SPE Library

Implantable thermoplastic polyurethanes (TPU) have been utilized in the medical industry for decades due to their combination of biocompatibility, abrasion resistance, and processability. The present review attempts to establish the main factors that affect the long term biostability of TPUs, based upon multiple in vitro and in vivo studies. TPUs present two main degradation modes: oxidation and hydrolysis, which accelerate under mechanical stress. Siloxane-based TPUs seem to be most resistant to biological degradation. In addition, their complex morphology makes accelerated in vitro predictions based on time-temperature superposition inaccurate.

The resin viscosity is an essential parameter to characterize the performance of injection molded products. However, it is very difficult to properly measure the viscosity of fiber reinforced composites during the injection molding process. In order to characterize the melt viscosity of fiber reinforced composites, capillary meters or rheometers are normally used. But the actual melt viscosities of composites in the injection molding process are not properly measured by those methods because shear rates realized by those methods are not high enough to mimic the shear rate during the injection molding process. In this study, an original molding tool is used to measure the melt viscosity of carbon fiber reinforced composites in the actual injection molding process. As a result, the influence of carbon fibers used in composites on melt viscosity during the injection molding process were properly characterized.

In this experimental series the influence of the initial moisture content of the materials in the extrusion-technical production of Polylactide Cellulose Fiber Compounds are examined. The target values in the tests are the mechanical properties (such as impact strength and tensile strength), the rheological behavior, the color, and the molecular weight of the produced compounds. The compounding was done by using a co-rotating twin screw extruder. The results show a significant effect of the variation of initial moisture of the materials on the tensile and flexural strength and the discoloration of the compounds as well as the melt temperature during compounding. Furthermore, it was found that the rheological properties of PLA-cellulose fiber compounds are linearly dependent on the material moisture before experiment. The other target values show no dependence on the moisture of the raw materials.

The aim of this work was to study the enhancement of the impact resistance of polypropylene via the addition of the thermoplastic elastomer styrene-butadiene-styrene, and fumed silicon dioxide nanoparticles. Polypropylene/styrene-butadiene-styrene silica nanocomposites were prepared using a twin screw brabender plasticorder, the weight percent of the SBS was varied at (0, 5, 10, 20 and 40) wt%, and the silica content was varied at (0, 0.05, 0.1, 0.5, 1 and 2) wt%. Throughout this study it was observed that increasing the SBS content lead to a drastic improvement in the impact strength, with over a 6-fold increase at maximum. It was an obvious conclusion that, contra to expectation, the silica nanoparticles didn't significantly enhance the impact property. This is most likely due to the poor dispersion of these powder nanoparticles in the polypropylene/SBS matrix. Therefore, the SBS properties had a greater effect on the enhancement of the impact properties than the silica.

Mechanical properties of fiber-reinforced thermoplastic products have a deep dependence upon flow-induced variations in fiber structure, involving fiber orientation, fiber length, and fiber concentration. However, few numerical studies have been done on fiber concentration to date. Using the suspension balance model of particle migration, the objective of this work is to perform the concentration calculation in mold filling of a center-gated disk. Consequently, the predicted concentration distribution of short glass fiber filled polybutylene terephthalate (PBT) with an average volume fraction of 0.177, through the thickness measured at the lubrication region of the disk, agrees well with related experimental results.

Injection molding is a typical batch process that transforms polymer granules into various high-value-added products. The aim of this paper is to improve the batch process control performance in the two-dimensional (2D, within batch and batch to batch) and hybrid frameworks by exploring the repetitive and multi-phase nature of batch process. This research involves a 2D hybrid prediction model, comprised of a 2D step response model and a piecewise affine model. With this prediction model, a novel 2D hybrid dynamic matrix control strategy is proposed. Application to the injection molding process shows the effectiveness of the proposed control algorithm.

Polyurethane (PU) foams were prepared using synthetic and bio-based polyol. In both cases, isocyanate content was reduced and cellulosic nanofibers and lignin were incorporated to achieve the desired rigidity. The experimental results indicated that the mechanical properties of 100% bio-based polyol PU foams exhibited higher performance compared to 100% synthetic polyol PU foam. The odor concentration of bio-based and synthetic PU foams showed in similar level. A automotive bumper energy absorber prototype has been developed from lignin and nanocellulose enhanced bio PU foams with reduced isocyanate content.

The visibility and shape of sink marks is an important criterion for the quality of a variety of injection molded parts. Due to necessary geometrical features on technical parts, the formation of sink marks is mostly inevitable. The aim of this work is to present a study on the influence of processing conditions, especially rapid heat cycle molding (RHCM), on the sink mark geometry. Several process settings were tested for enabling the recognition of the most influential process parameters. The Pseudo-Voigt distribution model, a superposition of the Gaussian- and the Lorentz-distribution was found to deliver an accurate mathematical description of the sink mark cross-section shape. For this work, specimens were measured via confocal microscopy to gain the sink mark shapes. Two different sample geometries were used. This enables to investigate various base-to-rip-thickness ratios as well as the dependence on the flow-path length. By applying RHCM, the mold surface temperature could be introduced as important factor. The Pseudo-Voigt-Model was then fitted on the measured sink mark shapes, resulting in several fitting parameters. These fitting parameters were then correlated with the process settings. The results show strong correlation of both, holding pressure and mold surface temperature, on the sink mark topography.

The onset of bubble formation or in other words the degassing pressure is an important value for the designing of a die for extrusion foaming. Therefore, the effect of flow channel geometry on the degassing pressure was examined with a newly developed slit die concept. The determination of the onset of bubble nucleation was carried out with an optical spectroscopy technique. In this study we used four different flow channel geometries to determine the degassing pressure for different flow conditions. Additionally simulation experiments were used to compare the different flow channel geometries in terms of shear rate, pressure drop rate and velocity changes to gain data for the scale-up. It was shown, that the degassing pressure is a function of the flow conditions. With increasing shear rate, elongation rate and pressure drop rate the degassing pressure increases.

Recent advances in processing-structure-property relationships of micro- and nanolayer polymeric systems are presented. Coextrusion via a series of layer multiplying dies has enabled the production of films of with two or more materials that contain tens to thousands of layers with individual layer thicknesses from the micro- to the nanoscale. Nanolayered films were demonstrated with improved gas barrier through confinement of a crystalline polymer layer. In addition, unique films with layer thickness dependent optical properties including novel reflective characteristics have been developed. Redesigned layer multiplication dies we have produced gradients layer thickness films including film-foam structures resulting in unusual properties.

New wear resistance (WR) thermoplastic co-polyester elastomers (COPE) deliver improved performance over a wide range of speed and load conditions in sliding or moving applications. These elastomers have excellent cold temperature impact strength and work well at a broad range of temperature and humidity conditions, primarily in injection molded articles. Various grades with wide range of hardness are suitable for applications requiring excellent tribological properties. These elastomers provide outstanding ductility combined with the excellent chemical and environmental resistance properties of polyesters. The unreinforced and higher flexibility COPE grades fill the property gap between standard thermoplastic polyester urethanes and vulcanized rubbers by providing excellent fatigue strength and hence an increased operational lifetime. These elastomers are easy to process, recyclable and retain their impact strength down to -30 °C.

This paper examines the tensile strength and Izod impact behavior of natural fibers and wood particles in recycled polypropylene composites for injection molding. The initial round of testing compares the performance of the straight recycled polypropylene resin versus non-compatibilized natural fiber or particle composites, and then the different composite performance was indicated through the addition of a compatibilizer. The mechanical properties of natural fiber or wood particle and recycled PP composites without a compatibilizer were firstly compared with those of only recycled PP. Then, some natural fiber or wood particle and recycled PP composites using various compatibilizers were investigated. It was found that the elongation at break and the Izod impact strength of some natural fiber or wood particle and recycled PP composites using specific compatibilizer were indicated for high flexibility and adhesive formation as compared with some natural fiber or wood particle and recycled PP composites without a compatibilizer. The difference between natural fibers and wood particle was also discussed.

Traditionally, setting of process parameters is significant for quality of molded parts and is a highly skilled job on the plant floor in plastic injection molding. The process window is especially instructive for this job. However, it is difficult to be depicted and obtained since it is an irregular region in a multi-dimensional space of process parameters. In this study, the process window is implicitly defined by a fitting of sample data from simulation results. Design of experiment, simulation and support vector machines classifier are combined to simultaneously fulfill the requirements of computational efficiency and prediction accuracy.

This research was carried out to improve mechanical properties of PBS by melt blending with recycled PET flakes from drinking bottles. Content of PET adding was 1, 2 and 5% by weight. Properties of polymer blends were evaluated by tensile test, impact test, SEM, DSC, and TGA. It is found that blending PET into PBS yielded stronger mechanical properties compared to neat PBS. However, melt blending between them required high temperature enough to melt PET flakes, so it caused thermal scission in PBS molecules as evidenced in TGA analysis. PBS/PET blends had higher tensile modulus but reduced flexibility with higher PET content. For DSC analysis, it is found that blending PBS with PET increased crystallinity of PBS matrix due to nucleating effect of PET dispersed spheres.

Semicrystalline thermoplastics generally have a smaller processing range for thermoforming compared to amorphous thermoplastics, due to their narrow temperature window for the transition from viscoelastic to viscous material behavior. Otherwise they offer superior properties for applications like ductility or chemical resistance. Previous research showed that cross linking of semicrystalline thermoplastics by high energy irradiation holds the potential to significantly improve their thermoformability. Within this article the effects of different degrees of cross linking and their interaction with processing conditions during thermoforming shall be discussed.

Phosphorous based flame retardants have been widely employed as eco-friendly flame retardants for impact modified polycarbonate (PC) blends but some of the liquid phosphates cause significant deterioration in key physical properties like impact strength and heat deflection temperature. This work shows results from recent developments at SABIC in order to achieve superior physical properties while maintaining thin-wall UL94 V0 ratings by using solid phosphorous based flame retardants. Additionally, some of these blends also show significantly improved hydrolytic stability which could translate into a more sustainable solution enabled by longer service life for parts made out of such materials.

The present investigation describes a facile and rapid approach of production of conductive nano-composites, and assessment of the opportunity for using them as electro-mechanical sensors. The new synthesis procedure includes an in-situ inverse emulsion polymerization method of aniline in the presence of CNT and dissolved thermoplastic elastomer, followed by a precipitation-filtration step. Incorporation of CNT/PANI in the SIS elastomeric matrix improves the thermal, mechanical and electrical properties of the nano-composites. Formation of the continuous three-dimensional CNT/PANI network, is responsible for enhancement of the resulting nano-composite properties, such as the relatively high electrical conductivity levels. The described novel approach provides an opportunity for developing tunable structures of remarkably distinctive architecture. The rapid electrical resistance response to the applied strain makes the developed nano-composites useful as sensitive strain sensors.

Carbon nanotubes (CNT) have drawn much attention in recent years. CNT have remarkable properties i.e. mechanical properties, electrical and thermal conductivity, thus offering opportunities for development of new nanocomposites. An homogeneous dispersion of nanoparticles in polymers using conventional processing techniques is difficult to produce since nanoparticles tend to agglomerate, thus efficient methods for agglomerate breakdown have been sought in recent years. The combination of CNT with intrinsically conductive polymers may lead to new and improved properties of the resulting materials. This work describes an in-situ inverse emulsion polymerization method of aniline in the presence of multiwalled carbon nanotubes (MWNT) in organic solvents using ultrasonication. PANI dispersion, as a reference, and the PANI/MWNT dispersions were stable for long periods of time without visible precipitation. Highresolution scanning electron microscopy (HRSEM) has shown that MWNT are coated with PANI, leading to a remarkably improved dispersability of the nanotubes, thus PANI coating reduces the tendency of MWNT to reagglomerate. The neat MWNT have a diameter of ~10nm, while the core-shell MWNT/PANI nanofibers exhibit a diameter of ~40nm. The dispersions obtained may have important potential applications in the fields of sensors, acoustic actuators, semi-conductors, solar cells and more. CNT containing materials suitable for the manufacture of thin, transparent, electrically conductive films have poor mechanical properties and are expensive. Our work on hybrid conducting nanocomposites has led to a remarkable combination of high conductivity and transparency along with low haze and good mechanical properties, aiming at competing with the existing ceramic materials, such as Indium Tin Oxide, (ITO).

This research presents a new fabrication method for tailoring polymer/carbon nanotubes (CNTs) nanostructures with controlled architecture and composition. The CNTs are finely dispersed in a polyacrylate latex, via ultrasonication, followed by a microfiltration process. This step allows preserving the uniform dispersion structure in the resulting solid nanocomposite. This original fabrication method is applied for supercapacitorc, biocatlytic membrane and low reflecting coatings. The combination of microfiltration and proper choice of the polymer latex allows the design of complex nanostructures with tunable properties e.g., porosity, mechanical properties. An important attribute of this methodology is the ability to tailor any desired composition of polymer-CNTs systems, i.e., nanotubes content can practically vary anywhere between 0 to 100 wt%. Thus, for the first time a given polymer/CNTs system is studied over the entire CNTs composition, resembling immiscible binary polymer blends. The polymer in these systems exhibits a structural transition from a continuous matrix (nanocomposite) to segregated domains dispersed within a porous CNTs network. An analogy of this structural transition to phase inversion phenomena in immiscible polymer blends is suggested.

Blends of polyaryletherketones (PAEK), such as polyetheretherketones (PEEK) and polyetherketone-ketones (PEKK), with polybenzimidazole (PBI) are of commercial interest due to their improved high-temperature stability and wear properties. Regarding the PBI component, the origins of the properties that are generally thought to be disadvantageous in thermally or chemically aggressive environments are not well understood. The same accounts for the specifics of the interactions between the PBI and PAEK components in melt or dry blend systems. In this presentation, we focus on the molecular changes of PEEK-PBI and PEKK-PBI blends and their pure components after treating them with liquid water and steam at elevated temperatures and pressures. The pure polymer components and the PAEK-PBI (50:50 wt%) blends are steam-treated at 150 °C (302 °F) and 315 °C (599 °F), also with deuterated water (D2O). The overall goal is to understand the chemical changes on the molecular scale that might take place upon high-temperature steam-treatment and to examine the extent and reversibility of moisture uptake. Changes of the materials, as well as interactions and reactions of the water with the functional groups of the polymer components have been studied by 15N and 13C CP/MAS, 2H MAS, and 1H wideline NMR spectroscopy, in combination with using deuterated water.