Showing papers in "Polymer Testing in 2013"
TL;DR: In this article, the melting temperature and the melting point change of the various components in the PBAT/PLA blend before and after the biodegradation essentially followed the process of the changes in the respective single polymers.
Abstract: Poly(lactic acid) (PLA) and poly(butylene adipate-co-terephthalate) (PBAT) were mixed at a ratio of 40:60, extruded to form granules and cast into film; then, the PLA, PBAT, and PBAT/PLA film samples were buried in real soil environments. The residual degraded samples were taken regularly from the soil and analyzed by SEM, DSC, TGA, IR spectroscopy and elemental analysis. The analyses showed that PBAT and PLA had different biodegradation mechanisms. Further, the melting temperature and the melting point change of the various components in the PBAT/PLA blend before and after the biodegradation essentially followed the process of the changes in the respective single polymers. After biodegradation, the carbon atom content in the molecular structure of the PBAT, PLA, and PBAT/PLA samples decreased, while the oxygen atom content increased, indicating that the samples indeed degraded. The biodegradation rates of PBAT and PLA in the PBAT/PLA blend were not the same as those for the single materials.
TL;DR: In this paper, the incorporation of limonene in PLA matrix was evaluated and quantified by Pyrolysis Gas Chromatography Mass Spectrometry (Py-GC/MS).
Abstract: Polymers derived from renewable resources are now considered as promising alternatives to traditional petro-polymers as they mitigate current environmental concerns (raw renewable materials/biodegradability). d -limonene can be found in a variety of citrus, indeed is the main component of citrus oils and one of most important contributors to citrus flavor. The incorporation of limonene in PLA matrix was evaluated and quantified by Pyrolysis Gas Chromatography Mass Spectrometry (Py-GC/MS). Transparent films were obtained after the addition of the natural compound. Mechanical properties were evaluated by tensile tests. The effect of limonene on mechanical properties of PLA films was characterized by an increase in the elongation at break and a decrease in the elastic modulus. The fracture surface structure of films was evaluated by scanning electron microscopy (SEM), and homogeneous surfaces were observed in all cases. Barrier properties were reduced due to the increase of the chain mobility produced by the d -limonene.
TL;DR: In this paper, a sampling of the basic structural properties of FDM polycarbonate parts as a function of orientation is presented, and repeatable measurements can be made of the ultimate tensile strength and elastic modulus in FDM manufactured poly carbonate parts.
Abstract: Rapid prototyping manufacturing techniques provide an avenue for quick and cost effective design assessments leading to shorter design cycles. In addition to providing first-of-a-kind and one-of-a-kind parts, rapid prototyped parts may be used as the actual part. In order for this to occur on a wide-spread basis, material properties of importance to design must be well understood. One pervasive rapid prototyping technique is Fused Deposition Modeling (FDM). A sampling of the basic structural properties of FDM polycarbonate parts as a function of orientation is presented. The results show that repeatable measurements can be made of the ultimate tensile strength and elastic modulus in FDM manufactured polycarbonate parts. The results also show a degradation in strength compared to bulk material properties (30%–53%, depending on orientation) and as manufactured properties as reported by the FDM vendor (36%–63%, depending on orientation).
TL;DR: In this paper, the influence of dynamic tension/compression loading on notched and unnotched nylon specimens fabricated by Injection Molding (IM) and Selective Laser Sintering (SLS) was analyzed and described.
Abstract: This paper describes the influence of dynamic tension/compression loading on notched and unnotched nylon specimens fabricated by Injection Molding (IM) and Selective Laser Sintering (SLS). The main objective of this work is to analyze and describe the differences in material structure and fatigue properties of as-built nylon parts produced by IM and SLM from the same polyamide 12 powder. The differences in dimensional quality, density, surface roughness, crystal structure and crystallinity are systematically measured and linked to the mechanical fatigue properties. The fatigue properties of the unnotched SLS specimens are found to be equal to those of the unnotched IM specimens. The presence of pores in the sintered samples does not lead to rapid failure, and the microvoid coalescence failure mechanism is delayed. The notched specimens show more brittle failure and increased fatigue resistance which is caused by local notch-strengthening. The results enable improved understanding of the difference in material structure and fatigue behavior of selective laser sintered and injection molded polyamide.
TL;DR: In this paper, the effect of graphene nano-platelets (GNPs) on mechanical properties of polymer nanocomposites was investigated using nanoindentation and nanoscratch methods.
Abstract: The effect of graphene nano-platelets (GNPs) on mechanical properties of polymer nanocomposites were investigated using nanoindentation and nanoscratch methods. The GNPs at different weight fractions namely 0, 0.05, 0.1, 0.25 and 0.5% were dispersed in the polymer matrix using a mechanical stirrer and ultrasonic apparatus. A standard Berkovich indenter was used for indentation at three different normal loads, i.e., 400, 600 and 800 μN. Both elastic modulus and hardness increased with the addition of 0.05 wt% GNP. The tribological behavior of nanocomposites was investigated by a nanoscratch test in conjunction with atomic force microscopy (AFM); less pile ups and high wear resistance were observed in the nanocomposites. Based on this research, mechanical properties of pure polymer matrix are improved significantly with addition of low amounts of the graphene nano-platelets.
TL;DR: In this paper, the thermal conductivity of five semi-crystalline and four amorphous polymers was determined within a wide range of temperature, starting at room temperature and going up to temperatures above the polymer melting point.
Abstract: The thermal conductivity of five semi-crystalline and four amorphous polymers was determined within a wide range of temperature, starting at room temperature and going up to temperatures above the polymer melting point (Tm) for semi-crystalline polymers or above the glass transition temperature (Tg) for amorphous polymers. Two transient techniques were employed in the experimental investigation: the hot wire technique for the group of amorphous polymers, and the laser flash technique for the semicrystalline polymers. As expected, the experimental results show that Tg exerts a measureable influence on the thermal conductivity of amorphous polymers. In the case of semi-crystalline polymers, a singular behaviour of the thermal conductivity is observed within the Tm range. In order to explain the anomalous behaviour, the influence of these transition temperatures on the thermal conductivity behaviour with temperature has been analysed in terms of a phonon conduction process and temperature variations of specific heat and modulus of elasticity of the analyzed polymers.
TL;DR: In this paper, the properties of PHBV/PLA blends were investigated through scanning electron microscopy (SEM) and morphological analyzes, and it was shown that the complex viscosity of these blends fits the mixing law well.
Abstract: The paper aims to study blend properties of biodegradable polymers of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) and polylactide (PLA) prepared by melt mixing. Blend compositions based on PHBV/PLA were investigated according to the following weight ratios, i.e. 100/0, 75/25, 50/50, 25/75 and 0/100 wt%. The study showed through scanning electron microscopy (SEM) that blends of PHBV/PLA are not miscible. This is consistent with differential scanning calorimetry (DSC) data which indicate the presence of two distinct glass transition temperatures (Tg) and melting temperatures (Tm), attributed to the neat polymers, over all the range of blend compositions. Water and oxygen barrier properties of PHBV/PLA blends are significantly improved with increasing the PHBV content in the blend. Further, morphological analyzes indicated that increasing the PHBV content in the polymer blends results in increasing the PLA crystallinity due to the finely dispersed PHBV crystals acting as a filler and a nucleating agent for PLA. On the other hand, the addition of PLA to the blend results in a very impressive increase in the complex viscosity of PHBV. Moreover, the rheological data showed that, excluding the specific behavior of the neat polymers at low frequencies, i.e. less than 0.1 Hz, the complex viscosity of PHBV/PLA blends fits the mixing law well.
TL;DR: A chemically modified tung oil was used as the main polyol component in the formulation of viscoelastic (low resilience) polyurethane foams in this article.
Abstract: A chemically modified tung oil was used as the main polyol component in the formulation of viscoelastic (low resilience) polyurethane foams. Rice Husk Ash (RHA), a residue from the rice process industry, was chosen to be incorporated as rigid filler in these materials because of its high silica content. Water was used as blowing agent in order to increase the green nature of the reinforced foams. Physico-chemical and thermal properties of the neat and reinforced foams were measured and analyzed. RHA addition leads to noticeable changes in several properties, mainly thermal conductivity, density and foam morphology, even at the low filler content used in this work. Although the thermal stability was almost unaffected by ash content, a stabilizing effect of the inorganic filler was identified, since the residual char was higher than predicted from theoretical calculations.
TL;DR: Chitosan membranes reinforced by halloysite nanotubes (HNTs) at concentrations from 2 to 15 (w/w%) have been prepared by solution casting to investigate the optimal physico-chemical properties for biomedical applications as discussed by the authors.
Abstract: Chitosan membranes reinforced by halloysite nanotubes (HNTs) at concentrations from 2 to 15 (w/w%) have been prepared by solution casting to investigate the optimal physico-chemical properties for biomedical applications. Tensile test data revealed that the membranes reinforced with 5 (w/w%) HNTs yielded the highest Young's modulus (0.52 ± 0.01 GPa) and strength (81.6 ± 4.4 MPa). Electron micrographs of the fractured surfaces implicated the interplay between individual HNTs and agglomerates of HNTs in the stress transfer mechanism. Infrared spectra revealed interaction between the HNT siloxane and chitosan functional groups. Thermogravimetric results demonstrated that the thermal stability of the membranes increased with HNT concentration.
TL;DR: In this article, the effects of temperature on the mechanical properties of silicone rubbers were investigated using differential scanning calorimetry tests to determine the crystallization and melting temperatures, up to 150°C.
Abstract: This paper investigates the effects of temperature on the mechanical properties of silicone rubbers. First, differential scanning calorimetry tests are performed to determine the crystallization and melting temperatures. Second, mechanical tests are carried out at different temperatures above that of crystallization, up to 150 °C. In this temperature range, the silicone rubbers exhibit entropic behaviour. The neo-hookean model is used to fit the mechanical response. Third, the effects of temperature on the hysteresis, the stress softening and the stress relaxation are studied. Strong differences are observed and discussed.
TL;DR: In this article, the degradation behavior of P(3-hydroxybutyrate-co-4-hydroxymethylbutyrates (P3-4HB)/PLA blends in real soil environments was investigated via appearance analysis, SEM, FTIR and elemental analysis of their degraded residues.
Abstract: Both poly(3-hydroxybutyrate-co-4-hydroxybutyrate) [P(3HB,4HB)] and poly(lactic acid) (PLA) are biobased polymers, and their blends can be used to prepare biodegradable polymeric materials with good comprehensive properties. In this paper, the biodegradation behavior of P(3HB,4HB)/PLA blends in real soil environments was for the first time investigated via appearance analysis, SEM, FTIR and elemental analysis of their degraded residues. It was found that P(3HB,4HB) and P(3HB,4HB)/PLA blends can be biodegraded under real soil conditions. The order of biodegradability is as follows: PHA-100 [P(3HB,4HB)] > PHA-75 [P(3HB,4HB)/PLA, 75/25] > PHA-50 [P(3HB,4HB)/PLA, 50/50] > PHA-25 [P(3HB,4HB)/PLA, 25/75] > PLA, which correlates well with the PLA content. Due to the different degradation mechanisms, P(3HB,4HB) and PLA have the fastest degradation rate in 20 and 40 cm soil depth, respectively. Their blends also have different degradation rates in different depths of soil.
TL;DR: In this article, cellulose nanocrystals (CNs) were fabricated from sulfuric acid hydrolysis of cottonseed linter and used to prepare nitrile rubber (NBR)/CNs nanocomposites by mixing a water suspension of CNs and the NBR latex directly.
Abstract: Cellulose nanocrystals (CNs) were fabricated from sulfuric acid hydrolysis of cottonseed linter. The crystals were then utilized to prepare nitrile rubber (NBR)/CNs nanocomposites by mixing a water suspension of CNs and the NBR latex directly. CNs formed a strong filler-filler network in the NBR matrix which resulted in an obvious “Payne effect”. The mechanical performance showed that CNs have a good reinforcing effect on NBR. The composites exhibited an increase of tensile strength from 7.7 to 15.8 MPa with the CNs content increasing from 0 to 20 phr. The scanning electron microscope (SEM) images showed that CNs dispersed in NBR matrix uniformly, which contributed to the considerable mechanical properties of the resultant composites. The results of dynamic mechanical analysis (DMA) demonstrated that the glass transition temperature ( T g ) of the composites was shifted from 10.8 to 17.2 °C with CNs content increasing to 20 phr，and the storage modulus increased simultaneously. Thermal gravimetric analysis (TGA) result shows that the degradation corresponding to CNs in NBR/CNs nanocomposites is much higher than the degradation temperature of pure CNs.
TL;DR: In this paper, six stretch PVC films have been formulated to have Shore A hardness of approx. 80 and nominal thickness of 15μm with the aim of evaluating the performance of plasticizers from renewable and non-renewable sources for stretch PVC film intended to be employed as packaging.
Abstract: Six stretch PVC films have been formulated to have Shore A hardness of approx. 80 and nominal thickness of 15 μm with the aim of evaluating the performance of plasticizers from renewable and non-renewable sources for stretch PVC films intended to be employed as packaging. The reference film was produced with DEHA and ESBO, while the other films were produced with conventional plasticizers (ATBC and Polyadipate), new plasticizers from renewable sources (Mixture of glycerin acetates and Acetic acid esters of mono- and diglycerides of fatty acids) or a plasticizer employed in toy and childcare applications (DEHT) as a third plasticizer. The films were evaluated as to their physical and mechanical properties (durometer hardness, tensile strength and elongation), IR spectroscopy and light transmission. The several plasticizers influenced the mechanical properties of the PVC films to different degrees. All films will probably show adequate performance when used in packaging applications. Nevertheless, the vegetable oil-based plasticizers showed better mechanical performance than the other plasticizers when compared to DEHA.
TL;DR: In this paper, the effect of the interphase properties, resulting from well controlled surface treatment of the natural fibers, on the behavior of a ductile polymer matrix composite under quasi-static loading using the essential work of fracture criteria was analyzed and discussed.
Abstract: Lignocellulosic fibers, such as henequen, sisal, coconut fiber (coir), jute, palm and bamboo, have been used as reinforcement materials for different thermosetting and thermoplastic resins because of their attractive physical and mechanical properties. Unlike the traditional engineering fibers, e.g. glass and carbon fibers, and mineral fillers, these lignocellulosic fibers are able to impart certain benefits such as low density, less machine wear, no health hazards, and a high degree of flexibility to the composite. The last attribute is especially true because these lignocellulosic fibers will bend rather than fracture, like glass fibers do, during processing of the composite. The mechanical properties and fracture behavior of a natural fiber reinforced polymer composite depend, not only on the properties of constituents, but also on the properties of the region surrounding the fiber, known as the interphase, where the stress transfer takes place. Moreover, the tailoring of the interphase by means of surface treatments, and carefully characterizing it, gives a better understanding of the performance of natural-fiber reinforced composites. The fracture toughness resulting from the use of natural fibers as reinforcing materials is quite different between ductile and brittle polymers, as well as between quasi-static and impact loading rates. The aim of this paper is to study the effect of the interphase properties, resulting from well controlled surface treatment of the natural fibers, on the behavior of a ductile polymer matrix composite under quasi-static loading using the essential work of fracture criteria. Specifically, the contribution of each of the different fiber-matrix interfacial adhesion levels towards the dissipation energy were analyzed and discussed. In the case of the plastic work βwp, there seems to be a synergy between the frictional and chemical interactions observed for both, low and high strain rates. The nonlinear mechanical behavior of the natural fiber under combined tensile-shear loads has also an effect on the fracture behavior of the composite. Additionally, different fiber surface treatments change the microstructural nature of the natural fiber, further affecting its behavior, particularly under high loading rates.
TL;DR: In this article, the effect of the blend ratio (90/10, 80/20, 70/30, 60/40 and 50/50 (phr/phr)) on the compounding, mechanical and morphological properties of carbon-black-filled natural rubber/virgin EPDM and NR/R-EPDM blends was studied.
Abstract: Blends of natural rubber/virgin ethylene-propylene-diene-monomer (NR/EPDM) and natural rubber/recycled ethylene-propylene-diene-monomer (NR/R-EPDM) were prepared. A fixed amount of carbon black (30 phr) was also incorporated. The effect of the blend ratio (90/10, 80/20, 70/30, 60/40 and 50/50 (phr/phr)) on the compounding, mechanical and morphological properties of carbon-black-filled NR/EPDM and NR/R-EPDM blends was studied. The results indicated that both the carbon-black-filled NR/EPDM and NR/R-EPDM blends exhibited a decrease in tensile strength and elongation at break for increasing weight ratio of EPDM or R-EPDM. The maximum torque (S′M H ), minimum torque (S′M L ), torque difference (S′M H −M L ), scorch time (ts 2 ) and cure time (tc 90 ) of carbon-black-filled NR/EPDM or NR/R-EPDM blends increased with increasing weight ratio of virgin EPDM or R-EPDM in the blend. SEM micrographs proved that, for low weight ratios of virgin EPDM or R-EPDM, the blends exhibited high surface roughness and matrix tearing lines. The blends also showed a reduction in crack path with increasing virgin EPDM or R-EPDM content over 30 phr. This reduction in crack path could lead to less resistance to crack propagation and, therefore, low tensile strength.
TL;DR: In this paper, the cure kinetics and rheology of an amine-cured TGMDA resin film, M18-1 (Hexcel, France), have been characterised in order to predict the viscosity behaviour under resin film infusion (RFI) process conditions.
Abstract: The cure kinetics and rheology of an amine-cured TGMDA resin film, M18-1 (Hexcel, France), has been characterised in order to predict the viscosity behaviour under resin film infusion (RFI) process conditions. The kinetic and rheological parameters were experimentally determined using DSC analysis and rheometry. An autocatalytic model was applied to describe the rate of cure accounting for diffusion controlled kinetics at the final cure stage. Further, a chemo-rheological resin model was employed to effectively predict the resin viscosity under non-isothermal and stepped cure cycle conditions, as applied in the RFI process. A preliminary analysis on the effect of fast curing methods on the resin viscosity suggests improved impregnation properties with high temperature ramp rates.
TL;DR: In this article, a correlation between dynamic and static fracture toughness of polyurethane rigid foams was presented, and the results showed that for all foam densities the dynamic fracture toughness is higher than the static toughness.
Abstract: The paper presents a correlation between dynamic and static fracture toughness of polyurethane rigid foams. Static three point bend tests and instrumented impact tests were performed using single edge notch specimens. The obtained results show that for all foam densities the dynamic fracture toughness is higher than the static toughness. Density appears to have the main influence on both static and dynamic fracture toughness. A quasi brittle fracture without plastic deformations and cushioning was observed for all foam densities.
TL;DR: In this article, the authors describe the evaluation of polyhydroxybutyrate (PHB) based natural fiber composites via an extrusion-injection molding process.
Abstract: The work outlined in this paper describes the evaluation of polyhydroxybutyrate (PHB) based natural fibre composites via an extrusion – injection moulding process. Virgin PHB was compounded with two different naturally occuring plant fibres, hemp and jute, and a third, regenerated cellulose fibre, lyocell. Composite materials containing 10–30 wt% of each type of fibre were obtained by twin screw extrusion and the resultant material was injection moulded to produce tensile samples suitable for mechanical characterisation. Mechanical properties were determined using tensile, impact and flexural testing. Melt flow index and water absorption studies were also carried out on the biocomposite materials, and Fourier transform infrared spectroscopy was used to examine the bonding between the polymer and each fibre type. The rate of biodegradation was also observed by placing composite samples in compost and measuring weight loss weekly. The biocomposites produced using this method were shown to have increased rates of biodegradation whilst exhibiting significantly improved flexural properties.
TL;DR: In this paper, a single cantilever measuring device was applied for dynamic mechanical analysis (DMA) of carbon fiber prepregs with dynamic heating in the temperature range −90 to 280°C.
Abstract: Carbon fibre prepregs have found widespread application in lightweight constructions. They are based on a carbon fibre fabric impregnated with reactive epoxy resin. Measurements were carried out using commercially available prepreg material. For Dynamic Mechanical Analysis (DMA), a single cantilever measuring device was applied. The DMA results were refined by additional DSC measurements. The measurements were carried out with dynamic heating in the temperature range −90 to 280 °C. The heating rates were 1 and 2 K/min, respectively. A glass transition of the uncured material (T g0 ) near 1 °C, and crosslinking-induced vitrification and devitrification at the maximal glass transition temperature of the cured material (T gmax ) in the temperature range 220 to 230 °C were found. The activation energies for the glass transitions were determined using an Arrhenius plot. By detailed consideration of the influence of the frequency on the DMA data, indications for gelation were deduced.
TL;DR: A feasibility study was carried out on the utilization of Alkanolamide (ALK) on silica reinforcement of natural rubber (NR) by using a semi-efficient cure system as discussed by the authors.
Abstract: A feasibility study was carried out on the utilization of Alkanolamide (ALK) on silica reinforcement of natural rubber (NR) by using a semi-efficient cure system. The ALK was incorporated into the NR compound at 1.0, 3.0, 5.0, 7.0 and 9.0 phr. An investigation was carried out to examine the effect of ALK on the cure characteristics and properties of NR compounds. It was found that ALK gave shorter scorch and cure times for silica-filled NR compounds. ALK also exhibited higher torque differences, tensile modulus, tensile strength, hardness and crosslink density of up to 5.0 phr of ALK loading, and then decreased with further increases of ALK loading. The resilience increased with increased ALK loading. Scanning electron microscopy (SEM) micrographs proved that 5.0 phr of ALK in the silica-filled NR compound exhibited the greatest matrix tearing line and surface roughness due to higher reinforcement level of the silica, as well as better dispersion and cure enhancement.
TL;DR: In this article, the micromechanical properties of PEEK based hybrid composites reinforced with short carbon fibers and nano-SiO2 particles were examined using nanoindentation and nanoscratching methods.
Abstract: The micromechanical properties of PEEK based hybrid composites reinforced with short carbon fibers (SCF) and nano-SiO2 particles were examined using nanoindentation and nanoscratching methods. The composites were fabricated by the melt-mixing process at 400 °C. The neat polymer was in granulated form, the size of the nanoparticles was 13 nm and the original length of short carbon fibers was 6 mm. More than 30 nanoindentation and 3 nanoscratching tests were performed on each specimen. Surface topography of the indented and scratched regions was evaluated using AFM. The effects of reinforcing particulates on the typical nanoindentation load-displacement curves of the composites were investigated. Also, the overall reinforcing effects of the carbon fibers and nanoparticles were investigated. Nanoscratching tests were effectively performed to evaluate the frictional properties in the matrix, fiber and interphase regions and also to estimate the thickness of the interphase. There were notable differences between the nanoindentation responses and the microfrictional properties of the composites in matrix and fiber phases. Results showed a significant increase in hardness and elastic modulus due to the presence of reinforcing agents.
TL;DR: Graphene oxide nanosheets (GONSs)/cyanate ester (CE) resin composites were prepared via a solution intercalation method as mentioned in this paper, and the structures of the GONSs and the composites are studied using Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), transmission electron microscopy (TEM), and scanning electron microscope (SEM).
Abstract: Graphene oxide nanosheets (GONSs)/cyanate ester (CE) resin composites were prepared via a solution intercalation method. The structures of the GONSs and the composites were studied using Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), transmission electron microscopy (TEM) and scanning electron microscopy (SEM). The mechanical and tribological properties of the composites were investigated. In addition, the thermal behavior of the composites was characterized by thermogravimetric analysis (TGA). Results show that the GONSs/CE resin composites were successfully prepared. The addition of GONSs is beneficial to improve the mechanical and tribological properties of the composites. Moreover, the composites exhibit better thermal stability in comparison with the CE resin matrix.
TL;DR: In this paper, a superabsorbent hydrogel composites were prepared using waste linear low density polyethylene (LLDPE), acrylic acid (AA), and modified montmorillonite (OMMT) clay through emulsion polymerization.
Abstract: Novel superabsorbent hydrogel composites were prepared using waste linear low density polyethylene (LLDPE), acrylic acid (AA), and modified montmorillonite (OMMT) clay through emulsion polymerization. The effects of major factors such as acrylic acid, initiator, crosslinking agent and OMMT contents and the degree of neutralization of acrylic acid on water absorbency were investigated to obtain optimum conditions with a high swelling capacity. The prepared samples were characterized using FTIR, XRD, SEM, TGA, solid state 13C NMR and 29Si NMR. SEM characterization of the samples showed that hydrogel composites have more pores and a higher swelling ratio than clay free hydrogels. The swelling behaviour of the hydrogel composite was investigated in various saline solutions. The hydrogel composite containing 3 wt% OMMT had the highest water absorbency (800 g/g in distilled water).
TL;DR: In this article, a PA 12-based polymer was used to study the temperature and time dependency of tensile properties of a servo-hydraulic system with an incremental extensometer.
Abstract: This work deals with the study of temperature and time dependency of tensile properties of a PA 12-based polymer. The range of variation of parameters in experiments was linked to in-service conditions of components manufactured with this material (temperature interval from −25 °C to 50 °C and average strain-rate magnitudes from 0.00028 s −1 to 9.4 s −1 ). For tests with different temperatures and low speed, an electro-mechanical machine, Zwick Z250, equipped with an incremental extensometer was used. To study the effect of strain rate at medium speeds, a servo-hydraulic system, Schenk PC63M, equipped with a strain-gauge extensometer was used, while at high speeds a servo-hydraulic machine, Instron VHS 160/20, equipped with a high-speed camera for strain evaluation by digital image correlation was employed. The changes of the rate of deformation with strain as well as elastic modulus variation with strain were studied. An increase in the elastic modulus and yield strength was observed with a drop in temperature and an increase in the strain-rate, temperature having a stronger influence on the variation of mechanical properties. The collected data was assembled in an elasto-plastic material model for finite-element simulations capable of rendering temperature- and strain-rate-dependency. The model was implemented in the commercial software Abaqus, yielding accurate results for all tests.
TL;DR: In this paper, the authors used the stepped isothermal method (SIM), originally developed for product testing of geosynthetics, to characterize the long-term creep behavior of polypropylene up to approximately 100 years.
Abstract: The increasing use of polymers in engineering applications requires suitable accelerated test methods for predicting their long-term behavior. The stepped isothermal method (SIM), originally developed for product testing of geosynthetics, was successfully applied in the presented work to characterize the long-term creep behavior of polypropylene up to approximately 100 years. Based on the time-temperature superposition principle, this method can be described as a short-term creep experiment during which the temperature is elevated stepwise. It is shown that the temperature steps can be rescaled and shifted to generate a master curve matching the prediction of long-term creep resulting from the conventional approach of the time-temperature superposition principle (TTSP). This compliance with established test methods and its good reproducibility suggests that SIM might be a useful tool for accelerated testing of long-term creep behavior, especially for comparative purposes such as quick screening of material formulations during the early development stages, or the at-line assessment of resins as part of quality assurance.
TL;DR: In this paper, the performance of carbon fiber reinforced polyphenylene sulfide (PPS) composite was studied by the microbond test and a novel homemade apparatus which is operated simply was employed and a different micro sample preparation method was introduced.
Abstract: Interfacial micromechanical performance of carbon fiber (CF) reinforced polyphenylene sulfide (PPS) composite was studied by the microbond test. A novel homemade apparatus which is operated simply was employed and a different microsample preparation method was introduced. Comparative tests at various loading speeds were made to investigate the influence of testing rate on the interfacial shear strength of CF/PPS micro-composite. It was found that the interfacial shear strength increased with increasing fiber embedded length at speeds below 0.02 mm/s and above 0.04 mm/s, but it was constant between 0.02 and 0.04 mm/s. It is recommended to perform the microbond test in the test rate range of 0.02–0.04 mm/s, where the interfacial shear strength does not change with the embedded length and no significant deviations are observed, thus could better reflect the true interface strength of the composite.
TL;DR: In this paper, the authors investigated the effect of electrospun polyamide 6 nanofibrous structures on the mechanical properties of a glass fiber/epoxy composite and found that the incorporation of polyamide nanofibrils has no negative effect on the impregnation of the epoxy.
Abstract: Recently, several types of nanoparticles are frequently incorporated in reinforced epoxy resin composites. A homogeneous dispersion of these nanoparticles is still a problem. Thermoplastic nanofibrous structures can tackle this dispersion issue. Therefore, this paper investigated the effect of electrospun polyamide 6 nanofibrous structures on the mechanical properties of a glass fibre/epoxy composite. The nanofibres were incorporated in the glass fibre/epoxy composite as stand-alone interlayered structures and directly spun on the glass fibre reinforcement. Both ways of nanofibre incorporation have no negative effect on the impregnation of the epoxy. Moreover, the nanofibres remain well dispersed within the matrix. Incorporation of nanofibres increases the stress at failure in the 0°-direction, the best results are obtained when the nanofibres are directly electrospun onto the glass fibres. Optical microscopic images also demonstrate that nanofibres prevent delamination when a 90° crack reaches a neighbouring 0° ply. Furthermore, mode I tests showed a small improvement when a thin nanofibrous structure is deposited directly onto the glass fibres. When the composites are loaded under 45°, it is proven that, for an identical stress, the glass fibre composite with deposited nanofibres has less cracks than when interlayered nanofibrous structures are incorporated. Generally, it can be concluded that the addition of polyamide 6 nanofibres improves some mechanical characteristics of a glass fibre/epoxy composite.
TL;DR: In this article, a free-rise pouring method was used to sample polyurethane (PU) foams with rice husk ash (RHA) to characterize their density, compression and dynamic mechanical behavior.
Abstract: Viscoelastic polyurethane (PU) foams based on modified tung oil, ethylene glycol and polymeric MDI, and reinforced with rice husk ash (RHA), were prepared by a free-rise pouring method and characterized in terms of density, compression and dynamic mechanical behavior. The density of foams ranged between 50 and 90 kg/m3, depending on the position of the sample with respect to the foam rise direction and filler content. As revealed by dynamic mechanical tests, the foams exhibited two different and broad thermal transitions, the temperature of their maxima depending on filler concentration. Compression modulus, compressive strength and storage modulus increase as foam density increases but decreases as rice husk ash concentration increases due to the detrimental changes induced by the filler in the foam cellular structure. However, densification strain exhibits the opposite behavior, indicating that reinforced foams can sustain slightly higher deformations without collapsing, probably due to a reduced reactivity of the components induced by the filler.
TL;DR: In this paper, a mechanistic view of the reversion phenomenon is proposed, which results in a decrease of the elastic modulus (related to the sulphur crosslink density) for long vulcanization times at high temperature.
Abstract: A novel kinetic model of natural rubber sulphur vulcanization is proposed The modeling approach takes into account current knowledge on the different polysulfidic structures present during vulcanization, and the associated individual reactions A simplified scheme is proposed, giving a mechanistic view of the reversion phenomenon, which results in a decrease of the elastic modulus (related to the sulphur crosslink density) for long vulcanization times at high temperature The resulting set of differential equations is solved by an appropriate numerical method to predict the evolution of the degree of vulcanization for isothermal cure conditions The vulcanization kinetics of a model natural rubber compound was characterized experimentally by rheological measurements, in order to test the proposed kinetic model A remarkable agreement between model predictions and experimental data is observed The identified kinetic parameters corresponding to the individual reactions taken into account by the mechanistic model are consistent with those of an existing, less refined, pseudo-mechanistic model The proposed model thus allows bridging the gap between the prediction of macroscopic variations of the elastic modulus and the evolution of molecular scale structure during vulcanization when the reversion phenomenon is present
TL;DR: In this paper, a commercial epoxy matrix was prepared by dispersing three different grades of graphite particles, expanded graphite, commercial graphene nanoplatelets and natural graphite.
Abstract: In this study nanocomposites were prepared by dispersing three different grades of graphite particles, expanded graphite, commercial graphene nanoplatelets and natural graphite, in a commercial epoxy matrix. Dielectric properties, thermal conductivity and permeability to oxygen of the composites were studied and compared to those of the unfilled epoxy matrix. An increase of all properties is obtained using expanded graphite, suggesting the presence of a good dispersion of the filler in the matrix and a strong polar interactions of the filler with the matrix, attributed to the partially oxidised surfaces of the expanded graphite. All the measured transport properties were fitted with simple mathematical models obtaining good agreement between the experimental results and theoretical predictions. The model parameters were related to the aspect ratio of the filler, defined as the ratio between the in-plane average dimension and the thickness of the reinforcement. An aspect ratio between 1250 and 1550 indicates that graphite thin platelets (or graphene stacks), characterized by a thickness of the order of a few tens of nanometers, were dispersed in the epoxy matrix.