Abstract
Cellulose nanofibers are often explored as biobased reinforcement for the production of high-performance composite materials. In this work, we fabricated transparent poly(methyl methacrylate) (PMMA) composites consisting of two-dimensional and three-dimensional bacterial cellulose (BC) nanofiber networks. Three different composite designs consisting of 1 vol % BC loading were fabricated and studied: (i) composites with a three-dimensional BC nanofiber network embedded uniformly throughout the PMMA matrix; (ii) sandwich-structured construction consisting of three-dimensional BC–PMMA sandwiched between two neat PMMA sheets; and (iii) dried and well-consolidated two-dimensional BC nanofiber network embedded in a PMMA matrix. All fabricated model BC–PMMA composites were found to be optically transparent, but PMMA composites consisting of the two-dimensional BC nanofiber network possessed higher light transmittance (73% @550 nm) compared to the three-dimensional BC nanofiber network counterparts (63% @550 nm). This is due to the higher specific surface area of the three-dimensional BC nanofiber network, which led to more light scattering. Nevertheless, it was found that both two-dimensional and three-dimensional BC nanofiber networks serve as excellent stiffening agents for PMMA matrix, improving the tensile modulus of the resulting composites by up to 30%. However, no improvement in tensile strength was observed. The use of three-dimensional BC nanofiber network led to matrix embrittlement, reducing the tensile strain-at-failure, fracture resistance, and Charpy impact strength of the resulting BC–PMMA composites. When the BC nanofiber network was used as two-dimensional reinforcement, cracks were observed to propagate through the debonding of BC nanofiber network, leading to higher fracture toughness and Charpy impact strength. These novel findings could open up further opportunities in the design of novel optically transparent polymeric composite laminates based on the two-dimensional BC nanofiber network for impact protection.
Highlights
Microbially-synthesized cellulose, more commonly known as bacterial cellulose (BC), is a lightweight (∼1.5 g cm−3)biomaterial produced by the fermentation of low molecular weight sugars using cellulose-producing Komagataeibacter.[1]
Three different BC−poly(methyl methacrylate) (PMMA) composites were prepared: (i) composite I, a 3 mm thick PMMA composite consisting of a three-dimensional BC nanofiber network embedded in the PMMA matrix uniformly, (ii) composite II, a 3 mm thick sandwich construction consisting of a 1.5 mm thick three-dimensional BC−PMMA composite laminated between two neat PMMA sheets, and (iii) composite III, consisting of a dried and well-consolidated two-dimensional BC nanofiber network embedded in a 3 mm thick PMMA composite
Light transmittance measurements showed that two-dimensional BC nanofiber network-reinforced PMMA composites possessed higher light transmittance (74−81%) compared to their three-dimensional counterparts (38−54%)
Summary
Microbially-synthesized cellulose, more commonly known as bacterial cellulose (BC), is a lightweight (∼1.5 g cm−3). As three-dimensional BC nanofiber networks possess high specific area (∼160 m2 g−1),[12] it can be anticipated that utilizing a three-dimensional BC nanofiber network as reinforcement will enhance the tensile performance and improve both the fracture resistance and impact strength of the resulting BC-reinforced composites. The high KIc value of a dried and well-consolidated dense twodimensional BC nanofiber network stems from its high degree of hornification, which requires a substantial amount of energy to cause nanofiber−nanofiber debonding. The introduction of such dense BC nanofiber network as a two-dimensional reinforcement into a brittle polymer is postulated to produce. The aim is to elucidate, if any, the different BC nanofiber network architectures on the transparency, tensile properties, fracture toughness, and impact strength of the resulting BC-reinforced PMMA composites
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