Alkali resistance of a casein‐acrylonitrile graft copolymer fiber

The casein‐acrylonitrile graft copolymer fiber was treated in sodium hydroxide, sodium carbonate, and sodium bicarbonate solutions to evaluate its alkali resistance which was very important for wet processing. The weight loss and whiteness of the treated fibers were examined. UV spectra of the alkaline treatment solutions and IR spectra of the treated fibers were analyzed. The study showed that the fiber exhibited poor alkali resistance. Treating temperature, alkali concentration, and strength affected the weight loss and whiteness of the treated fibers. A high weight loss was found even at low alkali concentration, and the obvious yellowing was observed at higher alkali concentration and temperature. The weight loss was primarily due to the hydrolysis of casein, whereas the yellowing was caused by the hydrolysis of nitrile groups and induced formation of C?N conjugated system. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Tensile stress relaxation of short‐coir‐fiber‐reinforced natural rubber composites

The stress relaxation behavior of natural rubber (NR) and its composites reinforced with short coir fibers under tension was analyzed. The rate of stress relaxation was a measure of the increase in the entropy of the compounds: the higher the rate was, the greater the entropy was. At lower strain levels, the relaxation mechanism of NR was independent of strain level. However, the rate of relaxation increased with the strain level. Also, the strain level influenced the rate of stress relaxation considerably in the coir‐reinforced NR composites. However, the relaxation mechanisms of both the unfilled compound and the composite were influenced by the strain rate. The rate of relaxation was influenced by fiber loading and fiber orientation. From the rate of stress relaxation, we found that fiber–rubber adhesion was best in the composite containing fibers subjected to a chemical treatment with alkali, toluene diisocyanate, and NR solutions along with a hexaresorcinol system as a bonding agent. In this study, the stress relaxation curves could not be viewed as segments with varying slopes; however, a multitude of inflection points were observed on the curves. Hence, we propose neither a two‐step nor three‐step mechanism for the coir‐fiber‐reinforced NR composites as reported for some other systems. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 96–104, 2004     

Novel eco‐friendly biodegradable coir‐polyester amide biocomposites: Fabrication and properties evaluation

Biocomposites are prepared from a cheap, renewable natural fiber, coir (coconut fiber) as reinforcement with a biodegradable polyester amide (BAK 1095) matrix. In order to have better fiber‐matrix interaction the fibers are surface modified through alkali treatment, cyanoethylation, bleaching and vinyl grafting. The effects of different fiber surface treatments and fiber amounts on the performance of resulting bio‐composites are investigated. Among all modifications, cyanoethylated coir‐BAK composites show better tensile strength (35.50 MPa) whereas 7% methyl methacrylate grafted coir‐BAK composites show significant improvement in flexural strength (87.36 MPa). The remarkable achievement of the present investigation is that a low strength coir fiber, through optimal surface modifications, on reinforcement with BAK show an encouraging level of mechanical properties. Moreover, the elongation at break of BAK polymer is considerably reduced by the incorporation of coir fibers from nearly 400% (percent elongation of pure BAK) to 16‐24% (coir‐BAK biocomposites). SEM investigations show that surface modifications improve the fiber‐matrix adhesion. From biodegradation studies we find that after 52 days of soil burial, alkali treated and bleached coir‐BAK composites show significant weight loss. More than 70% decrease in flexural strength is observed for alkali treated coir‐BAK composites after 35 days of soil burial. The loss of weight and the decrease of flexural strength of degraded composites are more or less directly related.     

Unsaturated polyester‐toughened epoxy composites: Effect of sisal fiber on thermal and dynamic mechanical properties

In the present study, the mechanical and thermal properties of sisal fiber‐reinforced unsaturated polyester (UP)‐toughened epoxy composites were investigated. The sisal fibers were chemically treated with alkali (NaOH) and silane solutions in order to improve the interfacial interaction between fibers and matrix. The chemical composition of resins and fibers was identified by using Fourier‐transform infrared spectroscopy. The UP‐toughened epoxy blends were obtained by mixing UP (5, 10, and 15 wt%) into the epoxy resin. The fiber‐reinforced composites were prepared by incorporating sisal fibers (10, 20, and 30 wt%) within the optimized UP‐toughened epoxy blend. Scanning electron microscopy was used to analyze the morphological changes of the fibers and the adhesion between the fibers and the UP‐toughened epoxy system. The results showed that the tensile and flexural strength of (alkali‐silane)‐treated fiber (30 wt%) ‐reinforced composites increased by 83% and 55%, respectively, as compared with that of UP‐toughened epoxy blend. Moreover, thermogravimetric analysis revealed that the (alkali‐silane)‐treated fiber and its composite exhibited higher thermal stability than the untreated and alkali‐treated fiber systems. An increase in storage modulus and glass transition temperature was observed for the UP‐toughened epoxy matrix on reinforcement with treated fibers. The water uptake behavior of both alkali and alkali‐silane‐treated fiber‐reinforced composites is found to be less as compared with the untreated fiber‐reinforced composite. J. VINYL ADDIT. TECHNOL., 23:188–199, 2017. © 2015 Society of Plastics Engineers     

Scanning electron microscopy study of chemically modified coir fibers

Chemical‐surface modification of coir fibers was done by dewaxing, using an alkali treatment (5% and 10% NaOH), vinyl grafting with methyl methacrylate (MMA) and cyanoethylation. The chemically modified fibers were characterized by Fourier transform infrared (FTIR) spectroscopy. In addition, the surface features of untreated, dewaxed, alkali‐treated, grafted, and cyanoethylated coir fibers were studied using scanning electron microscopy (SEM). Progressive changes in surface morphology were observed. SEM observations showed the removal of tyloses from the surface of coir as a result of alkali treatment (5%), resulting in a rough fiber surface with regularly spaced pits. At a lower percentage of grafting (PMMA), the surfaces became more or less uniform, while the surfaces of the coir fibers with a higher percentage of grafting were increasingly covered with grafted materials, resulting in canal‐like cavities between the overgrowths of the grafted materials on the unit cells. Cyanoethylated coir‐fiber surfaces showed an insufficient deposit of cyanoethyl groups. SEM analysis of the samples was corroborated by measurements of a mechanical property (maximum stress at break). © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 79: 1169–1177, 2001     

Effects of alkali and silane treatment on the mechanical properties of jute‐fiber‐reinforced recycled polypropylene composites

Jute‐fibers‐reinforced thermoplastic composites are widely used in the automobile, packaging, and electronic industries because of their various advantages such as low cost, ease of recycling, and biodegradability. However, the applications of these kinds of composites are limited because of their unsatisfactory mechanical properties, which are caused by the poor interfacial compatibility between jute fibers and the thermoplastic matrix. In this work, four methods, including (i) alkali treatment, (ii) alkali and silane treatment, (iii) alkali and (maleic anhydride)‐polypropylene (MAPP) treatment, and (iv) alkali, silane, and MAPP treatment (ASMT) were used to treat jute fibers and improve the interfacial adhesion of jute‐fiber‐reinforced recycled polypropylene composites (JRPCS). The mechanical properties and impact fracture surfaces of the composites were observed, and their fracture mechanism was analyzed. The results showed that ASMT composites possessed the optimum comprehensive mechanical properties. When the weight fraction of jute fibers was 15%, the tensile strength and impact toughness were increased by 46 and 36%, respectively, compared to those of untreated composites. The strongest interfacial adhesion between jute fibers and recycled polypropylene was obtained for ASMT composites. The fracture styles of this kind of composite included fiber breakage, fiber pull‐out, and interfacial debonding. J. VINYL ADDIT. TECHNOL., 2010. © 2010 Society of Plastics Engineers.     

Characterization of an alkali‐treated grass fiber by thermogravimetric and X‐ray crystallographic analysis

The thermal behavior of grass fiber was characterized by means of thermogravimetric analysis and differential scanning calorimetry analysis. The results proved that the removal of water‐soluble matter improved the thermal behavior of grass fiber over that of unleached fiber, and this was further enhanced by an alkali treatment of the grass fiber. The isothermal weight loss of the grass‐fiber specimens was analyzed at 100, 200, and 300°C for different time periods. Accelerated aging of the grass‐fiber samples was carried out to determine the effect of aging on the tensile strength. Partially delignified grass fiber showed maximum thermal stability. X‐ray diffraction analysis was also performed to verify the composition and to correlate the change in the tensile strength due to the water leaching and alkali treatment. The processing of grass fiber with NaOH and NaClO₂ reduced the amorphous fraction in the fiber sample. This may have been a result of the loss of the amorphous noncellulosic components of the fibers and the degradation of the unordered regions of the grass fiber. However, mercerization of the grass fiber revealed an increase in the amorphous fraction after a certain time exposure, confirming the decrease in the crystallinity. The morphology of the water‐leached and alkali‐treated grass fiber was studied with scanning electron microscopy © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Study of polypropylene/ethylene‐propylene‐diene monomer blends reinforced with sisal fibers

Thermoplastics reinforced with natural fibers have attracted much attention from researchers because of their advantages, especially regarding environmental aspects. However, poor impact strength, particularly at low temperatures, limits the application of some thermoplastics, such as polypropylene (PP). To minimize this drawback, impact modifiers have been used, including the terpolymer of ethylene‐propylene‐diene (EPDM). In this work, PP/EPDM/sisal composites of distinct compositions were investigated focusing on the effect of the alkali (NaOH) treatment of the vegetable fiber on the composites properties regarding physical, mechanical, thermal, and morphological behavior. The results indicated that flow rate decreases at higher fiber content due to flow hindering by the presence of the fibers. The addition of the fiber, in general, increased Young's modulus and strength (tensile and flexural), whereas impact strength increased for higher EPDM content. The alkali treatment was considered generally efficient in terms of mechanical properties, even though this was not found in the dynamic mechanical analysis. POLYM. COMPOS., 2012. © 2012 Society of Plastics Engineers     

Water absorption pattern and dimensional stability of oil palm fiber–linear low density polyethylene composites

The water absorption pattern and associated dimensional changes and solid loss of oil palm fiber–linear low density polyethylene composites was studied. The effects of fiber size (425–840, 177–425, and 75–177 μ), fiber loading (0, 10, 20, 30, 40, and 50%), and time of immersion (192 h at an interval of 24 h) on these parameters were also studied. Alkali treatment of fibers was done to reduce the hydrophilic nature of the composites and its effect was studied. It was found that the water absorption in most of the combinations followed typical Fickian behavior. The rate of water absorption and swelling increased with fiber loading. However, alkali treatment of the fibers resulted in a reduction of water absorption at higher fiber loadings only, and composites with higher fiber sizes exhibited higher water absorption. A sharp increase in the thickness swelling was observed in the initial days of immersion, which remained constant thereafter. The thickness swelling also increased with fiber size; however, a constant trend was not observed for the 75–177 μ fiber size. In addition to thickness swelling, composites also expanded linearly during water absorption; however, linear expansion was considerably less than thickness swelling. Higher fiber loading and alkali treatment caused more linear expansion. We observed that maximum solid loss on water immersion occurred with small‐sized and also alkali‐treated fiber composites. An increase in thickness and a decrease in linear dimension were observed after one sorption–desorption cycle. This irreversible change was also found to be proportional to fiber loading and alkali treatment. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Bio‐composites for structural applications: Poly‐l‐lactide reinforced with long sisal fiber bundles

Fully bio‐based and biodegradable composites were compression molded from unidirectionally aligned sisal fiber bundles and a polylactide polymer matrix (PLLA). Caustic soda treatment was employed to modify the strength of sisal fibers and to improve fiber to matrix adhesion. Mechanical properties of PLLA/sisal fiber composites improved with caustic soda treatment: the mean flexural strength and modulus increased from 279 MPa and 19.4 GPa respectively to 286 MPa and 22 GPa at a fiber volume fraction of V_f = 0.6. The glass transition temperature decreased with increasing fiber content in composites reinforced with untreated sisal fibers due to interfacial friction. The damping at the caustic soda‐treated fibers‐PLLA interface was reduced due to the presence of transcrystalline morphology at the fiber to matrix interface. It was demonstrated that high strength, high modulus sisal‐PLLA composites can be produced with effective stress transfer at well‐bonded fiber to matrix interfaces. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40999.     

The influence of chemical surface modification on the performance of sisal‐polyester biocomposites

This article concerns the effectiveness of various types and degrees of surface modification of sisal fibers involving dewaxing, alkali treatment, bleaching cyanoethylation and viny1 grafting in enhancing the mechanical properties, such as tensile, flexural and impact strength, of sisal‐polyester biocomposites. The mechanical properties are optimum at a fiber loading of 30 wt%. Among all modifications, cyanoethylation and alkali treatment result in improved properties of the biocomposites. Cyanoethylated sisal‐polyester composite exhibited maximum tensile strength (84.29 MPa). The alkali treated sisal‐polyester composite exhibited best flexural (153.94 MPa) and impac strength (197.88 J/m), which are, respectively, 21.8% and 20.9% higher than the corresponding mechanical properties of the untreated sisal‐polyester composites. In the case of vinyl grafting, acrylonitrile (AN)‐grafted sisal‐polyester composites show better mechanical properties than methyl‐methacrylate (MMA)‐grafted sisal composites. Scanning electron microscopic studies were carried out to analyze the fiber‐matrix interaction in various surface‐modified sisal‐polyester composites.     

Effects of alkaline and silane treatments on the water‐resistance properties of wood‐fiber‐reinforced recycled plastic composites

The water‐resistance properties of wood‐fiber‐reinforced recycled plastic composites (WRPCs) prepared from postconsumer high‐density polyethylene (HDPE) and wood fibers from saw mills were studied. Three methods consisting of an alkaline method (AM), a silane method (SM), and a combination of the alkaline and silane methods (ASM) were used to modify the wood fibers. The effects of fiber/matrix mix ratio and surface treatment on the moisture content, thickness swelling, and flexural strength change of the WRPCs, before and after immersion in 60°C water for 8 weeks, were studied and analyzed. The flexural fractured surfaces of the WRPCs before and after immersion in hot water were examined, and the fracture mechanism of the WRPCs was discussed. The results showed that the different surface treatments of the wood fibers had significant effects on the moisture content, thickness swelling, and flexural strength of the WRPCs after a long immersion time in hot water. For WRPCs treated by ASM, the moisture content was the lowest, the thickness swelling was at a minimum, and the flexural strength was the highest. Higher water absorption of composites with fiber treated by the AM or SM methods, as compared to those treated by ASM, could be attributed to the incomplete adhesion and wettability between the wood fibers and the polymer matrix, which may have caused more gaps and flaws at the interface. J. VINYL ADDIT. TECHNOL., 2008. © 2008 Society of Plastics Engineers.     

Mechanical properties of surface‐modified ultra‐high molecular weight polyethylene fiber reinforced natural rubber composites

The mechanical properties of ultra‐high molecular weight polyethylene (UHMWPE) fibers reinforced natural rubber (NR) composites were determined, and the effects of fiber surface treatment and fiber mass fraction on the mechanical properties of the composites were investigated. Chromic acid was used to modify the UHMWPE fibers, and the results showed that the surface roughness and the oxygen‐containing groups on the surface of the fibers could be effectively increased. The NR matrix composites were prepared with as‐received and chromic acid treated UHMWPE fibers added 0–6 wt%. The treated UHMWPE fibers increased the elongation at break, tear strength, and hardness of the NR composites, especially the tensile stress at a given elongation, but reduced the tensile strength. The elongation at break increased markedly with increasing fiber mass fraction, attained maximum values at 3.0 wt%, and then decreased. The tear strength and hardness exhibited continuous increase with increasing the fiber content. Several microfibrillations between the fiber and NR matrix were observed from SEM images of the fractured surfaces of the treated UHMWPE fibers/NR composites, which meant that the interfacial adhesion strength was improved. POLYM. COMPOS., 38:1215–1220, 2017. © 2015 Society of Plastics Engineers     

Curing characteristics and mechanical properties of alkali‐treated grass‐fiber‐filled natural rubber composites and effects of bonding agent

To improve adhesion between fiber and matrix, natural rubber was reinforced with a special type of alkali‐treated grass fiber (Cyperus Tegetum Rox b). The cure characteristics and mechanical properties of grass‐fiber‐filled natural rubber composites with different mesh sizes were studied with various fiber loadings. Increasing the amount of fibers resulted in the composites having reduced tensile strength but increased modulus. The better mechanical properties of the 400‐mesh grass‐fiber‐filled natural rubber composite showed that the rubber/fiber interface was improved by the addition of resorcinol formaldehyde latex (RFL) as bonding agent for this particular formulation. The optimum cure time decreased with increases in fiber loading, but there was no appreciable change in scorch time. Although the optimum cure time of vulcanizates having RFL‐treated fibers was higher than that of the other vulcanizates, it decreased with fiber loading in the presence of RFL as the bonding agent. But this value was lower than that of the rubber composite without RFL. Investigation of equilibrium swelling in a hydrocarbon solvent was also carried out. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 3151–3160, 2006     

Effects of poly(dimethyl siloxane) on the water absorption and natural degradation of poly(lactic acid)/oil‐palm empty‐fruit‐bunch fiber biocomposites

Composites were fabricated with poly(lactic acid) and oil‐palm empty‐fruit‐bunch (EFB) fibers with extrusion; this was followed by an injection‐molding technique. Before compounding, the surface of the fiber was modified through ultrasound and poly(dimethyl siloxane) (PDMS). The influences of the ultrasound and PDMS on the water absorption and biodegradability of the composites were investigated. Additionally, the composites were buried under soil for 6 months, and their biodegradability was assessed through different characterization techniques, such as tensile testing and weight loss and diffussability measurement. The changes on the surface of the fibers due to treatment were examined by scanning electron microscopy analysis, and the influences on the biodegradability of the composites were observed. Functional group analysis and possible changes before and after degradation were also examined by a Fourier transform infrared spectrophotometric technique. The results analyses revealed that the treatment of fibers improved the density of the fibers and reduced the water uptake of the composites. The overall weight loss due to soil burial testing was found to be maximum for the untreated‐fiber‐based composites (6.8%), whereas the ultrasound‐ and silane‐treated composites showed the minimum value of weight loss (3.7%). The deterioration of the tensile strength due to degradation was found to be at a maximum for the untreated‐fiber‐based composite (27%), whereas the ultrasound‐ and silane‐treated‐fiber‐based composites showed a minimum value of 8%. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42784.     

The use of Isocyanate as a Bonding Agent to Improve the Mechanical Properties of Polyethylene-Wood Fiber Composites

Abstract

Chemithermomechanical pulp (CTMP) of aspen was used as a filler in high density (HDPE) and linear low density (LLDPE) polyethylenes. To improve the bonding between the fiber and polymer, different chemical treatments of the fiber a) treatment with different isocyanates b) coating with maleic anhydride was carried out. Composites with isocyanate treated wood fibers produced higher tensile strength compared to untreated fiber composites. But when compared to diisocyanate, the polyisocyanate treated fibers produced higher gain in strength. HDPE or LLDPE filled with maleic anhydride coated CTMP aspen fibers showed a slight decrease in strength with the increase in filler concentration. Tensile modulus generally increased with filler loading and was not much affected by fiber treatment.     

Properties of ligno‐cellulose fiber Hildegardia

Studies on some properties such as the density, the degradation temperatures, the morphology and the spectral features of the ligno‐cellulose fiber Hildegardia were carried out in both untreated and alkali treated form. The fibers are found to have good morphology and moderate initial and final degradation temperatures. On alkali treatment, the lignin was found to be eliminated. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 2216–2221, 2002     

Unidirectional hemp and flax EP‐ and PP‐composites: Influence of defined fiber treatments

In some technical areas, mainly in the automotive industry, glass fiber reinforced polymers are intended to be replaced by natural fiber reinforced polymer systems. Therefore, higher requirements will be imposed to the physical fiber properties, fiber‐matrix adhesion, and the quality assurance. To improve the properties of epoxy resins (EP) and polypropylene (PP) composites, flax and hemp fibers were modified by mercerization and MAH‐PP coupling agent was used for preparing the PP composites. The effects of different mercerization parameters such as concentration of alkali (NaOH), temperature, and duration time along with tensile stress applied to the fibers on the structure and properties of hemp fibers were studied and judged via the cellulose I–II lattice conversion. It was observed that the mechanical properties of the fibers can be controlled in a broad range by using appropriate mercerization parameters. Unidirectional EP composites were manufactured by the filament winding technique; at the PP matrix material, a combination with a film‐stacking technique was used. The influence of mercerization parameters on the properties of EP composites was studied with hemp yarn as an example. Different macromechanical effects are shown at hemp‐ and flax‐PP model composites with mercerized, MAH‐PP‐treated, or MAH‐PP‐treated mercerized yarns. The composites' properties were verified by tensile and flexural tests. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 2150–2156, 2004     

Non‐traditional lightweight polypropylene composites reinforced with milkweed floss

Lightweight composites are preferred for automotive applications due to the weight restrictions and also due to the presence of inherent voids that can enhance the sound absorption of these composites. The density of the reinforcing materials plays a crucial role in such lightweight composites. Milkweed is a unique natural cellulose fiber that has a completely hollow center and low density (0.9 g cm^?3) unlike any other natural cellulose fiber. The low density of milkweed fibers will allow the incorporation of higher amounts of fiber per unit weight of a composite, which is expected to lead to lightweight composites with better properties. Polypropylene (PP) composites reinforced with milkweed fibers have much better flexural and tensile properties than similar PP composites reinforced with kenaf fibers. Milkweed fiber‐reinforced composites have much higher strength but are stiffer than kenaf fiber‐reinforced PP composites. Increasing the proportion of milkweed in the composites from 35 to 50% increases the flexural strength but decreases the tensile strength. The low density of milkweed fibers allows the incorporation of higher amounts of fibers per unit weight of the composites and hence provides better properties compared to composites reinforced with common cellulose fibers with relatively high density. This research shows that low‐density reinforcing materials can more efficiently reinforce lightweight composites. Copyright © 2010 Society of Chemical Industry     

Influence of alkali‐treated fibers on the mechanical properties and machinability of roselle and sisal fiber hybrid polyester composite

In this work, the alkali‐treated roselle and sisal fibers were used as reinforcement fillers for thermosetting matrix with aim of obtaining better mechanical properties and machinability of natural fiber hybrid polyester composite. However, their mechanical properties and machinability were compared with untreated fiber composites. The roselle and the sisal fibers were subjected to a 10% sodium hydroxide solution treatment at different duration of 2, 4, 6, and 8 h. Besides, the fractured surfaces of composite specimen were investigated using scanning electron microscopy. Drill hole profiles were analyzed using profile projector and machine vision inspection system. An improvement in strength and stiffness combined with high toughness was achieved by treating the fibers using 10% NaOH solution. POLYM. COMPOS., 2010. © 2009 Society of Plastics Engineers