The mechanical properties of woven tape all-polypropylene composites

The creation of highly oriented, co-extruded polypropylene (PP) tapes allows the production of recyclable “all-polypropylene” (all-PP) composites, with a large temperature processing window (>30 °C) and a high volume fraction of highly oriented PP molecules (>90%). This paper describes all-PP composites made from woven tape fabrics and reports the tensile and compressive properties of these, with reference to composite processing conditions and compares these mechanical properties to those of commercial alternatives.     

Filament Winding of Co-Extruded Polypropylene Tapes for Fully Recyclable All-Polypropylene Composite Products

The creation of high-strength co-extruded polypropylene (PP) tapes allows the production of recyclable “all-polypropylene” (all-PP) composite products, with a large temperature processing window and a high fibre volume fraction. Available technologies for all-PP composites are mostly based on manufacturing processes such as thermoforming of pre-consolidated sheets. The objective of this research is to assess the potential of filament winding as a manufacturing process for all-PP composites made directly from co-extruded tapes or woven fabric. Filament wound pipes or rings were tested either by the split-disk method or a hydrostatic pressure test in order to determine the hoop properties, while an optical strain mapping system was used to measure the deformation of the pipe surfaces.     

Direct Forming of All-Polypropylene Composites Products from Fabrics made of Co-Extruded Tapes

Many technologies presented in literature for the forming of self-reinforced or all-polymer composites are based on manufacturing processes involving thermoforming of pre-consolidated sheets. This paper describes novel direct forming routes to manufacture simple geometries of self-reinforced, all-polypropylene (all-PP) composites, by moulding fabrics of woven co-extruded polypropylene tapes directly into composite products, without the need for pre-consolidated sheet. High strength co-extruded PP tapes have potential processing advantages over mono-extruded fibres or tapes as they allow for a larger temperature processing window for consolidation. This enlarged temperature processing window makes direct forming routes feasible, without the need for an intermediate pre-consolidated sheet product. Thermoforming studies show that direct forming is an interesting alternative to stamping of pre-consolidated sheets, as it eliminates an expensive belt-pressing step which is normally needed for the manufacturing of semi-finished sheets products. Moreover, results from forming studies shows that only half the energy was required to directly form a simple dome geometry from a stack of fabrics compared to stamping the same shape from a pre-consolidated sheet.     

All-poly(ethylene terephthalate) composites by film stacking of oriented tapes

Self-reinforced polymer or all-polymer composites have been developed to replace traditional fibre reinforced plastic (FRP) with good interfacial adhesion and enhanced recyclability. Poly(ethylene terephthalate) (PET) is one of the most attractive polymers to be used in these fully recyclable all-polymer composites, in terms of cost and properties. In this work, all-PET composites were prepared by film stacking of oriented PET tapes. A processing temperature window was determined by a series of tests on PET tapes and co-PET films, including DSC and T-peel tests. Tensile properties of PET tape, co-PET film and all-PET composites are reported and compared with a commercial co-extruded PURE^® polypropylene tape. The effect of compaction temperatures and pressures on tensile properties of all-PET composites was investigated to explore the optimum processing parameters for balancing good interfacial adhesion between tapes and residual tensile properties of PET tapes.     

Tensile mechanical and perforation impact behavior of all-PP composites containing random PP copolymer as matrix and stretched PP homopolymer as reinforcement: Effect of β nucleation of the matrix

All polypropylene (all-PP) composites were manufactured by exploiting the polymorphic forms of PP, in which alpha (α)-PP homopolymer tapes worked as reinforcement and β-nucleated random PP copolymer (β-rPP) as matrix. Both unidirectional (UD) and cross-ply (CP) laminates were prepared by tape winding technology combined with a film stacking method followed by hot pressing. To study the efficacy of using β-rPP as matrix, all-PP composites were also prepared with α-PP tape as reinforcement and alpha random PP copolymer (α-rPP) as matrix and their properties were compared. The mechanical performance of the composites was investigated by dynamic mechanical thermal analysis (DMTA), static flexure and dynamic impact tests. The volume fractions of the reinforcement and the void content were estimated by using optical microscope images. Both the DMTA and the static flexural bending tests revealed that the α-PP tape acted as a more effective reinforcement for the β-rPP matrix than for the α-rPP, especially for all-PP composites of UD lay-up. The perforation impact properties were determined from instrumented falling weight impact (IFWI) tests, performed at room temperature. It was found that transcrystalline layer is responsible for the stress transfer from the β-rPP matrix to the α-PP reinforcement.     

Multivariable dependency of thermal shrinkage in highly aligned polypropylene tapes for self-reinforced polymer composites

Self-reinforced composites offer a unique combination of properties such as high specific strength, high impact resistance, and recyclability by incorporating highly aligned fibers within a random matrix of the same polymer. However, high temperatures will shrink the system to recover randomness in the aligned segments, compromising the composite thermal stability during processing as self-reinforced tapes are consolidated into the final composite through heating and pressure. Hence, the dynamic nonlinear multivariable (i.e., time, temperature, stress) shrinkage exhibited by self-reinforced polypropylene (SRPP) tapes was measured and modeled at the maximum shrinkage limit achieved in the proximity of the composite processing temperature [∼140 to160 °C]. At high stress (∼7.5 MPa) the thermal shrinkage of the SRPP tapes was reduced and a parallel creep mechanism was activated. The modeling, and prediction of the main factors governing the thermal shrinkage expand and diversify the dynamic design window for new SRPP composites.     

Dynamic mechanical thermal analysis of all-PP composites based on β and α polymorphic forms

All polypropylene (all-PP) composites were manufactured by exploiting the polymorphic forms of PP, in which alpha (α)-PP tapes worked as reinforcement and beta (β)-PP served as matrix. The mechanical performance of the composite was investigated in a range of frequencies and temperatures using dynamic mechanical thermal analysis (DMTA). The volume fractions of matrix and reinforcement were estimated using optical microscope images. Both the DMTA and the static flexural bending tests revealed that the α-PP tapes act as an effective reinforcement for the β-PP matrix. Time–temperature superposition (TTS) was applied to estimate the stiffness of the composites as a function of frequency (f = 10⁻⁹...10²³) in the form of a master curve. The Williams–Landel–Ferry (WLF) model described properly change in the experimental shift factors used to create the storage modulus versus frequency master curve. The activation energies for the α and β relaxations were also calculated by using the Arrhenius equation.     

The importance of bonding in intralayer carbon fibre/self-reinforced polypropylene hybrid composites

Polymer composites are usually either stiff or tough, but seldom both. Intralayer hybrids of carbon fibre and self-reinforced polypropylene (PP) do offer the potential to achieve a unique combination of toughness and stiffness. In these hybrids, the bonding between carbon fibre prepregs and PP tapes is a crucial parameter. For a weak bonding, the 20% ultimate tensile failure strain and high penetration impact resistance of self-reinforced PP were maintained. For a strong bonding, the ultimate tensile failure strain was strongly reduced, but the flexural performance was improved. For a homopolymer PP matrix in the prepregs, the weak bonding between fibre and matrix caused the penetration impact resistance to reduce according to a linear rule-of-mixtures. For a maleic anhydride modified PP matrix however, the strong fibre–matrix bonding greatly reduced the penetration impact resistance. These results provide new insights into designing hybrid composites with a unique balance of stiffness and failure strain.     

Producing toughened PP/HA-LLDPE ternary bio-composite using a two-step blending method

The mechanical and morphological properties of polypropylene/hydroxyapatite/linear low density polyethylene ternary bio-composites which were produced by blending of polypropylene (PP), hydroxyapatite, modified and unmodified linear low density polyethylene (LLDPE) were studied. In this research, effects of LLDPE weight percent, modification of PP/LLDPE interface by a high crystallizable high density polyethylene, and the method of blending on tensile strength, Young’s modulus and impact absorbed energy of composites were investigated. Results of mechanical tests showed that by adding LLDPE to these composites, ultimate tensile strength and Young’s modulus of the composites dropped slightly, while their impact strength was increased significantly. Mechanical properties of composites were improved by modification of PP/LLDPE interface and changing from one-step blending to two-step blending. However, for the composites produced by two-step blending, by adding modified LLDPE (15 wt.%), the impact strength was 90% more than that of pure PP/HA composites. Fractography of the surface fractures of the impact samples for both types of composites were performed using a scanning electron microscope (SEM). Two different toughening mechanisms of these composites were distinguished by drawing a schematic sketch of the mechanisms.     

Microcellular polypropylene single-polymer composites prepared by insert-microcellular injection molding

An insert-microcellular injection molding process was performed on an injection molding machine equipped with a supercritical fluid system. The prepared microcellular polypropylene (PP) single-polymer composites (SPCs) combine the advantages of SPCs with benefits of microcellular plastics, they hold the promise for further reduced weight, improved fiber-matrix interface and enhanced recyclability. In comparison with the solid PP, the weight reductions of the tensile and impact microcellular PP SPCs (MPPSPCs) could be up to 12.9% and 3.3% respectively, the tensile and impact strengths of the MPPSPCs were improved by 59% and 1799% respectively. Based on the tensile properties, the injection temperature of 220 °C and injection speed of 70 mm/s were the optimum processing for the tensile MPPSPC samples. The typical morphology structure of the MPPSPC sample includes five different layers: sandwiched fabric layer, transition layer between fabric and core, center core layer, transition layer between skin and center core, skin layer.     

硼酸酯改性Mg2B2O5W/PP复合材料界面及其力学性能

为了提高聚丙烯(PP)的强韧性能,采用熔融共混法分别制备了质量分数为0～15%的Mg2B2O5晶须(MBOw)和硼酸酯偶联剂(BE)改性MBOw填充PP基复合材料,测试了PP及其复合材料的拉伸、冲击性能,并通过红外光谱、接触角测试、扫描电镜分析等对复合材料界面作用机理进行了研究.结果表明:MBOw与BE之间存在化学和物理吸附层;PP与BE处理前后的MBOw之间不存在化学键合;BE改性MBOw/PP复合材料中PP与MBOw之间的粘附功和表面张力之比由BE表面处理前的8.7增至处理后的315.0,明显改善了基体中MBOw的分散性及其界面结合性能,提高了BE改性MBOw/PP复合材料的拉伸及冲击性能.     

Development of woven fabric reinforced all-polypropylene composites with beta nucleated homo- and copolymer matrices

In the present work self-reinforced polypropylene composites (SRPPC) were developed and investigated. As reinforcement a fabric, woven from highly stretched split PP yarns, whereas as matrix materials α and β crystal forms of isotactic PP homopolymer and random copolymer (with ethylene) were selected and used. The composite sheets were produced by film-stacking method and compression moulded at different processing temperatures keeping the holding time and pressure constant. The quality of the composite sheets was assessed by optical microscopy, density and peel-strength measurements. The SRPPC specimens were subjected to static tensile and flexural, and dynamic falling weight impact tests and the related results were analyzed as a function of processing temperature and polymorphic composition. Based on the results the optimum processing temperature was determined and found by 20–25 °C above the related matrix melting temperature. It was established that the β-modified PP homopolymer based one-component SRPPCs possessed similar attractive mechanical properties as the intensively studied α-random PP copolymer based two-component ones.     

Fabrication of the new structure high toughness PP/HA-PP sandwich nano-composites by rolling process

In this study a designed rolling setup was used to fabricate new structure polypropylene/hydroxyapatite-polypropylene (PP/HA-PP) sandwich nano-composites. To check the effect of rolling process and PP layers content on the structure and mechanical properties of these sandwich composites, different mechanical tests and analysis were performed on these composites. Results of tensile, bending and buckling tests show the rolling process improves the strength, modulus and flexural rigidity of composites significantly while with increasing the PP layers content from 10 vol.% to 20 vol.% decreases the stiffness, flexural rigidity and modulus of composites slightly. Results of impact test demonstrate the rolling process and increasing the volume percentage of the PP layers in sandwich composites cause a dramatic improve in impact absorbed energy of the PP/HA-PP sandwich composites. The results of Differential Scanning Calorimetry (DSC) analysis confirm the rolling process increases the crystallinity and molecular alignment of polypropylene in composites. The results of mechanical tests and DSC analysis show the increasing of polypropylene molecular alignment by rolling process is the most dominant reason of improvement the mechanical properties of sandwich composites.     

Improvement of impact property of natural fiber–polypropylene composite by using natural rubber and EPDM rubber

In this research, vetiver grass was used as a filler in polypropylene (PP) composite. Chemical treatment was done to modify fiber surface. Natural rubber (NR) and Ethylene Propylene Diene Monomer (EPDM) rubber at various contents were used as an impact modifier for the composites. The composites were prepared by using an injection molding. Rheological, morphological and mechanical properties of PP and PP composites with and without NR or EPDM were studied. Adding NR or EPDM to PP composites, a significant increase in the impact strength and elongation at break is observed in the PP composite with rubber content more than 20% by weight. However, the tensile strength and Young’s modulus of the PP composites decrease with increasing rubber contents. Nevertheless, the tensile strength and Young’s modulus of the composites with rubber contents up to 10% are still higher than those of PP. Moreover, comparisons between NR and EPDM rubber on the mechanical properties of the PP composites were elucidated. The PP composites with EPDM rubber show slightly higher tensile strength and impact strength than the PP composites with NR.     

Effect of a novel coupling agent,alkyl ketene dimer,on the mechanical properties of wood–plastic composites

The objective of this study was to investigate the incorporation of poplar wood fibers both with and without a novel coupling agent, alkyl ketene dimer (AKD), on the mechanical properties of wood fiber/polypropylene (PP) composites. The resulting properties were compared to those obtained with the most commonly used coupling agent, maleic anhydride grafted PP (MAPP). Tensile and impact strengths of the composites decreased with increasing poplar wood fibers content. Tensile modulus of the composites increased by the incorporation of the wood fibers content up to 70 wt% but further increment in the wood fibers decreased the tensile modulus. At the constant content of poplar wood fibers (70 wt%), the tensile strength determined for the coupled composites with 5% AKD increased by 41% in comparison with the non-coupled composites while the tensile modulus increased by 45%, the impact strength of the coupled composites increased by 38%. The performance of 5% AKD on the mechanical properties of the composites is a little better than 3% MAPP. The good performance of 5% AKD is attributed to the enhanced compatibility between the poplar wood fibers and the polymer matrix. The increase in mechanical properties of the composites demonstrated that AKD is an effective coupling agent for wood fiber/PP composites.     

Interply hybrid composites with carbon fiber reinforced polypropylene and self-reinforced polypropylene

The focus of the present study is on hybrid composites with interplied carbon fiber reinforced polypropylene (CFRPP) between self-reinforced polypropylene (SRPP) layers. SRPP is produced by hot compaction of a woven fabric of highly oriented polypropylene and has an intrinsic behavior of shrinkage under high temperatures. The aim of this research is to enhance the tensile properties of the CFRPP/SRPP hybrid composites by using the SRPP shrinkage to introduce a compressive pre-strain in CFRPP. The results from tensile testing show that the failure strain of the hybrid composites is improved in comparison with CFRPP. The modulus and strength are noted to be lower than the ones expected from the rule of mixture. This may be attributed to the introduction of local misalignment (waviness) of carbon fibers caused by the SRPP shrinkage during consolidation.     

热压法制备聚丙烯单聚合物复合材料

用聚丙烯的过冷性质,热压成型制备聚丙烯单聚合物复合材料(PP SPCs)。研究加工温度对PP SPCs拉伸强度的影响。用金相显微镜观察了PP SPCs的微观结构,用扫描电子显微镜观察了纤维从树脂拔出的表面结构。研究结果表明,PP SPCs拉伸强度随着加工温度升高而增大。当加工温度为150℃时,PP SPCs的拉伸强度比没有增强的PP提高了5倍以上。PP SPCs中的纤维与树脂基有着良好的界面粘接性。     

The hot compaction of woven polypropylene tapes

In this paper we describe the hot compaction of woven polypropylene (PP) tapes. It is shown that under suitable conditions of temperature and pressure, successful compaction is achieved by selective melting of the PP tapes. Mechanical measurements, combined with morphological studies, show that good tape to tape bonding, and good interlayer bonding, are achieved using an optimum compaction temperature of around 182 °C, while retaining a significant proportion of the original PP structure. Differential scanning calorimetry studies have shown that the compaction temperatures employed to produce a homogeneous coherent material have a significant annealing affect on the crystalline structure of the original drawn tapes, with a large change in the crystal size and a small increase in overall crystallinity (accompanied by a small increase in sample density). The mechanical properties of the compacted PP sheets show a combination of low density and good stiffness and strength.     

Dispersion,thermal and mechanical properties of polypropylene/magnesium hydroxide nanocomposites compatibilized by SEBS-g-MA

Isotactic polypropylene (PP)/nano-magnesium hydroxide (nano-MH) composites with 10 wt.% maleic anhydride grafted styrene–ethylene-butylene–styrene tri-block copolymer (SEBS-g-MA) as a compatilizer were prepared by melt extrusion compounding and injection molding. The effects of SEBS-g-MA on dispersion of nano-MHs in PP matrix and interfacial adhesion were studied in order to prepare highly filled PP/MH nanocomposites. The results showed that SEBS-g-MA improved both dispersion of nano-MHs and interfacial adhesion in PP/MH nanocomposites with up to 40 wt.% nano-MHs. The elastic moduli of PP/SEBS-g-MA /MH nanocomposites increased marginally and tensile yield strengths were almost invariant with nano-MH loading. Significant impact toughening of these ternary nanocomposites was, however, achieved due to the cavitation of SEBS-g-MA/MH particles and expansion of voids as well as plastic deformation of the PP matrix.     

Formation of novel thermoplastic composites using bicomponent nonwovens as a precursor

This study focuses on a novel technique to produce thermoplastic composites directly from bicomponent nonwovens without using any resins or binders. Conceptually, the structure of the bicomponent fibers making up these nonwovens already mimics the fiber–matrix structure of fiber reinforced composites. Using this approach, we successfully produced isotropic thermoplastic composites with polymer combinations of polyethylene terephthalate/polyethylene (PET/PE), polyamide-6/polyethylene (PA6/PE), polyamide-6/polypropylene (PA6/PP), and PP/PE. The effects of processing temperature, fiber volume fraction, and thickness of the preform on the formation and structure of the nonwoven composites were discussed. Processing temperatures of 130 and 165 °C for PE and PP matrices, respectively, resulted in intact composite structures with fewer defects, for fiber volume fraction values of up to 51%. Moreover, an insight into the changes on the fine structure of the bicomponent fibers after processing was provided to better explain the mechanics behind the process. It is hypothesized that the composite fabrication process can result in annealing and increases the degree of crystallinity and melting temperature of polymers by thickening lamellae and/or removing imperfections. One of the other outcomes of this study is to establish what combination of mechanical properties (tensile and impact) nonwoven composites can offer. Our results showed that compared to glass mat reinforced thermoplastic composites, these novel isotropic nonwoven composites offer high specific strength (97 MPa/g cm⁻³ for PA6/PE), very high strain to failure (152% for PP/PE), and superior impact strength (147 kJ/m² for PA6/PP) which can be desirable in many critical applications.