Effects of the molecular orientation and crystallization on film–substrate interfacial adhesion in poly(ethylene terephthalate) film‐insert moldings

A film and substrate consisting of poly(ethylene terephthalate) were adhered by means of film‐insert molding. Two injection speeds (i.e., 50 and 500 mm/s) were chosen to induce different shear rates (and molecular orientation) between the film and the substrate. Annealing was subsequently performed on these specimens at different times and temperatures to examine the extent of orientation‐induced crystallization of the substrate surfaces embedded under the film. Differential scanning calorimetry thermograms clearly indicated a shift in the position of the secondary (β) crystalline phase toward a higher temperature in specimens molded at a 500 mm/s injection speed, suggesting that a more densely packed and well‐formed crystalline structure was generated because of higher localized orientation of molecules. Polarized Fourier transform infrared spectroscopy analyses provided dichroic ratios of the 1340‐ and 1410‐cm⁻¹ wavelengths, which corresponded to the trans‐glycol conformer and the stable benzene ring, respectively. Drastic increases in the dichroic ratios were observed, especially in specimens molded at a 500 mm/s injection speed after being annealed for 1 min. This could have been caused by the reorientation of molecules fueled by residual stresses, particularly in regions experiencing high shear during molding. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Manufacturing and testing of long basalt fiber reinforced thermoplastic matrix composites

In this work, long basalt fiber reinforced composites were investigated and compared with short basalt fiber reinforced compounds. The results show that long fiber reinforced thermoplastic composites are particularly advantageous in the respects of dynamic mechanical properties and injection molding shrinkage. The fiber orientation in long basalt fiber reinforced products fundamentally differs from short basalt fiber reinforced ones. This results in more isotropic molding shrinkage in case of long basalt fiber reinforced composites. The main advantage of the used long fiber thermoplastic technology is that the special long fiber reinforced pellet can be processed by most conventional injection molding machines. During extrusion compounding the fibers in the compound containing 30 wt% fibers are fragmented to an average length of 0.48 mm (typical of short fiber reinforced thermoplastic compounds), this length decreases further during injection molding to 0.20 mm. Contrarily using long fiber reinforced pellets and cautious injection molding parameters, an average fiber length of 1.8 mm can be achieved with a conventional injection molding machine, which increased the average length/diameter ratio from 14 to 130. POLYM. ENG. SCI., 2010. © 2010 Society of Plastics Engineers     

Morphology and mechanical investigation of microcellular injection molded carbon fiber reinforced polypropylene composite foams

Employing microcellular injection molding technology, carbon fiber (CF)/polypropylene (PP) composite foams have been prepared. The influences of injection molding conditions and CF amounts relating to the flexural and impact performances have also been studied. X-ray computed tomography scanning has been used for morphological observation. For the flexural specimens, although the solid skin and foamed core layers can be confirmed significantly, the intermediate layer is indistinct. Moreover, the stretched cells can be confirmed dramatically for the Charpy impact specimens. The cell density increases to 12.0 × 10³ cell/cm² when the nitrogen content is 1%. By contrast, the cell densities decrease with the injection speed and CF content increasing accordingly. Further, the maximum specific flexural modulus and Charpy impact strength of the foams can achieve 14 GPa/(g/cm³) and 6.2 kJ/m², respectively, at the CF content of 30 wt%. Finally, the microcellular structure with the highest cell density can be confirmed with the nitrogen content of 1 wt%, the injection speed of 50 mm/s and the CF content of 10 wt%. Obviously, the CF contents have shown strong influences on the mechanical behaviors of the CF/PP composite foams compared with nitrogen contents or injection speeds.     

Development and characterization of flax fiber reinforced biocomposite using flaxseed oil‐based bio‐resin

In this study, acrylated epoxidized flaxseed oil (AEFO) resin is synthesized from flaxseed oil, and flax fiber reinforced AEFO biocomposites is produced via a vacuum‐assisted resin transfer molding technique. Different amounts of flax fiber and styrene are added to the resin to improve its mechanical and physical properties. Both flax fiber and styrene improve the mechanical properties of these biocomposites, but the flexural strength decreases with an increase in styrene content. The mass increase during water absorption testing is less than 1.5% (w/w) for all of the AEFO‐based biocomposites. The density of the AEFO resin is 1.166 g/cm³, which increases to 1.191 g/cm³ when reinforced with 10% (w/w) flax fiber. The flax fiber reinforced AEFO‐based biocomposites have a maximum tensile strength of 31.4 ± 1.2 MPa and Young's modulus of 520 ± 31 MPa. These biocomposites also have a maximum flexural strength of 64.5 ± 2.3 MPa and a flexural modulus of 2.98 ± 0.12 GPa. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41807.     

Effects of processing conditions on the fiber length distribution and mechanical properties of glass fiber reinforced nylon‐6

The effects of processing conditions on fiber length degradation were investigated in order to produce composites with higher performance. Nylon‐6 was compounded with glass fibers in a twin‐screw extruder for various combinations of screw speed and feed rate. Collected samples were injection molded and Izod impact and tensile tests were performed in order to observe the effect of fiber length on the mechanical properties. Also, by using the extruded and injection molded smaples, fiber length distribution curves were obtained for all the experimental runs. Results show that when the shear rate is increased through the alteration of the screw speed and/or the feed rate, the average fiber length decreases. Impact strength, tensile modulus and tensile strength increase, whereas elongation at break decreases with the average fiber length.     

Preparation of high-modulus and high-strength isotactic polypropylene fiber by zone-annealing method

The zone-annealing method was utilized to prepare a high-modulus and high-strength fiber from isotactic polypropylene. The dynamic storage modulus at room temperature of the fiber obtained reached 21 times; 10¹⁰ dyn/cm², which corresponded to 51% of the crystal modulus along the molecular chains, 41.2 × 10¹⁰ dyn/cm². The relationships between mechanical properties and superstructure were investigated based on results of measurements of orientation, crystallinity, tensile properties, and dynamic viscoelasticity. It was found that the excellent mechanical properties were directly attributed to the large number of tie molecules and to the high orientation of the amorphous chains. Further, the characteristics of this method were discussed compared with the results obtained by other investigators.     

Study of carbon films from PAN/VGCF composites by gelation/crystallization from solution

A carbon film with a cross-sectional area much larger than that of a commercial carbon fiber (>6000 times) and a thickness of about 0.3 mm was obtained using a new method. In this method, composite materials of polyacrylonitrile (PAN) and vapor-grown carbon fiber (VGCF) prepared by gelation/crystallization from dilute solutions were used as starting materials The gelation/crystallization method was adopted to ensure high orientation of PAN chains. The composite materials were heat-treated at 200-300°C in an oxidizing atmosphere for thermal stabilization and then heat-treated to 1500°C in argon gas to promote carbonization. The tensile modulus and electric conductivity for the carbon materials with cross-sectional areas of about 0.6 mm² (thickness 0.3 mm and width 2 mm) reached 18 GPa and 10 Ω⁻¹ cm⁻¹, respectively. The mechanical and electrical properties of the final carbonized materials were sensitive to the PAN/VGCF composition and the draw ratio. These phenomena were analyzed using Fourier transform IR and X-ray diffraction.     

Temperature dependence of critical fiber length for glass fiber-reinforced thermosetting resins

In discontinuous fiber-reinforced composites, the critical fiber length plays an essential role in determining the mechanical properties. A method was devised to accurately determine the critical fiber length and the temperature dependence of the critical fiber length was studied for glass fiberepoxy and glass fiber-unsaturated polyester resin composites. If a continuous glass fiber is embedded in the matrix and the system is subjected to a tensile strain greater than the fiber ultimate tensile strain, the fiber breaks into many pieces. If the average length of these broken pieces (l?) is measured, the critical fiber length (lc) is expressed as l_c = 4/3l?. The critical fiber length greatly increases with increasing temperature and the apparent shear strength at the interface, calculated from the critical fiber length, decreases linearly with increasing temperature.     

Fiber orientation structures and mechanical properties of injection molded short glass fiber reinforced ribbed plates

In this paper we describe a study of the fiber orientation structures present within a model ribbed injection molded plate. The details of the fiber orientation at each chosen location on the injection molded parts were measured using an in-house developed image analysis system, which enabled large areas to be scanned (up to 200 mm²) up to a limit of 1 million fiber images. Two materials were used for these experiments, short glass fiber filled PBT and short glass fiber filled nylon 66. First, a comparison was made between the fiber orientation at an identical position, 28 mm from the injection gate on a transverse rib, on two plates made from glass fiber filled PBT. It was found that the fiber orientation in these two separately manufactured components was virtually identical when comparing the whole scanned area, but the differences became more significant when comparing areas on the length scale of an individual fiber (∼ 200 μm). Second, the fiber orientation at the same position was compared for two plates made using the glass/PBT and glass/nylon 66 materials. The differences for the complete scanned areas were small, confirming that mold geometry plays a crucial role in determining fiber orientation structures, and that matrix properties are secondary. Third, the fiber orientation structures at various positions across one of the glass/PBT plates were examined in greater detail, in particular across a number of the transverse ribs: the chosen ribs were of various widths and heights. Differences in structure were found depending on the local rib geometry. Finally, the effect of the measured fiber orientation structures in determining the mechanical properties of the ribbed plate was investigated using simple modeling schemes. While the stiffness of the rib/web assembly was found to depend on the average fiber orientation of the two parts, the different thermal expansions of the web and the rib, caused by the different fiber orientation in the two regions, led to significant warpage of the rib/web assembly. Polym. Compos. 25:237–254, 2004. © 2004 Society of Plastics Engineers.     

Mullite fiber cloth-reinforced mullite composite fabricated via an optimized layer-by-layer assembly method

This article reports the fabrication of fiber cloth-reinforced mullite composite via an optimized layer-by-layer (LbL) assembly method involving the infiltration and pyrolysis of fiber cloth with mullite precursor (PIP) followed by brushing matrix onto the treated fiber cloth and hot pressing. The influence of fiber content on the microstructure and mechanical properties of composite are investigated and the crack propagation is discussed to explain the toughening mechanisms. The composite with 30?vol% fiber content exhibited a high density 2.89?g/cm³, flexural strength 135.5?MPa and fracture toughness 4.13?MPa?m^1/2. After PIP pretreatment, the gaps existed in the fiber bundle are filled with mullite matrix which transform from mullite precursor, improving the density from 2.89?g/cm³ to 2.94?g/cm³, flexural strength from 135.5?MPa to 163.2?MPa and fracture toughness from 4.13?MPa?m^1/2 to 4.55?MPa?m^1/2. The optimized LbL assembly method realizes the creation of fiber cloth-reinforced mullite composites with high density and excellent mechanical properties.     

Preparation of high-modulus and high-strength poly(ethylene terephthalate) fiber by zone annealing

To prepare high-modulus and high-strength PET fiber, a new method using zone drawing and zone annealing has been studied. The apparatus used for this method is the usual tensile tester equipped with a band heater 2 mm wide and a sample holder which can apply a high tension to the fiber. The experimental procedure consists of two stages: zone drawing and zone annealing. The zone drawing was done on the original as-spun fiber in order to produce a fiber with as high an orientation and as low a crystallinity as possible. The zone-drawn fiber was subsequently zone annealed under high tension by moving the band heater from one end to the other of the fiber at a temperature above the crystallization temperature at a considerably low moving speed. In spite of the simple apparatus and procedure, Young's modulus of the fiber obtained was 19.4 × 10¹⁰ dyn/cm², which is comparable to the maximum value of the high-tenacity PET filament commercially available. In order to elucidate the change in the superstructure with zone drawing or zone annealing, optical, x-ray, IR, DSC, and dynamic mechanical measurements were performed. It is suggested that the zone-annealed fiber consists of almost perfectly oriented crystallites and fully extended amorphous chains.     

Stress‐transfer micromechanics for fiber length with a photocure vinyl ester composite

The objective was to test how increasing fiber length above the critical length would influence mechanical properties and fracture crack propagation. Micromechanics considering fiber/matrix stress‐transfer was used to evaluate the results in addition to a shear debonding volume percent correction term necessary for the final analysis. Fiber lengths of 0.5, 1.0, 2.0, 3.0, and 6.0 mm with 9 μm diameters were added into a photocure vinyl ester particulate‐filled composite at a uniform 28.2 vol%. Mechanical flexural testing was performed using four‐point fully articulated fixtures for samples measuring 2 × 2 × 50 mm³ across a 40 mm span. Fiber length correlated with improved mechanical properties for flexural strength, modulus, yield strength, strain, work of fracture, and strain energy release, p < 0.001. In addition, sample fracture depth significantly decreased with increasing fiber lengths, p < 0.00001. All mechanical properties correlated significantly as predictors for fracture failure, p < 0.000001, and as estimators for each other, p < 0.0001. The stress‐transfer micromechanics for fiber length were improved upon for strength by including a simple correction factor to account for loss of fiber volume percent related to cracks deflecting around debonded fiber ends. In turn, the elastic property of modulus was shown to exhibit a tendency to follow stress‐transfer micromechanics. Polym. Compos. 27:153–169, 2006. © 2006 Society of Plastics Engineers.     

Molecular orientation distribution in injection-molded polycarbonate discs

The molecular orientation distribution of injection-molded polycarbonate discs is studied using birefringence and heat-shrinkage measurements and laser-Raman spectroscopy. Birefringence and heat shrinkage, which result from the molecular orientation, increase as the distance from the inflow gate decreases and as cylinder temperature decreases. Molecular orientation is reduced following annealing. Laser-Raman spectroscopy is used to measure the molecular orientation distribution along the disc cross-section perpendicular to the radial direction of disc. The relative intensity ratio for the 635 cm^?1 and 703 cm^?1 peaks in the Raman spectra correlate well with the degree of molecular orientation. The disk cross-section is found to consist of three different molecular orientation zones; a skin zone which is in contact with the mold, a core zone located at the center, and a shear zone between the skin and the core zones. Molecules in the skin zone are nonoriented while the orientation of molecules in the core zone is considerably relaxed. The shear zone consists of highly oriented molecules. The formation process of the molecular orientation distribution is discussed in relation to birefringence and heat shrinkage.     

长纤维增强聚合物注塑成型过程中三维网络结构的调控

以长玻纤增强聚丙烯(PP)注塑制品为研究对象,通过引入微、纳尺度第二增强相调控长纤维在注塑制品中的取向度,从而获得取向度较低的皮层结构,以诱导长纤维在注塑件空间内形成连续、均匀的三维网络结构,从而明显提高制品的力学性能。对不同尺度混杂填充长纤维注塑微观结构的比较分析结果表明:加入纳米尺度第二相碳纳米管(CNTs),在基体黏度提高和CNTs、长纤维交互作用的双重影响下,增加了纤维沿着基体流动方向的阻力,改变了纤维的取向,降低了注塑制品皮层的纤维取向度。但是,由于树脂黏度提高,对纤维的剪切作用增强,纤维折损率加大,其强化效应有所减弱。比较而言,长碳纤维与长玻纤混杂填充,由于纤维间的相互搭接形成的三维骨架结构,既降低了制品微观结构取向度,又提高了制品的力学性能。以自制的长纤维增强PP材料注塑成型了汽车座椅骨架,验证了该微观结构调控的有效性。     

Extrusion blow molding of long fiber reinforced polyolefins

A 58% (by weight) long glass fiber reinforced (LGF)‐HDPE master batch was blended with a typical blow molding HDPE grade. HDPE composites having between 5% and 20% (by weight) long fiber content were extruded at different processing conditions (extrusion speed, die gap, hang time). The parison swell (diameter and thickness) decreased with increasing fiber content. Although the HDPE exhibited significant shear rate dependence, the LGF/HDPE composites were shear rate insensitive. Both the diameter and weight swell results also indicated very different sagging behavior. The LGF/HDPE parisons did sag as a solid‐body (equal speed at different axial locations) governed by the orientation caused by the flow in the die. Samples taken from blown bottles showed that fiber lengths decreased to 1‐3 mm, from the original 11 mm fiber length fed to the extruder. No significant difference in fiber length distribution was found when samples for different regions of the bottle were analyzed. SEM micrographs corroborate the absence of fiber segregation and clustering or the occurrence of fiber bundles (homogeneous spatial fiber distribution) as well as a preferential fiber orientation with the direction of flow. The blowing step did not change the orientation of the fibers. Five‐percent (5%) and 10% LGF/HDPE composites could be blown with very slight variations to the neat HDPE inflation conditions. However, 20% LGF/HDPE composites could not be consistently inflated. Problems related to blowouts and incomplete weldlines were the major source of problems.     

The effect of ultrasonic waves on the structure of polyester fibers (PET)

The effect of ultrasonic waves at constant intensity of 20 W/cm² and frequency of 2 × 10⁶ Hz on the microstructure of polyester fibers has been examined. Crystallinity, crystallite size, total orientation, and crystallite orientation have been estimated. It has been found that when subjected to different ultrasonic tests, the degree of fiber orientation decreases and crystalline perfection improves. The changes in crystallinity and crystallite size proved to be particularly difficult to determine with certainty.     

Effect of microstructure induced by microcellular injection molding on electromagnetic interference shielding properties

Preparing lightweight and versatile products is the unremitting goal of industry to save resources and energy. Lightweight carbon fiber reinforced polypropylene (CF/PP) composite foams with high-performance electromagnetic interference (EMI) shielding materials were fabricated by microcellular injection molding (MIM) technology. The average length and distribution of CF in CF/PP composite foams were examined. Thanks to the introduction of foaming process, the average CF length of composite foams was 33.98% longer than that of solids, which effectively enhanced the electrical conductivity and EMI shielding properties. The effect of shot size, gas content, and injection rate on the electrical conductivity and EMI properties was investigated. With melt shot size of 2/3 of the cavity volume, gas content of 0.5 wt% N₂ and injection rate of 100 mm/s, optimal cellular structure of the composite material was obtained. The EMI shielding effectiveness (SE) reaches 36.94 dB, which is the highest value achieved by using MIM technology to the best of the authors' knowledge. In addition, the mechanical properties of cellular structure can still maintain good values, with the tensile strength and impact strength improved by 15.3% and 14.03%, respectively.     

黄麻纤维增强聚丙烯的力学性能

本文讨论了注塑成型黄麻纤维增强聚丙烯的制备方法和力学性能.将纤维重量含量分别为10%、20%和30%的复合材料进行比较,分析纤维含量对复合材料拉伸、弯曲和冲击性能的影响;将纤维分别切成约3mm、5mm和10mm长制成复合材料进行比较,分析纤维长度对复合材料拉伸、弯曲和冲击性能的影响.掺入黄麻纤维能使聚丙烯的拉伸和弯曲性能提高,但使其冲击强度降低;随纤维含量的增加或纤维长度的增加,复合材料的强度和模量是递增的,而冲击强度是递减的.     

Ultrahigh molecular weight polyethylene fibers prepared using conical dies with varying dimensions

Dimensions of conical dies were found to have a significant influence on thermal, morphological, orientation, ultradrawing, and dynamic mechanical properties of the as‐prepared and/or drawn ultrahigh molecular weight polyethylene (UHMWPE) fiber specimens prepared in this study. Many demarcated “micro‐fibrils” were found paralleling to fiber direction of the as‐prepared UHMWPE fiber specimens. The percentage crystallinity, melting temperatures, orientation factor (f_o) and achievable draw ratio (D_ra) values of each as‐prepared UHMWPE fiber specimen prepared at a fixed length of outlet land reach a maximum value, as the entry angles of the conical die approach the optimum value at 75°. The maximum f_o and D_ra values obtained for each F₂₀^75‐y as‐prepared fiber series specimens prepared using the optimum entry angle reach another maximum value as their length of outlet land approach the optimum value of 6.5 mm. The ultimate tensile strengths and moduli of the drawn UHMWPE fibers prepared at the optimum entry angle and length of outlet land are significantly higher than those of fibers prepared at other conditions but stretched to the same draw ratio. Possible reasons accounting for the above interesting properties were discussed in this study. POLYM. ENG. SCI., 2013. © 2013 Society of Plastics Engineers     

Injection and stabilization of mesophase pitch in the fabrication of carbon-carbon composites. Part I. Injection process

The fabrication of carbon-carbon composites by injection of low viscosity mesophase pitch through a fiber preform followed by stabilization and carbonization was examined. The fully transformed mesophase MOMP and AR pitches were injected through either soft or rigidized disk preforms 35 mm thick and 68 mm in diameter. Injection provided good even filling of major flow channels and fiber bundles. Flow-induced fibrous microstructures were retained by quenching and preserved by stabilization upon carbonization. A second injection cycle was effective in filling voidage created by thermal densification. A third cycle was applied, but required severe injection conditions and provided only incremental improvement. The carbon-carbon composite reached a density of 1.8 g/cm³ after three injection cycles.