Long Glass Fiber Reinforced Polypropylene Research Articles

The Low Breaking Fiber Mechanism and Its Effect on the Behavior of the Melt Flow of Injection Molded Ultra-Long Glass Fiber Reinforced Polypropylene Composites.

In this study, fiber breaking behavior, fiber orientation, length variation, and changes in melt flow ability of long glass fiber reinforced polypropylene (L-FRP) composites under different mold cavity geometry, melt fill path, and plasticization parameters were investigated. The matrix material used was polypropylene and the reinforcement fibers were 25 mm long. An ultra-long-fiber composite injection molding machine (with a three-stage plunger and injection mechanism design) was used with different mold cavity geometry and plasticization parameters. Different screw speeds were used to explore the changes in fiber length and to provide a reference for setting fiber length and parameter combinations. Flow-length specimen molds with different specimen thickness, melt fill path, and gate design were used to observe the effect of plasticizing properties on the flow ability of the L-FRP composite materials. The experimental results showed that the use of an injection molding machine with a mechanism that reduced the amount of fiber breakage was advantageous. It was also found that an increase in screw speed increased fiber breakage, and 25 mm long fibers were shortened by an average of 50% (to 10 mm). Long fibers were more resistant to melt filling than short fibers. In addition, the thickness of the specimen and the gate design were also found to affect the filling process. The rounded angle gate and thick wall product decreased the flow resistance and assisted the flow ability and fiber distribution of the L-FRP injection molding.

Design and multi‐objective optimization of the bumper beams prepared in long glass fiber‐reinforced polypropylene

AbstractThere is an increasing demand for lightweight materials in the automobile industry. In this study, the crashworthiness and crash safety performance of automobile bumper beams made of long glass fiber‐reinforced polypropylene (LGFR‐PP) composites were evaluated. First, LGFR‐PP with the 40% glass fiber was prepared by the hot‐melt impregnation method, the mechanical properties and Poisson's ratio of the LGFR‐PP specimens were tested, which are essential for the finite element analysis. Then a finite element model of aluminum alloy and LGFR‐PP bumpers was established to obtain their peak collision force, maximum intrusion, and energy absorption values under longitudinal and angular low‐speed collision conditions. Subsequently, the multi‐objective optimization was generated using optimized Latin square sampling and response surface test design, and the section thickness of the bumper beams was optimized. The results showed that Swift and Hockett's hardening model is suitable for the LGFR‐PP material. Based on the principle of equal stiffness, the mass of the anti‐collision beams made of LGFR‐PP is reduced by 17.4%, the specific energy absorption (SEA) is increased by 6%, and the cost is reduced by 69%, and both the peak impact force and the amount of collision intrusion are reduced. The multi‐objective optimized Latin hypercube experimental showed that the continuously variable cross‐section beam based on the thickness optimization balanced the impact resistance especially SEA and lightweight performance very well.

Effect of Fiber Length on Mechanical Properties of Injection Molded Long-Fiber-Reinforced Thermoplastics

Fibers of long-fiber-reinforced thermoplastic (LFT) pellets are longer than those of short-fiber-reinforced thermoplastic (SFT) pellets produced by extrusion. To overcome the fiber length limitations of the SFT pellets, LFT pellets were prepared by a pultrusion process using continuous fibers, which afforded longer fibers. Currently, long glass-fiber-reinforced polypropylene (LGF-PP) materials, which are one of the growing markets of the plastics industry, are typically used, particularly for applications in the automotive industry where lightweight performance and cost savings are required. The LFT pellets are primarily converted into the final product by injection molding. During the injection molding process, the LFT pellets are broken and the fiber length decreases as a consequence. In this study, glass and carbon-fiber-reinforced polypropylene of various pellet lengths (3-16 mm) were prepared by impregnating pultrusion process to evaluate the effect of mechanical properties according to fiber length. The length of the residual fibers recorded after injection molding were observed to decrease in proportion to the pellet length. Even with LFTs having the same material composition, the mechanical properties was different after injection molding according to the residual fiber length. In this injection molded LFT, the flexural modulus was higher as the residual fiber length was shorter. The impact strength was larger in samples without adhesive resin and the observed differences were larger for longer fiber lengths. From these results, the mechanical properties of LFT can be improved by understanding the properties of long fibers.

Theoretical study and physical tests of circular hole-edge stress concentration in long glass fiber reinforced polypropylene composite

The long glass fiber reinforced polypropylene (LGFRP) composite has been widely used in automotive components due to its remarkable advantages of high mechanical properties and flexible design features. Automotive structural components usually suffer various intrinsic hole-edge stress concentration in mechanical joints. Thus, the objective of this work is to investigate the circular hole-edge stress concentration of the LGFRP composite. A theoretical model, which is in view of cutting area and damage factor, is originally developed to predict the hole-edge stress concentration in LGFRP composite with regard to the hole size effect. Corresponding physical tests were conducted under tensile loading monitored by a digital image correlation (DIC) system. The experimental results reveal that the influenced area of the stress concentration is within the range of four times of the hole radius. The theoretical predictions are in good agreement with the experimental results. The stress concentration factor (SCF) is calculated to demonstrate that SCF increases with the increasing circular hole radius. The conclusions obtained from this work lay the basis on the mechanical performance of the LGFRP composite subject to hole-edge stress concentrations, and is of importance to rationalize appropriate design of the LGFRP composite in automotive components.

Fracture and Orientation of Long‐Glass‐Fiber‐Reinforced Polypropylene During Injection Molding

Injection processing parameters directly influence the final fiber length and may have a negative effect on the mechanical properties of a part. The aim of the work is to investigate and quantify the effects of the injection rate (2/10/50 cm3/s) on the fiber length, the distribution, and orientation during injection molding and the mechanical properties of long‐glass‐fiber‐reinforced polypropylene (LGF/PP) by experimental and simulated methods. When the injection rate increases from 2 to 10 cm3/s, the fiber length sharply decreases from the original 11 mm to 3.43 mm at the nozzle and 1.30 mm at the filling end, and almost 88% of the fibers are less than 3 mm when the injection rate is 50 cm3/s. A distinct hierarchical orientation (skin‐shear‐core) for the fiber distribution in the thickness is obtained via a metallographic microscope, which shows that the shear layer (here the shear stress is larger and the fiber is more inclined to oriented along the flow direction) decreases with increasing injection rate. Moreover, the numerical results of the residual fiber length and orientation at different injection rates are in accord with the trend of the measured results. POLYM. ENG. SCI., 60:13–21, 2020. © 2019 Society of Plastics Engineers

Coupling investigation on tensile and acoustic absorption properties of lightweight porous LGF/PP composite

Long glass fiber‐reinforced polypropylene (LGF/PP) foaming composite has been increasingly used in automotive components regarding its good mechanical and acoustic properties. However, the balance of its mechanical property and acoustic property is far from being understood. The objective of this study is to investigate the influences of molding thickness or foaming degree on both mechanical and acoustic properties of LGF/PP foaming composite by experimental tests. First, LGF/PP foaming composite felts with consistent surface density were fabricated, then specimens with a series of molding thicknesses were prepared by compression molding. Tensile and acoustic tests were conducted and a scanning electron microscopy was also used for analyzing microscopic characteristics. The results indicate that tensile strength and tensile modulus of the present LGF/PP composite decrease in exponential formats, whereas sound absorption coefficients of them increase in logarithmic formats, when molding thickness vary from 1.5 to 8 mm. The above curves intersect around 3 mm. Thus, both mechanical and acoustic properties should be balanced regarding structural size when designing a multi‐purpose vehicle component using the present composite. POLYM. COMPOS., 40:1315–1321, 2019. © 2018 Society of Plastics Engineers

Experimental and numerical investigation of Long Glass Fiber Reinforced Polypropylene composite and application in automobile components

Due to the good mechanical performances and design flexibility of Long Glass Fiber Reinforced Polypropyl-ene (LGFRP) composite, it has been increasingly used in the automotive components, in which the LGFRP components are likely to sustain different strain rates loading during a crash event. This study aims to investigate the correlations between the LGFRP and strain rate, which will be applied to crash-worthiness and energy absorbing property analysis of a bumper beam under the longitudinal impact. Firstly, strain rate dependent material properties are determined, for which the experimental procedure is explained in detail on the tensile specimens of long glass fiber and polypropylene matrix based composite configurations. The gained experimental results provide the input parameters for a numerical analysis of specimens. The numerical results of properties are compared with those from tests. The constitutive model that fits for LGFRP is employed to crash-worthiness and energy absorbing property analysis of a bumper beam under the longitudinal impact. First Published Online: 17 May 2017

Brominated flame retardant composed of decabromodiphenyl oxide and antimonous oxide flame retardant for long glass fiber-reinforced polypropylene

An efficiently brominated flame-retardant system which is composed of decabromodiphenyl oxide (DB) and antimonous oxide (AO) was used for long glass fiber-reinforced polypropylene (LGFPP), and the thermal stability, flame retardancy, and mechanical properties of DB-AO/LGFPP composites were investigated. When 12 wt% of DB-AO flame retardant was added into LGFPP, the limiting oxygen index of composites could reach 24.8 and pass the V-0 rating in UL-94 test. The results showed that DB and AO improved the flame retardancy of LGFPP more efficiently which could be proved by thermogravimetric test that had less effect on mechanical properties than widely used intumescent flame retardant to flame-retardant LGFPP. What’s more, analysis of cone calorimeter tests data indicated that gas phase flame-retardant mechanism exists in the DB-AO/LGFPP composites.

Flame Retardancy and Mechanical Properties of Brominated Flame Retardant for Long Glass Fiber Reinforced Polypropylene Composites

The effects of brominated flame retardant which composed of decabromodiphenyl ethane (DBDPE) and antimonous oxide (AO) on long glass fiber reinforced polypropylene (LGFPP) were investigated by means of limiting oxygen index (LOI), vertical burning (UL-94), thermogravimetry analysis (TGA), and mechanical properties. With the increase of DBDPE-AO content, the LOI values of DBDPE-AO/LGFPP composites increased from 21 to 27.6, and when the content of DBDPE-AO was 16wt%, the composites passed the V-0 rating in UL-94 testing. The experimental results showed that the brominated flame retardant improved flame retardancy of LGFPP, which was proved by the TGA testing. Whats more, the mechanical properties of composites even improved compared with pure LGFPP.

An Efficiently Brominated Flame Retardant Composed of Decabromodiphenyl Oxide and Antimonous Oxide for Long Glass Fiber Reinforced Polypropylene

An efficiently brominated flame retardant which composed of decabromodiphenyl oxide (DB) and antimonous oxide (AO) was used to flame retardant for long glass fiber reinforced polypropylene (LGFPP). In order to investigate the thermal stability, flame retardancy and mechanical property of DB-AO/LGFPP composites used by thermogravimetric analysis (TGA), limiting oxygen index (LOI), vertical burning (UL-94) and mechanical property tests. The results showed that brominated flame retardant improved flame retardancy of LGFPP efficiently can be proved by TGA, and had less affected on mechanical properties.

Mechanical properties of long glass fiber-reinforced polypropylene composites and their influence factors

In this article, long glass fiber-reinforced polypropylene (LFPP) was prepared using self-designed impregnation device. The effects of some processing parameters including impregnation time and temperature, compatibilizer and melt flow index (MFI) of matrix which was adjusted by chemical degradation masterbatch on the impregnation quality, and mechanical properties of injection molded LFPP were discussed. Our studies show that increase in MFI of polypropylene, impregnation time and temperature, as well as addition of compatibilizer maleic anhydride grafted polypropylene (PP-g-MAH), can improve impregnation quality and mechanical properties of LFPP. The results will be useful in making high performance LFPP.

Abrasive behavior of discontinuous fiber reinforced polypropylene material

PurposeThe purpose of this paper is to understand the influence of reinforced fiber length over material‐plastic energy of deformation, clogging, crystallinity, and correlates with the friction and wear behavior of polypropylene (PP) composites under multi‐pass abrasive condition. Also to identify wear mechanisms of glass fiber reinforced PP materials under various abrasive grit sizes and normal loads.Design/methodology/approachMulti‐pass abrasive wear tests were performed for unreinforced, short, and long glass fiber reinforced PP (LFPP) on a pin on disc machine under three different normal loads and two different abrasive grit sizes for a constant sliding velocity. Measured wear volume was correlated with the plastic energy of deformation by carrying out a constant load indentation test using servo hydraulic fatigue test system. Clogging behavior of test materials was examined with the aid of online wear measurement and wear morphology. Test materials crystallinity was estimated with the aid of X‐ray diffraction investigation and correlated with abrasive wear performance.FindingsFiber reinforcement in a PP material is found to improve the plastic deformation energy and crystallinity which results in improved abrasive resistance of the material. Increase in reinforced fiber length is found to improve the material cohesive energy and hence the wear resistance. Reinforcement is found to alter the material clogging behavior under multi‐pass condition. Fiber reinforcement is found to reduce the material coefficient of friction, and increase in reinforced fiber length further reduces the frictional coefficient.Research limitations/implicationsFriction wear tests using pin on disc equipment is carried out in the present investigation. However, in practice, part geometry may not be always equivalent to simple pin on disc configuration.Practical implicationsThe paper's investigation results could help to improve the utilization of LFPP material in many structural applications.Originality/valueInfluence of reinforced fiber length over multi‐pass abrasive wear performance of thermoplastic material, and online wear measurement to substantiate clogging behavior is unique in the present multi‐pass abrasive investigation.

An efficiently halogen-free flame-retardant long-glass-fiber-reinforced polypropylene system

In order to solve the “candlewick effect” caused by glass fibers, which results in the decrease of flame retardancy of flame-retardant long-glass-fiber-reinforced polypropylene (LGFPP) systems, and the deterioration of mechanical properties caused by adding an additional amount of flame retardants compared with flame-retardant non-glass-fiber-reinforced polypropylene systems so as to keep a same flame retardancy, a novel intumescent flame retardant (IFR) system, which is composed of a charring agent (CA), ammonium polyphosphate (APP) and organically-modified montmorillonite (OMMT), was used to flame retard LGFPP. The thermal stability, combustion behavior, char formation, flame retardant mechanism and mechanical properties of the IFR-LGFPP samples were investigated by thermogravimetric analysis (TGA), limiting oxygen index (LOI), UL-94 test, cone calorimeter test, scanning electronic microscopy, and mechanical property tests. When the content of IFR is 20 wt%, the LOI value of IFR-LGFPP reaches 31.3, and the vertical burning test reaches UL-94 V-0 rating, solving the “candlewick effect” caused by long glass fiber without additional amount of the IFR. All the relevant cone calorimeter parameters also show that IFR-LGFPP has much better flame-retardant behaviors than LGFPP. Furthermore, the mechanical properties of IFR-LGFPP almost remain unchanged in comparison with those of LGFPP containing no IFR. The flame retardant mechanism was also discussed.

Shear strength and meltdown behavior of reinforced polypropylene assemblies made by resistance welding

Resistance welding (RW) involves placing an electrically conductive implant between two parts that are mated under pressure. Heat is dissipated in the implant and causes melting, diffusion, flow and ultimately welding to occur. This research examines the RW of long-glass-fiber-reinforced polypropylene (LGF-PP) to continuous-glass-fiber-reinforced polypropylene (CGF-PP) using a stainless steel mesh-implant. The effects of welding time, applied current, and weld pressure on the temperature near the mesh, meltdown and the compression-shear strength of the welds were assessed. The results show that it is possible to attain shear strengths of the order of 20 MPa under optimized welding conditions. The meltdown and strength correlate well with a semi-empirical lumped parameter dependent on weld time, current squared and pressure. This parameter can be used to estimate appropriate welding conditions without the use of complex finite element modeling or extensive experimental work.

Comparison of the fracture and failure behavior of polypropylene composites reinforced by long glass fibers and by glass mats

The static fracture and related failure behavior of injection-molded long-glass-fiber-reinforced polypropylene (LGF-PP) and hot-pressed glass-fiber-mat-reinforced polypropylene (GMT-PP) with the same reinforcement fraction (V f ≈ 0.20) has been studied and compared. It was established that GMT-PP is superior to LGF-PP when fracture toughness and energy are considered under both static and dynamic conditions. The failure mode and sequence of the composites were determined from acoustic emission (AE) analysis by relating AE signal characteristics (amplitude and energy) to the individual failure events. GMT-PP failed in a stepwise manner related to the successive breakdown of the GF mat incorporated. This resulted in a more extended damage zone than for LGF-PP. Size and shape of the damage zone were estimated by mapping the located AE events and by considering infrared thermographic (IT) pictures showing heat evolution in the crack tip region. The damage zone size deduced from AE analysis proved to be lower than that obtained from IT studies. This was attributed to differences in the damage assessment: AE informs us about the development of the full damage zone at every stage of the loading, while IT is sensitive for the process zone (being a part of the damage zone) in the crack growth range. It may be stated that the energy-related toughness of GMT-PP is superior to that of the LGF-PP at the same reinforcement content.