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عنوان فارسی مقاله:
آمیزه قالب گیری ورقه بسیار سبک (SMC) مواد مرکب حاوی نانوبلورهای سلولز
عنوان انگلیسی مقاله:
Lightweight sheet molding compound (SMC) composites containing cellulose nanocrystals
سال انتشار : 2016
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مقدمه انگلیسی مقاله:
1. Introduction
The US transportation sector consumes 71% of the US total petroleum and despite the advances in vehicles with alternative fuels, petroleum still supplies 93% of the US transportation energy demand [1]. Increasing the fuel economy has become a vital part of US policy to ascertain its energy security and decrease the CO2 emission as the main contributor to climate change. Road transportation accounted for 17% of the global CO2 emissions in 2009 [2]. Corporate Average Fuel Economy (CAFE) standards require that passenger cars and light trucks improve the fuel economy level of 28.5 mi/gal in 2012 to 54.5 mi/gal by 2025 [3]. Light weighting identified as a cross cutting technology is a promising approach to meet the CAFE standards, as 10% reduction in the vehicle weight can result in 6–8% increase in fuel efficiency [4]. One approach toward light weighting is use of glass/carbon fiber reinforced polymer (G/CFRP) composites in vehicle structures [4]. In addition, GFRP in automobiles result in lower greenhouse gas emission from cradle to grave compared to conventional materials based on life cycle assessments [5,6]. Sheet molding compound (SMC) [7], which consists of short glass fibers (GF) impregnated between two layers of thermosetting resin are the precursor GFRP for automotive applications. The SMC manufacturing method allows for high volume production and excellent part reproducibility with high specific strength and stiffness and desired surface finish in a cost effective way due to the low labor requirements and minimum industry scrap. In addition, an SMC automotive component performs better than other lightweight materials (e.g. carbon fiber and magnesium) in life cycle cost and environmental performance [8]. One solution towards reducing the weight of composites is to replace the heavier component with a lighter but stronger material [9–13]. For example, nanoparticles can enhance the mechanical properties of the polymer matrix [14] once the major issues of inhomogeneous dispersion and agglomeration, thermal stability and a lack of scalable ways to introduce them in SMC manufacturing are addressed. There has been considerable interest in cellulose nanomaterials (CN) as polymer reinforcements. CN are cellulose-based nanoparticles that are obtained from plants, algae, bacteria and marine animals [15–17] and categorized generally based on the cellulose source and the extraction methods, leading to various CN types. In all CN types, cellulose chains stack parallel along the particle length resulting in similar properties for the various types within the scatter of experimental testing or atomistic model predictions [17]. Low density (1.6 g/cm3 ), high aspect ratio (10100) andsurface area, tensile strength of 3 GPa, elastic modulus of 110– 220 GPa, surfaces with accessible hydroxyl side groups that can be readily chemically modified and their low toxicity [18] make CN an ideal reinforcement for polymers and polymer composites. Cellulose nanocrystals, CNC, which are whisker shaped particles (3–20 nm in width and 50–500 nm in length), extracted from trees and plants by acid hydrolyses [15–17] with properties in the range listed above and having the potential to be produced at large quantities and reasonable cost [19] were used in this study. Addition of CNC in composites, either as a coating on GF [20,21] or dispersion in the polymer matrix [22] enhances the composites mechanical properties [23]. The main challenge in adding CNC into polymers is lack of scalable techniques to disperse hydrophilic CNC into mainly hydrophobic polymers. The current methods include use of waterborne epoxies [24–27], solvent exchange methods [28,29], CN preforms [30] or fiber mats [31] impregnated by epoxy and chemical modification of CN surfaces [32,33] are both time inefficient and costly and thus limited for scale up in production of GF/epoxy SMC composites. In this study we explored whether it is possible to reduce the weight of a typical 35 wt% GF/epoxy SMC composite by replacing part of the GF with CNC without compromising the mechanical performance. The idea of this study was built on our prior work where the mechanical properties of SMC composites were investigated as a function of the CNC content and it was shown that addition of CNC up to 0.9 wt% in the SMC composites improved the mechanical properties of the 35GF/epoxy composites [23]. Using the gained knowledge on capability of CNC in enhancing the mechanical properties, the purpose of the current study is reducing the weight of 35GF/epoxy SMC composites by removing part of GF as the heaviest component in the composite and adding a small amount of CNC to maintain the same mechanical performance. CNC were introduced in a SMC manufacturing line as a dispersion within the epoxy resin (abbreviated as CNC-epoxy) of SMC composites containing 25 wt% GF. The effect of 1 and 1.5 wt% CNC on mechanical properties of the 25GF/CNC-epoxy SMC composites were investigated and compared with those of 35GF/epoxy SMC composites with no CNC.
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کلمات کلیدی:
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