Green composites. I. physical properties of ramie fibers for environment-friendly green composites

The surface topography, tensile properties, and thermal properties of ramie fibers were investigated as reinforcement for fully biodegradable and environmental-friendly ‘green’ composites. SEM micrographs of a longitudinal and cross-sectional view of a single ramie fiber showed a fibrillar structure and rough surface with irregular cross-section, which is considered to provide good interfacial adhesion with polymer resin in composites. An average tensile strength, Young’s modulus, and fracture strain of ramie fibers were measured to be 627 MPa, 31.8 GPa, and 2.7 %, respectively. The specific tensile properties of the ramie fiber calculated per unit density were found to be comparable to those of E-glass fibers. Ramie fibers exhibited good thermal stability after aging up to 160°C with no decrease in tensile strength or Young’s modulus. However, at temperatures higher than 160°C the tensile strength decreased significantly and its fracture behavior was also affected. The moisture content of the ramie fiber was 9.9%. These properties make ramie fibers suitable as reinforcement for ‘green’ composites. Also, the green composites can be fabricated at temperatures up to 160°C without reducing the fiber properties.     

Green composites. II. Environment-friendly, biodegradable composites using ramie fibers and soy protein concentrate (SPC) resin

Fully biodegradable and environment-friendly green composite specimens were made using ramie fibers and soy protein concentrate (SPC) resin. SPC was used as continuous phase resin in green composites. The SPC resin was plasticized with glycerin. Precuring and curing processes for the resin were optimized to obtain required mechanical properties. Unidirectional green composites were prepared by combining 65 % (on weight basis) ramie fibers and SPC resin. The tensile strength and Young’s modulus of these composites were significantly higher compared to those of pure SPC resin. Tensile and flexural properties of the composite in the longitudinal direction were moderate and found to be significantly higher than those of three common wood varieties. In the transverse direction, however, their properties were comparable with those of wood specimens. Scanning electron microscope (SEM) micrographs of the tensile fracture surfaces of the green composite indicated good interfacial bonding between ramie fibers and SPC resin. Theoretical values for tensile strength and Young’s modulus, calculated using simple rule of mixture were higher than the experimentally obtained values. The main reasons for this discrepancy are loss of fiber alignment, voids and fiber compression due to resin shrinking during curing.     

Synthesis and application of ramie fiber soft modifier comprised of carboxylate-containing polymer

In effort to improve the soft properties of ramie fiber, we synthesized a carboxylate-containing polymer for use as a modifying agent, and successfully modified the ramie fiber in a strong base with the carboxylate-containing polymer. We applied Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), thermogravimetric analysis (TGA), and scanning electron microscopy (SEM) to investigate the structures of the raw and modified ramie fibers, and further investigated the mechanical and dyeing properties of the raw and modified ramie fibers. The results showed that the surface of the ramie fiber underwent significant changes due to the grafting reaction of the carboxylate-containing polymer and fiber. After the chemical modification, the flexural strength and initial modulus of the modified ramie fiber decreased while tensile strength increased, indicating that the softness of the modified ramie fiber increased though its tensile resistance remained high. In addition, the fixation of reactive dyes on the modified ramie fiber was larger than that of the reactive dyes on the raw ramie fiber. Our observations of mechanical properties and dye fixation indicated that the carboxylate-containing polymer is an effective and efficient soft modifier.     

Effects of surface treatment of ramie fibers in a ramie/poly(lactic acid) composite

The chemical and morphological properties of ramie fibers treated by chemical surface modification were examined with Fourier transform infrared (FT-IR) spectroscopy. The mechanical and thermal decomposition properties were evaluated with respect to tensile strength, tensile modulus and thermogravimetric analysis (TGA). Surface morphological changes were investigated with scanning electron microscopy (SEM). Finally, the capabilities of composites reinforced with various chemically treated fibers were analyzed by investigating tensile and impact strengths. Additionally, the thermal mechanical properties of the composites were investigated with thermal mechanical analysis (TMA). Based on the results of these analyses, we concluded that pectin, lignin and hemicellulose were removed and thermal stability was increased with chemical treatments. The composites reinforced with ramie fiber showed better properties compared with pure PLA matrix with respect to tensile and impact strengths. The peroxide-treated fiber composite had the smallest thermal expansion.     

Effect of water and fiber length on the mechanical properties of polypropylene matrix composites

This paper presents the results of a current study on polypropylene matrix composites processed by injection, with two different glass fiber lengths and five different volume fractions. Physical and mechanical properties were obtained, namely flexural strength, stiffness modulus and fracture toughness. The mechanical properties of the composites increased significantly with the increase of the fibers volume fraction in agreement with the Counto model. The effect of water immersion time was also analysed. Immersion in water promotes a marked decrease in mechanical properties in the early seven-ten days, and afterwards tends to stabilize. Water causes a decrease of the relative strength which increases with fiber volume fraction and reaches about 29 % and 32 % for 20 % of 4.5 mm fiber length and for 25 % of 12 mm fiber length respectively, after 28 days immersion in water. Fracture toughness increases with fiber volume fraction and is always higher for 12 mm fiber length composites than for 4.5 mm fiber length composites.     

Potential of using polyester reinforced coconut fiber composites derived from recycling polyethylene terephthalate (PET) waste

Unsaturated polyester resin synthesized from glycolyzed product of polyethylene terephthalate (PET) waste was used as a matrix to form coconut fiber/polyester composites. PET wastes were recycled through glycolysis and polyesterification reaction to produce a formulation for unsaturated polyester resin (UPR). FTIR spectra of glycolyzed product and prepared resin revealed that cross-links between unsaturated polyester chain and styrene monomer occurred at the saturated sites which resulted in the forming of cross linking network. To improve the adhesion between coconut fiber and polyester resin, various concentrations of alkali, silane and silane on alkalized fiber were applied and the optimum concentration of treatments was determined. The influence of water uptake on the sorption characteristics of composites was studied via immersion in distilled water at room temperature. Surface treatment of coconut fiber caused a significant increase in the tensile properties with the optimum treatment is 0.5 % silane on the 5 % alkalized coconut fiber/polyester composites. It was also observed that the treated fiber composites showed lower water absorption properties in comparison to those of untreated fiber composites. This observation was well supported by the SEM investigations of the fracture surfaces. From the study, it was concluded that polyester reinforced coconut fiber composites derived from recycling polyethylene terephthalate (PET) waste may have the potential application in the fields of construction and automotive interior substrates.     

Bioprocess preparation of wheat straw fibers and their characterization

Plant fiber reinforced thermoplastic composites have gained much attraction in structural applications such as building and automotive products. Agricultural residues such as wheat straw, bagasse, and corn stover can also be exploited as readily available natural fiber resources for similar applications. The objective of this study was to extract fibers from wheat straw and also to determine the usefulness of fungal retting of wheat straw before extracting the fibers. Wheat straw was mechanically defibrillated using a laboratory-scale mechanical refiner before and after fungal retting. Fiber characteristics such as physico-chemical and mechanical properties, surface characteristics, and thermal properties of the resultant fibers were measured in order to explore the possibilities of using the fibers as reinforcing materials. Retted fibers were stronger than un-retted fibers. The length and diameter of the retted fibers were lower than the un-retted fibers. FT-IR spectroscopic analysis of the wheat straw fibers indicated the fractional removal of hemicelluloses and lignin from the retted fiber. X-ray photoelectron spectroscopy (XPS) of the fibers showed the partial removal of extractives from the surface of the retted fibers. Also, the oxygen to carbon ratio (O/C) of the fibers illustrated that there is more lignin type surface structure for both retted and un-retted fibers. However, slightly higher ratio of oxygen to carbon in the retted fiber indicated a more carbohydrate-rich fiber than the un-retted fiber. Thermal degradation characteristics demonstrated the suitability of processing wheat straw fibers with thermoplastics.     

Performances of ramie fiber pretreated with dicationic imidazolium ionic liquid

The chemical structure of a new gemini dicationic imidazolium ionic liquid, 3,3′-[1,2-ethanediylbis (oxy-2,1-ethanediyl)]-bis[1-methyl-imidazolium]-dibromide (PEG₁₅₀-DIL) was established by ¹H-NMR and elemental analyses. Then, PEG₁₅₀-DIL was applied to pretreat ramie fiber. PEG₁₅₀-DIL treated ramie fiber was characterized by FT-IR, XRD, DSC-TG and FE-SEM. Finally, the mechanical and dyeing properties of PEG₁₅₀-DIL pretreated ramie fibers were studied. The optimum condition of PEG₁₅₀-DIL modification was carried out at 100 °C for 30 min. The color strength increased obviously with the duration time and temperature of the PEG₁₅₀-DIL. The tensile strength and strength retention of PEG₁₅₀-DIL -treated ramie fibers decreased with the increase of pretreating time and temperature. The tensile strength retention was 86.20 % under optimal PEG₁₅₀-DIL pretreating condition (100 °C, 30 min).     

Influence of chemically modified short hemp fiber structure on biosorption process of Zn2+ ions from waste water

Short hemp fibers, acquired as a waste from textile industry, were used as an efficient biosorbent for removal of zinc ions from polluted water. In order to obtain the material with better sorption properties, short hemp fibers were subjected to oxidative and alkali treatment. The following factors that may influence the sorption properties of short hemp fibers were examined: fiber structure and morphology were characterized by iodine sorption, water retention and scanning electron microscopy, while specific surface area was determined by BET method. Additionally, the amount of carboxyl groups was determined by calcium-acetate method, and the point of zero charge of the short hemp fibers samples was determined by the solid addition method. Biosorption of zinc ions was evaluated through the total uptake capacity, equilibrium and kinetic data. Obtained data were analyzed by nonlinear Langmuir and Freundlich isotherms, as well as pseudo-first and pseudo-second order kinetic models, and the best fitting model was chosen using Akaike information criterion. Chemical modification, used in this work, leads to structural and morphological changes of short hemp fibers, and improvement of their sorption properties. It was found that sorption properties of short hemp fibers are predominantly influenced by surface acidity and the amount of functional groups, while fiber structure and specific surface area have a secondary role in the biosorption of zinc ions. Akakike information criterion values showed that biosorption of zinc ions on all tested hemp fiber samples obey the pseudo-second order adsorption kinetics, while experimental isotherm data fit better with Langmuir model. Biosorption of zinc ions on the hemp fibers is a predominantly chemical process, which mainly follows the mechanism of ion exchange on acidic functional groups, and occurs through the fast surface adsorption, intraparticle diffusion and final equilibrium stage.     

Effect of chemical modifications on the performance of biodegradable photocured coir fiber

Coir fibers (Cocos nucifera) were treated with 1-ethyl-2-pyrrolidone (1-E-2-P) mixed with methanol (MeOH) under UV radiation. A series of solutions of different concentrations of 1-E-2-P in methanol along with a photoinitiator, Darocur-1173, were prepared. Monomer concentration, soaking time, and radiation dose were optimized in terms of grafting and mechanical properties. Ten percent 1-E-2-P, 6 min soaking time, and a 15th pass of radiation produced higher tensile strength (53 %) and elongation at break (230 %) than those of virgin fiber, as well as the highest grafting value (4.9 %). The effect of additives (1 %), such as urea and silane (3-trimethoxysilyl propyl methacrylate) on the properties of coir fiber was studied. Among the additives used, silane showed the best performance. For further improvement of the properties, the fibers were treated with alkali (potassium hydroxide) solution of different temperatures (0–60 °C). A 10 % alkali-treated fiber showed the best properties such as grafting (6.2 %), tensile strength (72 %) and elongation at break (330 %) over virgin fiber. The silane-treated fiber produced the minimum loss of the properties, as well as a lower water uptake than those of the untreated one. The effect of simulating weathering on the degradation properties of samples was also performed.     

Preparation,mechanical properties and microstructure of polyoxymethylene fiber through melt spinning and hot drawing by using injection-molding grade resins

The polyoxymethylene (POM) fiber was melt spun by use of different commercial grades of POM resin, and the effect of post-drawing on mechanical properties and microstructures was investigated extensively. The fiber obtained from the POM resin with a higher melt flow index (MFI) exhibits a better hot-drawing capability and also achieves a greater ultimate draw ratio. The mechanical evaluation reveals that the tensile strength and elastic modulus of POM fiber are improved significantly after post-drawing compared to the as-spun fibers. Although the greater draw ratios result in higher mechanical strength and modulus for the POM fiber, the fiber obtained from the POM resin with an MFI of 13.0 g/10 min achieves the optimal mechanical performance at the ultimate draw ratio. The morphologic and structural developments of POM fiber were studied by scanning electronic microscopy and X-ray powder diffraction. The results indicate that the POM fiber spun by the resin with an MFI of 13.0 g/10 min has a smooth lateral surface and a compact cross section after post-drawing. The fiber samples spun by the POM resins with low MFIs show some hollow disfigurements as well as a rough surface at the ultimate draw ratio, whereas the fiber obtained from the resin with a high MFI of 27.0 g/10 min presents the ununiformity of diameter after post-drawing. The POM fibers achieve a crystalline orientation during the hot-drawing process, which results in a transformation from the spherulitic crystals to the lamellar structure in the drawing direction. The level of crystalline orientation can be improved with an increase of draw ratio and thus results in a high modulus and strength for the resulting POM fiber samples. In addition, the thermal analysis indicates that the crystallinity of the as-spun fibers can be enhanced by post-drawing due to the orientation-induced crystallization.     

Effects of the reaction degree of melamine-formaldehyde resin on the structures and properties of melamine-formaldehyde/polyvinyl alcohol composite fiber

Composite fibers made of polyvinyl alcohol (PVA) and melamine-formaldehyde (MF) resins with different reaction degrees were prepared by wet spinning. The phase structures of MF/PVA spinning dopes and composite fibers were observed by using optical microscope (OM) and scanning electron microscope with energy-dispersive X-ray spetroscopy (SEM-EDS). Crystal structures of composite fibers were studied by X-ray diffraction (XRD) and differential scanning calorimetry (DSC). The loss of MF resins in the spinning process was calculated by using Kjeldahl. The mechanical properties, the flame retardant property, the water resistant property, and the thermal stability of composite fibers were also tested. Results show that with an increase in the reaction degree of MF resin, the phase separation degrees of spinning dopes and composite fibers rise up, the size of MF microphase grows larger, and the loss of MF resin diminishes; consequently, the hot water resistance and the flame retardancy of the fiber ameliorate while the tensile strength and the thermal stability perform a tendency of dropping after rising.     

Study on mechanical and thermal properties of fiber-reinforced Epoxy/Hybrid-silica composite

Recently, carbon fiber composites have been widely used as structural reinforcement materials of buildings, replacing reinforcing bars or concrete. And the increase in use of super fibers such as aramid and high strength PE, which is aimed at improving the reinforcement properties, has resulted in a demand for a resin system with excellent mechanical and thermal properties. In this research, a fiber-reinforced composite has been produced by using the super fibers such as carbon fiber or aramid fiber, reinforcement resin and the silica hybrid compound containing epoxy group. This study was carried out to confirm the effect of the silica hybrid on mechanical properties, heat resistance and adhesion strength of a fiber-reinforced epoxy composite, which was produced by blending silica or introducing silica hybrid through covalent bonds. And the silica hybrid containing epoxy group, which may be introduced to the structure of fiber-reinforced epoxy composite through covalent bonds caused by reaction with a hardener, has been used, so that the heat resistance and adhesion strength could be improved.     

Mechanical and thermal properties of recycled poly(ethylene terephthalate) reinforced newspaper fiber composites

This study presents the mechanical and thermal properties of environment-friendly composites made from recycled newspaper fibers reinforced recycled poly(ethylene terephthalate) (rPET) resin with the addition of styrene-ethylene-butylene-styrene grafted maleic anhydride (SEBS-g-MA) as compatibilizer. The effect of SEBS-g-MA addition (i.e., 10 phr) by using a twin-screw extruder to the rPET resin, followed by different fiber content (5, 10 and 15 wt.%) on the tensile, flexural and impact properties of the composites were determined. Stiffness of composites increased significantly compared to those of rPET/SEBS-g-MA blend. Fiber addition resulted in moderate increases in both tensile and flexural strength of the composites. Scanning electron microscope (SEM) photomicrographs of the impact fracture surfaces demonstrate good adhesion at 5 and 10 % fiber content. Differential scanning calorimetry (DSC) showed that the presence of newspaper fibers enhanced the nonisothermal crystallization kinetics and crystallinity. Thermal stability of the composites was improved as indicated by thermogravimetric analysis (TGA).     

Effects ofIn Vitro degradation on the weight loss and tensile properties of PLA/LPCL/HPCL blend fibers

PLA/LPCL/HPCL blend fibers composed of poly (lactic acid) (PLA), low molecular weight poly (ɛ-caprolactone) (LPCL), and high molecular weight poly (ɛ-caprolactone) (HPCL) were prepared by melt blending and spinning for bioabsorbable filament sutures. The effects of blending time and blend composition on the X-ray diffraction patterns and tensile properties of PLA/LPCL/HPCL blend fibers were characterized by WAXD and UTM. In addition, the effect ofin vitro degradation on the weight loss and tensile properties of the blend fibers hydrolyzed during immersion in a phosphate buffer solution at pH 7.4 and 37°C for 1–8 weeks was investigated. The peak intensities of PLA/LPCL/HPCL blend fibers in X-ray diffraction patterns decreased with an increase of blending time and LPCL contents in the blend fibers. The weight loss of PLA/LPCL/HPCL blend fibers increased with an increase of blending time, LPCL contents, and hydrolysis time while the tensile strength and modulus of the blend fibers decreased. The tensile strength and modulus of the blend fibers were also found to be increased with an increase of HPCL contents in the blend fibers. The optimum conditions to prepare PLA/LPCL/HPCL blend fibers for bioabsorbable sutures are LPCL contents of 5 wt%, HPCL contents of 35 wt%, and blending time of 30 min. The strength retention of the PLA/LPCL/HPCL blend fiber prepared under optimum conditions was about 93.5% even at hydrolysis time of 2 weeks.     

Modification of ramie with 1-butyl-3-methylimidazolium chloride ionic liquid

For a long time, alkali is the main modification reagent for ramie modification due to its good effect and low cost. However, the large consumption of alkali in the processing leads to a serious pollution to the environment. To develop a new eco-friendly modification method, a mixed green solvent composed of 95 wt% 1-butyl-3-methylimidazolium chloride ionic liquid and 5 wt% water was employed in the paper. The swelling ratio, surface composition and crystal index was studied in detail with video microscope, FTIR and XRD analysis. Results showed that the solvent system had a distinct swelling effect on ramie. The crystal index of ramie fiber decreased from 74.2 % to 54.5 % after the treatment. Otherwise, the modification also removed some gummy substances including 75 % content of pectin in ramie. These changes improved the wetability and dyeing properties of ramie. However, the treatment also did much harm to the tensile strength.     

Effect of hybrid post treatments on the structural property and water flux of polysulfone hollow fiber membrane

The application of post treatments in preparation of high flux membranes is expanding rapidly. In this work, several hybrid post treatments have been introduced and used for change in the water flux of polysulfone (PSf) hollow fiber membranes. Dry wet spinning method was employed for fabrication of PSf hollow fiber membrane from spinning dope in mass ratio of 15:5:80 of PSf/PVP-K90/NMP. The simultaneous effects of single and hybrid post treatments containing traditional hypochlorite; high pressure injection technique (HPI) of hypochlorite, hot air and hot water treatments on the morphology and water flux of fabricated hollow fibers has been investigated. AFM analysis and image processing of SEM microphotographs of hollow fibers were used for structural studies. The mechanical properties of hollow fibers as well as strain at break and strength also were studied. It was found that the pores size and surface roughness parameter of hollow fiber membranes have been increased after traditional hypochlorite, HPI technique and hot water treatments while decreased when heat treated in air. In general all the employed hybrid post treatments caused to increase in the pores size of hollow fibers although the pores size increase rate in the membranes treated by the hybrid post treatments involving hot air was much lower than the others. The mechanical properties of hollow fibers have been decreased after hybrid and single post treatments containing traditional hypochlorite, HPI technique and hot water treatment while slightly increased after post treatments containing hot air. It was stated that the fabricated PSf hollow fibers were considerably affected by the employed hybrid post treatments. This can be attributed to the combine effects of used post treatments.     

Influence of alkaline metal ions on flame retardancy and thermal degradation of cellulose fibers

Cellulose-Na and cellulose-K fibers are obtained by alkalization and etherification of viscose fiber. Flame retardancy and thermal degradation of cellulose-Na and cellulose-K fibers are investigated using limiting oxygen index (LOI), cone calorimetry (CONE), thermal gravimetry (TG), and differential TG (DTG). The LOI values of cellulose-Na and cellulose-K fibers are 33 and 30, compared with about 20 for viscose fiber. In CONE studies, cellulose-Na and cellulose-K fibers show much lower heat release rates, total heat release and effective heats of combustion than viscose fiber does. In addition, TG and DTG studies reveal that the second initial degradation temperature, the temperature of maximum degradation rate and the maximum degradation rate for cellulose-Na and cellulose-K fibers are much lower than those of viscose fiber. Cellulose-Na and cellulose-K fibers generate much more residue or carbonaceous char than viscose fiber does. Scanning electron microscopy studies of combustion residues after LOI testing indicate that cellulose-Na and cellulose-K fibers produce massive, thick residue crusts.     

麻纤维厌氧生物脱胶系统的脱胶特性研究

基于具有自主知识产权的麻纤维厌氧生物脱胶系统,对苎麻、剑麻、大麻和棕榈麻进行厌氧脱胶处理。结果表明:该系统运行过程中pH值稳定在7.2左右,化学需氧量(COD)在327 mg/L以下,氨氮质量浓度在5.2 mg/L以下,能实现近零排放;试验参数条件下苎麻脱胶效果优于剑麻、大麻和棕榈麻:苎麻纤维残胶率可达1.32%(低于化学脱胶),剑麻、大麻和棕榈麻残胶率分别为16.03%、20.13%、35.49%;各纤维强力指标能够达到传统化学脱胶法水平,其中苎麻的各项指标满足《苎麻精干麻》(GB/T 20793-2015)的一等水平。     

Effects of recycling processes on physical, mechanical and degradation properties of PET yarns

Mechanical properties and the long-term degradation properties of the recycled PET yarns are typically lower than the virgin PET yarns due to the contaminants coming from non-PET bottles, labels and caps etc. For environmental reasons, recycling of post-consumer polyester bottles into textile fibers has become commercially attractive. We studied mechanical and chemical recycling processes and examined their effects on yarn properties such as tensile properties, thermal characteristics, hydrolysis and photo-degradation. It was found that the virgin and the chemical recycled yarns with sufficient purification show similar processability, physical and mechanical properties, and long-term degradation behavior. The results provide useful information on recycled PET yarns for processability and serviceability for the high-end use.