Bacterial Cellulose Nanopaper as Reinforcement for Polylactide Composites: Renewable Thermoplastic NanoPaPreg

Transparent Multilayer Acrylic Composites Reinforced with Poly(Acrylated Urethane) Filled Low Grammage Bacterial Cellulose Nanopaper

Cellulose nanopaper is a material structure that possesses high mechanical performance and is widely regarded as a promising 2D reinforcement for polymer matrix composites. This work explores the use of low grammage bacterial cellulose (BC) nanopaper as reinforcement for poly(acrylated urethane) interlayer adhesive to increase the impact performance of multilayer acrylic composites. The BC nanopaper is impregnated with an acrylated urethane resin and laminated between acrylic sheets to create BC/acrylic composites consisting of one, three, and five layers of BC nanopaper-reinforced poly(acrylated urethane) interlayer adhesive(s). Both the poly(acrylated urethane)-filled BC nanopaper interlayer adhesive and the resulting laminated acrylic composites are optically transparent. The incorporation of BC nanopaper into the poly(acrylated urethane) interlayer adhesive improves the tensile modulus by eightfold and the single-edge notched fracture toughness by 60% compared to neat poly(acrylated urethane). It is also found that using poly(acrylated urethane)-filled BC nanopaper interlayer adhesive proves beneficial to the impact properties of the resulting laminated acrylic composites. In Charpy impact testing, the impact strength of the multilayer acrylic composites increases by up to 130% compared to the "gold-standard" impact-modified monolithic acrylic, with a BC loading of only 1.6 wt%.

The Effect of Layering Structures on Mechanical and Thermal Properties of Hybrid Bacterial Cellulose/Kevlar Reinforced Epoxy Composites

The effect of layering structures on mechanical and thermal hybrid bacterial cellulose (BC) sheet/Kevlar reinforced epoxy composites was investigated. The BC sheet was extracted from Nata de Coco and used as green reinforcement material hybrid with Kevlar reinforced epoxy composites. The BC/Kevlar reinforced epoxy composite was fabricated by using hand lay-up technique equipped with vacuum bagging system and the BC sheets and Kevlar layers were laminated into different layered structures. The performance of the hybrid BC/Kevlar reinforced epoxy composites was characterized through tensile test and low velocity impact according to ASTM D3039 and ASTM D7136, respectively. The thermal performance of the hybrid composites was characterized by using dynamic mechanical analysis (DMA) test. Tensile test on BC sheet composites with Kevlar and epoxy demonstrated that the addition of BC sheet in BC/Kevlar could not withstand the tensor stress by reducing the tensile stress and Young's modulus. The one layer of Kevlar which was replaced with three to six BC sheets had increased the ability to absorb impact force. The storage modulus (E′) and Tan δ were significantly dependent on the number of BC sheets and its layering structure. The highest value of E′ was observed when BC sheets were arranged alternately with the Kevlar layers. Different damage mechanisms associated with the number of BC sheets and its layered-structure suggested that the BC sheet was functioning as an impact energy absorber as well as strengthening fibers. This study will upsurge interest in BC reinforced composites and the development of new ideas in automotive, marine and bullet applications.

Anomalous tensile response of bacterial cellulose nanopaper at intermediate strain rates

Nanocellulose network in the form of cellulose nanopaper is an important material structure and its time-dependent mechanical response is crucial in many of its potential applications. In this work, we report the influences of grammage and strain rate on the tensile response of bacterial cellulose (BC) nanopaper. BC nanopaper with grammages of 20, 40, 60 and 80 g m⁻² were tested in tension at strain rates ranging from 0.1% s⁻¹ to 50% s⁻¹. At strain rates \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\le$$\end{document}≤ 2.5% s⁻¹, both the tensile modulus and strength of the BC nanopapers stayed constant at ~ 14 GPa and ~ 120 MPa, respectively. At higher strain rates of 25% s⁻¹ and 50% s⁻¹ however, the tensile properties of the BC nanopapers decreased significantly. This observed anomalous tensile response of BC nanopaper is attributed to inertial effect, in which some of the curled BC nanofibres within the nanopaper structure do not have enough time to uncurl before failure at such high strain rates. Our measurements further showed that BC nanopaper showed little deformation under creep, with a secondary creep rate of only ~ 10^–6 s⁻¹. This stems from the highly crystalline nature of BC, as well as the large number of contact or physical crosslinking points between adjacent BC nanofibres, further reducing the mobility of the BC nanofibres in the nanopaper structure.

Current progress on the production, modification, and applications of bacterial cellulose

Adoption of biomass for the development of biobased products has become a routine agenda in evolutionary metabolic engineering. Cellulose produced by bacteria is a "rising star" for this sustainable development. Unlike plant cellulose, bacterial cellulose (BC) shows several unique properties like a high degree of crystallinity, high purity, high water retention, high mechanical strength, and enhanced biocompatibility. Favored with those extraordinary properties, BC could serve as ideal biomass for the development of various industrial products. However, a low yield and the requirement for large growth media have been a persistent challenge in mass production of BC. A significant number of techniques has been developed in achieving efficient BC production. This includes the modification of bioreactors, fermentation parameters, and growth media. In this article, we summarize progress in metabolic engineering in order to solve BC growth limitation. This article emphasizes current engineered BC production by using various bioreactors, as well as highlighting the structure of BC fermented by different types of engineered-bioreactors. The comprehensive overview of the future applications of BC, aims to provide readers with insight into new economic opportunities of BC and their modifiable properties for various industrial applications. Modifications in chemical composition, structure, and genetic regulation, which preceded the advancement of BC applications, were also emphasized.

Thermoplastic Processing of PLA/Cellulose Nanomaterials Composites

Over the past decades, research has escalated on the use of polylactic acid (PLA) as a replacement for petroleum-based polymers. This is due to its valuable properties, such as renewability, biodegradability, biocompatibility and good thermomechanical properties. Despite possessing good mechanical properties comparable to conventional petroleum-based polymers, PLA suffers from some shortcomings such as low thermal resistance, heat distortion temperature and rate of crystallization, thus different fillers have been used to overcome these limitations. In the framework of environmentally friendly processes and products, there has been growing interest on the use of cellulose nanomaterials viz. cellulose nanocrystals (CNC) and nanofibers (CNF) as natural fillers for PLA towards advanced applications other than short-term packaging and biomedical. Cellulosic nanomaterials are renewable in nature, biodegradable, eco-friendly and they possess high strength and stiffness. In the case of eco-friendly processes, various conventional processing techniques, such as melt extrusion, melt-spinning, and compression molding, have been used to produce PLA composites. This review addresses the critical factors in the manufacturing of PLA-cellulosic nanomaterials by using conventional techniques and recent advances needed to promote and improve the dispersion of the cellulosic nanomaterials. Different aspects, including morphology, mechanical behavior and thermal properties, as well as comparisons of CNC- and CNF-reinforced PLA, are also discussed.

Better together: synergy in nanocellulose blends

Cellulose nanopapers have gained significant attention in recent years as large-scale reinforcement for high-loading cellulose nanocomposites, substrates for printed electronics and filter nanopapers for water treatment. The mechanical properties of nanopapers are of fundamental importance for all these applications. Cellulose nanopapers can simply be prepared by filtering a suspension of nanocellulose, followed by heat consolidation. It was already demonstrated that the mechanical properties of cellulose nanopapers can be tailored by the fineness of the fibrils used or by modifying nanocellulose fibrils for instance by polymer adsorption, but nanocellulose blends remain underexplored. In this work, we show that the mechanical and physical properties of cellulose nanopapers can be tuned by creating nanopapers from blends of various grades of nanocellulose, i.e. (mechanically refined) bacterial cellulose or cellulose nanofibrils extracted from never-dried bleached softwood pulp by chemical and mechanical pre-treatments. We found that nanopapers made from blends of two or three nanocellulose grades show synergistic effects resulting in improved stiffness, strength, ductility, toughness and physical properties.This article is part of a discussion meeting issue 'New horizons for cellulose nanotechnology'.

Current progress in production of biopolymeric materials based on cellulose, cellulose nanofibers, and cellulose derivatives

Cellulose has attracted considerable attention as the strongest potential candidate feedstock for bio-based polymeric material production. During the past decade, significant progress in the production of biopolymers based on different cellulosic forms has been achieved. This review highlights the most recent advances and developments in the three main routes for the production of cellulose-based biopolymers, and discusses their scope and applications. The use of cellulose fibers, nanocellulose, and cellulose derivatives as fillers or matrices in biocomposite materials is an efficient biosustainable alternative for the production of high-quality polymer composites and functional polymeric materials. The use of cellulose-derived monomers (glucose and other platform chemicals) in the synthesis of sustainable biopolymers and functional polymeric materials not only provides viable replacements for most petroleum-based polymers but also enables the development of novel polymers and functional polymeric materials. The present review describes the current status of biopolymers based on various forms of cellulose and the scope of their importance and applications. Challenges, promising research trends, and methods for dealing with challenges in exploitation of the promising properties of different forms of cellulose, which are vital for the future of the global polymeric industry, are discussed. Sustainable cellulosic biopolymers have potential applications not only in the replacement of existing petroleum-based polymers but also in cellulosic functional polymeric materials for a range of applications from electrochemical and energy-storage devices to biomedical applications.

Surface-Sensitive Approach to Interpreting Supramolecular Rearrangements in Cellulose by Synchrotron Grazing Incidence Small-Angle X-ray Scattering

The supramolecular rearrangements of biopolymers have remained difficult to discern. Here, we present a versatile approach that allows for an in situ investigation of two major types of rearrangements typically observed with cellulose, the most abundant biopolymer on earth. Model thin films were employed to study time-resolved pore size changes using in situ grazing incidence small-angle X-ray scattering (GISAXS) during regeneration and drying.

Silane meets click chemistry: towards the functionalization of wet bacterial cellulose sheets

The modification of cellulosic materials is of great interest in materials research. Wet bacterial cellulose sheets were modified by an alkoxysilane under mild conditions to make them accessible to click chemistry derivatization. For this purpose (3-azidopropyl)triethoxysilane was grafted covalently onto the cellulosic surface. The silanized bacterial cellulose sheets were characterized comprehensively by attenuated total reflectance FTIR spectroscopy, solid-state NMR spectroscopy, thermogravimetric analysis, SEM with energy-dispersive X-ray spectroscopy, and elemental analysis. To demonstrate subsequent click chemistry functionalization, a new fluorophore based on fluorescein was synthesized and clicked to the silane-modified bacterial cellulose. The new method renders bacterial cellulose and other never-dried cellulosic materials susceptible to direct and facile functionalization in an aqueous medium without the need to work in water-free organic phases or to employ extensive protecting group chemistry and functional group interconversion.