The SPE Library contains thousands of papers, presentations, journal briefs and recorded webinars from the best minds in the Plastics Industry. Spanning almost two decades, this collection of published research and development work in polymer science and plastics technology is a wealth of knowledge and information for anyone involved in plastics.
The tensile properties of two different molecular weight polycarbonates were examined in relation to injection-molding conditions, such as low and high temperatures & speeds (affecting injection pressures), that were beyond those recommended by the supplier. We found conditions that prompted higher injection pressures led to decreases in tensile elongation-at-break, with more significant decreases for higher molecular weight (and high viscosity) PC. Examination of molded samples under polarized light suggested higher degrees of molded-in stress along the flow length as an important contributor to the changes in elongation at break. Additionally, corresponding to the elongation at break, the onset of strain hardening decreased under injection molding conditions that produced higher injection pressures.
Thermoplastic elastomers (TPE) are a combination of a rubber and a thermoplastic to create a recyclable blend combining the properties of both resins. The objective of this work is to produce and characterize rotomolded parts based on polyamide 6 (PA6) as the matrix and recycled ground tire rubber (GTR) as the dispersed phase. In order to improve the adhesion between PA6 and GTR, and consequently the mechanical properties of the resulting TPE, a treatment with formic acid was used on the GTR surface. All the samples were initially mixed via dry-blending using 5 and 10% wt. of GTR and then rotomolded. For these concentrations, successful rotomolded parts were produced to report on their morphological and mechanical properties. The results show that increasing the GTR content led to lower tensile modulus and tensile strength, but higher elongation at break and impact strength compared to the neat matrix.
In this work, polypropylene (PP) was dry-blended with ground tire rubber (GTR) to produce composites by rotational molding. In particular, the effect of GTR content was investigated to modify the mechanical properties of the PP matrix. Each compound was characterized via morphology, density and mechanical properties (tensile, flexural and impact). As expected, the results showed that all the mechanical properties decreased with increasing GTR concentration due to its low modulus and strength. Also, the crosslinked structure of the GTR particles is believed to limit the interfacial PP-GTR interaction, thus also limiting mechanical stress transfer.
A series of stereocomplex polylactide (SC-PLA) blends (PLLA 95 wt%/PDLA 5 wt%) were prepared by spunbond technology. For this, the compounds of linear PLLA, and low and high molecular weight as well as branched PDLAs were spun at two different temperatures. They were spun at 190 °C, which was below the melting temperature of the stereocomplex crystals. And, they were melt-spun at 230 °C, which was above the melting temperature of the stereocomplex crystals. Morphological observation of the etched samples showed that the samples spun at 190 °C demonstrated tiny spherical crystals exhibiting diameters in the range of 100–200 nm; however, the samples spun at 230 °C showed thin fibers in the size range of 60–70 nm. The obtained results were supported by shear and elongational rheological measurements. Moreover, crystallization kinetics of the samples was also enhanced after spinning and was largely dependent on the spinning temperature. Tensile modulus and strength of the spun samples was also significantly improved. The spun samples also presented a considerable decrease in boiling water and hot air shrinkage.
In the current research, hybrid laminates having veneer facesheets and natural fibre composite cores were fabricated to investigate their fire and mechanical properties and to observe a suitable combination. Wool and flax fibres were selected for fibre reinforcement. Ammonium polyphosphate (APP) was used as the primary flame retardant for all the composites. The mechanical performance of the flax fibre reinforced fire retardant polypropylene (flax-FRPP) and fire retardant wool-polypropylene (FR-wool-PP) hybrid layered panels were further studied and compared to plywood made similarly. The results showed that hybrid laminates have better fire properties and the hybrid layered veneer composites can have significant structural applications if proper bonding between the composite and the veneer layers can be achieved. The tensile properties showed a reduction in Young’s modulus and ultimate tensile strength, though the wool-veneer hybrid laminates outperformed the flax-veneer ones. Moreover, the impact test showed that the wool-veneer hybrid laminates had the best resistance when compared to all the veneer-based samples tested. The results point towards the possibility of manufacturing a superior fire-resistant hybrid veneer composite laminate.
In this work, two compostable adhesive formulations, i.e., Resin A – MPP (Major PLA phase) and Resin B – MINPP (Minor PLA phase), were developed and evaluated for their performance as an adhesive in the extrusion lamination process. The densities of both the resins were in the range of 1.26-1.32 g/cc. The MFI values of Resin A and Resin B were 5 and 3 (g/10 min at 190ºC/ 2.16 kg), respectively. The complex viscosity of Resin A was lower than the complex viscosity of Resin B. The percent neck-in of Resin A at 235ºC was almost 4 times as that of Resin B at same conditions. The percent neck-in increased with increasing the temperature and distance from the die. Multilayer laminates were made using cellophane and metalized cavitated PLA as substrates, and Resin A or Resin B as adhesive. The adhesive strength of the Resin B to the cellophane was 20 g/cm, which was 10 times higher than the adhesive strength of Resin A (2 g/cm) to the cellophane. Also, the adhesive strength over the period of two weeks did not decrease significantly.
The present study aims to design a comonomer based resin matrix with a prolonged gel time while maintaining low viscosity and minimal curing time to ensure its processability with high filler contents in fabricating polymer concrete composites (PCC) for bases of tool machines. In this work, a copolymerization route was adopted to optimize the processability of a commercially available epoxy vinyl ester. Comonomer resin systems were prepared from addition of Methyl methacrylate (MMA) as a reactive diluent into the commercial epoxy vinyl ester resin (VE) which was premixed with styrene (ST) diluent (48 wt. %). Compositions of comonomer resin systems were varied systematically to achieve an optimum mixture design. The viscosity and gel time of comonomer resin systems were measured by a digital Brookfield viscometer. The influence of MMA on the curing behavior, elastic modulus and glass transition temperatures of comonomer resin systems have been investigated by differential scanning calorimeter (DSC) and dynamic mechanical analyses (DMA) respectively. The obtained optimum comonomer resin system was 40wt% VE resin, 23wt% MMA and 37wt% ST. This formulation exhibited 80% lower viscosity and about 45% longer gel time as compared to the viscosity and gel time of commercial VE resin system with just half the styrene monomer content, thereby not only ensuring its processing with high filler contents, but also reducing the volatile organic compounds associated with the large-scale manufacturing of PCC products. Also, this composition showed the shortest curing time and 60% higher flexural strength (53.6 MPa) compared to that of the commercial VE resin system (17.3MPa).
The incorporation of technical lignin, a multifunctional natural polymer, into rigid polyurethane foam (RPUF) for the enhancement of thermal insulation performance has gained increasing interest in academia and industry. However, the structural complexity of technical lignin hinders its dispersion in the polyols commonly used for the preparation of RPUF. Poor dispersion of technical lignin in polyols inhibits the chemical reactions and limits the potential improvement in the thermal and mechanical properties of RPUF. Herein we report enhanced dispersion of unmodified kraft lignin, at a loading of 3 wt % in a mixture of glycerol and an aromatic polyester polyol (20:80) for the preparation of RPUF. It has improved the insulation property by 30% while retaining its mechanical performance compared to the control RPUF without lignin. Such a level of improvement, to the best of our knowledge, has not been reported in RPUF using chemically unmodified lignin to date. This is attributed to the enhanced dispersion of the kraft lignin in the polyol blend causing changes in the cell morphology of the resultant RPUF, as supported by microscopic and rheological analysis. To this end, the insights into the influence of kraft lignin on the polyol-precursor on the properties of the RPUF are discussed.
An enzymatic degradation mechanism of Poly- ε-Caprolactone (PCL) is discussed in this paper. A ping-pong bi-bi reaction mechanism with esterase is chosen to obtain the model equations. The reaction rate constants were either estimated or fitted in the model. The model is then utilized to predict concentration vs time plots for PCL and a degradation product, hydroxycaproic acid. The reaction between the enzyme and polymer is found to be rate limiting because of the limited polymer surface available for reaction. The predictions of the model are compared to experimental results reported in literature.
The preparation and characterization of a multilayer film reservoir with clay/essential oil (EO) composites was described. The goal is to analyze the potential use of these reservoirs with clay/EOs composites as aroma-controlled release for various applications such as pesticide or attractant for pest control as well as antimicrobial control. Two types of clays were analyzed, porous halloysite (HNT) and octadecyl modified montmorillonite (MMT) nanoclay; as well as two types of essential oils, orange (OO) and thyme oil (TO). The DRX results confirmed that MMT clay presented higher thyme oil adsorption and better interactions than orange oil. Clay/EO composites encapsulated in multilayer film showed a prolongated aroma release during longer times. Polyamide (PA) barrier layer thickness has an effect on the liberation of the volatile compounds through the multilayer film.
There is an ever increasing need for sustainable and biobased materials. Plant-based feedstock such as cellulose and lignin can potentially become competitive resources as alternatives to fossil-based materials. Lignin as an inexpensive feedstock has been examined toward preparing polymer composites. It however faces some challenges including its detrimental impact on the mechanical and thermal properties of the resultant composites. This work reports the fabrication and characterization of polylactic acid/lignin composites with the incorporation of a new type of lignin, called deep eutectic solvent (DES) extracted lignin. White fir sawdust was used as feedstock to extract DES lignin. For comparison, commercial alkali lignin (CAL) was also used as a benchmark. PLA/lignin composites containing 0-15 wt.% lignin were fabricated using twin screw extrusion process followed by compression molding. Composites characterization were conducted using thermogravimetric analysis (TGA), differential scanning calorimetry (DSC) and tensile testing. The results revealed that the mechanical and thermal behaviors of DES lignin composites significantly outperformed their CAL counterparts. For composites with 15 wt.% DES, the tensile strength, Young’s modulus, and elongation at break dropped by ~33, 7 and 45%, respectively, compared to those of neat PLA. However, the composites with 15 wt.% CAL showed 90, 45 and 86% drop in the strength, modulus, and elongation, respectively. The initial thermal degradation temperature of PLA dropped by ~ 8-27 °C with the incorporation of 5-15 wt.% DES lignin. On the other hand, the introduction of CAL to PLA lowered the degradation temperature by ~89-124 °C. DSC also showed a drop in the glass transition temperature (Tg) and melt temperature (Tm) for both the composites but the drop was less significant for DES lignin composites. The good performance of PLA/DES lignin composites may be associated with the DES lignin’s high purity, low heterogeneity, low molecular weight, fine particle size as well as its homogenous dispersion and compatibility with PLA matrix.
ASTM D-2863 is a small-scale fire performance classification test, part of ASTM C-578 standard for polystyrene rigid thermal insulations, with a binary pass/fail outcome at a given oxygen concentration level. When applied to foams, the test is highly variable and is easy to manipulate, putting its accuracy as a test method into question. In this work, macro-imaging was used to closely monitor the foam – flame interaction to gain a better understanding of variability levers. For example, one of the levers is duration of flame application to a sample. Our imaging studies indicate that the pass / fail boundary oxygen level is strongly correlated with the flame application duration.
In this paper, a decorative material was first applied onto the light weight reinforced thermoplastic (LWRT) composite core mat during the core manufacturing, and then followed by a consolidation process through the calender rolls. This method is defined as an in-line lamination process with a finished A-surface panel in comparison with conventional off-line decorative materials lamination process, in which the decorative layer is applied in a separate process from core manufacture. Decorative layers with two patterns, namely woodgrain and marble, have been studied. The adhesion performance between the decorative skin material and LWRT composite substrate has been evaluated by 180° peel adhesion test following ASTM standard D903. The separation between the decorative layer and the substrate was difficult to initiate, which demonstrates an outstanding adhesion between the two components. A stylus method quantitatively confirmed the decorative surface is smooth and able to cover the core’s texture. Flatwise tensile test results by ASTM standard C297 method showed the decorative panels could not be delaminated, indicating strong bonding between decorative skin material and core mat. Materials produced with the woodgrain pattern were tested to have better flexural strength and stiffness than the sample made with marble decorative pattern material. In addition, flame retardancy results showed the laminated decorative panels can meet ASTM E84 requirement of Class C and above. The decorative material with custom design provides the decorative A-surface with an appearance of wood, stone, textile or other natural materials as desired, opening a window for the LWRT composite to be used inside an RV such as the interior layer of sidewall and ceiling.
Injection molded and then electroplated plastic parts are mainly made of acrylonitrile butadiene styrene (ABS) or polycarbonate/acrylonitrile butadiene styrene (PC/ABS) blends. Nevertheless, compared to these materials, polyamide (PA) has superior physical properties. However, the coating quality is inferior to that of conventional polymers and the scrap rates of 25% to 30% are higher. The coating quality depends not only on the electroplating parameters but also on the surface of the injection molded part. The aim of this paper is to determine the influence of injection molding parameters on the surface structure of injection molded, mineral-filled polyamide parts. Therefore, mineral-filled polyamide parts are produced in a full-factorial design of experiments (DoE) and electroplated subsequently. Afterwards, surface parameters from DIN EN ISO25178 are determined by confocal microscopy for different pre-treatments of the electroplating process chain and at different positions.
A novel approach of producing foamed polyamide/ glass fiber (PA/GF) composite parts using gas-laden pellets was proposed. Gas-laden pellets loaded with nitrogen (N2) were produced by introducing sub-critical N2 into PA/GF during compounding using a twin-screw extruder equipped with a simple gas injection unit. Compared to the commercial microcellular injection molding (MIM) technologies, gas-laden pellets enable production of foamed parts with a standard injection molding machine, which is more cost-effective and easier to operate. The shelf life of N2-laden PA/GF pellets was examined. Results showed that the N2-laden pellets still possessed good foaming ability after one week of storage under the ambient atmospheric conditions. With this approach, the weight reduction of foamed PA/GF parts was able to reach 12.0 wt%. The tensile strength, cell morphology, and densities of foamed PA/GF parts were also investigated.
Co-injection molding has been developed for decades. However, due to too many factors which can affect its processing, it is very difficult to obtain good quality of co-injected products all the time. One of the major challenges is that the prediction and management of the advancement of core material is very difficult. In this study, both CAE simulation (Moldex3D) and experimental methods have been applied to investigate the advancement distance of core material in co-injection molding based on the standard tensile bar (ASTM D638 TYPE V) system. Specifically, the flow behavior of the core material has been predicted numerically and verified experimentally through short shot testing, and skin/core ratio effect testing. Moreover, based on the optimized skin core ratio, the major factors to influence of the advancement of core materials have been conducted. Finally, to quantify the advancement of the core material in co-injection molding, both simulation prediction and experimental observation were performed. Results showed that the advancement of the core material is strongly proportional to the core ratio in co-injection molding system. Moreover, the flow rate and the different skin/core material arrangement also can influence the advancement of the core material.
This research was focused on the synergistic effect of nucleating agents and an oscillatory motion on the crystallinity development of poly-lactic acid (PLA) during vibration assisted injection molding (VAIM). A differential scanning calorimetry (DSC) study was performed to understand the efficacy of orotic acid, a nucleating agent for 2500 HP PLA, under quiescent conditions. A new protocol for quantitative characterization of crystallization kinetics from DSC data was developed to gain insight on the crystallization kinetics. It was observed that the 1 wt.% orotic acid provided significant enhancement in crystallization kinetics. The isothermal crystallization, injection molded and VAIM data obtained from DSC were compared. The shear stresses introduced during traditional injection molding enhanced PLA crystallization at 90°C and 70° C mold temperature as compared to crystallization under quiescent conditions. The crystallization was enhanced by ~250% when VAIM was introduced at 70°C mold temperature as compared to traditional injection molding was observed. The effect of VAIM was nominal when the mold temperature was 90°C indicating that VAIM is more effective at lower mold temperatures.
A Kenics static mixer was introduced into the runner system of a convex-concave circular disc mold and simulated using Moldex3D. The set-up was tested with two mixers with the same diameter, length, and pitch but different mixer element thickness as well as various polymer resins with different rheological properties. The maximum sprue pressure rose with increasing mixer thickness but stayed within normal machine capabilities. Overall, simulations with the thin mixer exhibited improvements regarding melt homogeneity and part quality for polymers such as polyamide 6 (PA6), polycarbonate (PC), and poly-propylene (PP), while the thick mixer had a neutral or negative effect on the same properties. The fiber analysis showed a decrease in fiber alignment in runs including a mixer. Polymers with more extreme rheological properties, such as polybutylene terephthalate (PBT) and polymethyl methacrylate (PMMA), revealed unsatisfactory results.
This paper compares the strain-rate behavior of injection and compression molded Polycarbonate plates in compression through Split Hopkinson Pressure Bar (SHPB) experiments. The samples are tested under strain rates ranging from 0.01 to 6,000 /s and at a temperature ranging from - 25°C to 75°C. The difference in mechanical response of specimens fabricated using the two different processes is relatively well understood when tested in plane and is influenced by the different molecular orientation distributions resulting from processing [1-4]. However, there has not been a systematic study of out-of-plane response of such materials, particularly for higher strain rates relevant to impact performance of Polycarbonate. The results of this study suggest that an orientation distribution difference between the samples fabricated via the two paths may not fully account for the observed differences, which become more pronounced at the higher ranges of strain rate based on SHPB testing.
We report systematic studies on the foamability of our novel high-melt-strength long-chain branched polypropylene under supercritical CO2. Continuous foaming experiments were conducted using a tandem extrusion system and a set of filamentary dies with similar pressure drops but different pressure drop rates. The foam expansion was controlled by varying the temperature at the die exit. Under identical CO2 loadings, the expansion ratio plotted as a function of die temperature exhibited similar shapes across multiple pressure drop rates. However, the shape of the curve varied across different amounts of CO2, under which the highest achievable expansion ratio occurred at a lower die temperature with increasing CO2 content. The cell density displayed strong dependence on both the pressure drop rate and the amount of dissolved CO2. The effect of the latter became more apparent at lower pressure drop rates. The average cell size decreased with increasing CO2 loading but generally showed weak dependence on pressure drop rate except at the highest value.
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