Single Polymer Composites Research Articles

Development of recyclable, lightweight polypropylene-based single polymer composites with amorphous poly-alpha-olefin matrices

In the present study, we produced and investigated polypropylene-based single-polymer composites (SPCs) using four amorphous poly-alpha-olefin (APAO) grades as matrices and two plain-woven polypropylene fabrics as reinforcement. Our goal was to investigate the applicability of APAOs as matrix materials of SPCs and to widen the processing temperature window of SPCs utilizing the low melting temperature of APAOs. We produced the composites with a double-belt press at 120 °C, 140 °C, and 160 °C, and investigated them by density measurement, and static tensile and dynamic falling weight impact (IFWI) tests at room temperature, −40 °C, and 80 °C. The composites showed adequate tensile and excellent dynamic mechanical properties. The tensile test results indicated that the optimal consolidation temperature is between 120 °C and 140 °C, depending on the matrix applied. Increasing the test temperature resulted in reduced tensile strength. Increasing processing temperature caused a drop in perforation energy because of the reduced extent of the delamination of the better-consolidated composites. Both static and dynamic mechanical properties can be improved with the use of a stronger fabric. Furthermore, the processing temperature window can be widened with APAOs as matrix materials, and these single-polymer composites possess many beneficial properties.

Polyethylene-Based Single Polymer Composites Prepared under Elongational Flow for High-Voltage Applications

Recently, polyethylene (PE)-based single polymer composites (SPCs) have been found to be potential candidates for high-voltage applications (HVAs) due to their ability to form supramolecular struct...

Development of Polypropylene-Based Single-Polymer Composites With Blends of Amorphous Poly-Alpha-Olefin and Random Polypropylene Copolymer

We developed polypropylene-based single-polymer composites (PP-SPC) with blends of amorphous poly-alpha-olefin (APAO) and random polypropylene copolymer (rPP) as matrix material and polypropylene (PP) woven fabric as reinforcement. Our goal was to utilize the lower melting temperature of APAO/rPP blends to increase the consolidation of the composites and decrease the heat load of the PP reinforcement. We produced the composites by film-stacking at 160 °C, and characterized the composites with density, peel, static tensile and dynamic falling weight impact tests, and by scanning electron microscopy. The results indicate that consolidation can be enhanced by increasing the APAO content of the matrix. We found that the APAO content of 50% is optimal for tensile properties. With increasing APAO content, the perforation energy decreased, but even the well-consolidated composites showed very high perforation energy. In the case of a pure APAO matrix, fiber content can be increased up to 80 wt% without a severe loss of consolidation, resulting in good tensile properties. The PP-SPCs developed possessed excellent mechanical properties, and well-consolidated composites can be produced with APAO/rPP blends as a matrix with high fiber content.

FBG monitoring of curing in single fiber polymer composites

In this study, a fiber Bragg grating (FBG) sensor and a thermocouple (TC) were embedded inside an epoxy system cured at 121 °C to determine its curing characteristics. The curing behavior of this higher temperature (HT) system was also compared with a room temperature (RT) epoxy cured at 30 °C to independently verify the recently published approach developed for the RT system (Ref. 1; Hoffman, Khadka and Kumosa, 2020). The previously suggested algorithms developed to extract the gel point, the end of cure, and the curing and manufacturing strains for the RT system were successfully applied to the HT epoxy. This methodology was effectively extended to include the start of cure determination for the HT system. It was established that the manufacturing strains of both resin systems significantly exceeded the strains which could be predicted from the thermal contraction of the resins cooling from the ambient curing temperature to RT especially for the HT epoxy. The curing strains in both epoxy systems were shown to be significant, contributing to the overall manufacturing strains approximately 28% for the RT epoxy and about 45% for the HT resin. Efforts were also made to explain the source of sizable scatters in the strain measurements by evaluating temperature variations within individual and across multiple curing samples. As previously conjectured, the local temperature concentrations (hot spots) were responsible for the scatters in the strain measurements.

Development of polyamide 6 based single polymer composites reinforced by novel stitched plain fabrics

In the present study, novel woven reinforced single polymer composites (WSPC) based on polyamide 6 (PA6) is developed via a combination of powder-coating of PA6 textile reinforcements with PA6 empty microcapsules (EMC) and compression molding techniques. Activated anionic ring-opening polymerization of ε-caprolactam was employed to synthesize the PA6-EMC which was transformed during the compression molding into WSPC matrix without damaging the PA6 textile reinforcements. A promising novel class of PA6 woven fabrics, stitched plain, which are patented by Jakob Müller company AG® were used as reinforcements. The tensile properties of stitched plain reinforced WSPC were studied and compared to ones reinforced by the plain-woven structure and the PA6 neat matrix reference materials. The parametric studies are performed on the stress field along the elements of reinforcements, using image processing to correlate the influence of reinforcement architectures with the failure mechanism of WSPC.

Manufacturing of Single-Polymer Composite Materials Based on Ultra-High Molecular Weight Polyethylene Fibers by Hot Compaction

This paper describes the manufacturing process and properties of single-polymer composites based on ultra-high molecular weight polyethylene fibers produced by hot compaction. The hot compaction results in partial surface melting of the initial fibers, and melted part after cooling forms a matrix of the self-reinforced composites. Using high pressure during hot compaction allows to increase the fibers’ melting point and allows to avoid relaxation processes. Moreover, the fiber-to-matrix ratio may be changed using this approach by varying pressure and temperature. The flexural test was carried out to determine the mechanical properties. Samples obtained at 160 °C and 50 MPa have optimum properties (flexural strength and Young’s modulus were equal to 116.5 MPa and 15.3 GPa, respectively). It was found that mechanical properties of the obtained composites depend on both matrix amount and preservation of oriented fibers structure. The small amount of melted fibers does not allow to form matrix for load transferring. But the excessive melting of the fibers can result in a significant decrease in the fibers’ mechanical properties.

Study on mechanical properties of co-injection self-reinforced single polymer composites based on micro-morphology under different molding parameters

Self-reinforced single polymer composites (SRCs), which are fabricated by combining the same type of polymer with different properties into one body, have high specific strength, no interfacial heterogeneity, and ease of recycling. To better understand the relationship between the micro-morphology and mechanical properties of SRCs, the co-injection molding process was used in this study to process SRCs parts with different molding parameters and obtain the co-injection self-reinforced single polymer composites parts(CI-SRCs parts). Further, the micro-morphology of CI-SRCs parts were observed by polarizing microscope (PLM), scanning electron microscope (SEM), differential scanning calorimetry (DSC) and wide Angle X-ray diffraction (WAXD). From the results, it was found that the tensile properties of CI-SRCs parts with different molding parameters were improved by up to 23.94% compared with the conventional parts. Through PLM observation, it is found that the section shape of CI-SRCs parts perpendicular to the flow direction shows a double ‘skin-core’ structure, and the area ratio of skin layer was higher than that of conventional parts, with a maximum increase of 68%. The low-temperature and low-speed environment were conducive to the formation of skin layer, and the tensile property of CI-SRCs parts were positively correlated with the area ratio of skin layer. SEM was carried out on the skin layer near the fusion position of the interface, and the highly oriented ‘shish-kebab’ structure was observed. The 1D-WAXD pattern analysis shows that the crystallinity of CI-SRCs parts were lower than that of conventional parts, with a maximum reduction of 19.32%. The crystallinity of CI-SRCs parts were positively correlated with melt temperature gradient, and its tensile properties were negatively correlated with the change of crystallinity. The 2D-WAXD pattern analysis shows that the molecular orientation of CI-SRCs parts were higher than conventional parts, with the maximum increase of 37.44%. Low temperature and low speed can improve the molecular orientation of CI-SRCs parts, and the change of molecular orientations were positively correlated with the tensile properties of CI-SRCs parts. By means of response surface method, the molecular orientation obtained was the decisive factor affecting the performance of CI-SRCs parts. Furthermore, by means of the least squares minimization program, the dimensionless equations among molding parameters, micro-morphologies and mechanical properties were established. The prediction of mechanical properties of CI-SRCs parts based on micro-morphologies were realized, providing theoretical support for the ‘adjustability’ of CI-SRCs parts properties.

Development and characterization of single polymer composites prepared by compression molding of polyamide 6 empty microcapsules and novel woven textile structures

In the present study, novel polyamide 6 based woven single polymer composites (WSPC) were developed by powder-coating of woven textile structures with polyamide 6 empty microcapsules (EMC) and subsequent compression molding. To synthesize EMC, activated anionic ring-opening polymerization of ε-caprolactam by solution/precipitation was applied. Stitched plain fabrics that are promising novel class of woven fabrics and two conventional woven patterns (plain and satin-5 harness) were used as textile reinforcements. The thermal and mechanical properties of all composites were characterized and related to the reinforcements´ morphology, fiber volume fraction and ply orientation. For better understanding of the bonding state at the matrix-fiber interface, stereo-optical microscopy and SEM image analysis by image processing were performed. The data obtained confirmed the existence of a transcrystalline layer (TCL) in the interface region. The mechanical behavior of the composites was related also to the PA6 polymorph content of the samples and their crystallinity indexes determined by wide-angle X-ray diffraction experiments.

Mechanical and Tribological Characterization of Hybrid Composites: A Review

Abstract A review on the mechanical and tribological characterization of hybrid fibers reinforced polymer (FRP) composite materials is presented in this article. Fiber reinforced polymer composites are used in aircraft, boats, ships, helicopters, sporting equipments, chemical processing instruments and automobiles. Using more than one fibers in a single polymer matrix gives the more improvements than single fiber polymer composites. Hybridization (A mixture of fibers, during a process known as hybridization, so as to take advantage of the two fibers) in the field of FRPs can enhance the mechanical characteristics of particular fibre-reinforced polymer composite. By the addition of filler to the composite materials will further increase the performance of composites. This revise shows that tribological and mechanical characteristics of FRP composite improves because of inclusion of comparably high elongation fibers (Glass and basalt).Now a day’s hybrid composites are used in high end applications

Unidirectional continuous fiber-reinforced polypropylene single-polymer composites prepared by extrusion–calendering process

An extrusion–calendering process was developed to continuously manufacture unidirectional continuous fiber-reinforced polypropylene single-polymer composites (PP SPCs). The process combined “undercooling” property of the matrix and “overheating” property of the fiber, which can not only establish a wide processing temperature window but also enhance the mechanical properties of the final SPCs. The best tensile strength and modulus of the PP SPCs with only 5 wt% fiber content were up to 53.34 ± 3.56 MPa and 1.81 ± 0.14 GPa, 2 times and 1.59 times higher than those of pure PP, respectively, and they also exceeded the theoretical values due to the high performance of the uniaxial fibers and the optimized process. The influences of the die temperature, fiber contents, and fiber distribution were studied. Scanning electron microscopy was also used to observe the morphological properties of the PP SPCs.

Novel Bicomponent Functional Fibers with Sheath/Core Configuration Containing Intumescent Flame-Retardants for Textile Applications.

The objective of this study is to examine the effect of intumescent flame-retardants (IFR’s) on the spinnability of sheath/core bicomponent melt-spun fibers, produced from Polylactic acid (PLA) single polymer composites, as IFR’s have not been tested in bicomponent fibers so far. Highly crystalline PLA-containing IFR’s was used in the core component, while an amorphous PLA was tested in the sheath component of melt-spun bicomponent fibers. Ammonium polyphosphate and lignin powder were used as acid, and carbon source, respectively, together with PES as a plasticizing agent in the core component of bicomponent fibers. Multifilament fibers, with sheath/core configurations, were produced on a pilot-scale melt spinning machine, and the changes in fibers mechanical properties and crystallinity were recorded in response to varying process parameters. The crystallinity of the bicomponent fibers was studied by differential scanning calorimetry and thermal stabilities were analyzed by thermogravimetric analysis. Thermally bonded, non-woven fabric samples, from as prepared bicomponent fibers, were produced and their fire properties, such as limiting oxygen index and cone calorimetry values were measured. However, the ignitability of fabric samples was tested by a single-flame source test. Cone calorimetry showed a 46% decline in the heat release rate of nonwovens, produced from FR PLA bicomponent fibers, compared to pure PLA nonwovens. This indicated the development of an intumescent char by leaving a residual mass of 34% relative to the initial mass of the sample. It was found that the IFRs can be melt spun into bicomponent fibers by sheath/core configuration, and the enhanced functionality in the fibers can be achieved with suitable mechanical properties.

Mechano-morphological studies of polyamide 6 based single polymer laminate composites prepared by different reactive processing techniques

Abstract Single polymer laminate composites based on polyamide 6 (PA6) were prepared by two methods: (i) reactive injection molding and (ii) powder coating/compression molding, both carried out in the presence of PA6 woven textile plies. The effect of the textile volume fraction Vf on the tensile properties of all composites was investigated. The laminates obtained by powder coating/compression molding displayed best mechanical performance, whereby in the composites with Vf = 15%, the improvement of the elastic modulus reached 98% in respect to commercial hydrolytic PA6 reference, or 50–86% as compared to neat anionic PA6 samples. Polarizing light microscopy with image processing was used for morphological characterization. A transcrystalline layer at the fiber-matrix interface was detected in all laminates with thicknesses between 0.5 and 3.0 μm, depending on the preparation technique applied. The thermal stability was studied in the temperature range of 30°C-550 °C. The laminates obtained by reactive injection molding displayed the lowest initial decomposition temperature due to the presence of oligomers. Selected laminate composites were reprocessed by grinding and injection molding. The recycled composites obtained by powder coating displayed a 38% increase of the elastic modulus in respect to commercial hydrolytic PA6 thus confirming the sustainability and recyclability of PA6-based single polymer composites.

Nanoscale Restructuring of Polymer Materials to Produce Single Polymer Composites and Miscible Blends.

I summarize work conducted in our laboratories over the past 30 years using small host molecules to restructure polymer materials at the nanometer level. Certain small molecules, such as the cyclic starches cyclodextrins (CDs) and urea (U) can form non-covalent crystalline inclusion compounds (ICs) with a range of guest molecules, including many polymers. In polymer-CD- and -U-ICs, guest polymer chains reside in narrow channels created by the host molecule crystals, where they are separated and highly extended. When the host crystalline lattice is carefully removed, the guest polymer chains coalesce into a bulk sample with an organization that is distinct from that normally produced from its melt or from solution. Amorphous regions of such coalesced polymer samples have a greater density, likely with less chain entanglement and more chain alignment. As a consequence, after cooling from their melts, coalesced amorphous polymers show glass-transition temperatures (Tgs) that are elevated above those of samples prepared from their solutions or melts. Upon cooling from their melts, coalesced samples of crystallizable polymers show dramatically-increased abilities to crystallize more rapidly and much closer to their melting temperatures (Tms). These unique behaviors of polymers coalesced from their CD- and U-ICs are unexpectedly resistant to extended annealing above their Tgs and Tms. Taking advantage of this behavior permits us to create polymer materials with unique and improved properties. Among these are amorphous polymers with elevated Tgs and semi-crystalline polymers with finer more uniform morphologies. Improved mechanical properties can be achieved through self-nucleation with small amounts of the same polymer made rapidly crystallizable through coalescence from its CD- or U-IC. This can lead to single polymer composites with as-received polymer matrices and self-nucleated reinforcements. Through simultaneous formation and subsequent coalescence from their common CD–ICs, stable well-mixed blends can be achieved between any two or more polymers, despite their inherent immiscibilities. Such coalesced and well-mixed blends are also resistant to phase segregation when heated for extensive periods well above their Tgs and Tms.

Dimensional accuracy improvement by parametric optimization in pulsed Nd:YAG laser cutting of Kevlar-29/basalt fiber-reinforced hybrid composites

Laser cutting proves its suitability for cutting of single fiber-reinforced polymer (FRP) composites compared with conventional cutting techniques due to reduced fiber delamination, matrix cracking and fiber pullout. However, the performance of the laser cutting process of hybrid FRP composites is yet to be revealed, which paves the way of the present study. In this article, an experimental investigation of the laser cutting process is carried out on 1.35-mm-thick Kevlar-29 and basalt fiber-reinforced polymer (KBFRP) hybrid composite laminates using 250 W pulsed Nd:YAG laser system. The performance of laser cutting was evaluated by quantifying different kerf quality characteristics such as top and bottom kerf width, top and bottom kerf deviation and kerf taper. These kerf quality characteristics define the geometrical accuracy of the laser cut. Response surface methodology-based Box–Behnken design was adopted for conducting the experiments with varied settings of laser cutting parameters, viz. lamp current, pulse width, pulse frequency, compressed air pressure and cutting speed. Second-order regression models of each response were developed and validated by using standard error plots. A parametric effect analysis was carried out by using the variation of performance measures predicted through developed mathematical models. In order to achieve the optimal levels of the process parameters for all kerf quality characteristics, a self-developed python language-coded TLBO algorithm was used. Finally, the confirmation experiments were performed at obtained optimal levels of laser cutting parameters. An overall improvement of 22.23% in multiple kerf quality characteristics was achieved through optimal settings of laser cutting parameters. The individual improvement of 11.44%, 8.47%, 17.65%, 15.22% and 58.87% was recorded in top kerf width, bottom kerf width, top kerf deviation, bottom kerf deviation and kerf taper, respectively. The developed mathematical models and suggested optimal conditions are able to provide direction to the researchers for obtaining higher-dimensional accuracy in Nd:YAG laser cutting of KBFRP hybrid composites.

Micromechanical finite element parametric study of polyamide 6 based single polymer composites reinforced by woven textile structures

This study presents a finite element-based micromechanical analysis of woven single polymer composites (WSPC), prepared by compression molding from polyamide 6 (PA6) woven fabrics powder-coated with PA6 microparticles. Initially, the PA6 microparticles (MP) were synthesized by solution/precipitation activated anionic ring-opening polymerization of ε-caprolactam. After the powder coating, the MP fraction upon each textile ply was transformed into the continuous PA6 matrix by hot pressing at a temperature lower than the melting of the PA6 textile reinforcements. Plain and satin PA6 woven fabrics were selected as reinforcements that were stretched and annealed prior to molding so as to enhance their mechanical performance. The tensile and Izod impact properties of WSPC were characterized in relation to the reinforcement architecture, fiber content and ply orientation. Finite element analysis was used for a parametric study of woven reinforcements and to correlate the deformation and stress distribution of the structures with the tensile failure of the composites. Moreover, to assess the interfacial matrix-reinforcements bonding state, a study of the surfaces fracture, obtained by SEM topography, using image processing was performed.

Synergistic effects of metal hydroxides and fumed nanosilica as fire retardants for polyethylene

AbstractThis work aims to study the synergistic effect of aluminum/magnesium hydroxide microfillers and organomodified fumed silica nanoparticles as flame retardants (FRs) for linear low-density polyethylene (LLDPE), and to select the best composition to produce a fire-resistant polyethylene-based single-polymer composite. The fillers were added to LLDPE at different concentrations, and the prepared composites were characterized to investigate the individual and combined effects of the fillers on the thermo-oxidation resistance and the fire performance, as well as the microstructural, physical, thermal and mechanical properties. Both filler types were homogeneously distributed in the matrix, with the formation of a network of silica nanoparticles at elevated loadings. Melt flow index (MFI) tests revealed that the fluidity of the material was not considerably impaired upon metal hydroxide introduction, while a heavy reduction of the MFI was detected for silica contents higher than 5 wt%. FRs introduction promoted a noticeable enhancement of the thermo-oxidative stability of the materials, as shown by thermogravimetric analysis (TGA) and onset oxidation temperature (OOT) tests, and superior thermal properties were measured on the samples combining micro- and nanofillers, thus evidencing synergistic effects. Tensile tests showed that the stiffening effect due to a high content of metal hydroxide microparticles was accompanied by a decrease in the strain at break, but nanosilica at low concentration contributed to preserve the ultimate mechanical properties of the neat polymer. The fire performance of the samples with optimized compositions, evaluated through limiting oxygen index (LOI) and cone calorimetry tests, was strongly enhanced with respect to that of the neat LLDPE, and also these tests highlighted the synergistic effect between micro- and nanofillers, as well as an interesting correlation between fire parameters and viscosity.

The Choice of Recycling Methods for Single-Polymer Polyester Composites

This work has described the production of single-polymer composites by the film-stacking method. Two types of single-polymer composites with different mass fractions of the polyester reinforcement phase (10% and 20%) and the PETG matrix were investigated. The produced composites were subsequently recycled by injection moulding, pressing, and extrusion. Selected properties of the processed composites were determined: density, viscosity-average molecular weight, impact resistance, and tensile strength. The work done in this paper has demonstrated the benefits and drawbacks of each recycling method for these materials. The selected properties of single-polymer polyester composites and single-polymer polyester composites that were recycled by extrusion have also been compared.

VO2-enhanced double positive temperature coefficient effects of high density polyethylene/graphite composites

High density polyethylene/graphite (HDPE/Gr) composites were fabricated by the melt-blending method, and displayed the enhanced positive temperature coefficient (PTC) effect and decreasing room-temperature resistivity with the addition of vanadium dioxide (VO2). Especially, HDPE/Gr composite with 6 wt% VO2 showed the remarkable double PTC effects and excellent reproducibility. Based on obvious two-shape structure and heating amorphous evolution of HDPE composites, the simple filler-compensated conductive networks and unique dispersion model were constructed to further understand the PTC behavior. Finally, it was concluded that the excellent double PTC effects of single polymer composites were achieved by the introduction of second filler.

Multilayer hybrid polypropylene composite with single and wood-polymer composites

Single polymer composites (SPCs) are relatively new type of composite materials where reinforcement and matrix are made of the same polymeric material or the same group of materials. The favorable mechanical properties of SPC are due to the macromolecular orientation of fibers or tapes used in their production. This paper presents the results of selecting the most favorable SPC manufacturing process temperature and the use of such materials for a three-layer polypropylene composite production, where the core layer is made of 50 wt % filler polypropylene-wood composite (WPC). The developed material reveals better mechanical bending properties, compared to unfilled polypropylene and to traditional WPC with 30 wt % wood flour content.

Comparative Structural and Mechanical Studies on Polyamide 6 Knitted‐Reinforced Single Polymer Composites Prepared by Different Reactive Processing Techniques

Single polymer laminate composites based on anionic polyamide 6 (PA6) matrix‐reinforced by PA6 knitted textile structures (KSPC) were produced by nylon reactive injection molding and powder coating/compression molding (PCCM) processing techniques. The effect of the reinforcement's structure and the fiber volume fraction on the mechanical properties of the knitted‐reinforced PA6 composites resulting from the two methods were investigated and compared. The morphology and the crystalline structure of KSPC materials were studied to identify the main factors determining the tensile properties. The results showed that the PCCM method produced laminate composites with higher Young's modulus and mechanical strength in tension. Microscopy, differential scanning calorimetry and X‐ray diffraction experiments were carried out to correlate the morphology and crystalline structure of the composites and their precursors with the different tensile behavior of KSPC prepared using the two techniques. The microscopy and X‐ray scattering studies suggested the formation of a transcrystalline layer at the matrix/reinforcement interface. POLYM. COMPOS., 40:E886–E897, 2019. © 2018 Society of Plastics Engineers