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.     

Preparation,Characterization and Properties of High-salt-tolerance Sodium Alginate/Krill Protein Composite Fibers

Sodium alginate (SA) and krill protein (AKP) were blended to obtain composite solution, and functional SA/AKP composite fibers were prepared via wet spinning. To further improve the salt tolerance, SA/AKP composite fibers were modified with copper sulfate aqueous solution as secondary coagulation bath because of the strong adsorption to copper ions. The CSA/AKP composite fibers with high salt tolerance have been successfully prepared. The intermolecular interaction of SA/AKP composite system and the two-order structure of protein in the composite system were characterized by Fourier transform infrared spectroscopy (FT-IR). Besides, the crystallinity, morphology, mechanical properties, salt tolerance and water resistance and thermal stability of SA/AKP composites were investigated respectively. The results showed that the adsorption rate and the adsorption capacity of the composite solution to copper ion were significantly higher than those to calcium ion. Under the effect of secondary solidification by copper sulfate, the β-sheet chain of the composite fibers increased from 41.48 % to 49.21 %, the intramolecular hydrogen bond increased from 38.18 % to 44.26 %, the intermolecular hydrogen bond decreased from 59.84 % to 54.70 % and free hydroxyl slightly decreased. The water resistance of the modified composite fibers was improved by about 22 %; when the swelling time was 25 min, the salt resistance increased by about 150 %; the number of grooves on the surface of the composite fibers obviously increased, and the grooves on the surface of CSA/AKP composite fibers and the fiber section structure were much denser; Meanwhile, copper sulfate had some influence on the crystallization, thermal stability and mechanical properties of the composite fibers.     

Fabrication and characterization of polyamide6-room temperature ionic liquid (PA6-RTIL) composite nanofibers by electrospinning

In the present work, polyamide6-room temperature ionic liquid (PA6-RTIL) composite nanofibers and membranes were successfully prepared for the first time by an electrospinning technique. The surface morphology, component analysis, mechanical properties, thermal properties and conductivity of the PA6-RTIL composite membranes were investigated by field-emission scanning electron microscope (FE-SEM), fourier transform infrared spectrometer (FT-IR), tensile testing, thermogravimetric analysis (TGA), differential scanning calorimetry (DSC) and digit multimeter, respectively. The morphology, fiber diameter, mechanical strength of the obtained fibers can be controlled by changing experimental parameters for electrospinning, especially the content of RTIL in original electrospun mixture solution. The composite fibrous membranes showed ideal mechanical properties and significantly enhanced conductivity, which may be attributed to intrinsic high mechanical strength of PA6 and conductivity of RTIL.     

Preparation and characterization of PVA/PU blend nanofiber mats by dual-jet electrospinning

A series of blend nanofiber mats comprising poly(vinyl alcohol) (PVA) and polyurethane (PU) were prepared by dual-jet electrospinning in various parameters. Orthogonal experimental design was used to investigate how those parameters affected on fiber diameters and fiber diameter distribution. Altogether three parameters having three levels each were chosen for this study. The chosen parameters were tip-to-collector distance (TCD), voltage and tip-to-tip distance (TTD). Fiber diameters, thermal properties, mechanical properties and hydrophilicity of the blend nanofiber mats were examined by scanning electron microscopy (SEM), thermogravimetric analysis (TGA), tensile test, contact angle and water absorption test, respectively. The results showed that the optimum conditions for PVA/PU blend nanofiber mats fabricated by dual-jet electrospinning were TCD of 20 cm, voltage of 18 kV and TTD of 4 cm. Besides, the thermal stability of PVA/PU blend nanofiber mats had been improved compared with pure nanofibers. Furthermore, the elongation and tensile strength of the blend nanofiber mats were significantly increased compared with pure PVA and pure PU, respectively. And the blend nanofiber mats exhibited well hydrophilicity.     

Structure and properties of syndiotactic polystyrene fibers prepared in high-speed melt spinning process

High-speed melt spinning of syndiotactic polystyrene was carried out using high and low molecular weight polymers, HMs-PS and LMs-PS, at the throughput rates of 3 and 6 g/min. The effect of take-up velocity on the structure and properties of as-spun fibers was investigated. Wide angle X-ray diffraction (WAXD) patterns of the as-spun fibers revealed that the orientation-induced crystallization started to occur at the take-up velocities of 2–3 km/min. The crystal modification wasα-form. Birefringence of as-spun fibers showed negative value, and the absolute value of birefringence increased with an increase in the take-up velocity. The cold crystallization temperature analyzed through the differential scanning calorimetry (DSC) decreased with an increase in the take-up velocity in the low speed region, whereas as the melting temperature increased after the on-set of orientation-induced crystallization. It was found that the fiber structure development proceeded from lower take-up velocities when the spinning conditions of higher molecular weight and lower throughput rate were adopted. The highest tensile modulus of 6.5 GPa was obtained for the fibers prepared at the spinning conditions of LMs-PS, 6 g/min and 5 km/min, whereas the highest tensile strength of 160 MPa was obtained for the HMs-PS fibers at the take-up velocity of 2 km/min. Elongation at break of as-spun fibers showed an abrupt increase, which was regarded as the brittle-ductile transition, in the low speed region, and subsequently decreased with an increase in the take-up velocity. There was a universal relation between the thermal and mechanical properties of as-spun fibers and the birefringence of as-spun fibers when the fibers were still amorphous. The orientation-induced crystallization was found to start when the birefringence reached — 0.02. After the starting of the orientation-induced crystallization, thermal and mechanical properties of as-spun fibers with similar level of birefringence varied significantly depending on the processing conditions.     

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.     

Preparation of self-clustering highly oriented nanofibers by needleless electrospinning methods

Polyacrylonitrile (PAN) oriented nanofibers were produced by homemade needleless electrospinning device. Spiral coils were adopted to replace the traditional spinning needles in this equipment. The tracks of multi-jets were controlled by adjusting the microcurrent during the eletrospinning process. The microcurrent value and the motion track of the spinning jet during the spinning process were observed, the fiber morphology and the mechanical properties of fiber membranes were measured. The results revealed that the average diameters of the electrospun fibers were increased from 490 nm to 740 nm. with the addition of organic salt. Meanwhile, the self-clustering phenomenon was obviously observed, and the mechanical properties of obtained fibers were also altered, the tensile strength was improved from 3.63 MPa to 23.90 MPa, while the strain decreased from 74.6 % to 27.1 %.     

Experimental study on structure and mechanical properties of hemp/PBTG composites with fiber contents and thermal exposures

Most materials used in daily life are polymeric materials based on petrochemistry. The used polymeric materials can cause land pollution and air pollution after landfill or incineration. In contrast, natural fiber reinforced (NFR) composites are more suitable for the environment, however the reliability in terms of the durability and weatherability of NFR composites is still lacking. Thus, NFR composites require the reliability involved with durability and weatherability. In this work, poly(butylene terephthalate-co-glutarate) (PBTG), with a chemical structure similar to biodegradable PBAT, was used as the matrix in the composites, and hemp fibers were used as the reinforcement. Hemp/PBTG composites were fabricated by stacking hemp-fiberwebs and PBTG films with various fiber contents and thermal exposure times. Characteristics of the composites, such as the morphological structure, chemical structure, tensile properties, compressive properties, flexural properties, and impact strength, were analyzed to obtain the effects of fiber volume fraction and thermal exposure. As a result, hemp/PBTG composites were hardened in proportion to fiber volume fractions, and the hardening behavior of the composites increased tensile strength and flexural strength. However, the hardened structure of the composites decreased the impact strength and compressive strength of the composites. On the other hand, the mechanical properties of hemp/PBTG composites with thermal exposure times, were governed significantly by the brittleness behavior of the resin and the increased crystallinity of hemp fibers. Thus, the hemp fibers contributed to the improvements on structural stability, tensile strength and flexural strength of the hemp/PBTG composites, and increased the thermal durability of the composites with various thermal exposures.     

Novel high flux nanofibrous composite membrane based on polyphenylsulfone thin barrier layer on nanofibrous support

A novel thin film nanofibrous composite (TFNC) polyphenylsulfone (PPSU) membrane was fabricated by casting a thin PPSU barrier layer on the surface of the electrospun nanofibrous PPSU support. Polyethylene glycol (PEG) 400 was applied in the electrospinning solution to prevent the penetration of coating solution into the support. The membrane morphology and filtration performance were investigated via scanning electron microscopy (SEM), and filtration of canned beans production wastewater, respectively. Atomic force microscopy (AFM) was utilized to evaluate the surface roughness of the membranes. Furthermore, the mechanical strength and thermal stability of the membranes were determined via tensile test and thermogravimetric analysis (TGA). Comparison of the TFNC membrane and the unsupported membrane prepared through the wet phase inversion method with almost equal rejection values indicated a 2.3 fold higher PWF using the former.     

Fabrication and properties of dope-dyed Poly(m-phenylene isophthalamide) fibers via wet spinning

Poly(m-phenylene isophthalamide) (PMIA) fibers play an irreplaceable role in the area of high-temperature resistance. It is usually difficult to dye PMIA fibers due to their rigid molecular structure and high crystallinity. In this study, the dope-dyed PMIA fibers with different amounts of pigment were fabricated by wet spinning. The properties of the pigment were analyzed, including size distribution and dispersive properties. The results showed that the pigment was easy to disperse in the fibers when the average diameter of the pigment was smaller than 500 nm. The color fastness of the colored PMIA fibers was tested, and their thermal properties and mechanical properties were also analyzed. The results of thermal gravity analysis (TGA) indicated that the colored PMIA fibers maintained good thermal performance. Compared to uncolored PMIA fibers, the colored PMIA fibers became lighter after exposing to simulated sunlight for 50 h. The breaking tenacity of fibers exceeded 2.0 cN/dtex, and the retentivity was above 80 % after being exposed to simulated sunlight for 50 h. These suggested the good mechanical performance of colored PMIA fibers. Dope-dyed PMIA fibers with good mechanical properties and thermal performance were successfully developed.     

Microstructure and mechanical properties of polyurethane fibrous membrane

A series of PU fibrous membranes were fabricated by using electrospinning method. The microstructure of the membranes was characterized by field-emission scanning electron microscopy, X-ray diffraction and Fourier transform infrared spectrum. Their mechanical properties were tested by dynamic mechanical thermal analysis and stress-strain behaviors. The solution concentration, the applied voltage and the tip-collector distance had an effect on the crystallinity degree and molecular orientation of PU, the size and distribution of the fiber diameter and the point-bonded structures between the fibers, leading to the change in the microstructure and the mechanical properties of the fibrous membrane. Fibers with a smaller diameter had higher strength but lower ductility. The fibrous membranes indicated the similar stress-strain behaviors, which slopes in the initial stage were low and that in the later stage were high. The initial elastic behavior with the low Young’s modulus were attributed to the network structure of the fibrous membranes and that with the high Young’s modulus was from the electrospun PU fibers.     

Study of synthesizing energy storage microcapsules in PVA spinning solution and thermal regulating fibers prepared by this solution

Thermal regulating fiber has been a research hotspot worldwide recently. In this paper, the energy storage microcapsules composed of silicon dioxide (SiO₂) as shell and paraffin as core were synthesized in the spinning solution of polyvinyl alcohol (PVA). This solution was used to prepare thermal regulating PVA fibers by wet spinning directly. Orthogonal experiment was conducted to optimize the synthetic conditions of the microcapsules. Chemical structure and morphology of the fibers were characterized by Fourier transform infrared-attenuated total reflectance (FTIR-ATR) and scanning electron microscope (SEM) respectively. The thermal properties of the fibers were studied by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). Results present that energy storage microcapsules are successfully synthesized in PVA spinning solution with a mean particle size of 1.39 µm. The fibers containing such microcapsules show a high latent heat storage density of 45.39 J g^?1, which also achieve a relatively better thermal stability.     

Fabrication and surface modification of melt-electrospun poly(D,L-lactic-co-glycolic acid) microfibers

In this study, biodegradable poly(D,L-lactic-co-glycolic acid) (PLGA) fibers were prepared by a melt-electrospinning and treated with plasma in the presence of either oxygen or ammonia gas to modify the surface of the fibers. The effects of processing parameters on the melt-electrospinning of PLGA were examined in terms of fiber morphology and diameter. Among the processing parameters, the spinning temperature and mass flow rate had a significant effect on the average fiber diameter and its distribution. The water contact angle of melt-electrospun PLGA fibers decreased significantly from 123 ° to 55 ° (oxygen plasma treatment) or to 0 ° (ammonia plasma treatment) by plasma treatment for 180 sec, while their water content increased significantly from 2.4 % to 123 % (oxygen plasma treatment) or to 189 % (ammonia plasma treatment). Ammonia gas-plasma enhanced the surface hydrophilicity of PLGA fibers more effectively compared to oxygen gas-plasma. X-ray photoelectron spectroscopy analysis supported that the number of polar groups, such as hydroxyl and amino groups, on the surface of PLGA fibers increased after plasma treatment. Overall, the microfibrous PLGA scaffolds with appropriate surface hydrophilicity and fiber diameter could be fabricated by melt electrospinning and subsequent plasma treatment, without a significant deterioration of fiber structure and dimensional stability. This approach of controlling the surface properties and structures of fibers could be useful in the design and tailoring of novel scaffolds for tissue engineering.     

Processing and characterization of nickel-plated PBO fiber with improved interfacial properties

A new application of conventional electroless nickel plating to improve the interfacial properties of PBO fibers was reported. The relationship between surface morphology and interfacial properties of nickel-plated PBO fiber was explored. The continuous nickel coating consisted of nickel and phosphorus elements determined by Energy dispersive spectrometer (EDS) and transmission electron microscope (TEM), exhibiting high adhesive durability. The influence of bath temperature and plating time on the crystal structure, microstructure and mechanical properties of nickel-plated PBO fibers was systematically investigated. X-ray diffractometer (XRD) results revealed that the crystal structure among nickel-plated PBO fibers did not show differences. Scanning electron microscope (SEM) and Atomic force microscope (AFM) images showed that the process parameters had a great influence on surface morphology and roughness of nickel-plated PBO fibers, which could directly affect the interfacial properties of nickel-plated PBO fibers. Single fiber pull-out testing results indicated that the interfacial shear strength (IFSS) of PBO fibers after electroless nickel plating had a significant improvement, which reached maximum at 85 °C for 20 min. Single fiber tensile strength of nickel-plated PBO fibers was slightly lower than that of untreated one. Thermo gravimetric analysis (TGA) indicated that nickel-plated PBO fiber had excellent thermal stability.     

Thermo-mechanical and morphological properties of short natural fiber reinforced poly (lactic acid) biocomposite: Effect of fiber treatment

Untreated oil palm empty fruit bunch (REFB), alkali treated EFB (AEFB), ultrasound treated EFB (UEFB) and simultaneous ultrasound-alkali treated EFB (UAEFB) short fibers were incorporated in poly(lactic acid) (PLA) for fabricating bio-composites. The REFB fiber-PLA (REPC) and treated EFB (TEFB) fiber-PLA (TEPC) composites were prepared and characterized. Glass transition temperature, crystal melting temperature, decomposition temperature, melt flow index, density and mechanical properties (tensile strength, tensile modulus and impact strength) of TEPC are found to be higher than those of REPC. The observed crystallization temperature of TEPC is lower than that of REPC. Among all samples, TEPC prepared from UAEFB fiber shows better performances than other samples fabricated by REFB and AEFB fibers. Scanning electron microscopy, Fourier transform infrared spectroscopy and XRD analyses well support all the observed results.     

Mechanical behavior of composites reinforced with fibers caroa

Composites were prepared with 13, 23 30 and 40 % fiber and evaluated the mechanical performance in tensile, flexural and impact. The mechanical properties of these composites were also evaluated function of time at 110 °C thermal exposure. Caroa fibers were characterized by techniques such as thermal gravimetric analysis (TGA), X-ray diffraction (XRD) and scanning electron microscopy (SEM). It was found that the best mechanical properties were achieved for composites containing 23 to 30 % fiber. The incorporation of 23 % fiber caroa increased both the modulus of elasticity in the tensile test as the flexural strength and impact, the composite with 30 % fiber caroa showed higher tensile strength. The results show that the tensile and flexural strength of the composite decreased with time of thermal exposure. The thermal aging at 110 °C caused a decrease in tensile properties of the composites.     

The structural development and the thermal behaviours in the heat treated poly(p-phenylene terephthalamide) fibers

Poly(p-phenylene terephthalamide) fibers prepared by dry-jet wet spinning processes have a notable response to very brief heat treatment (seconds) under tension. The modulus of the as-spun fiber can be greatly affected by the heat treatment conditions (temperature, tension and duration). The crystallite orientation and the fiber modulus will increase by this short-term heating under tension. The present research reports the heat treatment techniques, devices and its process conditions. It reports in details the structural relationships between the fiber properties which are influenced by the heat treatment process. In particular, focuses deeply on the effect of the crystal orientation changes of the fibers, on the mechanical properties and, also, investigates the thermal degradation steps & behaviours of the heat treated fibers. The heat treated PPTA fibers have a molecular orientation higher than that for the as-spun one.     

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.     

Air-gap spinning of cellulose/ionic liquid solution and its characterization

In order to study the effects of the spinning conditions on the structure and the properties of the regenerated fiber, cellulose was dissolved in ionic liquid and then spun into fiber using an air-gap spinning process. The solution concentration, the take-up speed and the fixation of the fiber ends during coagulation improved the crystallinity and the tensile strength at the same time. The fiber surface became smooth by addition of DMF (dimethylformamide). However, it decreased the crystallinity and the tensile strength of the fibers. We revealed that the developed structure during coagulation determined the morphology and the properties of the fibers. The co-solvent resulted in smooth surface of the fiber and also changed the mechanical properties.     

Thermomechanical and Shape Memory Performances of Thermo-sensitive Polyurethane Fibers

This study is the first step to investigate usability of shape memory polyurethane (SMPU) fibers for smart garment applications. SMPU fibers were spun by wet spinning process and chemical/mechanical characterization was carried out. SMPU solutions were prepared with two different concentrations (20 % and 25 %) and three different coagulation bath concentrations (0 %, 1 % and 3 %) were used for determining optimum spinning parameters. For investigating influences of spinning process on crystal structure, mechanical, thermal and shape memory performances of fibers, X-ray diffraction (XRD), differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), scanning electron microscopy (SEM) and mechanical tests were conducted. DSC and DMA analysis results show that shape memory polyurethane fibers have a glass transition temperature about 35-40 oC which is suitable for body temperature. Moreover, SMPU fibers showed good tensile performance with an average tenacity of 1.38 cN/dtex and elongation at break of 350 %. Thermo mechanical test results showed that, all shape memory fibers have good shape memory effect with recovery and fixity ratios up to 91 % and 71 % respectively.