Properties of bamboo flour/high-density polyethylene composites reinforced with ultrahigh molecular weight polyethylene

In order to improve the properties of bamboo-plastic composites (BPCs), bamboo flour/high-density polyethylene (HDPE) composites were reinforced with ultrahigh molecular weight polyethylene (UHMWPE). The effects of UHMWPE on properties of composites were studied. The crystallinity of composites decreased slightly. Compared with non-UHMWPE added bamboo powder/HDPE composite, the composite with 6 wt % UHMWPE, showed decrease in water absorption to 0.41%, whereas its tensile strength and flexural strength increased to 34.51 and 25.88 MPa, respectively, a corresponding increase of 34.59 and 12.87%. The temperatures corresponding to initial degradation temperature (T_initial) and maximum degradation temperature (T_max) of the composite increased from 282.7 and 467.4 °C to 288.5 and 474.7 °C respectively. Scanning electron microscopic images showed that UHMWPE was well dispersed and fully extended as long fibers in the composite, forming a “three-dimensional physically cross-linked network structure,” which contributed to the improved properties of the composites. © 2020 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48971.     

Thermal and geometry impacts on the structure and mechanical properties of part produced by polymer additive manufacturing

A relatively new additive manufacturing machine called Freeformer was employed as an alternative to common Fused Filament Fabrication (FFF) machines. While FFF machines are fed with expensive and few commercially available filament feedstock, Freeformer is fed with cheap and common polymer pellets. In this study, more than 400 dumbbells made of Acrylonitrile Butadiene Styrene (ABS) were processed varying many processing conditions to evaluate their impacts on the structure and so on, the mechanical properties of 3D parts. Among processing parameter, nozzle temperature, manufacturing chamber temperature, discharge parameters, filling density, raster geometry, slicing distance, number of contour lines, processing speed, filling raster-contour lines overlap, and processing angles were studied. Images obtained with a scanning electron microscope and 3D part density estimations reveal strong changes on the 3D part structure as a function of the processing parameters so that tensile tests exhibit high variations between the 3D part mechanical properties.     

Nanomechanical and tribological behavior of hydroxyapatite reinforced ultrahigh molecular weight polyethylene nanocomposites for biomedical applications

A hydroxyapatite (HA) particulate reinforced ultrahigh molecular weight polyethylene (UHMWPE) nanocomposite is fabricated by internal mixer at 180°C and using of paraffin oil as a processing aid to overcome the high viscosity of melted UHMWPE. The reinforcing effects of nano‐HA are investigated on nanomechanical properties of HA/UHMWPE nanocomposites by nanoindentation and nanoscratching methods. Results show that the nanocomposite with 50 wt % nano‐HA exhibits a Young's modulus and hardness of 362.5% and 200% higher, and a friction coefficient of 38.86% lower than that of pure UHMWPE, respectively. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42052.     

Effects of strain rate and temperature on the mechanical behavior of high-density polyethylene

The objective of this work is to initiate the discussion about multiphysics relationships between the molten and solid states of high-density polyethylene (HDPE). The extrusion and the injection processes are employed to prepare samples, and the experimental procedures, using differential scanning calorimetry, dynamic thermomechanical analysis (DMTA), thermal gravimetric analysis, and rheological measurements, are defined to choose the optimal variables. After different characterizations, the extrusion and injection temperatures of 220 and 230 °C have been chosen. To investigate the viscoelastic behavior of HDPE, the DMTA is used. To perform the high strain rate tensile tests, tensile machine was equipped with a specific furnace. Two temperatures, −20 and 20 °C, with strain rates varying from 0.001 to 100 seconds⁻¹ were used to compare the flow characteristics. Results showed that by increasing the strain rate the molecular mobility of the HDPE chains is decreased. In addition, to the tests at −20 °C, the increase of Young's modulus can be properly observed, under high strain rates. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48778.     

Effect of mechanical recycling on crystallization,mechanical, and rheological properties of recycled high-density polyethylene and reinforcement based on virgin high-density polyethylene

This study investigated the effects of mechanical recycling on the crystallization, mechanical, thermal, and rheological properties of recycled high-density polyethylene (rHDPE), as well as vHDPE/rHDPE pellets and films made by different compositions. The results confirmed the presence of contaminants in rHDPEs, and the crystalline diameter of rHDPE is smaller than that of virgin high-density polyethylene (vHDPE), with diameters ranging from 0.60 to 0.72 μm. The content of 75 wt% vHDPE in rHDPE film could repair the defects of crystalline morphology to approximate that of vHDPE films and significantly improve the elongation at break. The temperature required for the transition from crystalline to amorphous state of rHDPE film was 2°C lower than that of vHDPE, and the crystallization time and crystallinity declined compared to that of vHDPE. For rheological performance, the apparent shear viscosity and melt fluidity of rHDPE were worse than those of vHDPE. The blending of low rHDPE with vHDPE is a feasible option not only to reduce plastic waste but also to maintain acceptable properties of the blend composition.     

Mechanical properties and stem cell adhesion of injection‐molded poly(ether ether ketone) and hydroxyapatite nanocomposites

A nanocomposite of poly(ether ether ketone) (PEEK) with 10 wt % hydroxyapatite (HA) was produced by extrusion and injection molding. Afterward, the samples were thermally treated. Thermal and short‐ and long‐term mechanical characterizations of the samples were made. The adhesion of human adipose stem cells (h‐ASCs) on the samples was also monitored. The ultimate tensile strength (UTS) and elastic modulus values of the nanocomposite were found to be much higher than those of trabecular bone. The impact strength of PEEK was not modified by HA; this suggested that there was no formation of large agglomerates of nanoparticles that could concentrate the stresses. With regard to fatigue life, both the thermally and nonthermally treated nanocomposites did not fail after 10⁶ cycles when maximum stresses of 30 and 50% of the UTS were applied, but they failed when the maximum applied stress was 75% of the UTS and behaved as cortical bone. After 5 days of culturing, the h‐ASCs had a higher proliferation in the nanocomposite than in pure PEEK because of the presence of HA. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41748.     

Preparation and properties of carbon-fiber- and pine-cone-fiber-reinforced high-density polyethylene composites

In this study, we were concerned with the physical properties of carbon-fiber- and pine-cone-fiber-reinforced high-density polyethylene prepared by compression molding. The resulting composites were characterized by scanning electron microscopy, X-ray diffraction, Fourier transform infrared (FTIR) spectroscopy, thermogravimetric analysis, differential scanning calorimetry, and mechanical testing. The results indicate that the manufacturing properties of the composites were improved with the addition of carbon fibers. The FTIR results showed that the carbon-fiber reinforcement of the composites was mainly achieved through physical effects. An appropriate content of carbon-fiber addition improved the interface combination between the fibers and matrix; carbon fibers improve the water absorption of the material, and the relative crystallinity of the composite increased with increasing carbon-fiber addition. With increasing carbon-fiber content, the thermal decomposition temperature of the composites increased, and the thermal stability of the composites improved. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47304.     

Time-dependent properties of graphene nanoplatelets reinforced high-density polyethylene

The deformation of polymers at constant applied stress is one of their major drawbacks, limiting their use in advanced applications. The study of this property using classical techniques requires extensive testing over long periods of time. It is well known that reinforced polymers show improved behavior over time compared to their neat counterparts. In this study, the effect of adding different amounts of graphene nanoplatelets (GNPs) on the time-dependent properties of high-density polyethylene (HDPE) is investigated using short-term creep tests and load/unload recovery tests. The results are discussed in terms of the test profile and the influence of loading history. Viscoplasticity/viscoelasticity analysis is performed using Zapas model and by comparing creep, creep compliance and pure viscoelasticity curves. The results show that the reinforcement of 15 wt% GNP have the most significant effect on the time-dependent behavior, reducing the strain by more than 50%. The creep compliance curves show that nano-reinforced HDPE behaves nonlinearly viscoelastically even at very low stresses. In addition to demonstrating the effect of nano-reinforcement, the discussion of the results concludes that the influence of loading history can be quite significant and should not be neglected in the design and evaluation of material behavior.     

Inkjet printing of polyvinyl alcohol multilayers for additive manufacturing applications

Here we demonstrate that inkjet printing technology is capable of producing polyvinyl alcohol (PVOH) multilayer structures. PVOH water‐based inks were formulated with the addition of additives such as humectant and pigments. The intrinsic properties of the inks, such as surface tension, rheological behavior, pH, wetting, and time stability were investigated. The ink's surface tension was in the range 30–40 mN/m. All formulated inks displayed a pseudoplastic (non‐Newtonian shear thinning and thixotropic) behavior at low‐shear rates and a Newtonian behavior at high‐shear rates; were neutral solutions (pH7) and demonstrated a good time stability. A proprietary 3D inkjet printing system was utilized to print polymer multilayer structures. The morphology, surface profile, and the thickness uniformity of inkjet printed multilayers were evaluated by optical microscopy and FT‐IR microscopy. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43572.     

Polylactic acid and high-density polyethylene blend: Characterization and application in additive manufacturing

This research reports a novel polylactic acid (PLA) blend with high density polyethylene (HDPE) and polyethylene graft maleic anhydride (PE-g-MAH) to mitigate the PLA degradation issues associated with high temperatures, soil and water exposure. The blend was prepared with a melt blending process and directly printed with a custom-built pellet printer to maintain the “as prepared” properties. Thermal stability was analyzed in terms of mechanical strength at different bed temperatures and postprinting aging for 10 days. Soil burial degradation and water absorption were investigated in terms of mechanical strength and effects on mass at three intervals (15, 30, 45 days). The proposed blend revealed high stability to all three degradation mechanisms due to the chemical grafting along with physical interlocking. Finally, Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA) and scanning electron microscopy (SEM) were used to confirm the enhancement in molecular interactions, melt crystallization, onset temperatures and phase distribution, respectively.     

Solution processed low‐k dielectric core‐shell nanoparticles for additive manufacturing of microwave devices

This study introduces a new core‐shell structured polytetrafluoroethylene (PTFE)/polyimide (PI) nanoparticle for additive manufacturing of microwave substrates. Materials were synthesized using a solution processed method through the electrostatic interaction between PTFE with negative potential and poly(amic acid) salt (PAAS, a PI precursor) with positive potential followed by the thermal imidization of PAAS. Microscopic studies by transmission electron microscopy, scanning electron microscopy, and atomic force microscopy confirmed the formation of core‐shell nanoparticles, a porous material network, and a reduction of surface roughness upon imidization. In addition to excellent high temperature stability (<0.4% weight loss at 500 °C), the synthesized materials showed improved particle‐to‐particle adhesion and particle‐to‐substrate adhesion compared to PTFE alone, and good dielectric properties measured at 7.2 GHz utilizing a cavity perturbation technique. The materials consisting of 5% to 35% of PI exhibited low relative permittivity (?′) of 2.14 to 2.38 and loss tangent (tan δ) of 0.001 to 0.0018, which make them well suited for use in additive manufacturing. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134 , 45335.     

Mechanical properties of poly(ether-ether-ketone) for engineering applications

An outline of the characteristics of PEEK and the versatility of its compositional forms (micro and macro composites) are given to illustrate its wide potential for success in engineering applications. Although it is necessary to have particular tabulations of mechanical properties for engineering design, these are seldom available and consequently it is argued that an understanding of stiffness, toughness and strength properties are required to fully exploit available manufacturer's data and thus develop the full potential of PEEK and its composites. Stiffness characteristics are considered in terms of a modulus function which is dependent on time under load and temperature. In its composite forms, whether reinforced with short or continuous fibres, stiffness anistropy can be both considerable and complex, but some empirical ground-rules are apparent. For continuous fibre composites even in the form of complex lay-ups, it is also possible to attempt some stiffness prediction from certain pseudo-elastic constants. Toughness of PEEK and its composites is described in terms of both comparative and intrinsic properties. Instrumented falling weight impact data, particularly as a function of temperature enable some insight into ductile-brittle transitions for the unreinforced material, but crack initiation and crack propagation processes for the various fibre reinforced forms. Intrinsic toughness is described in terms of linear elastic fracture mechanics theory. Strength properties are described for static and dynamic loading configurations. In particular, PEEK and its composites are evaluated for increasing test severities for strength characteristics; stress concentration, loading form and test temperature are considered.     

The effect of annealing on tensile properties of injection molded biopolyesters based on 2,5-furandicarboxylic acid

In this study, we investigate four polyesters based on 2,5-furandicarboxylic acid and different diols including 1,2-ethylene glycol, 1,3-propylene glycol, 1,4-butylene glycol, and 1,6-hexylene glycol. Poly(ethylene 2,5-furanoate), poly(propylene 2,5-furanoate), poly(butylene 2,5-furanoate), and poly(hexylene 2,5-furanoate) (PHF) were characterized by thermogravimetric analysis, X-ray diffraction, differential scanning calorimeter, and tensile tests. In addition, the influence of annealing polyesters on their thermal and mechanical properties was investigated. For these reasons samples for the tensile test were prepared by injection molding. The tensile properties of injection molded samples were compared with samples that were additionally annealed after injection molding. All studied polyesters after heating treatment showed multiple melting behavior. The increase in the degree of crystallinity significantly influenced also the mechanical properties of the samples. It was found that the length of the aliphatic chain and degree of crystallinity plays a major role in the final properties of furan-based polyesters.     

Influence of soapstone waste on the mechanical and rheological properties of high-density polyethylene

Soapstone is an abundant mineral in Ouro Preto - Minas Gerais, Brazil and its main destination is in the production of craftsmanship. Rock recovery in those activities is low and the waste disposal is done with little control, which can be hazardous to the environment. This work proposes an alternative use of such potentially harmful waste as reinforcement in a novel polymer matrix composite, which can be particularly attractive to the automotive industry and of which very little information is available elsewhere in the literature. Firstly, the characterization of the waste was performed. Particle size and shape parameters were determined by automated image analysis and the mineralogical composition was determined by X-ray diffraction, infrared, and Raman spectroscopy. High-density polyethylene was used as matrix and the composites were made in three matrix/filler ratios: 90/10, 80/20, and 70/30 by weight. Tensile and rheological properties were measured in order to determine the influence of the particles on the polymer mechanical behavior and processing conditions. The materials showed a pseudoplastic behavior and the filler's influence was more pronounced in the 70/30 composites, which showed higher viscosities than the neat polymer. The addition of particles resulted in more brittle and rigid composites, with higher values of tensile strength.     

Mechanical and thermal properties of coal gasification fine slag reinforced low density polyethylene composites

Coal gasification fine slag (CGFS) was processed via a grading technique. The CGFS products (CGFS‐S1, CGFS‐S2, CGFS‐S3) with different sizes were obtained. Effects of particle size and unburned carbon on tensile properties of filled low density polyethylene (LDPE) were studied within the CGFS weight fractions ranging from 10 to 50 wt %. The tensile strength was found to increase with decreasing CGFS size, and the tensile properties exhibited good performance, owing to unburned carbon. The tensile strength of the composites increased with increasing CGFS‐S3 weight fraction. The analysis of mathematical model and SEM revealed that the firm improvement of tensile strength resulted from the strong interactions between LDPE polymer chains and CGFS‐S3 particles, and good dispersion of CGFS‐S3 in resin. Thermogravimetric analysis proved obvious reinforcement in thermal‐oxidative stability by incorporation of CGFS‐S3. The degree of crystallinity of LDPE/CGFS‐S3 showed the first increased and then decreased variation tendency. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46203.     

Thermal and tensile properties of polysialate composites

Polysialate, or geopolymer, composites have gained interest due to their inherent high temperature resistance, low density and ease of manufacturing. These characteristics also suggest that polysialate composites have significant potential as materials in high temperature structures, although little is known about their thermal and mechanical properties. This study aimed to determine relevant thermal and mechanical properties over a representative temperature range. The results show that polysialate composites can exhibit stable thermal properties up to 1000 °C. Tensile properties up to 760 °C highlight a significant reduction in stiffness, but a retention of strength, at these temperatures. The thermal and mechanical results achieved provide strong evidence that polysialate composites can be suitable for use in high temperature structures, whilst subsequently providing an understanding of their limitations. In addition to this, the values ascertained also provide the data required for the design and modelling of next generation high temperature structures.     

A comparative study for the behavior of 3D-printed and compression molded PLA/POSS nanocomposites

Because of the biocompatible and nontoxic character of both PLA (polylactide) and POSS (Polyhedral Oligomeric Silsesquioxane) nanoparticles, recently being a significant alternative for biomedical parts; the main purpose of this study was to investigate performance of the 3D-printed PLA/POSS nanocomposites with respect to the compression molded PLA/POSS specimens. Due to the higher uniformity and higher homogeneity in the distribution of POSS nanoparticles in each PLA matrix layer, mechanical tests (tensile, flexural, and toughness) revealed that the improvements in the strength, elastic modulus and fracture toughness values of the 3D-printed specimens were much higher compared to their compression molded counterparts, the benefits starting from 13% increasing up to 78%. It was also observed that there was almost no deterioration in the physical structure and mechanical properties of the 3D-printed specimens, even after keeping them 120 days at 37°C in a physiological solution prepared by using the standard PBS (phosphate buffered saline) tablet.     

Effects of sunshine UV irradiation on the tensile properties and structure of ultrahigh molecular weight polyethylene fiber

This study investigated sunlight‐simulated ultraviolet (UV) beam irradiation on the tensile properties and structure of ultrahigh molecular weight polyethylene (UHMWPE) fibers. The tensile results showed that after 300 h sunlight UV irradiation, the tensile properties of the UHMWPE fibers were obviously degraded. Investigation of morphology revealed that the crystallinity was slightly increased, whereas the overall orientation and molecular weight of the fibers were decreased. SEM observations indicated that the degradation process was nonuniform throughout the fiber and a change from a ductile to a brittle fracture mechanism was found after UV irradiation. DMA results showed two β‐relaxations and one α‐relaxation in the original single filament, and UV irradiation led to the increased intensity of the high‐temperature β‐relaxation and the lowered position of the low‐temperature β‐relaxation. This indicated that irradiation‐induced molecular scission and branching were located primarily in the amorphous and the interface areas of the fiber. Changes in the thermal behavior were also examined by DSC. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 2757–2763, 2003     

Study on the liquid crystal display mask photo-curing of photosensitive resin reinforced with graphene oxide

Graphene oxide has the characteristics of high specific surface area, high strength, and high modulus. The tensile and compressive properties of the cured resin part can be reinforced after the graphene oxide is mixed into the photosensitive resin. A self-developed liquid crystal display (LCD) mask photo-curing machine is adopted to prepare photosensitive resin parts mixed with graphene oxide. The influence of graphene oxide content on the surface roughness, tensile, and compressive properties of the cured resin is analyzed by the combination of finite element simulation and experiment. It is concluded that the accumulation of graphene oxide is the main reason affecting the tensile and compressive properties of the cured part. By applying ultrasonic vibration and extending the time of magnetic stirring at 80°C, the dispersion uniformity of graphene oxide is improved, the agglomeration of graphene oxide is reduced, and the tensile and compressive strength of cured parts are strengthened.     

Effects of mechanical recycling on optical properties and microstructure of recycled high-density polyethylene pellets and bottles

The demand for recycling high-density polyethylene (HDPE) utilizing mechanical recycling technologies is currently felt strongly by both society and industry. However, thermal oxidation of the polymer during the recycling process may lead to irreversible changes in the material properties of recycled high-density polyethylene (rHDPE). The effects of mechanical recycling on the optical characteristics and microstructure of rHDPE pellets and bottles were investigated in this study. The results revealed that the apparent color of the rHDPE became more yellow and gray compared to the virgin HDPE (vHDPE), and showed a signal at 670–680 nm in the solar reflectance spectrum. The thermal oxidation of rHDPE considerably raised the absorption intensities of carbonyl, ester, and hydroxyl groups in attenuated total reflection Fourier transform infrared spectrum. In addition, the presence of carbonyl and hydroxyl unsaturated chemicals might make it challenging to recognize the distinctive peaks of vHDPE in the ultraviolet–visible diffuse reflectance (UV–Vis-DIR) spectra at wavelengths less than 400 nm. Thermal oxidation of rHDPE was also confirmed in the C OH, CO, and O CO valence structures of C1s and O1s. A characteristic valence band (VB) profile at 25 eV can be used as the recognizable information for the oxidation of rHDPE. The microstructure of the surface of rHDPE pellets exhibited rough and uneven morphological defects. The higher recycled content made rHDPE bottles' surface morphology rougher and their cross-section microstructure thinner and more porous than vHDPE bottles.