongation with Young’s modulus 0.4 GPa and particle diameter measurement of stiffness was conducted was around 4.9 micrometer. The composites of thoroughly to evaluate the effect of surface these cellulose nano-fibers were prepared polarity of cellulose nano-fibers on mechanical through the methods described in our earlier performance. work [9] by keeping 3 and 5 % (w/w) filler loads. The results of composites loaded with 5 % filler were discussed in detail in order to reduce the volume of manuscript. The mixing of composite components was performed in a mechanical stirrer for 10 hrs. followed by 5 minute sonication [10]. TEM analysis was performed by putting drops of cellulose nano-fiber suspension on carbon grid, followed by 24 drying. SEM microscopy was carried out directly in JEOL microscope. Specimens for tensile testing were molded in a specially designed mold and average value of 5 samples was taken into account. Universal tensile testing machine Instron Corp. Model 5567 was used to evaluate the mechanical Figure 1. Components of biodegradable resin. performance of resulting composites. 2. Experimental Procedure. 2.1 Preparation of cellulose nano-fibers and Composites Crystalline cellulose was obtained from Daicel Chemical Industries Ltd. Japan having brand name KY-100G. This product has 10 % solid content in water and the fiber thickness is refined to between 0.1 and 0.01 µm. The material was further sonicated for 35 minutes at 45 % output at 5 minute intervals causing 2a. TEM of Cellulose nanofibers Figure further individualization of fibers. This sample extracted through acid hydrolysis was named as Neutral Nano Fiber (NNF). In another attempt the cellulosic material was

the tensile strength, modulus and elongation of the prepared composites. Comparison with neat polymer showed a little improvement in tensile strength and modulus at 5 % filler load in case of NNF reinforced composites which may be attributed to smoother energy transfer from matrix to filler at the interface resulting in a delay failure of composites. This behavior may also be explained on the basis of slippage mechanism in micro-fibrils which can take 2b. TEM of Cellulose nano-fibers Figure place at interface probably by creating a flexible extracted through acid hydrolysis at higher region, after removal of surrounding cementing magnification. material from fibers such as hemicellulose and lignin [11]. The composites of CNF showed a decrease in the properties and values were lower than both neat and NNF in the present system. Such types of observations were strongly suggesting that surface charges of cellulose nano-fiber may play a decisive role during mechanical performance of PCL-Starch composites. There may be few possibilities to explain the higher strength and modulus of 2c. Cellulose nano-fibers through Figure NNFs than CNFs. i) micro-fibrillation of mechanical analysis. cellulose may influence the bulk properties by 3. Results and Discussions enhancing the matrix interactions and depend on the parameter that how fine is the reinforcing Morphology of cellulose nano-fibers fiber [15]. ii) CNF was extracted through acid were observed through TEM as presented in treatment (sulphuric acid) and carrying negative Figure 2a, b and c for acid and mechanically charges that repelled each other and form treated samples. During treatment with colloidal suspension in the water [12]. As soon sulphuric acid, the hydrolysis usually could as water evaporates during drying, CNF must cleave the amorphous region transversely, have higher tendency to agglomerate inside resulting diameter reduction from macro to nano matrix. These agglomerated clusters may act as level [7,13] as could be seen in figure 2 a and b. stress concentration points during load, The whiskers like structures were highly generating catastrophic failure of matrix. There populated with many aggregated cluster. The should be higher possibility of brittle, formation of aggregated cluster is obvious in heterogeneous and active interface in these such type of specimens due to water evaporation specimens [16] due to higher charge density during drying process. On the other hand, than NNF. iii) Since the resin constitutes starch mechanically extracted fibers by as one of its phase, the degree of electrostatic homogenization process (from Daicel attraction in the form of hydrogen bonding with Chem.Ind.) exhibited highly fibrillated web like NNF should be better than CNF due to more network, those are entangled with each other number of unbalanced and exposed hydroxyl randomly. The entangled network was supposed groups. A non-liner stress-strain behavior of to be destroyed during sonication treatment both the composites may be attributed to the before employing as filler [14]. Table 1 present 3