Hierarchical wood cellulose fiber/epoxy biocomposites – Materials design of fiber porosity and nanostructure

Delignified chemical wood pulp fibers can be designed to have a controlled structure of cellulose fibril aggregates to serve as porous templates in biocomposites with unique properties. The potential of these fibers as reinforcement for an epoxy matrix (EP) was investigated in this work. Networks of porous wood fibers were impregnated with monomeric epoxy and cured. Microscopy images from ultramicrotomed cross sections and tensile fractured surfaces were used to study the distribution of matrix inside and around the fibers – at two different length scales. Mechanical characterization at different relative humidity showed much improved mechanical properties of biocomposites based on epoxy-impregnated fibers and they were rather insensitive to surrounding humidity. Furthermore, the mechanical properties of cellulose-fiber biocomposites were compared with those of cellulose-nanofibril (CNF) composites; strong similarities were found between the two materials. The reasons for this, some limitations and the role of specific surface area of the fiber are discussed.     

Lignocellulosic fibre mediated rubber composites: An overview

The rising concern towards the reduction in the use of petroleum-based, non-renewable resources and the need for more versatile polymer-based composite materials have led to increasing interests on natural polymer composites filled with natural organic fillers, i.e. coming from renewable and biodegradable sources. This paper reviews wood flour and other lignocellulosic fibres filled rubber composites, including cellulosic rubber composites, cellulosic thermoplastic elastomers, nanocellulose based rubber nanocomposites, with the aims at providing the most state of the art information for directing further scientific research, possible commercialization and design of cellulosic rubber composites. It has been found that 1) the surface properties of natural cellulose, hence the compatibility and interface of the natural cellulose and matrix rubber/plastics, are crucial for the successful development of the composites, such, physical and chemical modification and additives have been widely attempted to improve the incompatibility and poor interfacial adhesion between the filler and matrix; 2) the curing characteristics, mechanical properties, thermal stability and morphologies of the composites are complex but closely related to not only the interfacial properties, but also the compositions (e.g. the concentration of cellulosic materials) and other processing parameters; 3) the nature of hydrophilic cellulosic and hydrophobic matrix rubber and/or plastics requires an accurate introduction of coupling agent, one end of its structure shall be compatible to hydrophilic and the other to hydrophobic. The reviews on the main paths and results of study on the advanced nanocellulose reinforced rubber nanocomposites and sandwiches indicate much potentials and needs for further in-depth studies.     

All-cellulose composites of regenerated cellulose fibres by surface selective dissolution

All-cellulose composites of Lyocell and high modulus/strength cellulose fibres were successfully prepared using a surface selective dissolution method. The effect of immersion time of the fibres in the solvent during composite’s preparation and the effect of the starting fibre’s structure on their properties were investigated. Scanning electron microscopy, X-ray diffraction, dynamic mechanical analysis, and tensile testing were used to assess the structure and properties of the composites. These all-cellulose composites of regenerated cellulose fibres demonstrate a promising route to biocomposites with excellent mechanical and thermal properties which can also be tuned depending upon a selection of fibres and preparation parameters.     

Isocyanate as a compatibilizing agent on the properties of highly crystalline cellulose/polypropylene composites

Composites of a highly crystalline cellulosic microfibres with polypropylene (PP) as well as with maleic anhydride grafted polypropylene (MAPP) were prepared by using 1,6-diisocyanatohexane (DIC) as a compatibilizing agent, their mechanical properties, morphologies, and thermal properties were investigated. Results show that the tensile strength and young’s modulus of the composites improved intensively by using DIC. The enhancement is proposed to be due to stronger interfacial adhesion caused by the reduction of the polarity and hydrophilicity of cellulose fiber in PP-based composites, while much more chemically bound MAPP chains on cellulose fiber in MAPP-based composites. A maximum on tensile properties of the composite can be obtained by optimizing of the DIC content. Scanning electron microscopy (SEM) indicates that the interfacial adhesion between cellulose fibers and PP or MAPP matrix was improved in DIC coupled composites. Furthermore, DIC yields also some effects on thermal dynamic mechanical properties, as well as melting and crystallization behavior of the composites.     

Biodegradability of all-cellulose composite laminates

The high mechanical properties of single-polymer composites based on degradable non-derivatised cellulose, aka all-cellulose composites, have recently captured the attention of researchers. All-cellulose composites possess the intriguing combination of high strength and biodegradability. However, the biodegradation behaviour of all-cellulose composites has so far not been reported. In this work, soil burial experiments were carried out to compare the biodegradation behaviour of all-cellulose composites with conventional biocomposites in order to investigate the end-of-life disposal of this relatively new class of bio-based composite materials. All-cellulose composites are characterised by exceptional biodegradability with mass losses of up to 73% following a soil burial time of 70 days. An investigation of the mechanisms of biodegradation of all-cellulose composites is undertaken for the first time.     

A review of the recent developments in biocomposites based on natural fibres and their application perspectives

The growing ecological and environmental consciousness has driven efforts for development of new innovative materials for various end-use applications. Polymers synthesized from natural resources, have gained considerable research interest in the recent years. This review paper is intended to provide a brief outline of work that covers in the area of biocomposites, major class of biodegradable polymers, natural fibres, as well as their manufacturing techniques and properties has been highlighted. Various surface modification methods were incorporated to improve the fibre–matrix adhesion resulting in the enhancement of mechanical properties of the biocomposites. Moreover, an economical impact and future direction of these materials has been critically reviewed. This review concludes that the biocomposites form one of the emerging areas in polymer science that gain attention for use in various applications ranging from automobile to the building industries.     

纳米SiO2/纤维素复合材料的非均相制备及其性能

采用硅酸四乙酯(TEOS)作为无机前聚物,纤维素为有机组分,利用溶胶-凝胶法在非均相乙醇溶液中制备了纳米SiO₂/纤维素复合材料。通过傅里叶红外光谱(FTIR)、透射电镜(TEM)和热重分析(TGA)对复合材料的形貌、结构以及热稳定性进行表征。讨论了SiO₂含量对材料力学性能的影响。研究了主要因素碱催化剂氨水对纤维素与SiO₂复合效果的影响。结果表明,纳米复合材料的弹性模量、拉伸强度随SiO₂含量的增加先增加后减少,质量分数分别为3.1％、10.6％时弹性模量、拉伸强度达到最大。氨水加入量为3.70×10-4 mol/L时,纤维素与SiO₂的复合效果最佳。非均相制备的纳米SiO₂/纤维素复合材料同样也明显提高了纤维素材料的疏水性、热稳定性和力学性能。     

Chopped glass and recycled newspaper as reinforcement fibers in injection molded poly(lactic acid) (PLA) composites: A comparative study

Natural/bio-fibers are replacing synthetic reinforcements traditionally used for the preparation of the environmentally friendly composites. Composite materials are also replacing conventional materials in various fields due to their ease of processability. Chopped glass fiber- and recycled newspaper cellulose fiber (RNCF)- reinforced poly(lactic acid) (PLA) composites were processed using a full size twin-screw extruder and an injection molder. Additionally, a glass-reinforced polypropylene (PP) composite was compounded and molded, and compared to PLA/RNCF and PLA/glass fiber composites. The tensile and flexural moduli of RNCF- reinforced composites were significantly higher when compared to the virgin resin. The morphology, evaluated by scanning electron microscopy, indicated uniform dispersion of both fibers in the PLA matrix. The mechanical and thermo-physical properties of PLA/RNCF, PLA/glass and PP/glass fiber composite were studied and compared using dynamic mechanical analysis (DMA) and thermogravimetric analysis (TGA). DMA results confirmed that the storage and loss moduli of the PLA/RNCF composites increased with respect to the pure polymer, whereas the mechanical loss factor (tan delta) decreased. The results of the TGA experiments indicated that the addition of fibers increased the thermal stability of the biocomposites compared to neat PLA. The heat defection temperature of PLA/RNCF was found to be comparable to that of the glass fiber-reinforced PLA composites. Such studies are of great interest in the development of environmentally friendly composites from biodegradable polymers.     

氧化石墨烯/壳聚糖生物复合材料的制备及应用研究进展

氧化石墨烯/壳聚糖复合材料是近几年发展的一种新型生物复合材料,具有独特的力学性能、吸附性能、电化学性能以及抗菌性能等。本文综述了近几年来氧化石墨烯/壳聚糖复合材料的研究进展,简单介绍了该复合材料的制备方法,详细阐述了该复合材料在高机械强度材料、废水处理、电化学传感器、生物医学材料等领域的应用研究,最后对氧化石墨烯/壳聚糖复合材料在低成本、大规模制备,复合材料的结构性质以及在新领域的应用等方面进行了展望。     

Influence of the process parameters on the mechanical properties of engineering biocomposites using a twin-screw extruder

The utilization of bio-based engineering polymers as a matrix material for cellulosic fiber reinforced composites has become an important focus in materials research. This is due to a rising demand for sustainable materials from renewable resources. In addition to this aspect, the bio-based materials provide an advantage for lightweight applications with their lower density. In this investigation, the completely bio-based polyamide 10.10, with a melting point above 200 °C, was used as a polymer matrix. Chopped man-made cellulose fibers (Cordenka CR-Type) were investigated as reinforcement for use in injection molded applications. A co-rotating twin-screw extruder with a screw-diameter of 18 mm was used for compounding. It was verified that reinforcing polyamide 10.10 with 20 wt% and 30 wt% cellulosic fibers is possible, resulting in an increase of impact and tensile properties. Furthermore, it was shown that the temperatures and screw-configurations of the twin-screw extruder only result in different fiber length distributions but in minor differences of the morphological structure and mechanical properties of PA 10.10 with 20 wt% fibers. Compounds with 30 wt% cellulose fibers show significant higher impact properties that those with 30 wt% glass fibers.     

Improvement of physico-mechanical properties of coir-polypropylene biocomposites by fiber chemical treatment

In preparing polymer–matrix composites, natural fibers are widely used as “reinforcing agents” because of their biodegradable characteristic. In present research, coir fiber reinforced polypropylene biocomposites were manufactured using hot press method. In order to increase the compatibility between the coir fiber and polypropylene matrix, raw coir fiber was chemically treated with basic chromium sulfate and sodium bicarbonate salt in acidic media. Both raw and treated coir at different fiber loading (10, 15 and 20 wt%) were utilized during composite manufacturing. During chemical treatment, hydrophilic –OH groups in the raw coir cellulose were converted to hydrophobic –OH−Cr groups. Microstructural analysis and mechanical tests were conducted. Scanning electron microscopic analysis indicates improvement in interfacial adhesion between the coir and polypropylene matrix upon treatment. Chemically treated specimens yielded the best set of mechanical properties. On the basis of fiber loading, 20% fiber reinforced composites had the optimum set of mechanical properties among all composites manufactured.     

Novel lightweight sandwich-structured bio-fiber-reinforced poly(lactic acid) composites

Novel bio-based lightweight sandwich-structured composites with both skin and core materials made from biofiber and poly(lactic acid) (PLA) matrix were developed. The composites contained 48 wt% cellulose fiber and 52 wt% PLA matrix. The fabrication process was simple and required no adhesive for the skin–core bonding. The effects of fiber weight fraction and density on the core compressive properties were evaluated experimentally. Fifty percent of fibers gave the best results among the three fiber weight fractions studied and was used in preparing cores for subsequent fabrication of the sandwich-structured composites. The flexural properties and failure modes of the sandwich-structured composites were assessed. The flexural properties of the composites met the published deflection requirements for automotive load floor applications. Since these biocomposites were made using natural renewable materials that are fully biodegradable and recyclable, they show potential to be used as environmentally friendly alternatives to the existing products.     

Characterisation of polylactic acid biocomposites made from prepregs composed of woven polylactic acid/hemp–Lyocell hybrid yarn fabrics

This paper describes the mechanical properties and water absorption characteristics for biocomposites made from woven PLA/hemp/Lyocell prepregs. The aim was to improve the properties with the addition of Lyocell fibre into a hybrid yarn. Well-aligned hybrid yarns composed of hemp/PLA, hemp–Lyocell/PLA, respective, Lyocell/PLA were made by wrap spinning. Unidirectional satin fabrics were made by weaving with PLA (warp) and the hybrid yarns (weft). Uniaxial composites were fabricated with 30 fibre mass% using compression moulding. The composites were investigated for tensile, flexural and impact properties. Combining hemp with Lyocell in a PLA matrix improves the mechanical properties, compared to hemp/PLA composites. The composite made from the satin Lyocell/PLA fabric gave the best mechanical properties. The type of fibre reinforcement compositions did not significantly affect the water absorption of the biocomposites. Scanning electron microscopy showed that fibre pull-outs appear more often in hemp/PLA composites than in composites also including Lyocell fibre.     

Mechanical behavior of cellulignin based composites

A powder derivative of acid pre-hydrolysis processing of cellulosic wastes, known as cellulignin, was used as filler in resin matrix composites. The flexural mechanical properties of cellulignin-polyester, epoxy or urea-formaldehyde matrix composites was evaluated. The results obtained show that the urea-formaldehyde and epoxy based composites can be used as alternative materials for low cost and low strength applications. Their advantages over the common wooden agglomerates or composites are presented and are based on the fact that cellulignin can be obtained virtually from any cellulosic waste.     

Bast Fibres Reinforced Thermoplastic and Thermoset PLA Biocomposite

Flax/Hemp mat reinforced biodegradable thermoplastic and thermoset PLA biocomposites were prepared by non-woven and hot pressing (HP) methods.The effects of fibres weight-fraction and composites processing conditions were investigated.The morphology,structure,thermal and mechanical properties of the biocomposites were examined by scanning electron microscopy (SEM),Differential Scanning Calorimetry(DSC) and tensile testing.The bast fibres/PLA composites can potentially be used for a wide range of applications including automotive interior materials and architecture materials.     

High performance hybrid PP and PLA biocomposites reinforced with short man-made cellulose fibres and softwood flour

This paper presents the research on hybrid thermoplastic biocomposites reinforced with a combination of short man-made cellulose fibres and softwood flour. The introduced short fibre composites are meant to be processed with injection moulding and may be an alternative to glass-fibre reinforced thermoplastics on account of their comparable specific strengths. The occurring positive hybrid effect enables to substitute up to half the weight of short fibre cellulose reinforcement with softwood flour without a significant reduction of material flexural strength. The flexural modulus of investigated hybrid biocomposites remained approximately at the same level, while impact strength was reduced with increasing softwood flour content. The proposed hybridisation leads to establishing biocomposites of suitable performance with competitive density, price and recycling possibilities in comparison to standard glass fibre reinforced counterparts. Moreover, the application of biobased polymers like polylactide as biocomposite matrix, contributes to the development of so called “green” high performance materials.     

Compressive and Tensile Behaviours of PLLA Matrix Composites Reinforced with Randomly Dispersed Flax Fibres

Nowadays, the ecological footprint of a material is becoming tremendously important. The Poly l-Lactide Acid (PLLA) matrix composites reinforced by randomly scattered flax fibres have mechanical properties similar to polyester/glass composites [1], lower environmental impacts and can be compost at the end of their lives. In this study, the mechanical characterization of biocomposites has been pushed further with the determination of the compressive and tensile properties. Furthermore, the mechanical properties of single flax fibres have been measured and implemented in a micro-mechanical estimation of the composite elastic modulus. Tensile and compressive stiffness determined by the mechanical analyses show very good correlations with the mathematical estimation.     

Cellulosic fibers from rice straw and bamboo used as reinforcement of cement-based composites for remarkably improving mechanical properties

The cement-based composites reinforced with cellulosic fibers isolated from rice straw were fabricated by a slurry vacuum de-watering technique. The physical structures and mechanical properties of the composites with fiber contents ranging from 2% to 16% by weight (wt.%) were investigated. Moreover, the composites reinforced with bamboo cellulosic fibers and the control cement paste, sample without cellulosic fibers, were also fabricated as reference materials. As a result, the cement-based composites reinforced by cellulosic fibers showed a remarkable improvement in the mechanical properties. The measurements of the flexural strength and the fracture toughness of the optimal sample were found to be increased by 24.3% and 45 times, respectively. The bulk density of the composites was decreased by 12.4–37.3% as a result of the introduction of cellulosic fibers. Additionally, the field emission scanning electron microscope (FSEM) observations and energy dispersive spectroscopy (EDS) analyses revealed that the hydration products of Portland cement migrated to the fiber lumens, resulting in mineralizing the cellulosic fibers and decreasing the fracture toughness of the composites.     

The effects of cellulose nanowhiskers on electrospun poly (lactic acid) nanofibres

The effects of cellulose nanowhiskers on the microstructure and thermal behaviour of electrospun poly (lactic acid) (PLA) nanofibres have been investigated in this study. The PLA/cellulose nanowhiskers composite nanofibres are successfully produced by electrospinning the mixtures of cellulose whiskers with PLA solution. The diameters of PLA and its composites are around 300 nm. The scanning electron micrographs show that the cellulose nanowhiskers do not protrude out of the outer surfaces of PLA nanofibres. The existence of cellulose nanowhiskers in the electrospun PLA matrix nanofibres, and the microstructural evolution are investigated by using X-ray diffraction, Fourier transform infrared spectroscopy (FTIR) analysis shows the formation trend of PLA α crystal with the addition of cellulose nanowhiskers. The electrospun PLA and PLA/cellulose nanowhiskers composites reveal very low crystallinity due to the rapid solvent evaporation and relatively slow crystallisation kinetics character of PLA. The electrospun nanofibres show particularly different thermal behaviour from that of the solution cast films. The nanofibres of pure PLA and PLA/cellulose nanowhiskers experience two consecutively overlapping crystallisation processes. The cellulose nanowhiskers act as heterogeneous sites for nucleation of PLA by decreasing the cold crystallisation onset temperature. The incorporation of cellulose nanowhiskers into PLA nanofibres is expected to improve mechanical properties and bring new functionalities to the electrospun matrix nanofibres.     

天然纤维素增强聚乳酸复合材料性能研究进展

目的 生物源高分子材料聚乳酸（PLA）具有优良的力学性能、加工性能和生物降解性，为了降低成本同时获得更优产品性能以扩大产品用途，将其与来源广泛的天然纤维素共混是一种绿色有效的途径。方法 本文从复合材料力学性能、热性能与降解性能等方面进行梳理，综述近年来天然纤维增强聚乳酸复合材料的研究，并提出发展趋势。结论 考察了不同类型、比例和形态的天然纤维与不同的纤维改性技术用于多功能应用的PLA基复合材料的制备和改进，降低成本的同时获得更优产品性能以扩大产品用途。