Lightweight Sheet Molding Compound Composites With Enhanced Mechanical Performance via Cellulose Nanocrystal Reinforcement

ABSTRACT The use of cellulose nanocrystals (CNCs) as a sustainable, high‐performance alternative to partially replace calcium carbonate (CaCO ₃ ) in polyester sheet molding compound (SMC) composites is investigated. CaCO ₃ is a widely used and affordable filler; however, it contributes to high density and compromises the mechanical properties of the composites. It was found that addition of 0.5 wt.% CNCs into the polyester resin on glass fiber‐polyester SMC composite panels resulted in an increase of 22% and 37% of the tensile modulus and flexural strength respectively, with no effect on the tensile strength, flexural modulus and impact energy. Increase of CNC content to 1 wt.% resulted in similar enhancement of the composite properties. Most importantly, it was concluded that composites containing 0.5 wt.% of CNC and only half of CaCO ₃ compared to the standard glass fiber/polyester SMC formulations commonly used, exhibited the same tensile, flexural, and impact properties and ~21% lower density. This study highlights the potential of CNCs for advanced lightweight composite solutions.