Electrospun-fiber induced transcrystallization of isotactic polypropylene matrix

To reveal the influences of fiber diameter and characteristics on the surface-induced matrix crystallization, four different fibers, i.e. syndiotactic polystyrene (sPS), Nylon 6, and polyhydroxyamide (PHA) and poly(p-phenylene benzobisoxazole) (PBO) fibers, were used to study their nucleating abilities towards isotactic polypropylene (iPP) matrix. Among them, micron-sized PBO fibers were obtained from the supplier, whereas submicron-sized fibers of sPS, Nylon 6 and PHA were prepared by the solution electrospinning process developed in this laboratory. To resolve the observation difficulty due to the fast nucleation rate and crystal growth at high supercooling degrees (>60 °C), a high speed camera was mounted on the polarized optical microscope equipped with a hot stage to successfully snapshot the corresponding processes at various crystallization temperatures (T_c) in the range of 96-120 °C. For all the active fibers, only α-form iPP transcrystallites were observed at the fiber/matrix interface. Two crucial parameters were proposed for characterizing the fiber nucleating ability, i.e. the interfacial free energy difference (Δσ) based on the heterogeneous nucleation from a thermodynamic point of view, and the maximum temperature for transcrystalline layer observed (T_max) based on a kinetic consideration. Values of Δσ for different fibers were derived on the basis of the tertiary nucleation taking place in the selective “grooves” at the fiber surface. It was found that the nucleating rate of sPS fibers was scaled with the fiber diameter, and Δσ showed a negligible diameter dependence, but T_max slightly increased with increasing fiber diameter. For all the fibers investigated, an intimate relation between the Δσ and T_max was derived and used to compare their nucleating abilities.     

Combined effect of shear and fibrous fillers on orientation-induced crystallization in discontinuous aramid fiber/isotactic polypropylene composites

The shear-induced crystallization behavior in isotactic polypropylene (iPP) composite melt containing short aramid fibers was investigated by means of WAXD (wide-angle X-ray diffraction) and SAXS (small-angle X-ray scattering) techniques using synchrotron radiation. The study was carried out in a post-shear isothermal crystallization mode at temperatures of 140-160 °C. Parameters pertaining to the crystallization morphology and kinetics were analyzed, including total crystallinity, orientated crystalline and amorphous fractions, dimensions of the formed shish-kebab structure, as well as induction time and rate of crystallization. The individual contributions of shear and fibers were evaluated and the combined effect was compared. The results clearly indicated that the effect is synergistic rather than additive.     

A comparison of short glass fiber reinforced polypropylene plates made by conventional injection molding and using shear controlled injection molding

This paper describes a comparison of the fiber orientation structures and resulting elastic properties of samples of short glass fiber filled polypropylene made by conventional injection molding and by the SCORIM (Shear Controlled Orientation in Injection Molding) process developed at The University of Brunel. The 3D fiber orientation distributions of the composites were measured using a unique transputer based image analysis system developed at The University of Leeds. The mechanical properties of the samples were characterized using an ultrasonic velocity technique, which allows a full set of elastic constants to be determined for each material. The link between fiber orientation distributions and measured elastic properties was then investigated using theoretical models developed in this laboratory.     

Study of the flexural modulus of natural fiber/polypropylene composites by injection molding

Effect of fiber compression on flexural modulus of the natural fiber composites was examined. The kenaf, bagasse, and polypropylene were mixed into pellets, and composites were fabricated by injection molding. To predict flexural modulus of the composites, the Young's modulus of kenaf and bagasse fiber were measured. Using the obtained Young's modulus, the flexural modulus of the composites was predicted by Cox's model that incorporates the effect of fiber compression. It was found that those fibers with high Young's modulus were more compressed than that with low Young's modulus. Moreover, the distribution of fiber length and orientation in the composites were also investigated. To calculate the orientation factor for the prediction model, the distribution function of fiber orientation was determined to a triangular function. The flexural modulus of the composites increased with increase of volume fraction. The predicted values were in good agreement with the experimental values. Furthermore, it was revealed by SEM that the porous structure of the natural fibers was compressed. The fiber compression ratio (3.6) in bagasse was higher than that in kenaf (1.4) due to the difference in porous structure. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 911–917, 2006     

热压成型和注塑成型CF/PP复合材料的力学性能对比

通过热压成型和注塑成型2种不同加工方法制备了碳纤维(CF)/聚丙烯(PP)导电复合材料,对比了2种复合材料的力学性能,结果表明注塑成型的CF/PP具有较高的拉伸强度和弹性模量。结合扫描电子显微镜观察,分析了这2种加工方法对CF/PP复合材料的微观结构和力学性能的影响。     

Hierarchic structure and mechanical property of glass fiber reinforced isotactic polypropylene composites molded by multiflow vibration injection molding

Maleic anhydride‐grafted polypropylene (Ma‐PP) and β nucleation agents (β‐NA) were used to modify the glass fiber (GF)/isotactic polypropylene (iPP) composite. The interface adhesion, degree of orientation, and crystalline morphologies of the PP/GF composites molded by multiflow vibrate‐injection molding (MFVIM) and conventional injection molding (CIM) were studied by polarized light microscopy (PLM), scanning electronic microscopy (SEM), and X‐ray measurements. Results prove that the interface adhesion was improved by the Ma‐PP; γ crystal was generated by the MFVIM due to the instant high pressure and shear during the multiflow; and a hierarchical structure which has a strengthened skin and a toughened core was formed. As a result, the final PP/GF/β‐NA composite has a 60% increase in tensile strength and 80% improvement in impact strength compare with the CIM pure PP/GF composite. Based on the observations, a modified model is proposed to interpret the strengthening and toughening mechanism. Our work paves the way to obtain high‐performance GF/iPP composites. POLYM. COMPOS., 38:2707–2717, 2017. © 2015 Society of Plastics Engineers     

长玻璃纤维增强聚丙烯复合材料的韧性

以玻璃纤维和聚丙烯为原料,制备了长玻璃纤维增强聚丙烯(LFT-PP)复合材料,研究了基体韧性、纤维长度和界面相容剂对LFT-PP韧性的影响。结果表明LFT-PP韧性随基体韧性增加而增加;当玻璃纤维长度从2.06mm增加到4.66mm时,LFT-PP的悬臂梁缺口冲击强度从134.4J/m提高到238.0J/m,增加了约80%;添加界面改性剂降低了LFT-PP悬臂梁缺口冲击强度,从311.4J/m降为181.8J/m。     

Reaction injection molding process of glass fiber reinforced polyurethane composites

Structural reaction injection molding (SRIM) was used to produce polyurethane composites containing random continuous glass fiber mats. A long rectangular mold was used to carry out the SRIM experiments. 4,4′‐diphenylmethane diisocyanate and poly(propylene oxide) triol were used to formulate a thermoset polyurethane system. Dibutyltin dilaurate was used as a catalyst. A second order Arrhenius equation described the PU polymerization kinetic data obtained from the adiabatic temperature rise measurement. A viscosity as a function of temperature and conversion was developed using rheometer data. The pressure rise at the gate was measured during filling. The flow behavior within the mold was described by Darcy's law and the Kozeny's equation. The temperature profile within the mold measured by thermocouples during filling and curing coincided fairly well with the simulation results. The thermal transient problem at the wall was solved using the overall heat transfer coefficient, and it was analyzed as a function of Biot number. The dimensional stability of the fiber reinforced PU parts was excellent compared to the pure PU parts.     

Polypropylene–glass fiber/basalt fiber hybrid composites fabricated by direct fiber feeding injection molding process

Hybrid composites of polypropylene reinforced with glass fibers and basalt fibers were fabricated by vented injection molding machine which is named the direct fiber feeding injection molding (DFFIM) process. Polyamide 6 and maleic anhydride‐grafted polypropylene has been used as a coupling agent to improve the interfacial bonding between the fibers and matrix. Two types of vented injection molding machines with a different check ring and mold were used for making specimens. The fiber lengths were analyzed to identify the most suitable check ring and mold for the DFFIM process. The mechanical properties of the hybrid composites were investigated by tensile, flexural and Izod impact tests. The interfacial morphology of the fractured tensile specimens was studied by using scanning electron microscopy and showed that there is a fiber agglomeration phenomenon that occurs in the hybrid composites, and it has a significant effect on the mechanical properties of hybrid composites. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45472.     

The study of short-shot water-assisted injection molding of short glass fiber reinforced polypropylene

water penetration length and fiber orientation (along the melt flow direction) are important indicators for water-assisted injection molding products of the fiber-reinforced polymer. The effects of melt short shot size, water injection delay time and water injection pressure on these two important indexes are analyzed theoretically and experimentally. The study found that with the increase of the melt short shot size, the extension of the water injection delay time and the increase of the water injection pressure, the water penetration length changed from 216 to 96 mm, 170 to 210 mm, and 215 to 180 mm, respectively. Therefore, it can be known that melt short shot size has the greatest influence on water penetration length, followed by water injection delay time, and finally water injection pressure. Meantime, due to the fiber orientation and change degree of water-assisted injection-molded products along the melt flow direction, the fiber orientation in the water channel layer along the melt flow direction has the highest and lowest change degree, followed by the wall layer and finally the core layer. It can be known that the melt short shot size has the greatest influence on the fiber orientation and the degree of change along the melt flow direction, followed by the water injection delay time, and finally the water injection pressure.     

Comparative study of EMI shielding effectiveness for carbon fiber pultruded polypropylene/poly(lactic acid)/multiwall CNT composites prepared by injection molding versus screw extrusion

The electrical conductivity and electromagnetic interference (EMI) shielding effectiveness of the composites of polypropylene/poly(lactic acid) (PP/PLA) (70/30, wt %) with single filler of multiwall carbon nanotube (CNT) or hybrid fillers of nickel‐coated carbon fiber (CF) and CNT were investigated. For the single filler composite, higher electrical conductivity was observed when the PP‐g‐maleic anhydride was added as a compatibilizer between the PP and PLA. For the composite of the PP/PLA (70/30)/CF (20 phr)/CNT (5 phr), the composite prepared by injection molding observed a higher EMI shielding effectiveness of 50.5 dB than the composite prepared by screw extrusion (32.3 dB), demonstrating an EMI shielding effectiveness increase of 49.8%. The higher values in EMI shielding effectiveness and electrical conductivity of the PP/PLA/CF (20 phr)/CNT (5 phr) composite seemed mainly because of the increased CF length when the composites were prepared using injection molding machine, compared with the composites prepared by screw extrusion. This result suggests that the fiber length of the conductive filler is an important factor in obtaining higher values of electrical conductivity and EMI shielding effectiveness of the PP/PLA/CF/CNT composites. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45222.     

玻纤增强酚醛注塑料的制备技术和性能

研究了玻纤增强酚醛注塑料制备过程中基质树脂的选择、固化作用与交联结构的控制及玻纤分散技术,考察了不同基质树脂制备的酚醛注塑料的固化成型结构形态和固化流变特性.进一步采用热固性与热塑性酚醛树脂相复配的基质树脂体系,经配方和制备工艺的优化,制备了高填充量玻纤增强酚醛注塑料.该注塑料具有良好的注塑成型性能,注塑制品具有高强度, 冲击强度达到4.3 kJ•m^-2,弯曲强度137.4 MPa,同时热变形温度为 245 ℃,阻燃性通过美国UL 94 V-0级认证,并具有优良的尺寸稳定性、电绝缘性能和低成本优势.     

Orientated crystallization in discontinuous aramid fiber/isotactic polypropylene composites under shear flow conditions

Melt blends of short aramid fibers (AF) and isotactic polypropylene (iPP) are subjected to shear at 145°C and the structural evolution and final morphology are examined by in situ synchrotron X‐ray scattering/diffraction and high‐resolution scanning electron microscopy, respectively. The results indicate that the presence of short AFs significantly enhances the crystallization of iPP. It is argued that shear flow in this system exerts a twofold orientating action, namely, on the bulk iPP molecules and on the short AFs. The resultant crystalline morphology reflects the combined effects of crystallization on orientated iPP molecules to facilitate a shish kebab morphology and at the interface of the aligned fibers, to form transcrystallinity. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 1113–1118, 2005     

Fibers from polypropylene/nano carbon fiber composites

Fibers from polypropylene and polypropylene/vapor grown nano carbon fiber composite have been spun using conventional melt spinning equipment. At 5 wt% nano carbon fiber loading, modulus and compressive strength of polypropylene increased by 50 and 100%, respectively, and the nano carbon fibers exhibited good dispersion in the polypropylene matrix as observed by scanning electron microscopy.     

Injection molding of glass fiber reinforced phenolic composites. 2: Study of the injection molding process

This study of injection molding of glass fiber reinforced phenolic molding compounds examines fiber breakage and fiber orientation with key material and processing variables, such as injection speed, fiber volume fraction, and the extent of resin pre-cure. The fiber orientation, forming discrete skin-core arrangements, is related to the divergent gate to mold geometrical transition, the extent of pre-cure and injection speed functions of the melt viscosity. Transient modifications to the melt viscosity during mold filling produce variations in skin/core structure along the flow path, which are correlated to the mechanical properties of injection moldings. The melting characteristics of the phenolic resin during plasticization impose a severe environment of mechanical attrition on the glass fibers, which is sequentially monitored along the screw, and during subsequent flow through runners and gates of various sizes. Differences found between the processing characteristics of thermosets and thermoplastics raise questions concerning the applicability of thermoplastic injection molding concepts for thermosets.     

Effects of polyamide 6 incorporation to the short glass fiber reinforced ABS composites: an interfacial approach

The properties of 30 wt% short glass fiber (SGF) reinforced acrylonitrile-butadiene-styrene (ABS) terpolymer and polyamide 6 (PA6) blends prepared with extrusion were studied using the interfacial adhesion approach. Work of adhesion and interlaminar shear strength values were calculated respectively from experimentally determined interfacial tensions and short beam flexural tests. The adhesion capacities of glass fibers with different surface treatments of organosilanes were evaluated. Among the different silanes tested, γ-aminopropyltrimethoxysilane (APS) was found to be the best coupling agent for the glass fibers, possibly, because of its chemical compatibility with PA6. Tensile test results indicated that increasing amount of PA6 in the polymer matrix improved the strength and stiffness of the composites due to a strong acid–base interaction at the interface. Incorporation of PA6 to the SGF reinforced ABS reduced the melt viscosity, broadened the fiber length distributions and increased the toughness of the composites. Fractographic analysis showed that the incorporation of PA6 enhanced the interactions between glass fibers and the polymeric matrix.     

An impact study of epoxy resin composites reinforced with glass fiber fabrics

The impact properties of epoxy resin composites reinforced with three types of fabrics which are welf-knitted structural fabrics (WKSF), three-dimensional fabrics (3D-3A & 3D-5A) and plain-weave structural fabrics (2D-2A) have been investigated. The results of experiments show that WKSF composite has total impact energy about 1.5 and 3.5 times those of 3D and 2D fabrics composite respectively. The ductility index of WKSF is about 2.2 times of those of 3D and 2D. WKSF composites are very ductile materials and can absorb much more impact energy than 3D and 2D composites. The pushed-out volume of WKSF composites after the impact test was calculated from the photographs and the results show that the volume of the pushed-out zone is proportional to impact energy.     

Crystal morphology and tensile properties of LLDPE containing PP fibers as obtained via dynamic packing injection molding

The fibrillated linear low-density polyethylene (LLDPE)/isotactic polypropylene (iPP) fiber blends were subjected to dynamic packing injection molding (DPIM), in which the prolonged shear was exerted on the melt during solidification stage. Transcrystallization of LLDPE on PP fibers, with stacked lamellae parallel to each other and aligned approximately perpendicular to the long axial of the fibers, has been achieved for the first time in DPIM due to the prolonged shear. PP fibers were found to align parallel to the flow direction along thickness up to the oriented zone of sample prepared by DPIM. The presence of oriented PP fibers enhanced the orientation of LLDPE that developed row-nucleated type morphology. The molding temperatures were changed between 160 °C and 200 °C to investigate the effect of molding temperature on the crystalline microstructure of the blends. As increasing the molding temperature from 160 °C to 200 °C, the partial melting of PP fiber was changed to complete melting, resulting in a dramatic change of the crystal morphology and the mechanical properties as well.     

Flame retardant synergy between interfacial and bulk carbonation in glass fiber reinforced polypropylene

Glass fiber reinforced polypropylene (GF-PP) composites have high flammability on account of wick effect which leads to accelerated flow of the polymer melt along the glass fibers (GF) surface to the flame zone. In this study, dipentaerythritol (DPER), a charring agent, was adsorbed on the GF surface through the hydrogen bond between silane coupling agent and DPER. DPER has a synergistic effect with the intumescent flame retardants (IFR) added in the composites, which can induce interfacial carbonization on the surface of GF, thus transforming the intrinsic smooth GF surface into roughness one. In this way, the negative effect of the wick effect in flame retardancy is weakened. Moreover, the char residues remained on the surface of GF can bring an improved adhesion between GF and char residues formed in the resin so that a more stable barrier char layer is formed. The PP composites with 20 wt% modified glass fiber (M-GF) and 30 wt% IFR can achieve the UL-94V-0, and its limiting oxygen index (LOI) value increased from 16.5% to 29.5%. Simultaneously, the heat release rate (HRR), total heat release (THR) and total smoke release (TSR) decreased significantly, and the peak of heat release rate (PHRR) reduced 60.6% compared with GF-PP.     

Two-dimensional mapping of tensile strength for injection molded composites of glass fiber reinforced polypropylene

An array of polypropylene composites were injection molded into rectangular plaques having a single side gate. As a consequence of non-symmetrical flow patterns, giving complex distribution of fiber orientations, measured tensile strength of test specimens cut along X-Y directions produced nonlinear and anisotropic trendlines. Chemical coupling, glass fiber content, and the choice of short or long glass fiber reinforcement are shown to be material variables influencing the magnitude of the tensile strength at any given localized position. These data verify the notion that tensile strength evaluation along just the flow direction is insufficient for anticipating end use performance.