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Abstract This paper explores a novel modification to the Bell Test (ASTM-D1693) for minimizing its variability in failure time by the introduction of heat notching. The new notching technique for [...]

An approach based on controlled crazing and post‐polymerization was used to incorporate a nanoscaled conductive co‐continuous network into commercial ENGAGE™ Polyolefin Elastomers (POEs). Three POE films of differing crystallinity and phase morphology were stretched in a reactive mixture of acrylic polymerization precursors that possessed an affinity for the olefinic materials and acted as a surface‐active agent for craze promotion. As a result, a rigid acrylic hydrogel phase was grown in the void space associated with crazing, which prevented the formed channels from collapsing after mechanical stresses were removed. The hydrogel phase offered ion conductivity properties to the POE. Simply replacing the acrylic monomer with an aniline emulsion for polymerization did not lead to the same outcome in terms of a continuous network; the materials became insulative after the removal of mechanical stresses due to fragmentation of the polyaniline channels from the unrestrained elastic relaxation of the POE. This problem was overcome by solution‐casting POE with polycaprolactone (PCL) into films and, subsequently, partially dissolving and leaching PCL from the blend while a sample was stretched in an aniline emulsion medium containing formic acid. The residual PCL left in the crazes reinforced the polyaniline to prevent fragmentation, allowing the formation of a highly electron‐conductive secondary phase. [ABSTRACT FROM AUTHOR]

Thermally induced wrinkling during thermoforming of a commercial multi-layered polymer film/substrate laminate has been reported. The differential thermal expansion of component layers coupled with phase transition of the substrate with increasing temperature, determined the critical conditions for wrinkling with a specific wavelength and amplitude. An effective technique to minimize wrinkling by biaxially stretching the samples at high temperature before the forming operation, has been proposed. The samples were biaxially stretched by inflating the samples using a specially designed blowing unit retrofitted to a conventional vacuum thermoformer. This method involved heating, inflation and forming, together to provide stretch-assisted thermoforming. During biaxial stretching the stored compressive stresses in a wrinkled sample were relieved before the forming step, producing a decorative part without losses in surface appearance., INTRODUCTION Multi-layered polymeric films are widely used for applications such as electronics [1-4], packaging [5], biomedical components and devices [6], and decorative surface finishes [7], Decorative multi-layered films are being [...]

Decorative polymer films are finding applications in processes that require forming at elevated temperatures and significant strain. In order to satisfy their function in these applications, the appearance of these films must remain unaltered or at least any changes must be predictable. This paper examines four different high gloss decorative films comprised of different materials in the layers of their construction. The films were uniaxially stretched up to failure (which was up to 75% strain) at isothermal conditions of 25, 40, or 75°C and then examined. Gloss (at 20°) was the most strongly altered parameter concerning the appearance of the films after thermomechanical deformation while color intensity was relatively unaffected. The change in gloss was higher for the two amorphous films compared to the two that exhibited crystallinity. The films were analyzed for their surface roughness using a white light interferometer, for their crystallinity by X-ray diffraction and for their morphology by atomic force microscopy (AFM). Surface roughness increased with crystallinity for the two films that exhibited crystals but overall showed no correlation to the gloss measurements. Only evidence of altered domain morphology in the films as determined by AFM appeared to correlate with the changes in gloss reported., INTRODUCTION Little research exists in the area of surface appearance for manufactured polymer products. Color and gloss and their relationship to surface topography have been studied by a few authors [...]

This work explores the influence of rheological properties on polymer foam development in nonpressurized systems. To understand the complex contributions of rheology on the mechanism of bubble growth during different stages of foam processing, visualization studies were conducted by using a polymer-foaming microscopy setup. The evolving cellular structure during foaming was analyzed for its bubble surface density, bubble size, total bubble projected area, and bubble size distribution. Morphological analysis was used to determine the rheological processing window in terms of shear viscosity, elastic modulus, melt strength and strain-hardening, intended for the production of foams with greater foam expansion, increased bubble density and reduced bubble size. A bubble growth model and simulation scheme was also developed to describe the bubble growth phenomena that occurred in nonpressurized foaming systems. Using thermophysical and rheological properties of polymer/gas mixtures, the growth profiles for bubbles were predicted and compared to experimentally observed data. It was verified that the viscous bubble growth model was capable of depicting the growth behaviors of bubbles under various processing conditions. Furthermore, the effects of thermophysical and rheological parameters on the bubble growth dynamics were demonstrated by a series of sensitivity studies. POLYM. ENG. SCI., 54:1947-1959, 2014., INTRODUCTION Polymer foaming is a complicated process that involves complex mechanisms and unique morphology transformations. This field of processing combines material principles, engineering design, processing methodologies, and property characterization. Polymeric [...]

The mechanism of bubble nucleation in the foaming process under atmospheric pressure is investigated in the present study. The experimental observations using a plastic-foaming visualization setup revealed two stages of nucleation, primary nucleation in interstitial regions and secondary nucleation in the polymer melt, which followed the sintering and densification of the polymer matrix. Statistical analysis of the evolving cellular structure during the nucleation stage was used to study the significance of rheology on the behavior of polymer materials during the nucleation. The role of viscosity on the nucleation rate was also investigated theoretically by using a modified form of the classical nucleation theory and it was verified with the experimentally observed data. POLYM. ENG. SCI., 54:1201-1210, 2014. © 2013 Society of Plastics Engineers, INTRODUCTION Commercial interests in polymeric foams continue to increase due to the new emerging applications for foamed materials and the ability to foam a wider variety of plastic materials. Despite [...]

This study evaluated the paired performance of different signal processing techniques and supervised learning models being capable of identifying subtle differences in otherwise similar acoustic signals related to detecting the fiber orientation of a polymer composite. Projection of Latent Structures models demonstrated poor predictive capabilities of the composite structure based on spectral analysis of the acoustic signal. AI based models showed great improvements to the capabilities, with artificial neural network modeling exceeding Convolutional Neural Networks for correct classification accuracies. The continuous wavelet transfer highlighted the greatest degree of differences in the signal response compared with fast Fourier Transformation or short time Fourier transformation. The use of regression‐based predictions over classification‐based was found to greatly improve the predictive capabilities of the models, especially when multiple fiber orientations were present in a sample. A time‐based analysis of spectral data showed the frequencies of the signal changed based on the orientation of the fibers. The acoustic signals for the samples with multiple fiber orientations contained individual artifacts representing components of each individual orientation. Use of the frequency domain was shown as capable of observing the targeted fiber information within the bulk material in real‐time. This work shows great promise for composite material predictions using active ultrasonics, with the potential to be implemented into in‐line systems. [ABSTRACT FROM AUTHOR]