Injection molding of long sisal fiber–reinforced polypropylene: Effects of compatibilizer concentration and viscosity on fiber adhesion and thermal degradation

A two‐step process was used to obtain long sisal fiber‐polypropylene (SF/PP)–reinforced thermoplastic composites, using maleic anhydride grafted polypropylene (MA‐g‐PP) as a compatibilizer. At a first stage, modified polypropylenes (mPP) were used for an extrusion impregnation process, for the preparation of composite pellets containing about 70 wt% of SF. SF/mPP pellets with a large aspect ratio were prepared by continuous extrusion impregnation of a continuous SF yarn, using a single screw extruder and an adequate impregnation die. The mPP used were MA‐g‐PP and regular polypropylene (PP), modified by reaction with different amounts of an organic peroxide. The composite pellets were thus dry blended with regular PP pellets in an injection machine hopper, and injection molded to obtain composite tensile specimens with a minimum quantity of modified polypropylene, minimum fiber breakage and thermal degradation, and excellent mechanical properties. It is shown that the fiber breakage is reduced to a minimum, even for recycled composites, due to the presence of the low‐viscosity polymer layer wetting the SF fibers. The bulk composite effective viscosity and the fiber breakage extent and thermal degradation during the injection‐molding step are found to be closely related. Blending with much less expensive mPP at the impregnation stage optimizes the amount of expensive MA‐g‐PP. POLYM. ENG. SCI., 45:613–621, 2005. © 2005 Society of Plastics Engineers     

Performance of long glass fiber‐reinforced polypropylene composites at different injection temperature

Long glass fiber‐reinforced polypropylene composites were prepared using self‐designed impregnation device. Effects of the different injection temperature on mechanical properties, crystallization, thermal, and dynamic mechanical properties of long glass fiber‐reinforced polypropylene composites were discussed. The differential scanning calorimetry (DSC) results indicate that the melting peak temperature of PP/LGF composites gradually reduced, however, the crystallinity of PP/LGF composites gradually increased with increasing injection temperature. Thermo‐gravimetric analyzer (TGA) results demonstrate that with increasing injection temperature, the temperature of the PP/LGF composites melt increased, the viscosity of the PP/LGF composites melt lowered, the mold filling of the PP/LGF composites melt was easy, the shear force of glass fiber was relatively low, which made the residual length of glass fiber in products increase. Dynamic thermal mechanical analyzer (DMA) results show that the storage modulus of PP/LGF composites is the highest while the injection temperature is at 290°C, and the peak value of tan σ of PP /LGF composites at 290°C is minimal, which indicates that the mechanical properties of PP /LGF composites at 290°C is the best. What' more, the injection temperature at 290°C significantly ameliorated “glass fiber rich skin” of products of glass fiber‐reinforced composites. J. VINYL ADDIT. TECHNOL., 24:233–238, 2018. © 2016 Society of Plastics Engineers     

Effect of packing pressure on fiber orientation in injection molding of fiber‐reinforced thermoplastics

Injection molding of fiber‐reinforced polymeric composites is increasing with demands of geometrically complex products possessing superior mechanical properties of high specific strength, high specific stiffness, and high impact resistance. Complex state of fiber orientation exists in injection molding of short fiber reinforced polymers. The orientation of fibers vary significantly across the thickness of injection‐molded part and can become a key feature of the finished product. Improving the mechanical properties of molded parts by managing the orientation of fibers during the process of injection molding is the basic motivation of this study. As a first step in this direction, the present results reveal the importance of packing pressure in orienting the fibers. In this study, the effects of pressure distribution and viscosity of a compressible polymeric composite melt on the state of fiber orientation after complete filling of a cavity is considered experimentally and compared with the simulation results of Moldflow analysis. POLYM. COMPOS. 28:214–223, 2007. © 2007 Society of Plastics Engineers     

Kudzu fiber‐reinforced polypropylene composite

Kudzu fiber‐reinforced polypropylene composites were prepared, and their mechanical and thermal properties were determined. To enhance the adhesion between the kudzu fiber and the polypropylene matrix, maleic anhydride‐grafted polypropylene (MAPP) was used as a compatibilizer. A continuous improvement in both tensile modulus and tensile strength was observed up to a MAPP concentration of 35 wt %. Increases of 24 and 54% were obtained for tensile modulus and tensile strength, respectively. Scanning electron microscopy (SEM) showed improved dispersion and adhesion with MAPP. Fourier transform infrared (FTIR) spectroscopy showed an increase in hydrogen bonding with an increase in MAPP content. Differential scanning calorimetry (DSC) analysis indicated little change in the melting temperature of the composites with changes in MAPP content. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 1961–1969, 2002     

Effect of dynamical converging channels on fiber organization and damage during vane extrusion of sisal fiber‐reinforced polypropylene composites

It is well known that converging channel can generate elongational deformation field. In this study, novel dynamical converging channels were successfully incorporated into plant fiber‐reinforced thermoplastics composites processing. A dynamical elongational deformation field (DEDF) generated by these channels was studied. The fiber organization and damage in the DEDF has been investigated in terms of its relationship to changes in rotating speed of the channels. A vane extruder based on these channels was used to prepare sisal fiber‐reinforced polypropylene composites. By investigating rapidly cooled samples in the vane extruder, sisal fiber in the center part of these channels has an orientation with an angle to the discharging direction. Rotating speed increases from 30 to 90 r/min result in 30.99–42.7% decreases in average fiber length. The issues of fiber distribution and voids formation have been related to the mechanical properties of the composites, particularly tensile strength and modulus. Increased rotating speeds from 30 to 90 r/min results in tensile strength and modulus increases of about 21.3% and 11.6%, respectively. The majority of this change is caused by decreased voids formation with the increases of speed, which is in agreement with scanning electron microscopy of the composites. POLYM. COMPOS., 2012. © 2011 Society of Plastics Engineers     

Properties enhancement of short glass fiber‐reinforced thermoplastics via sandwich injection molding

This article demonstrates using sandwich injection molding in order to improve the mechanical properties of short glass fiber‐reinforced thermoplastic parts by investigating the effect of fiber orientation, phase separation, and fiber attrition compared to conventional injection molding. In the present case, the effect of short glass fiber content (varying from 0–40 wt%) within the skin and core materials were studied. The results show that the mechanical properties strongly depend not only on the fiber concentration, but also on the fiber orientation and the fiber length distribution inside the injection‐molded part. Slight discrepancies in the findings can be assumed to be due to fiber breakage occurring during the mode of processing. POLYM. COMPOS., 26:823–831, 2005. © 2005 Society of Plastics Engineers     

Properties and process ability of long fiber‐reinforced polymeric composites

The addition of nanoparticles to polymeric matrices has shown great promise for improving mechanical and thermal properties; however, this improvement comes with a decrease of processability. In this study, two different glass fabrics were used. One of them was Windstrand, a stitched equally‐biaxial R‐glass fabric the other was Advantex, a unidirectional glass fiber mat. Both of them are provided by Owens Corning. The mats were sprayed with carbon nanofibers (CNF) on both sides. Mechanical properties of composites manufactured via vacuum‐assisted resin transfer molding were obtained. Permeability, as a measure of processability, of the sprayed glass mats was measured. Mechanical properties are improved, whereas permeability decreases with the addition of CNF. POLYM. COMPOS., 35:655–664, 2014. © 2013 Society of Plastics Engineers     

Influence of fiber orientation on high stress wear behavior of sisal fiber‐reinforced epoxy composites

Sisal fiber‐reinforced epoxy composites having three different fiber orientations, namely LL, LT, TT mentioned in the text were prepared and tested for their high stress abrasive wear behavior. Effect of fiber orientation, sliding distance, and load on abrasive wear of sisal–epoxy composites have been determined. Wear data of composites have been compared with the pure epoxy. Incorporation of fibers decreases the wear rate of epoxy resin, which varies with the fiber orientation. Wear rate in case of TT composite is found minimum as compared to other two composites. Wear rate follows the following trend, W_TT < W_LT < W_LL. Owing to minimum exposed area of fiber to the sliding asperities, lowest wear rate occurs in the case of TT composite. Increase of load and sliding distance increases the wear volume in all the composites, because of the progressive loss of material. Wear mechanism has been discussed by using SEM micrographs of the worn surfaces. POLYM. COMPOS., 28:437–441, 2007. © 2007 Society of Plastics Engineers.     

Fracture behavior of sisal fiber–reinforced starch‐based composites

The fracture behavior of biodegradable fiber–reinforced composites as a function of fiber content under different loading conditions was investigated. Composites with different fiber content, ranging from 5 to 20 wt%, were prepared using commercial starch‐based polymer and short sisal fibers. Quasistatic fracture studies as well as instrumented falling weight impact tests were performed on the composites and the plain matrix. Results showed a significant increase in the crack initiation resistance under quasistatic loading. This was caused by the incorporation of sisal fibers to the matrix and the development of failure mechanisms induced by the presence of the fibers. On the other hand, a modest increasing trend of the resistance to crack initiation with fiber loading was detected. An improved fracture behavior was also observed when the impact loading was parallel to the thickness direction. Under these experimental conditions, the composites exhibited higher values of ductility index, energy at initiation and total fracture energy than the plain matrix. Furthermore, an increasing trend of these parameters with fiber content was detected in the biocomposites. Overall, the addition of sisal fibers to the biodegradable matrix appears to be an efficient mean of improving fracture behavior under both quasistatic and impact loading conditions. POLYM. COMPOS. 26:316–323, 2005. © 2005 Society of Plastics Engineers     

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.     

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.     

Correlation between processing conditions and fiber breakage during compounding of glass fiber‐reinforced polyamide

The inter‐relationship between processing conditions and fiber breakage has been studied for glass fiber‐reinforcedpolyamide 12, prepared using (i) an internal batch mixer, (ii) a laboratory scale corotating twin screw extruder, and (iii) an industrial scale twin screw extruder. The average fiber lengths and fiber length distributions were measured for various compounding conditions (screw or rotor speed, mixing time, feed rate). Experimental results have shown that fiber breakage depends on both screw speed and mixing time, the later being controlled, in an extruder, by the feed rate. For a given compounding system (batch mixer or twin screw extruder), the energy input (specific mechanical energy, SME) during the compounding process is found to be a reliable parameter, which governs fiber length (average, minimal, and maximal) evolution. Experimental data are correctly described with a model defining change in fiber length as a function of SME. POLYM. COMPOS., 2011. © 2011 Society of Plastics Engineers     

Effect of impregnation time on performance of long glass fiber‐reinforced polypropylene composites

Long glass fiber (LGF)‐reinforced polypropylene (PP) composites were prepared using self‐designed impregnation device. Effects of impregnation time on mechanical properties, crystallization, dynamic mechanical properties, and morphology of PP/LGF composites were investigated. The experiment results demonstrate that the excellent tensile strength, Notched Izod impact strength was 152.9 MPa, 31.2 KJ/m², respectively, and the stiffness of PP/LGF composites was higher, when the impregnation time was 7.03 s. The excellent interfacial adhesion between PP and glass fiber indicates that PP/LGF composites possess the outstanding mechanical properties. The impregnation time scarcely influenced thermal properties of PP/LGF composites. J. VINYL ADDIT. TECHNOL., 24:174–178, 2018. © 2016 Society of Plastics Engineers     

Flow‐induced fiber orientation in injection molded fit fiber reinforced polypropylene

A through experimental study of flax fiber orientation in a plate processed by injection molding is presented. The state of orientation is described by oriental tensors and partly by frequency distribution diagrams. Composite stiffness is predieted by use of a modified classical laminate theory including unidirectional mels and orientation averaging. Comparison of the measured and calculated modulus in tension shows good agreement.     

Mechanical properties of short sisal fiber‐reinforced polypropylene composites: Comparison of experimental data with theoretical predictions

Sisal fibers were used for the reinforcement of a polypropylene (pp) matrix. Composites consisting of polypropylene reinforced with short sisal fibers were prepared by melt‐mixing and solution‐mixing methods. A large amount of fiber breakage was observed during melt mixing. The fiber breakage analysis during composite preparation by melt mixing was carried out using optical microscopy. A polynomial equation was used to model the fiber‐length distribution during melt mixing. The experimental mechanical properties of sisal/PP composites were compared with existing theoretical models such as the modified rule of mixtures, parallel and series models, the Hirsch model, and the Bowyer–Baders model. The dependence of the tensile strength on the angle of measurement with respect to fiber orientation also was modeled. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 602–611, 2003     

Impact fracture behavior of injection molded long glass fiber reinforced polypropylene

In this work the variation in Izod impact strength with spatial location was examined for injection molded long glass fiber polypropylene composite plaques. These plaques were fabricated at different sets of processing conditions, with injection speed and melt temperature being varied. By carefully machining test specimens, fifteen different plaque locations both in the in-flow and cross-flow directions were tested. The part morphology was described with the use of characteristic layer thickness ratios, i.e., the shell and the core to part thickness ratios, which were measured experimentally. It was shown that the variation in impact strength with sample location strongly correlates to shell to part thickness ratio. In addition, it was observed that different failure mechanisms exist for different fiber orientations, i.e., for fibers oriented transversely to the crack plane or on the crack plane itself. Scanning electron microscopy (SEM) of the fracture surface was conducted and the results supported our findings on the microstructural level.     

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

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

The 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.     

Long jute fiber‐reinforced polypropylene composite: Effects of jute fiber bundle and glass fiber hybridization

Two types of long jute fiber pellet consisting of twisted‐jute yarn (LFT‐JF/PP) and untwisted‐jute yarn (UT‐JF/PP) pellets are used to prepare jute fiber–reinforced polypropylene (JF/PP) composites. The mechanical properties of both long fiber composites are compared with that of re‐pelletized pellet (RP‐JF/PP) of LFT‐JF/PP pellet, which is re‐compounded by extrusion compounding. High stiffness and high impact strength of JF/PP composites are as a result of using long fiber. However, the longer fiber bundle consequently affects the distribution of jute fiber. The incorporation of 10 wt % glass fibers is found to improve mechanical properties of JF/PP composites. Increasing mechanical properties of hybrid composites is dependent on the type of JF/PP pellets, which directly affect the fiber length and fiber orientation of glass fiber within hybrid composites. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41819.     

Localized thermal analysis of carbon fiber‐reinforced polypropylene composites

The effect of carbon fiber (CF) and annealing temperature on polypropylene (PP) microstructure was studied. The crystalline state of polymer matrix was found to be a strong function of thermal history. The effect of annealing temperature on the microstructure evolution of PP in the presence of CFs was characterized by using X‐ray diffraction, DSC and localized thermal analysis. The melting behavior of CF‐reinforced PP composite was strongly dominated by the thermal history and was weakly influenced by the presence of CFs. The interface between a CF and PP matrix was found to be weak. POLYM. COMPOS., 2012. © 2012 Society of Plastics Engineers