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.
Understanding the mechanical failure of additively manufactured (AM) polymers is becoming more important as engineers increasingly fabricate end-use parts. Knowing how the mechanical limits of a given AM polymer depend upon material orientation is a critical aspect of maximizing mechanical performance. We have characterized the tensile failure of an SLS polyamide 12 in detail using tensile test specimens and subsequently examined how the anisotropy of the material impacts the failure of a lattice structure loaded in three-point bending. Additionally, an anisotropic material model is presented that we have used to simulate the deformation of the lattice structure using finite element analysis.
One of the chief impediments to the wider adoption of nanocomposites is the challenge of maintaining nanoscale features while employing bulk preparative techniques. Nanoparticle fillers may tend to aggregate or become destabilized during processing at temperatures required to process engineering thermoplastics. We report a study where nanoparticles of varying aspect ratios were stabilized with robust shells and then compounded using a laboratory scale extruder. Optical plaques were produced via injection molding, and the resultant nanocomposites were assessed for their optical and morphological properties.
Color (pigment) concentration levels play a significant role in changing the mechanical properties of an injection molded part. Higher concentration levels could result in functional failure of the parts . A general rule of thumb, concentration levels between 3 - 5% or 5 - 10% are being used across different industries to achieve the required color. The above concentration levels are considered as small range concentration levels in this manuscript. Effects of sterilization (radiation) plays an important role on the plastic injection molded parts. The combination of gamma radiation sterilization and color concentration is very useful to the medical devices and food processing Industry. An experimental study is conducted to find out the effects of both small range color concentration and gamma radiation sterilization on the mechanical properties such as tensile strength, strain at yield and break on the Injection molded parts. In this study, Injection molded specimen made up of PP (polypropylene) and Acrylonitrile Butadiene Styrene (ABS) which are exposed to gamma sterilization of 25 kGy (kilo gray) dose are considered as it common normal dose used for plastics . Depending upon the specific polymer and additives involved. There is no impact on tensile strength, while the strain at yield and at break shown an considerable decreasing trend with increase in the percentage of pigments in case of PP(polypropylene). There is no trending observed in case of ABS resin. Outcomes may influence performance and should be evaluated in advance by functional testing. Hence product designers may need to assess the impact of these small pigment concentration levels in combination with the sterilization effect with respect to the base resin and need to specify the acceptable pigment concentration levels in combination with sterilization in their product drawings or in product specification documents.
Creep is the inelastic response of materials exposed to constant load at a particular temperature. Creep characteristics play an important role in the design consideration of injection molded plastic parts where they can provide enable one to measure or estimate the creep strain when there are mating parts. However this does not consist of the information necessary to determine or calculate the outcome of creep failure of the mating parts under a constant load up to the end of the shelf life of the product. If the designer can understand the limits of creep failure in the plastic engineering part design then it aids in the determination of shelf life of the product. Also, the plastic parts which are predominantly used in the medical device industry, are exposed to sterilization prior to use. A common radiation dose used for plastics is in the range 15–25 kGy . Therefore the objective of this study was to understand the creep failure of parts with or without gamma sterilization and help enable the designer to determine the shelf-life of the plastic components when they are exposed to gamma sterilization. Finite Element Analysis (FEA) was utilized to determine the impact of creep on the two mating PP (polypropylene) injection molded parts. The inputs needed for the FEA model, which are the temperature dependent coefficients (A, m and n) were determined by curve fitting the creep test results for PP with a time hardening formulation of power law creep model for the strain vs time data at 23°C, 40°C and 60°C with and without gamma sterilization . It is found that the Creep strain at given total time showed a decreasing trend . The FEA model contains two PP resins namely a bearing and sleeve having a mating interference fit. Sleeve is inserted into the bearing and this insertion force is termed as attachment force and later the sleeve is pushed out from bearing and this force is termed as detachment force. In FEA model, in order to find creep strain produced between both mating parts, the Sleeve is retained in bearing for intended self-life duration. The detachment force of sleeve before and after shelf life for unexposed parts and 25kGy gamma exposed PP resins parts were calculated. The results shows that the detachment force reduces after aging, regardless of gamma exposure. These results assist the product designer to estimate the reduction in detachment force due to creep strain between the mating parts. It is also found that material and geometry are important to consider, so that the failure due to the creep can be avoided early in the design process and it is very critical to consider creep in order to ensure product performance. Therefore the results of this study can help one determine the required shelf life of the product by considering the creep failure in the successful design of the plastic Injection molding parts.
Previous work on rubber toughening by incorporating reactive functional modifiers into epoxy formulations show that they phase separate into rubbery domains necessary for effective increases in fracture toughness both in the neat resin as well as carbon fiber reinforced composites. However, their relative reactivity with respect to the epoxy or the amine used in the system can lead to imbalance in stoichiometry and disruption of the network structure. Also, due to their different solubility in different resins and hardeners, they can act as plasticizers instead of phase separating into necessary rubbery domains which can be seen from the decrease in Tg of these formulations. This work aims to investigate the detrimental effects of impact modification on network structure by measuring thermal and non-linear mechanical properties of the network using non-standard compression testing. Compression tests were done on impact modifier free diglycidyl ether bisphenol A (DGEBA) crosslinked with diaminodiphenylmethane (DDM) with varying stoichiometric ratios of excess amine or epoxy groups in the network. For the amine-rich networks, yield stress and modulus is not affected significantly as the network is a completely intact loosely crosslinked network however the strain hardening modulus decreases systematically as the network goes further out of stoichiometry. In contrast, the results of the epoxy rich networks show complex trends with increasing yield stress and modulus as we go further out of stoichiometry. This is due to the densification of the network due to parts of the epoxy network filling in the free volume giving rise to a fragmented network and a mechanically fragile glass as excess epoxy groups are added to the system. The strain hardening modulus of the epoxy rich networks show a steeper decrease than those of amine excess networks. Compression testing on DGEBA-DDM formulations with impact modifiers can be used to and calculate network connectivity and effectively distinguish between effects of plasticization and network disruption due to stoichiometric imbalance for glassy thermosets.
Nylon66 composites (PA66 with 40wt% long glass fiber) were used as molding material for injection molded part (tensile specimen with thickness of 1.8mm and 2.5mm). The Taguchi method with L18 orthogonal array was used to determine important factors affecting weldline tensile strength in long glass fiber reinforced Nylon66 molded parts. It was found that the significant contributing factors in the descending order were melt temperature (38.70%), part thickness (28.66%), mold temperature (14.40%), screw speed (10.44%) and filling time (4.27%); moreover, lower melt temperature, part thickness of 1.8 mm, higher mold temperature, higher screw speed and longer filling time would increase the weldline tensile strength for long glass fiber reinforced Nylon66 molded parts with vent design.
The touch sensitivity of piezoelectric-based sensors is inversely proportional to their dielectric permittivity. Introducing a cellular structure into these sensors can decrease the permittivity while enhancing their mechanical flexibility. In this work, various cellular thermoplastic polyurethane (TPU)/lead zirconate titanate (PZT) composites having several PZT contents were fabricated using physical foaming, and their dielectric properties and microstructure were studied. Composite foams with PZT contents of 2.5-10vol.%, relative densities of 0.2-1, and void fractions of 50-75vol.% were obtained, providing a platform to assess the evolution of relative permittivity with the foaming degree. The relative permittivity continuously decreased in both the neat TPU and TPU/PZT composites, up to a maximum of 4 times, as the volume expansion increased. At higher expansion ratios, the relative permittivity of the composites appeared to be independent of the PZT loading, due to the volumetric dominance of the low-dielectric air phase. The experimental relative permittivity measurements also showed good agreement with the predictions made by the Yamada model, extended to ternary system of piezoceramic polymer composite foams. Voltage sensitive foams can have applications in aerospace, robotics, and flexible electronics.
The paper is aimed at the observation and modeling of thin plastic film delamination from a substrate and its progression. The authors are addressing the following issues: 1) what physical and geometrical parameters of the film-adhesive-substrate system play the major role in initiation and progression of delamination; 2) what is the root cause of slow delamination growth in time; and 3) formulation of a quantitative model of the process. A brief review of existing approaches, simple experimental setup, observations and the modeling results are reported.
The use of thermoplastic polyurethanes (TPUs) in the medical device industry is widespread due to the unique combination of biological properties, abrasion resistance, and processability that they provide. Phase separation at the microscopic level within the morphology of TPUs results in the presence of hard and soft polymer block segments, creating these desirable characteristics. However, the microphase separation also complicates the understanding of TPU structural properties, particularly their flow properties, and creates difficulties during melt processing. Properties of several TPUs were characterized with a novel rheological method to quantify the effects of time dependence and are reported in this study.
Today, most CAD systems have integrated simulation features. These accelerate the development of injection-molded parts because of tight connection of the CAD and CAE system. Knowledge-based design and analysis features are as well implemented as tools for the determination of the gate position. The drawbacks of these solutions are the limited access to the calculation methods and the possibility for modifications or extensions. Therefore, a knowledge-based approach for an automatic flow balancing was developed. By local decreases or increases of the nominal wall thickness the filling of the cavity is improved. The positions and sizes of these geometry changes are determined iteratively during an optimization routine, which is presented in this paper. Finally, the approach is verified in a case study.
In this work, NanoXplore’s proprietary graphene nanoplatelets, heXo-G V20, are melt-extruded into thermoplastics LLDPE, HDPE and TPU. Graphene is shown to effectively increase the stiffness and the strength of a matrix TPU. The flexural and tensile moduli increase with loading levels of graphene whereas the tensile strength increases at low loading levels, but does not further increase at higher graphene concentrations. A ten fold increase in thermal conductivity was achieved by adding heXo-G V20 graphene to LLDPE matrix. The thermal conductivity percolation threshold was reached at 10% loading. At 1% loading of graphene the onset of the decomposition temperature and maximum weight loss temperatures were shifted by about 50°C, significantly improving the thermal stability of the PE matrix. Fourteen orders of magnitude increase in electrical conductivity of HDPE was obtained at 30% loading of graphene. Excellent EMI shielding of 40 dB was achieved with 20 wt% addition of graphene in a TPU matrix.
Polymers have been widely used in asphalt roofing industries in order to reduce premature failure and improve final performance such as cracking and impact resistance, which is difficult to be achieved by asphalts alone. This work focuses on styrene-butadiene-styrene block copolymer (SBS), styrene-ethylene/butylenestyrene copolymer (SEBS), and Elvaloy modifications on asphalt roof coatings. The thermal susceptibility, low temperature cracking propensity were investigated and compared with unmodified version to present the advantages and challenges of polymer modifications. From the perspective of manufactures, the possibility to double stack roof pallets were estimated based on blocking resistance evaluation via an axial rheological method.
Efficient molecular orientation of polymers in the melt- or solution state requires concentric contraction flows, which result in single or multi-filament fiber shaped products. Directed molecular orientation in pipes, sheets, foils and films, like strip bi-axially, planar or tri-axial, are difficult to achieve and require complex multi-stage processing often supported by the addition of extra external magnetic, electric, or temperature gradient fields that put constraints to the materials to be processed. Here we aim at a simple continuous process to produce uni-axially oriented foils, by designing a special die in a standard miniaturized laboratory scale film casting process. The internal of the die consist of a fiber forming, and a fiber fusing part. The specific design of the fiber forming part allows the combination of the fibers formed, without them crossing, into a line that forms a sheet. Flow in the total volume around the slit ends up in molecularly oriented flow inside the slit. To preserve orientation, an air gap extrusion process follows the exiting slit flow, to allow for a strong draw down under high melt stress. Small air-gaps and a cold cooling nose, combined with a supporting carrying film, make the total process easy, clean and cheap, and the products unique. We will demonstrate that, mounted on the miniature Xplore MC 15 lab compounder, the device is able to produce not only high performance fully oriented foils based on a thermotropic liquid crystalline polyester (Vectra), but also extremely thin foils of polyamides and polyesters. In the last application, the melt orientation is used only to temporary obtain a high melt strength that allows a high draw-ability in the air gap.
the expanding industry of polymer processing, a prominent area of current research is to process polymers efficiently without creating any environmental hazards. Processing of intractable polymers like PPO requires high processing temperature and toxic plasticizers. Very few research works have reported the use of superheated liquids to process intractable polymers. This research work presents a systematic study to explore the advantages of processing PPO with superheated liquids composed of ethanol and water. Microcellular foams of PPO having a density range from 0.13 to 0.56 g/cm3 can be produced with the aid of superheated ethanol, water and ethanol/water mixtures. Such foams also exhibit high specific strength. In addition, PPO can also be extruded with superheated ethanol or ethanol/water mixtures at a temperature which is 150 to 180 °C below the conventional extrusion temperature for PPO.
Manufactured products are expected to serve their useful lifetime without premature failure. When premature failure does occur, it is important to determine the root cause. This is particularly important in high-consequence applications such as medical products. In this case study, the analysis of polyurethane tubing that became yellowed and cracked is presented. The mode of failure was determined using multiple analytical methods, the hypothesis was tested, and additional analyses were performed to confirm the root cause hypothesis. In addition, a modification to the composition of the medical tubing was suggested and implemented. The efficacy of the modified composition was assessed, similar to the failure analysis protocol, using microscopy, spectroscopy, and chromatographic methods. The results of this failure analysis and product improvement project will be presented.
The objective of this study is to prepare a toughened and strengthened electrospun fibrous biodegradable poly(lactic acid) (PLA) mat blended with Biomax, an ethylene copolymer designed to modify PLA to improve toughness properties, using electrospinning. Morphological, thermal, mechanical, and thermomechanical properties of PLA/Biomax blends were investigated. Morphological findings indicated that the electrospun PLA/Biomax fibers were uniform and smooth with an average diameter of 1.4-1.5 µm when Biomax contents below 2 % (w/v). The addition of 1 % of Biomax improved both thermal stability and mechanical properties of PLA/Biomax fibrous mats. PLA/Biomax mats with 1 % (w/v) of Biomax exhibited the maximum tensile strength of 4.6 MPa and tensile modulus of 103 MPa showing 64.3 % and 101 % improvement; as compared to neat PLA values of 2.83 MPa and 51 MPa, respectively. Furthermore, the presence of 1 % Biomax into electrospun PLA fiber mats improved the storage modulus by 107.5 % compared to PLA fiber mat (41.5 MPa). Strong and toughened PLA/Biomax biodegradable fibrous mat might be potentially suitable to be used in packaging, filtration, reinforcement of composite, etc.
This paper focuses on the processing of high performance Polyvinyl alcohol (PVA) and wood flour (WF) fibrous nanocomposite mats using electrospinning. Successfully fabricated PVA filled with WF fibrous nanocomposites using electrospinning are hereby reported in the open literature for the first time. The effect of filler materials on fiber surface morphologies was investigated using environment scanning electron microscopy (ESEM). The respective mechanical and thermal properties of the resulting nanocomposite mats were determined as a function of WF contents. The mechanical properties such as tensile strength and tensile modulus improved significantly with the addition of fillers indicating good adhesion and dispersion of filler materials into the matrix. PVA/WF (20 wt%) fibrous nanocomposite showed the maximum tensile strength, and tensile modulus but minimum elongation at break. Thermal results show that introducing WF had no distinct effects in the thermal stability of nanocomposites. The developed fibrous PVA/WF nanocomposites could be of potential use for many industrial applications where high mechanical strength is needed, such as, filtration and mechanicaly reinforced applications.
The stretching of semi crystalline materials such as isotactic polypropylene leads to an increase of the material characteristics (tensile strength, E-Modulus etc.). The trend towards using wider and faster film production lines causes the need to develop a better understanding of the complex correlation between molecular structure of the raw material, the processing conditions, the morphology of the cast film and the final film properties. In this investigation a viscoelastic model for the simulation of the stretching process is selected. In this study the definition of the suitable material parameters is supported by further characterization of the material.
The low temperature impact performance of rotationally molded specimen is of great importance for the final products. Crosslinked high density polyethylene (XL-HDPE) is a preferred material for large chemical and fuel tank due to its superior environmental stress crack resistance and high impact strength. In the present research the drop weight impact strength (defined as ARM impact strength) of rotationally molded XL-HDPE was carried out at -40°C and the relationships between impact strength and microstructures were investigated. The results confirmed that the microstructures of XLHDPE molecules in the innermost surface layer dominated the low temperature impact performance of rotationally molded XL-HDPE articles.
In injection molding, gas in the melt causes various defects in molded parts. As well as many other sources of gas in the injection molded parts, the entrapped air during the plasticizing process would be an important source of gas in the parts. The entrapped air bubbles in the screw channel were examined by the screw quenching experiment. To reduce time for investigating the effect of plasticizing condition on the bubble size distribution, a bubble detecting device with a capillary and pressure sensor was designed in this work. The result from the bubble detector experiment with different plasticizing conditions showed a similar trend which is observed in the samples in the screw quenching experiment. It proves the feasibility of the bubble detecting device to examine the bubble size distribution in the screw channel.
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