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.
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Micropatterning Poly(Acrylamide) on PLA Films Using Photolithography
Micropatterning is a robust tool to surface-modify bioplastics like poly(lactic acid) (PLA) for biomedical applications. We used a sequential two-step photografting and photomask approach to micropattern poly(acrylamide) (PAAm) on PLA film. In step one, a PLA specimen, dip coated in benzophenone solution in ethanol covered with the photomask, was sandwiched between two glass plates and exposed to UV in an inert atmosphere. In step two, benzophenone-micropatterned film was immersed in 10% v/v monomer solution in water and exposed to UV for 3 h to grow poly(acrylamide) (PAAm) from the film surface. The resultant film surfaces were examined by AFM and optical microscopy, which revealed the resolution and acuity of the micropatterns.
Towards Lower Crystallization Temperatures in Polyethylene
Recent advances in experimental techniques such as rapid cooling, droplet crystallization and in-situ light scattering have made it possible to extend the crystallization range of polyethylene to temperatures as low as 90-75°C. The current study reports the development of a simple, yet effective technique that allows quench-crystallization at unprecedented low temperatures in the neighborhood of 30°C. The veracity of this claim is supported by slope analysis of cooling curves, lamellar thickness and crystallinity measurements as well as melting studies using SAXS, wide-angle XRD and DSC respectively. The results indicate that this technique has made it possible to crystallize HDPE over a series of hitherto unreported temperatures ranging from 30-70°C corresponding to lamellar thickness of 67-100Å respectively. At the temperatures being reported, linear PE is expected to exhibit growth rate kinetics consistent with the diffusion controlled region of the growth rate-temperature curve, something that has never been demonstrated to date.
Estimation of Bulk Melt Temperature from In-Mold Sensors: Part 2 - Convection
An analytical approach for estimating the bulk melt temperature within a mold cavity using data from in-mold temperature sensors has been further developed. The analysis uses a convective boundary condition to approximate the contact resistance of the mold-melt interface. The measured mold coolant temperature was also taken into account. The accuracy of the predictions was tested over a wide processing window. While most trends were correctly predicted, the magnitude of the predictions varied greatly due to the high sensitivity of the analysis to the temperature measurements.
A Non-Newtonian Model of Flow in a Special Mixing Element Region of a Modular Intermeshing Corotating Twin Screw Extruder
The flow of non-Newtonian fluid in screw and kneading disk block regions of an intermeshing co-rotating twin screw extruder has been analyzed by various investigators using different methods for non-Newtonian flow models. New types of new special mixing elements have been developed and frequently used in the polymer industry. The fluid mechanisms and pumping characteristics of these elements needs to be better understood. The screw characteristic curves of special mixing element were calculated and compared with other traditional screw and kneading disk blocks.
Surface Modification of PLA-PHA Blend Films
Addition of a small amount of PHA to PLA markedly improves the toughness of the resultant blend. When a blend comprising 90 weight percent PLA and 10 weight percent PHA was solvent cast from a chloroform solution, it did not show any remarkable toughness improvement. When the blend was melt processed, it showed a significant toughness improvement. Melt processed blends were then surface modified using a sequential two-step photografting method. The modified films were characterized using water contact angle goniometry and ATR-FTIR spectroscopy. We studied the effect of surface modification on the surface and bulk properties of melt processed PLA, PHA, and blend films.
The Use of Scanning Electron Microscopy for Analysis of Skin Thickness in Polyvinylchloride
Scanning Electron Microscopy (SEM) was used to evaluate the skin thickness of polyvinyl chloride under various conditions. This investigation had two objectives: to determine if SEM is a practical tool for quantifying the skin thickness of a polymer and to determine if mold temperature and lubricant concentration effect skin thickness.Even though the measurements of the skin thickness are subjective, this investigation concluded that SEM is a practical method for quantifying skin thickness when multiple measurements are made along the cross section.The hypothesis that increasing mold temperature decreases skin thickness in PVC was confirmed with SEM measurements and with hardness results. The hypothesis that increasing lubricant amount increased skin thickness was confirmed with hardness measurements.
Investigation of Fracture Mechanism of HDPE Subjected to Environmental Stress Cracking
Environmental stress crack resistance (ESCR) is a commonly used test to characterize cracking failure of high density polyethylene (HDPE) used in rigid packaging applications. From a resin design standpoint it is important to understand the mechanism of environmental stress cracking (ESC) especially in the case of materials with significantly different ESCR values. In this report, the morphology of ESC is studied by scanning electron microscopy (SEM). A model to predict polymer ESCR using tie chain concentration considering the permeability of IGEPAL® solution is proposed.
Microstructure of Thermoplastic Laser Welded Joints
Laser welded joints were examined using optical and polarized light microscopy, under both reflected and transmitted light, as well as scanning electron microscopy. The following materials were used: polycarbonate, polyamide-6, and polyamide-6 reinforced with 30% glass fibers. The influence of laser power on the shape, dimensions, and quality of laser-welded joints was evaluated, in both the absorbent and non-absorbent parts of the joint. Glass fiber orientation distributions were also examined. The effects of polymer type and fiber reinforcement, as well as laser power, on the dimensions and quality of the joints are reported.
Improving the Dispersion of the Carbon Nanotubes in Polymer Based Nanocomposites by Dry Coating
Carbon nanotubes tend to agglomerate in the polymer matrix, and it is difficult to separate individual nanotubes, even when surfactants are used during the mixing. To overcome the problems associated with agglomeration of nanofillers, the feasibility of dispersing carbon nanotubes in a polymer matrix by a novel methodology which involves mechanically pre-coating the polymer particles with the nano-fillers in the dry state prior to melt processing is being investigated. This paper presents the results of an experimental study for the purpose of evaluating the effectiveness of the surface coating techniques versus the conventional mixing methods used in dispersing nano-fillers in polymer matrices.
Evaluation of Nanoclay Exfoliation Strategies for Thermoset Polyimide Nanocomposite Systems
Prior works show exfoliated layered silicate reinforcement improves polymer composite properties. However, achieving full clay exfoliation in high performance thermoset polyimides remains a challenge. This study explores a new method of clay exfoliation, which includes clay intercalation by lower molecular weight PMR monomer under conditions of low and high shear and sonication, clay treatments by aliphatic and aromatic surfactants, and clay dispersion in primary, higher molecular weight PMR resin. Clay spacing, thermal, and mechanical properties were evaluated and compared with the best results available in literature for PMR polyimide systems.
Effects of Processing Parameters on the Cellular Morphology and Mechanical Properties of Mineral-Filled Thermoplastic Polyolefin Microcellular Foams
In this study, the effect of processing parameters on the cellular morphologies and tensile mechanical properties of mineral-filled thermoplastic polyolefin microcellular foams prepared by using a two-stage batch process are investigated. The findings show that the mechanical properties were significantly affected by the foaming parameters, which altered the cell morphologies. The results from this study can be used to predict the microstructure and tensile mechanical properties of microcellular polymeric DTPO foams prepared with different processing parameters.
High-Temperature De-Molding for Cycle Time Reduction in Hot Embossing
Hot micro-embossing is a promising manufacturing technique for replicating millimeter- to nanometer-scale features in thermoplastic parts. However, the thermal cycle time limits production rate, and thermal contraction mismatch between the part and the tool can lead to damage during cooling. It is thus desirable to reduce or eliminate the thermal cycle. One approach is to de-mold at higher temperature, but elastic recovery can degrade accuracy. The degree of recovery depends on processing conditions. Proper selection of these conditions permits de-molding near or above the glass transition with little or no degradation of quality.
Composites in the Trucking Industry
Over the years, the transportation industry has incorporated more and more composite materials into its vehicles. The automotive industry has used composites for exterior body panels, e.g. hoods, fascias, hatches and doors, as well as under the hood and structural reinforcements. The truck industry followed, by introducing composites for hoods, doors, roofs, bumpers and fairings. This paper will focus on the advancements made in composite materials, from hand-spray up open molded parts to the various improvements in sheet molding compounds to liquid molded resin materials. It will concentrate on parts used in the trucking industry and how quality, especially in cosmetic and surface properties, has improved over the years.
Analysis of Weld Seam Quality for Laser Transmission Welding of Thermoplastics Based on Fluid Dynamical Processes
Even though laser transmission welding (LTW) has already been implemented in industrial production, there are still process limitations rendering it uncompetitive with conventional processes and preventing its reaching full potential. The influence of the key process parameters and their interdependence is still not completely understood. This understanding is a condition for the optimization of the weld joint along with a more detailed theoretical description of the thermo-physical processes involved. This paper will present the results of an on-line detection method, the correlation to the mechanical properties and the FEA simulation, as well as possible approaches for overcoming existing limitations.
Structure-Property Investigation of Novel Multi-Layer Nanoclay Composites Formed Controllably with a Continuous Chaotic Blender
A continuous chaotic blender (CCB) has been used in prior work to controllably form a variety of polymer blend morphologies and arrange solid additives into networks. Low permeation films, electrically conducting plastics, and toughened plastics are examples of materials produced. In this study, initial property measurements are presented for extruded nanocomposite films having platelets localized and oriented within numerous discrete layers. The films have hierarchical internal structures and multiple nano-scales. The relation of barrier properties to structure is investigated by using the controlled in situ structuring capabilities of CCBs. Internal structure, crystalline morphology, degree of crystallinity, and oxygen permeation are presented.
Diffusivity Measurement of a Hydrophilic Migratory Additive in IPP Films
This paper describes the measurement of the diffusivity of a commercial hydrophilic additive, Irgasurf HL560, in polypropylene (PP) films at different temperatures. The model used was a standard 1-D diffusion model, in which the film weight was expressed as a function of time as the additive concentration at the film surface was kept at zero at all times. Experimentally, two cases were compared: 1. washing additive off the film with limited contact with the solvent; 2. immersing the film in solvent with continuous stirring. The effect of solvent diffusion into PP film was evaluated by thermogravimetric analysis (TGA). In both cases, film weight was measured after completely drying the film. Diffusivity was calculated by fitting experimental data to the mathematical model. Activation energy was obtained through the plot of diffusivities at different temperatures.
Functionally Graded Shape Memory Polymer
In this paper, we present a new concept in for shape memory polymers (SMPs): functionally graded SMP. To make such a material, a commercially available UV curable polymer, NOA63, was cured by high intensity ultraviolet irradiation for various reaction times ranging from 5 min to 3.5 hours. The photo-cured NOA63 samples were characterized using differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), and optical microscopy (OM) in order to investigate the high quality of shape fixing and recovery. The glass transition temperature was precisely controlled by varying the UV exposure time, resulting in NOA63 having Tg from 30 °C to 47 °C. DMA measurements for NOA63 revealed increasing tensile storage modulus with increasing crosslink density. A NOA63 sample was photo-cured in a spatially graded fashion, with different exposure times at different positions on for the same sample, demonstrating the possible usage of an optical temperature sensor or medical devices. Bulk and surface shape memory responses were investigated, revealing high quality shape fixing and recovery.
Weldability Evaluation on Effects of Filler Content of Polypropylene Copolymers for the Electromagnetic Welding Process
The weldability using the electromagnetic process has been evaluated for different grades of polypropylene copolymers being used for automotive and domestic applications. As previous publications [1 – 2] have revealed, the electromagnetic welding process has demonstrated its robustness on various resins and applications.In this paper, comparative study between the vibration welding process and the electromagnetic welding process has been performed to evaluate effects of filler (talc and glass) content on weldability for polypropylene copolymers.Extensive DOE procedures to optimize the vibration welding process and electromagnetic welding process have been performed. In Ref. , a definition of weldability for the material has been suggested. For more conclusive evaluation, both welding strength and failure modes of the welded plaques need to be investigated. The same definition for weldability has been used for this study.In this study, it has been found that talc and glass content adversely affects weldability, while the electromagnetic welding process showed slightly better performance in welding strengths.
Recent Developments in Infrared Weld Technology
This paper will present new developments in equipment and product in the field of Infrared Welding. These developments are a significant improvement over hot plate technologies and allow infrared welding to compete with other welding techniques at a lower cost for equipment and tooling. Recent developments in Polyamide materials allow one major headache associated with infrared welding of polyamides to be reduced. The paper will cover possible uses, advantages and design considerations. The overall benefit for the industry is to allow welding of a high strength high heat material in smaller production runs and for applications that use processes other than injection molding or non-glass reinforced grades which can present welding issues for other welding techniques.
Birefringence, Anisotropic Shrinkage and Luminance in Light Guide Plates: Modeling and Experiment
The frozen-in birefringence and anisotropic shrinkage of an injection molded light-guide plate (LGP) was simulated using a combination of a CV/FEM/FDM technique, a nonlinear viscoelastic constitutive equation and orientation functions. Various moldings were prepared from two optical grade polycarbonates (PC) and all of the components of birefringence along with shrinkages in the length, width and thickness were measured. The numerical results have been compared with experimental measurements at various processing conditions. The luminance of LGP moldings were found to be strongly dependent on processing conditions.
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