Effect of processing route on the composition and properties of hemp fibre

There is great interest in the plant Cannabis sativa (hemp) as a source of technical fibres for the reinforcement of polymers in composite materials due to its high mechanical properties. In this work, the effect of enzymatic, hydrothermal and alkaline treatments on the composition and mechanical properties of hemp fibre are compared. The influence of enzyme concentration and treatment time was examined (2.5–80 % Pectinex® Ultra SP-L, 6–48 hrs). Additionally, hydrothermal (170 °C, 10 bars) and alkaline treatments (18 wt. % NaOH, 40 °C) were used as pre-treatments to observe their effect on subsequent enzymatic treatment. The composition of hemp fibre was analysed by wet chemistry and Fourier transform infrared spectroscopy, while microstructure and mechanical properties were examined by scanning electron microscopy and tensile testing, respectively. Enzymatic treatment resulted in extensive fibrillation and removal of non-cellulosic components, especially when combined with hydrothermal treatment. However, a lengthy enzymatic treatment or combinative enzymatic-alkaline treatment led to extensive fibre breakdown that was accompanied by a pronounced reduction in the mechanical properties. Enzymatic treatment decreased Young’s modulus and tensile strength by 77 and 73 % respectively, and alkaline treatment by 83 and 36 %. The hydrothermal treatment resulted in only minor changes in these properties.     

A comparative study of wool fibre surface modified by physical and chemical methods

The wool scale present on the fibre surface gives rise to certain unwanted effects such as felting and poor wettability in textile wet processing. In general practice, the removal of scale was done either by surface modification through physical/chemical degradation of scale or by deposition of a polymer on the scale. In modern treatment, combination of both methods is usually carried out. Since the deposition of a polymer on the fibre surface depends much on the surface characteristic of the fibre, therefore, the surface property of modified fibre is an important factor for polymer application. On the other hand, the surface modification methods may also result in improved hydrophilicity of fibre. The present paper investigated the surface physico-chemical properties of wool fibre under the influence of different surface modification treatments: (i) low temperature plasma (LTP) treatment with nitrogen gas and (ii) chlorination. The surface physico-chemical properties of the LTP-treated and chlorinated wool fibres were studied which included contact angle measurement with different solvents, determination of critical surface tension and surface free energy. Experimental results showed that these selected properties were altered after the surface modification treatments. In addition, a polymer was deposited in the treated wool fabrics and scanning electron microscope was used for assessing the surface morphology.     

Surface modifications of natural Kanchipuram silk (pattu) fibers using glow discharge air Plasma

Experimental investigations have been carried out to modify the surface properties of natural Kanchipuram silk (pattu) fibers using a low temperature DC glow discharge air Plasma. Silk is an externally spun fibrous protein secretion formed into fibers. Plasma treatment is an eco-friendly, dry, and clean process over wet chemical method and does not suffer from any environmental and health concerns. Experiments have been performed considering three parameters such as discharge current, treatment time, and working pressure. The structural, thermal, morphological, optical, and mechanical studies of raw and plasma treated silk fibers have been obtained out using attenuated total reflection-Fourier transform infrared spectroscopy (ATR-FTIR) spectroscopy, X-ray diffraction (XRD), thermo gravimetric analyzer (TGA), scanning electron microscope (SEM) with energy dispersive spectroscopy (EDS), diffuse absorbance spectroscopy, and tensile test. A comparative study has been done for the untreated and different treated fibers. Various characterization analyses reveal that surface roughness of the plasma treated silk fiber is increased and also crystallite size of treated samples is enhanced, plasma treated silk fibers maintain the whiteness effect and it is observed that UV transmittance region (A & B) is more for the treated fiber which signifies enhanced UV protection.     

Effect of different fractions of zein on the mechanical and phase properties of zein films at nano-scale

The phase behavior of zein films has been investigated at nano-scale using atomic force microscopy (AFM) and compared to the phase behavior of the bulk using a thermal characterization technique. The local surface properties of the films were evaluated as a function of water activity using AFM. The glass transition temperature (T_g) of zein films decreased with increasing water activity. Adhesion forces measured by the AFM force curves increased with increasing water activity. Topography of zein and zein fractions were evaluated both qualitatively and quantitatively by the use of AFM and dedicated software to calculate the surface roughness. It has been found that processing technologies (solvent casting, drop deposition and spin casting) has influence on the surface structures of films. The films which were formed by the alpha zein rich fraction were found to have highest roughness values. Sectional surface profiles revealed that α-zein films have mean roughness (R_a) of 1.808 nm and root mean square roughness (RMS) of 2.239 nm while β-zein films have mean roughness (R_a) of 1.745 nm and root mean square roughness (RMS) of 3.623 nm. The discussions conducted on the differences/similarities in the observations were based on the hydrophobic/hydrophilic properties and interactions of these zein fractions.     

Characterization of zein modified with a mild cross-linking agent

Zein, a predominant corn protein, is an alcohol-soluble protein extracted from corn and is an excellent film former. The characteristic brittleness of zein diminishes its usefulness as a film. It is well known that zein has a propensity for forming aggregates in solution. When zein molecules were cross-linked with 1-[3-dimethylaminopropyl]-3-ethyl-carbodiimide hydrochloride (EDC) and N-hydroxysuccinimide (NHS), it was found that the film-forming property was improved and the aggregation phenomenon in solution was suppressed. At the air/water interface, native zein forms brittle film with rough surface, whereas cross-linked zein forms rigid film with very smooth and even surface. Tensile strengths of the films were shown to be greatly increased by cross-linking. Objectives of this study are to determine the cross-linking mechanism of zein, the optimum reaction conditions, characteristics of the reaction product, and mechanical properties of cross-linked zein film. Through viscosity and dynamic light scattering, the cross-linking reaction was monitored. Optimum amount of EDC and NHS was determined to be 30 mg each per gram of zein. The cross-linking of zein with EDC and NHS seemed to be self-terminating because the cross-linking reaction did not proceed to precipitation.     

Effect of chemical softening of coconut fibres on structure and properties of its blended yarn with jute

Coconut fibres were subjected to chemical treatment to obtain softer and finer fibres, suitable to blend with other finer fibre like jute. The chemical softening recipe was optimized using Box-Behnken design of experiments as 40 % Na₂S, 10 % NaOH and 6 % Na₂CO₃, which notably reduced the fineness (33 %) and flexural rigidity (74 %) and improved tensile property of coconut fibre. Effect of softening of coconut fibre on its process performance was studied in high speed mechanized spinning system at different blend ratios with jute. Blending with jute assists in spinning of coconut fibre to produce yarn of 520 tex at production rate of 5-6 kg/h, as compared to 15 kg/day for hand spun 5300 tex raw coconut fibre yarn in manual system. Analysis of blended yarn structure in terms of packing density, radial distribution of fiber components (SEM) and mass irregularity were investigated. SEM shows yarns made from softened coconut fibre -jute blends are more compact than raw coconut fibre -jute blend yarns. Coconut fibres were preferentially migrated to core of the yarn. Major yarn properties viz., tensile strength, and flexural rigidity of raw and chemically softened blended yarns were compared against their finest possible 100 % coconut fibre yarn properties. Yarn made up to 50:50 chemically softened coconut fibre-jute blend showed much better spinning performance, and having superior property in terms of reduced diameter, higher compactness, strength, initial modulus and less flexural rigidity than 100 % raw, 100 % chemically softened coconut fibre rope, and raw coconut fibre-jute blend yarns.     

Preparation and characterization of micro- and nano-fibrils from jute

In order to prepare micro- and nano-fibrils from jute, the binder has to be cleaned off. A new technique including chemical (room temperature alkaline, acid steam, and 80 °C alkaline) and physical (high pressure steam) treatments of natural fibers was developed. The effects of chemical and physical treatments on the morphological development of jute fibers from micro- to nano-scale were observed by using scanning electron microscopy (SEM). This novel natural fibers treatment technology has two advantages compared with others. One is the long strands of natural fibers keep their length by special acid steam treatment, but the traditional acid solution treatment makes the length of natural fibers short. Another one is the high pressure steam treatment that made jute fibers nano-fibrils. The thermal property of untreated and treated fibers was determined by using thermogravimetric analysis (TGA) which indicated that the thermal stability of the jute fibers was enhanced after treatments. The lignin acted as binder was mainly removed by analyzing solid residues using fourier transform infrared spectrometer (FTIR).     

Improvement of zein dough characteristics using dilute organic acids

The replacement of gluten in dough products poses a major challenge. Preparing zein doughs in dilute acetic acid and lactic acid, such as produced during sourdough fermentation, was investigated. Increasing acid concentrations (0.7, 1.3 and 5.4% [v/v]) increased zein extensibility and reduced the stress and related parameters. Preparation of zein-maize starch/-rice doughs in dilute organic acids improved dough properties to the extent that the doughs could hold air and be inflated into a bubble by Alveography. Further, they exhibited similar Stability (P), Distensibility and deformation energy (W) to wheat flour dough. Confocal laser scanning microscopy revealed an ordered linear fibril network in zein and zein-rice flour doughs prepared in the dilute acids, which became uniform with increasing acid concentration. SDS-PAGE showed that the acids did not hydrolyse or polymerise the zein. FTIR indicated that the acidic conditions slightly increased the proportion of α-helical conformation in the zein doughs, possibly as a result of deamination. This conformational change may be responsible for the considerably improved zein dough properties. Zein doughs prepared in dilute organic acids show potential as a gluten replacement in gluten-free formulations.     

Melt-processed blends of zein with polyvinylpyrrolidone

Melt-processed blends of zein and polyvinylpyrrolidone (PVP) of varying molecular weights (55K, 360K and 1.3M) were compared based on mechanical and thermal properties. Generally, all samples stored at 50% RH exhibited a slight improvement in tensile strength, with the PVP360K samples showing the greatest improvement. At the higher levels of PVP, samples stored at 70% RH showed a decrease in tensile strength. Elongation was also more significantly impacted at higher humidity, with the higher levels of PVP causing greater elongation increases. Differential scanning calorimetry data for the blends showed single T_g values intermediate between the zein and PVP controls. Kinetic thermogravimetric data suggested a multi-step degradation interaction for the zein/PVP blends. Scanning electron microscope imaging of compression molded samples showed homogeneous surface contours for even the 20% PVP1.3M blend. Melt-processed blends of zein with polyvinylpyrrolidone of various molecular weights appear to be compatible. This work represents the first melt-processed blend of zein with PVP to generate a compatible blend.     

Oil palm fiber (OPF) and its composites: A review

Twenty first century has witnessed remarkable achievements in green technology in material science through the development of biocomposites. Oil palm fiber (OPF) extracted from the empty fruit bunches is proven as a good raw material for biocomposites. The cellulose content of OPF is in the range of 43%–65% and lignin content is in the range of 13%–25%. A compilation of the morphology, chemical constituents and properties of OPF as reported by various researchers are collected and presented in this paper. The suitability of OPF in various polymeric matrices such as natural rubber, polypropylene, polyvinyl chloride, phenol formaldehyde, polyurethane, epoxy, polyester, etc. to form biocomposites as reported by various researchers in the recent past is compiled. The properties of these composites viz., physical, mechanical, water sorption, thermal, degradation, electrical properties, etc. are summerised. Oil palm fiber loading in some polymeric matrices improved the strength of the resulting composites whereas less strength was observed in some cases. The composites became more hydrophilic upon addition of OPF. However treatments on fiber surface improved the composite properties. Alkali treatment on OPF is preferred for improving the fiber–matrix adhesion compared to other treatments. The effect of various treatments on the properties of OPF and that of resulting composites reported by various researchers is compiled in this paper. The thermal stability, dielectric constant, electrical conductivity, etc. of the composites improved upon incorporation of OPF. The strength properties reduced upon weathering/degradation. Sisal fiber was reported as a good combination with OPF in hybrid composites.     

Effect of pH and ethanol content of solvent on rheology of zein solutions

Zein, a corn protein, is a mixture of the polypeptides α-, γ-, β-, and δ-zein. α-Zein and γ-zein comprise 70–85% and 10–20% of total zein mass, respectively. Both peptides have similar amino acid composition, except γ-zein is rich in cysteine. The presence of cysteine has been associated with gelation of zein solutions. A common solvent for zein is aqueous ethanol. Preliminary results suggested that pH and ethanol content affect the rheology of zein solutions. Our objective was to investigate the effect of ethanol content (65–90%) and pH of the solvent (2, 6, and 12) on rheological properties of zein solutions (20% w/w) containing γ-zein. Steady shear tests and oscillatory time sweeps were performed to determine flow behavior and gelation time of zein solutions. Results indicated that α-zein solutions were nearly Newtonian while those containing γ-zein showed shear thinning behavior. At high pH, γ-zein increased the consistency index (K) and shortened gelation time. Results were attributed to the cysteine in γ-zein. High pH promoted formation of disulfide bonds leading to higher K values and shorter gelation times. Results of this work are expected to be useful in the design of zein extraction processes and the development of new zein applications.     

Extraction of natural cellulosic fibers from cornhusk and its physico-chemical properties

A natural long staple ligno-cellulosic fibers have been extracted from the cornhusks using an alkali treatment. Physico-chemical properties such as chemical composition, length, fineness, crystallinity, surface properties, etc. measured by standard methods are reported in this paper. The physico-chemical and morphological properties of the extracted cornhusk fibers are discussed in detail and compared with other cellulosic like cotton and ligno-cellulosic fibers such as jute. Scanning electron microscopy was used to study the morphological and cross-sectional view and energy dispersive X-ray and FTIR were used for the identification and quantification of elements, groups present in the cornhusk and other cellulosic and lignocellulosic fibers. In addition, fibers are characterized by thermo-gravimetric analysis. Results showed that morphological and physico-chemical behavior is more or less similar to other multicellular ligno-cellulosic fibers like jute.     

Improvement in fastness properties of phase-change material applied on surface modified wool fabrics

The comfort of textiles is important and one area under evaluation is the development and application of Phase Change Materials, PCMs, in order to impart thermal adaptability. PCMs research for textiles has also focused on the use of polyethylene glycol (PEG). While there is a good adhesion between fibre and PEG polymer for cotton and polyester fibres, polymer adhesion to wool fibres appears poor and loosely bound within the yarn and had dislodged and crumbled. Therefore in this paper, the effect of changing the wool fibre surface energy and surface charge, shrinkproofing, on performance properties of thermally adaptable wool fabrics were studied. Untreated, gaseous fluorinated, as well as Chlorine-Hercosett treated 100 % wool fabrics have been evaluated to obtain highly cross-linked PEG with acceptable fastness properties. The surface interface was effectively probed by XPS & ToF-SIMS and characterised the loss of surface lipids, the nature of the fibre oxidation and deposition of Hercosett polymer on the wool fibre. The results indicate the necessity of having high surface energy in order to obtain appropriate adhesion and binding higher amount of solid polymer to wool fibres which results in superior thermal activity, better durability, and enhancement in felting performance.     

Morphological and crystalline characterization of NaOH and NaOCl treated Agave americana L. fiber

This study investigates the effect of NaOH and NaOCl treatments on chemical composition, morphology and crystalline structure of Agave americana L. fibers. These fibers have been subjected to NaOCl and NaOH alkali treatments at different concentrations.The percentages of lignin and hemicellulose show a decrease with alkaline treatments which, in turn, induces a modification of both morphological and crystalline structures.Unit cell dimensions and crystallite size were more affected with NaOH treatment than NaOCl one. This may result from the mercerisation process which occurs with caustic soda treatment.The observed defibrillization on the treated fiber surface proves the dissolution of the non-cellulosic components present in the fiber cell wall by NaOH and NaOCl treatments. These morphological changes may improve the interaction between matrix and fiber in composites.     

Production of composites by using gliadin as a bonding material

In previous papers, a new technology that produces biopolymer composites by particle-bonding was introduced. During the manufacturing process, micrometer-scale raw material was coated with a corn (Zea mays L.) protein, zein, which was then processed to form a rigid material. The coating of raw-material particles with zein makes use of the unique property of this protein in aqueous ethanol solution. In this paper, it is shown that the behavior of a wheat (Triticum aestivum L.) protein, gliadin, is very similar to zein in aqueous ethanol. Size variation of aggregates in 45-65% aqueous ethanol was investigated with a turbidimeter in conjunction with Size Exclusion Chromatography. Confirming the resemblance of gliadin to zein in terms of aggregation behavior in aqueous alcohol, composites were fabricated by particle-bonding and their mechanical property was measured with a Universal Testing Machine. Test results showed that gliadin is a good substitute for zein in the production of composites.     

Reliability improvement of hemp based bio-composite by surface modification

The influence of the surface treatments on the performance of the hemp/PP (polypropylene) composite was investigated. The composites were prepared from the fiber modified by the alkalis and the oil under various conditions. The mechanical properties of the composites were measured using the tensile test, and the service time of the composite was assessed under accelerated condition by the stepped isothermal method. The alkaline treatment removed the lignin successfully and resulted in better fibrillation. The oil treatment improved the mechanical properties of the composites and extended the service life time of the composites.     

Multivalent carboxylic acids to modify the properties of zein

Methods must be developed to improve both the processability and physical properties of zein-based articles. Typical plasticizing agents that improve processability have a negative impact on physical properties at elevated humidities. Continued efforts must be employed to discover improved plasticizers. Carboxylic acids having more than one carboxylic acid moiety have been evaluated in zein melt formulations produced in a torque rheometer. These reagents were effective plasticizers for zein, lowering zein viscosity, and delaying the onset of rapid viscosity increase. These reagents altered viscosity differently than the traditional plasticizers such as triethylene glycol. These additives also lowered the tensile strength (TS) of zein formulations at 50% RH. Surprisingly, TS at 70% RH was higher than that at 50% RH at elevated levels of these additives. NMR analysis of Soxhlet extracted samples showed that these multivalent carboxylic acids do not cross-link the zein under the reaction conditions employed.     

Surface modification of PET film and fabric by oligo-chitosan treatment

Poly(ethylene terephthalate) (PET) films, comprising surfaces hydrolyzed with caustic soda solution to incorporate the functional groups of carboxylic acids, were treated with a solution containing chitosan oligomer, a cross-linking agent, and a catalyst in order to modify various surface characteristics, including hydrophilicity and anti-staticity. Chitosan oligomers were prepared by depolymerizing chitosan with sodium nitrite. The chitosan molecules were fixed to the PET film surface by the reaction between the carboxylic groups in the PET film and the amino groups of the chitosan molecules. FT-IR(ATR) spectra, surface free energies, anti-staticity and other properties were measured and interpreted in relation to the structural change that was induced in the PET films by these treatments. In addition, we investigated the effect of chitosan oligomer treatment on the handle of polyester fabrics by using Kawabata evaluation system. The hydrophilic and anti-static properties of the PET film were highly improved by alkaline hydrolysis and low-molecular-weight chitosan treatment. The handle of PET fabric was gradually hardened by chitosan treatment with increasing the concentration of chitosan.     

Physical properties of zein films containing salicylic acid and acetyl salicylic acid

Zein films containing salicylic acid (SA) and acetyl salicylic acid (ASA) between 2 and 10% (initial zein weight basis) with or without glycerol were evaluated for structure, mechanical and dissolution properties. The random coils, α helices and β sheets mainly governed the secondary structure of zein, depending on glycerol and level of model molecules. Adding ASA resulted in an increase in α helices whereas β sheets increased at the expense of α helices when SA was used. Including SA or ASA decreased the tensile strength and the stiffness of films containing glycerol indicating the synergistic effect of SA and ASA. The strain at failure decreased with increasing content of SA but increased with increasing level of ASA. The dissolution properties were glycerol and drug dependent. ASA release in comparison to SA was quite low. The release was only observed above 10% ASA whereas it was detected in all films containing SA. The possible interactions between active components and proteins are discussed together with their implications on the physical properties of zein films.     

Effect of surface treatment of jute fibers on the interfacial adhesion in poly(lactic acid)/jute fiber biocomposites

Jute fibers have immense potential to be used as natural fillers in polymeric matrices to prepare biocomposites. In the present study jute fibers were surface treated using two methods: i) alkali (NaOH) and ii) alkali followed by silane (NaOH+Silane) separately. Effects of surface treatments on jute fibers surface were characterized using fourier transform infrared spectroscopy (FT-IR) and scanning electron microscopy (SEM) analyses. Further, the effects of surface treatments on jute fibers properties such as crystallinity index, thermal stability, and tensile properties were analyzed by X-ray diffraction method (XRD), thermo gravimetric analysis (TGA), and single fiber tensile test respectively. The effects of surface treatment of jute fibers on interphase adhesion between of poly(lactic acid) (PLA) and jute fibers were analyzed by performing single fiber pull-out test and was examined in terms of interfacial shear strength (IFSS) and critical fiber length.