Natural sub-bituminous coal as filler enhances mechanical, insulation and flame retardant properties of coir-polypropylene bio-composites.

Additives provide substantial improvement in the properties of composites. Although bio-based composites are preferred over synthetic polymer and metal-based composites, they do not have the requisite properties to meet specific needs. Hence, organic, inorganic and metallic additives are included to improve the properties of bio-based composites. Coal is a readily available resource with high thermal insulation, flame resistance and other properties. This work demonstrates the addition of 20-30% natural sub-bituminous coal as filler for coir-reinforced polypropylene (PP) composites and exhibits an increased tensile strength by 66% and flexural strength by 55% compared to the composites without any filler. Such composites are intended for insulation applications and as a replacement for gypsum-based false ceiling tiles. Various ratios of coal samples were included in the composites and their effect on mechanical, acoustic, thermal insulation, flame and water resistance have been determined. A substantial improvement in both flexural and tensile properties has been observed due to the addition of coal. However, a marginal improvement has been observed in both thermal conductivity (0.65 W/mK) and flame resistance values due to the presence of coal. Adding coal increases the intensity of noise absorption, particularly at a higher frequency, whereas water sorption of the composites tends to decrease with an increase in the coal content. The addition of coal improves and adds unique properties to composites, allowing coir-coal-PP composites to outperform commercially available gypsum-based insulation panels.

Using polyvinyl alcohol-ionic hydrogels containing a wound healing agent to manage wounds in different environments.

OBJECTIVE: To explore the effects of pH on properties of polyvinyl alcohol (PVA)-ionic hydrogels containing wound healing promoters. METHOD: PVA was combined with a natural wound healing promoter (silk sericin (SS)), and an anionic agent (eosin (ES)) or cationic agent (methylene blue (MB)), and made into hydrogels. Properties of the hydrogels and behaviour at different pHs were investigated. RESULTS: The density and gel fraction of PVA/SS-ES hydrogel and PVA/SS-MB hydrogel were considerably lower compared with hydrogel without SS. The swelling ratio and degradation of the hydrogels increased with increasing SS concentration in all pH solutions. The influence of SS in interrupting long-chain PVA molecules was confirmed based on changes in Fourier-transform infrared spectroscopy (FTIR). The SS released from the gels was found to interact with the ionic agent and influenced the release profile of the ionic agent. Surprisingly, the anionic agent in PVA/SS-ES hydrogel showed 70% release in high pH solution whereas the cationic agent in PVA/SS-MB hydrogel showed 86% release in low pH solution. Moreover, the active agent could accumulate on the skin layer and had a positive effect on a specific wound area. CONCLUSION: Based on the results obtained in this study, it is suggested to use anionic hydrogels containing wound healing promoter for wounds at high pH and cationic hydrogels containing wound healing promoter for wounds with low pH. Ability to improve wound healing using a natural healing agent combined with ionic agents and controlling the pH of hydrogels will help in developing quick and low-cost treatment for wounds.

Epidermis of Cereus hildmannianus as a biomimetic scaffold for tissue engineering.

A thin plastic-like film separated from the epidermis of Cereus hildmannianus has excellent tensile strength, resistance to water and high antimicrobial activity and supports the growth of mouse fibroblast cells. Cactuses are one of the most under explored plant species with high potential for food, materials, pharmaceutical and other applications. Although studies have shown the ability of cactuses to be used for food, as a source for fibers, as reinforcement for composites and other applications, the role of individual layers and their properties has been studied to a limited extent. In this paper, a thin translucent layer was separated from the epidermis of C. hildmannianus and studied for its composition, structure and properties. The layer is composed of about 73% cellulose and 2% lignin and morphologically, shows surface with uneven and serrated edges. Films with length of up to 36 cm, strength of 6.8 MPa and elongation of 2.5% could be peeled from the cactus suggesting their suitability for food packaging and other applications. X-ray diffraction patterns and FTIR spectrums indicated that the films are similar to that of cellulose and major thermal degradation occurred above 280°C. Compared to standards, the cactus films showed about 41% and 44% inhibition against gram positive and gram negative bacteria and 67% inhibition of the common fungal strain (A. niger). Films showed high stability in water and to common chemicals. When used as substrates for mouse fibroblast cell growth, no cytotoxicity was observed and the cactus peel supported the attachment and proliferation of cells demonstrating potential to be used as a biomaterial for tissue engineering applications.

A review on the synthesis and properties of hydroxyapatite for biomedical applications.

Hydroxyapatite (HA or HAp) is one of the most preferred biomaterials, specifically for bone tissue engineering. HAp is available naturally and is also chemically synthesized. The properties, shape, size and crystalline structure and applications of HAp vary widely depending on the source and extraction methods used. In addition to conventional chemical approaches such as precipitation or sol-gel techniques, newer methods such as microwave synthesis and atomic-layer deposition provide an opportunity to generate HAp with desirable structure and properties. Various methods used for the synthesis of HAp have their own pros and cons. Hence, it is essential to understand the role of specific methods and conditions on the properties and structure of HAps in order to obtain HAp with properties suitable for specific applications. In addition to pure HAp, substantial efforts have been made to dope HAp with various minerals or bioentities to enhance their suitability for medical, environmental remediation and other approaches. In this review, we provide an overview of the various chemical methods used to produce HAp, properties of the HAp produced and its potential applications. Particular focus of this paper is on the co-relation between properties and processes used to synthesis HAp. This review will enable readers to quickly understand the importance of synthesis methods and conditions on the properties of HAp and choose appropriate means to generate HAp with desired properties for specific applications.

Litter to Leaf: The Unexplored Potential of Silk Byproducts.

Silk has remained the most preferred protein fiber since its discovery in 3000 BC. However, the cost, availability, and resources required to rear the silkworms and process silk are imposing considerable constraints on the future of silk. It is often unrealized that apart from the fibers, production and processing of silk are a source for a diverse range of sustainable, biodegradable, and biocompatible polymers. Hence, delineating itself from being the primary source of protein fibers for millenniums, the silk industry worldwide is transitioning into a biobased industry and as a source for pharmaceuticals, biomaterials, cosmetics, food, and energy. Toward this, byproducts (BPs) and co-products (CPs) that are inevitably generated are now being considered to be of immense economic value and could be up to 10 times more valuable than the silk fibers. Here, we elucidate the properties and potential applications of silk BPs and CPs to present the true potential of silkworms and to promote the establishment of silkworm-based bioeconomy and biorefineries.

Extraction and characterisation of natural cellulose fibers from Kigelia africana.

Kigelia africana also known as sausage plant, yields highly fibrous fruit with a hard shell. Many medicinal uses are reported for the extracts from the fruits, seeds and leaves of sausage trees. In this research, natural cellulose fibers were extracted from the fruit using NaOH and later bleached and characterized for their properties. Results revealed that significant amount of hemicellulose and lignin was lost after the alkali treatment and bleaching leading to a highly cellulosic fiber (up to 71 %). Morphologically, surface of the fibers varied from rough to smooth depending on the extent of treatment. The thermal stability, crystallinity and hydrophobicity increased after the treatment. Sausage fibers also possessed anti-microbial activity against common gram negative and gram positive bacteria. Overall, sausage fibers have properties similar to that of cotton and better than fibers obtained from many unconventional sources. With improved hydrophobicity and anti-bacterial properties, sausage fibers could be potentially applied in functional polymer composites.

Preparation and properties of starch acetate fibers for potential tissue engineering applications.

This article reports the development of fibers from starch acetates that have mechanical properties and water stability better than most polysaccharide-based biomaterials and protein fibers used in tissue engineering. In this research, starch acetates with three different degrees of substitution (DS) have been used to develop fibers for potential use as tissue engineering scaffolds. Varying the DS of starch acetate will provide fibers with different mechanical properties, hydrophilicity, and degradation behavior. Fibers made from DS 2.3 and 2.8 starch acetates have mechanical properties and water stability required for tissue engineering applications. The starch acetate fibers support the adhesion of fibroblasts demonstrating that the fibers would be suitable for tissue engineering and other medical applications.

Biofibers and biocomposites from sabai grass: A unique renewable resource.

Natural cellulose fibers were extracted from a fast growing perennial grass Eulaliopsis binata (commonly known as Sabai) and characterized for their structure and properties. The untreated sabai grass has been used as reinforcement for polypropylene composites and properties of the composites have been investigated. Although the composition of the sabai grass is typical to other lignocellulosic sources, there is a high content of flavonoids (630 mg/g) and phenols (510 mg/g) which provides high antibacterial, and antifungal properties to the fibers and composites developed. Fiber bundles extracted from the grass had tensile strength of 493 MPa and tensile modulus of 21 GPa, similar to common natural cellulose fibers. Both tensile and flexural properties of polypropylene composites increased with increasing ratio of sabai grass. Polypropylene composites reinforced with sabai grass show high noise insulation and thermal resistance properties suggesting their suitability for automotive and building applications.

Characterizing natural cellulose fibers from velvet leaf (Abutilon theophrasti) stems.

Velvet leaf (Abutilon theophrasti) that is currently considered a weed and an agricultural problem could be used as a source for high quality natural cellulose fibers. The fibers obtained from the velvet leaf stems are mainly composed of approximately 69% cellulose and 17% lignin. The single cells in the fiber have lengths of approximately 0.9 mm, shorter than those in common bast fibers, hemp and kenaf. However, the widths of single cells in velvet leaf fibers are similar to the single cells in hemp and kenaf. The fibers exhibited breaking tenacity from 2.4 to 3.9 g/denier (325-500 MPa), breaking elongation of 1.6-2.4% and Young's modulus of 140-294 g/denier (18-38 GPa). Overall, velvet leaf fibers have properties similar to that of common bast fibers such as hemp and kenaf. Velvet leaves fibers could be processed on the current kenaf processing machineries for textile, composite, automotive and other fibrous applications.

Biomimetic approaches for tissue engineering.

Advancement in medical technologies, emergence of new diseases and need for quick and effective treatments have increased the requirement for unique and distinct materials. A plethora of materials in various forms, shapes and sizes have been developed from polymers, metals and ceramics and extensively explored for both in vitro and in vivo applications. When used inside the body, biomaterials include metals, polymers and ceramics typically as implants, scaffolds, drug or gene carriers and also as protective agents. Although various materials are used for biomedical products, natural polymers are preferred over synthetic or metallic materials since they have better biocompatibility and ability to degrade in vivo without releasing toxic substances. In addition to the material, the structure and properties of the biomedical device/product plays a crucial role, particularly, when used for in vivo applications. It is desirable that the materials or products developed resemble the structure and replicate the biological functions in the body. For instance, 3D, nanofibrous structures similar to the extracellular matrix are considered suitable as tissue engineering scaffolds. Hence, extensive studies have been done to biomimic the biological systems and develop biomedical materials and devices using natural and synthetic polymers. For instance, successful replication of the biomineralization and bone formation and regeneration of tissue have been done. There are unlimited choice of materials, approaches and potential products that can be developed using the biomimetic approach. In this review, we provide an overview of the materials and methods used to develop biomimetic products for various medical applications. The objective of this study to provide readers with information on the various methods, materials and approaches that can be used to develop biomimetic materials to address the challenges and needs of the medicine and health care industries. This manuscript is restricted to discussions on biomimetic approaches for tissue engineering applications. However, there are considerable other medical applications of biomimetic materials which are not part of this review.

Crosslinked chitosan films with controllable properties for commercial applications.

In this research, sustainable and green bioproducts with controlled sorption and good mechanical properties have been developed from chitosan for commercial applications. Addition of citric acid, a biocompatible crosslinker, and later treating with alkali imparts excellent tensile strength and aqueous stability to the chitosan films. Films were developed from chitosan and studied for their sorption capabilities, mechanical properties, oxygen/water vapour transmission rates and antimicrobial abilities. Moisture sorption of up to 1466% based on the dry weight of chitosan was seen when the films were untreated. However, treating the films with alkali decreased their water sorption to 100-250% and made the films resistant even to boiling water. Modified chitosan could be moulded into various forms and made into bioproducts that could replace plastic based materials. The chitosan bioproducts developed have the potential to replace plastic based products and will help to provide a greener alternative for the plastic based commodity products in current use.

Structure and properties of natural cellulose fibers obtained from sorghum leaves and stems.

For the first time, sorghum leaves and stems have been used to produce natural cellulose fibers with properties suitable for composite, textile, and other high-value fibrous applications. The leaf and stems fibers produced are multicellular and have similar cellulose contents. The breaking tenacity and elongation of the fibers are similar to that of natural cellulose fibers such as kenaf and cornstalk fibers. However, the sorghum fibers have a modulus of about 113 g/denier (15 GPa) similar to the modulus of cornstalk fibers but higher than that of cotton and cornhusk fibers. At least 7 million tons of natural cellulose fibers can be produced by using the sorghum stems and leaves available as byproducts every year. Using the sorghum byproducts as a source for cellulose fibers will help to add value to the sorghum crops and also make the fiber industry more sustainable.

Preparation and characterization of long natural cellulose fibers from wheat straw.

Long natural cellulose fibers with properties suitable for textile and composite applications have been obtained from wheat straw. This study aims to understand the potential of using wheat straw as a source for long natural cellulose fibers for textile, composite and other fibrous applications. The presence of wax on the outer layer of the straw and a unique zip-like structure that locks individual fibers makes it difficult to obtain fibers from wheat straw using the common methods of fiber extraction. A novel pretreatment with detergent and mechanical force followed by an alkaline treatment was used to obtain high quality fiber bundles. The structure and properties of the fibers are reported in comparison to common cellulose fibers, cotton, linen, and kenaf. Wheat straw fibers have coarser (wider width) single cells and lower crystallinity than cotton, linen, and kenaf. The breaking tenacity (force at break) of wheat straw fibers is similar to kenaf but lower than that of cotton and linen, % breaking elongation is similar to linen and kenaf but lower than cotton, and Young's modulus of the fibers is similar to cotton but lower than that of linen and kenaf.

Highly porous carbon from a natural cellulose fiber as high efficiency sorbent for lead in waste water.

The persistence of hollow centre in the carbon obtained from milkweed floss provides exceptional sorption characteristics, not seen in common biomasses or their derivatives. A considerably high sorption of 320mg of lead per gram of milkweed carbon was achieved without any chemical modification to the biomass. In this research, we have carbonized milkweed floss and used the carbon as a sorbent for lead in waste water. A high surface area of 170m2g-1 and pore volume of 1.07cm3g-1 was seen in the carbon. Almost complete removal (>99% efficiency) of lead could be achieved within 5min when the concentration of lead in the solution was 100ppm, close to that prevailing in industrial waste water. SEM images showed that the carbon was hollow and confocal images confirmed that the sorbate could penetrate inside the hollow tube.

Properties of high-quality long natural cellulose fibers from rice straw.

This paper reports the structure and properties of novel long natural cellulose fibers obtained from rice straw. Rice straw fibers have 64% cellulose with 63% crystalline cellulose, strength of 3.5 g/denier (450 MPa), elongation of 2.2%, and modulus of 200 g/denier (26 GPa), similar to that of linen fibers. The rice straw fibers reported here have better properties than any other natural cellulose fiber obtained from an agricultural byproduct. With a worldwide annual availability of 580 million tons, rice straw is an annually renewable, abundant, and cheap source for natural cellulose fibers. Using rice straw for high-value fibrous applications will help to add value to the rice crops, provide a sustainable resource for fibers, and also benefit the environment.

Biofibers from agricultural byproducts for industrial applications.

Lignocellulosic agricultural byproducts are a copious and cheap source for cellulose fibers. Agro-based biofibers have the composition, properties and structure that make them suitable for uses such as composite, textile, pulp and paper manufacture. In addition, biofibers can also be used to produce fuel, chemicals, enzymes and food. Byproducts produced from the cultivation of corn, wheat, rice, sorghum, barley, sugarcane, pineapple, banana and coconut are the major sources of agro-based biofibers. This review analyses the production processes, structure, properties and suitability of these biofibers for various industrial applications.

Crosslinking biopolymers for biomedical applications.

Biomaterials made from proteins, polysaccharides, and synthetic biopolymers are preferred but lack the mechanical properties and stability in aqueous environments necessary for medical applications. Crosslinking improves the properties of the biomaterials, but most crosslinkers either cause undesirable changes to the functionality of the biopolymers or result in cytotoxicity. Glutaraldehyde, the most widely used crosslinking agent, is difficult to handle and contradictory views have been presented on the cytotoxicity of glutaraldehyde-crosslinked materials. Recently, poly(carboxylic acids) that can crosslink in both dry and wet conditions have been shown to provide the desired improvements in tensile properties, increase in stability under aqueous conditions, and also promote cell attachment and proliferation. Green chemicals and newer crosslinking approaches are necessary to obtain biopolymeric materials with properties desired for medical applications.

Effects of monomers and homopolymer contents on the dry and wet tensile properties of starch films grafted with various methacrylates.

Starch grafted with four different methacrylates was compression molded to form thermoplastic films with good strength and water stability. Starch is an inexpensive and biodegradable polymer but is nonthermoplastic and needs to be chemically modified to make starch suitable for various applications. In this research, starch was grafted with four methacrylates (methyl, ethyl, butyl, and hexyl), and the effect of the length of the alkyl ester group on grafting parameters, thermoplasticity, and properties of thermoplastic films developed have been studied. Influence of grafting conditions on % grafting efficiency, % homopolymers, and % monomer conversion were studied, and the grafted starch was characterized using thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), and nuclear magnetic resonance ((1)H NMR). At similar grafting ratios, butyl methacrylate (BMA) provided better strength and elongation to the starch films than the other three methacrylates. Grafting of methacrylates appears to be an economical approach to develop thermoplastic products from starch.

Cytocompatible and water-stable camelina protein films for tissue engineering.

In this research, films with compressive strength and aqueous stability were developed from camelina protein (CP) for tissue engineering. Protein based scaffolds have poor mechanical properties and aqueous stability and generally require chemical or physical modifications to make them applicable for medical applications. However, these modifications such as crosslinking could reduce biocompatibility and/or degradability of the scaffolds. Using proteins that are inherently water-stable could avoid modifications and provide scaffolds with the desired properties. CP with a high degree of disulfide cross-linkage has the potential to provide water-stable biomaterials, but it is difficult to dissolve CP and develop scaffolds. In this study, a new method of dissolving highly cross-linked proteins that results in limited hydrolysis and preserves the protein backbone was developed to produce water-stable films from CP without any modification. Only 12 % weight loss of camelina films was observed after 7 days in phosphate buffer saline (PBS) at 37°C. NIH 3T3 fibroblasts could attach and proliferate better on camelina films than on citric acid cross-linked collagen films. Therefore, CP films have the potential to be used for tissue engineering, and this extraction-dissolution method can be used for developing biomedical materials from various water-stable plant proteins.

Development and characterization of thermoplastic films from sorghum distillers dried grains grafted with various methacrylates.

Distillers Dried Grains (DDG) obtained during production of ethanol from grain sorghum were grafted with methacrylates and compression molded into films with good dry and wet tensile properties. Since sorghum DDG contains up to 45% proteins that are indigestible by animals, it is necessary to find alternative applications to make sorghum ethanol economically competitive. In this research, sorghum DDG was grafted with methyl, ethyl, and butyl methacrylates, the grafted DDG was compression molded into films, and the properties of the grafted DDG and films were studied. At a grafting ratio of 40%, butyl methacrylate (BMA) grafted films had a strength of 4.8 MPa and elongation of 1.8% when dry and 3.1 MPa and 8.1% when wet, indicating that the films had good strength and wet stability. Films developed from grafted DDG show the potential to overcome the brittleness and poor water stability of biopolymer-based films and be useful for various applications.