Lightweight Approaches to Sheet Molding Compound (SMC) Composites: Nanocellulose and Kaolin
Author(s)
Biederman, Eric
Advisor(s)
Editor(s)
Collections
Supplementary to:
Permanent Link
Abstract
The focus of this study is to investigate how to lightweight sheet molding compound (SMC) composites for automotive applications without compromising their performance. This is accomplished by replacing heavy constituents such as glass fibers (GF) and calcium carbonate (CaCO3) with nanocellulose (CNC) and kaolin (nanoclay), respectively. First, traditional randomly oriented, chopped E-GF are replaced by CNC coated unidirectional 0° S2-GF fabric to reduce composite density while allowing reinforcement orientation and property control. GF fabric is coated with CNC/emulsion solution using a scalable spraying technique that leads to homogeneous coatings varying in CNC concentration. CNC concentration proportionally decreased thermal degradation of the emulsion coating on the GF fabrics. CNC coated GF SMC composites exhibited 14% decrease in maximum weight gain during water uptake tests and 42% increase in flexural strength suggesting a tortuous and strong fiber/matrix interface at sites of water entry and surface stress concentrations, respectively. However, CNC coated GF SMC composites exhibited no decrease in density, tensile properties, and a negative effect on impact strength. Second, industry standard CaCO3 filler is replaced by various kaolin fillers to reduce density without any property compromise. Kaolin fillers varied in commercial availability, particle size (fine vs. coarse), structure, and surface treatments, SMC loading level, and resin paste viscosity. SMC included unsaturated polyester resin (UPR) and chopped E-GF to focus the study on the inclusion of these various fillers. SMC feasibility was primarily governed by resin paste viscosity allowing 30 vol% of CaCO3, 17 vol% of coarse kaolins, and 12 vol% of fine kaolins. CaCO3/GF/UPR SMC composites exhibited well balanced properties. All kaolin/GF/UPR SMC composites decreased density by up to 10% and increased tensile modulus likely due to kaolin plate-like structure contributing orientation and high aspect ratio capable of reinforcing the matrix. Coarse kaolins exhibited poor SMC manufacturability, fiber wetting, and thus properties. Although kaolin resin formulations with low viscosity exhibited lower maximum weight gain during water uptake and quick saturation possibly due to decreased filler particle agglomeration after processing shear. Conversely, saturation is consistently slowed by kaolin silane surface treatment and provides resin affinity during curing. Fine kaolin formulations significantly increased curing enthalpy, and thus matrix crosslinking, at most leading to a 200% increase in tensile modulus, a 25% increase in impact strength, and a 40% decrease in uptake weight gain.
Sponsor
Date
2023-05-01
Extent
Resource Type
Text
Resource Subtype
Thesis