M. Misra

Sustainable Bio-Composites from Renewable Resources: Opportunities and Challenges in the Green Materials World

Sustainability, industrial ecology, eco-efficiency, and green chemistry are guiding the development of the next generation of materials, products, and processes. Biodegradable plastics and bio-based polymer products based on annually renewable agricultural and biomass feedstock can form the basis for a portfolio of sustainable, eco-efficient products that can compete and capture markets currently dominated by products based exclusively on petroleum feedstock. Natural/Biofiber composites (Bio-Composites) are emerging as a viable alternative to glass fiber reinforced composites especially in automotive and building product applications. The combination of biofibers such as kenaf, hemp, flax, jute, henequen, pineapple leaf fiber, and sisal with polymer matrices from both nonrenewable and renewable resources to produce composite materials that are competitive with synthetic composites requires special attention, i.e., biofiber–matrix interface and novel processing. Natural fiber–reinforced polypropylene composites have attained commercial attraction in automotive industries. Natural fiber—polypropylene or natural fiber—polyester composites are not sufficiently eco-friendly because of the petroleum-based source and the nonbiodegradable nature of the polymer matrix. Using natural fibers with polymers based on renewable resources will allow many environmental issues to be solved. By embedding biofibers with renewable resource–based biopolymers such as cellulosic plastics; polylactides; starch plastics; polyhydroxyalkanoates (bacterial polyesters); and soy-based plastics, the so-called green bio-composites are continuously being developed.

Surface modifications of natural fibers and performance of the resulting biocomposites: An overview

A review of biocomposites highlighting recent studies and developments in natural fibers, bio-polymers, and various surface modifications of natural fibers to improve fiber-matrix adhesion is presented. One of the most important factors which determine the final performance of the composite materials is the quality of the fiber-matrix interface. A sufficient degree of adhesion between the surface of hydrophilic ligno-cellulosic natural fibers and the polymer matrix resin is usually desired to achieve optimum performance of the biocomposite. Dewaxing, alkali treatment, isocyanate treatment, peroxide treatment, vinyl grafting, bleaching, acetylation, and treatment with coupling agents are useful ways to improve fiber-matrix adhesion in natural fiber composites. Two major areas of biocomposites will be discussed in this article. One is the most predominant biocomposite currently being commercialized for semi-structural use in the durable goods industries, e.g. auto-industries, i.e. natural fiber-polypropylene composites. The second type is the biocomposites from natural fibers and biodegradable plastics. Two major classes of biodegradable plastics are available, one being derived from renewable resources and the second type being synthesized in the laboratory from petrochemical sources which can also be used as matrix materials to make value-added biocomposites.

Studies on mechanical performance of biofibre/glass reinforced polyester hybrid composites

Abstract The degree of mechanical reinforcement that could be obtained by the introduction of glass fibres in biofibre (pineapple leaf fibre/sisal fibre) reinforced polyester composites has been assessed experimentally. Addition of relatively small amount of glass fibre to the pineapple leaf fibre and sisal fibre-reinforced polyester matrix enhanced the mechanical properties of the resulting hybrid composites. Different chemically modified sisal fibres have been used in addition to glass fibers as reinforcements in polyester matrix to enhance the mechanical properties of the resulting hybrid composites. The surface modification of sisal fibres such as alkali treatment produced optimum tensile and impact strengths, while cyanoethylation resulted in the maximum increase in flexural strength of the hybrid composites. It has been observed that water uptakes of hybrid composites are less than that of unhybridized composites. Scanning electron microscopic studies have been carried out to study the fibre-matrix adhesion.

The influence of fibre treatment on the performance of coir-polyester composites

Abstract Surface modifications of coir fibres involving alkali treatment, bleaching, and vinyl grafting are made in view of their use as reinforcing agents in general-purpose polyester resin matrix. The mechanical properties of composites like tensile, flexural and impact strength increase as a result of surface modification. Among all modifications, bleached (65°C) coir-polyester composites show better flexural strength (61.6 MPa) whereas 2% alkali-treated coir/polyester composites show significant improvement in tensile strength (26.80 MPa). Hybrid composites comprising glass fibre mat (7 wt.%), coir fibre mat (13 wt.%) and polyester resin matrix are prepared. Hybrid composites containing surface modified coir fibres show significant improvement in flexural strength. Water absorption studies of coir/polyester and hybrid composites show significant reduction in water absorption due to surface modifications of coir fibres. Scanning electron microscopy (SEM) investigations show that surface modifications improve the fibre/matrix adhesion.

Fully Biodegradable and Biorenewable Ternary Blends from Polylactide, Poly(3-hydroxybutyrate-co-hydroxyvalerate) and Poly(butylene succinate) with Balanced Properties

A ternary blend of entirely biodegradable polymers, namely polylactide (PLA), poly(3-hydroxybutyrate-co-hydroxyvalerate) (PHBV), and poly(butylene succinate) (PBS), was first melt-compounded in an effort to prepare novel fully biodegradable materials with an excellent balance of properties. The miscibility, morphology, thermal behavior, mechanical properties, and thermal resistance of the blends were investigated. DMA analysis revealed that PHBV and PLA showed some limited miscibility with each other, but PBS is immiscible with PLA or PHBV. Minor phase-separated structure was observed from SEM for all the blends composition except PHBV/PLA/PBS 60/30/10 blend, which formed a typical mixture of core-shell morphology. The morphologies were verified by analysis of the spreading coefficients. Excellent stiffness-toughness balance was achieved by ternary blends of PLA, PHBV, and PBS. Significant enhancement of the toughness and flexibility of PLA was achieved by the incorporation of PBS and PHBV without sacrificing the strength apparently. Both the stiffness and toughness were improved for PHBV in the ternary blends with PHBV as matrix. The crystallization of the PLA and PBS were enhanced by presence of PHBV in the blends, while the crystallization of PHBV was confined by PLA and PBS phases. Moreover, the thermal resistances and melt flow properties of the materials were also studied by analysis of the heat deflection temperature (HDT) and melt flow index (MFI) value in the work.

Graft Copolymerization of Acrylonitrile on Chemically Modified Sisal Fibers

Graft copolymerization of acrylonitrile (AN) on chemically modified sisal fibers was studied using a combination of NaIO 4 and CuSO 4 as initiator in an aqueous medium in the temperature range of 50-70°C. Effects of reaction medium, variation of time and temperature, concentration of CuSO 4 , NaIO 4 and AN, and the amount of sisal fiber on the percentage of graft yield have been investigated. Water absorption (%) and tensile properties such as tensile strenght, Youngs modulus and extension at break of untreated, chemically modified and AN-grafted sisal fibers were evaluated and compared. FTIR spectroscopy and scanning electron microscopy (SEM) of the chemically modified and AN-grafted sisal fibers have been carried out.

Novel Biobased Polyurethanes Synthesized from Soybean Phosphate Ester Polyols: Thermomechanical Properties Evaluations

Biobased polyurethanes from soybean oil–derived polyols and polymeric diphenylmethane diisocyanate (pMDI) are prepared and their thermomechanical properties are studied and evaluated. The cross-linked biobased polyurethanes being prepared from soy phosphate ester polyols with hydroxyl contents ranging from 122 to 145 mg KOH/g and pMDI within 5 min of reaction time at 150°C in absence of any catalyst show cross-linking densities ranging from 1.8 × 103 to 3.0 × 103M/m3, whereas glass transition temperatures vary from approximately 69 to 82°C. The loss factor (tan δ) curves show single peaks for all these biobased polyurethanes, thus indicating a single-phase system. The storage moduli (G′) at 30°C range from 4 × 108 to 1.3 × 109 Pa. Upon postcure at 150°C, the thermomechanical properties can be optimized. Cross-link densities are improved significantly for hydroxyl content of 139 and 145 mg KOH/g at curing time of 24 h. Similarly, glass transition temperature (Tg) and storage moduli around and after Tg are increased. Meanwhile, tan δ intensities decrease as result of restricted chain mobility. Longer exposure time (∼24 h) induces thermal degradation, as evidenced by thermogravimetric analysis (TGA). The dynamic mechanical (DMA) analysis shows that postcure at 100°C for times exceeding 24 h also leads to improved properties. However, cross-linking densities are lower compared to postcure carried out at 150°C.

Preparation and characterization of plasticized cellulose acetate biocomposite with natural fiber

Biodegradable polymers such as poly (hydroxybutyrate) [1, 2], poly(e-caprolactone), polylactide [3], biodegradable aliphatic polyesters [4–6], and bio-based composite materials have been investigated to reduce environmental problems caused by plastic wastes, since they have low manufacturing costs and easy processibility in large-scale production. Among these biodegradable polymers or bio-based polymer products, cellulose from trees are found to be the most attractive substitute for petroleum feedstock in making plastics for the consumer market [7]. Cellulose plastics, such as cellulose acetate (CA), cellulose acetate propionate, and cellulose acetate butyrate, are thermoplastic materials produced through the esterification of cellulose. A variety of raw materials such as cotton, recycled paper, wood cellulose, and sugarcane are used in making cellulose ester biopolymers in powder form. In processing polymer composites, biofibers such as henequen, hemp (HP), and kenaf can be successful candidates for reinforcing the strength and stiffness in the final composite [8–11]. In the current study, we melt-processed the plasticized CA (CAP) with a biofiber, hemp, and then investigated its characteristics of thermal stabilities, fractured surface morphologies, and rheological properties. Most commercial cellulose acetate products are clear, strong, and stiff. Some applications of cellulose ester biopolymers are film substrates for photography, toothbrush handles, selective filtration membranes in medicine, and automotive coatings [12]. The main drawback of cellulose acetate is that its melt processing temperature is very close to its decomposition temperature, as determined by the structure of its parent cellulose. This means that cellulose acetates should be plasticized if they are to be used in thermoplastic processing applications [13]. In this study, we used CAP containing 30 wt% of plasticizer i.e., plasticized cellulose acetate, as dispersing medium for biofiber. The major constituents of biofibers (lignocelluloses) are cellulose, hemicellulose and lignin. Cellulose is a hydrophilic glucan polymer consisting of a linear chain, containing hydroxyl groups. Therefore, all the natural fibers are hydrophilic in nature. The details on these

Biodegradability and Compostability of Lignocellulosic Based Composite Materials

Lignocellulosic composites have attracted interest from both academia and industry due to their benefi cial environmental and sustainability attributes. The lignocellulosic industry has seen remarkable improvements in the development of composites for high performance applications. Both biodegradable as well as non-biodegradable polymers are used in the design and engineering of lignocellulosic composites. Biodegradability studies of lignocellulosic composites in soil and composting environments help in planning their end-life management. Biodegradability tests are complex and dependent on the environment in which the testing is carried out. Due to this, standards have been developed by international agencies such as the American Society for Testing and Materials (ASTM) and International Organization for Standardization (ISO) to adopt and test plastic materials in both composting and soil environments. The fi rst part of this intended review article deals with the classifi cation of lignocellulosic composites, biodegradation and composting concepts, biodegradability testing standards, and factors affecting biodegradation. A comparative analysis of ASTM and ISO biodegradability standards in terms of testing methodology and results interpretation is provided.. A special focus is given to the biodegradation mechanisms found in polymers and their composites. The second part of this review article is devoted to biodegradation studies of lignocellulosic composites under composting conditions and soil environments. The effect of fi ller type, environmental conditions, and compatibilization on the biodegradation of lignocellulosic composites is discussed in detail. Also, a special section on the biodegradability of lignin-based materials is given.

1 – Commercial potential and competitiveness of natural fiber composites

Todays social conscience, driven by environmental consciousness, is challenging and demanding the industry and designers to develop ingenious and revolutionary materials that will reduce the greenhouse gas footprints left on the earth. Several years of cumulative research has been conducted on the usage of natural fibers for various applications, one main area being composite materials. Natural fiber composites (NFCs) are also alternatively referred to as biocomposites. For any potential application of NFCs to be commercially successful, it is important to realize the full advantage of material properties and have a general understanding of challenges involved in adopting them, including processabilty on a commercial scale and sustainable scalability. The first part of this chapter provides an overview of natural fiber classification, advantages, and challenges with a special focus on supply chain management. Factors that offer NFCs a competitive edge over traditional composites are elaborated, followed by a discussion on the current market scenario, growth prospects, and future developments.