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Abstract: This article reports the comparison of different chemical methods to produce graphite-based particles with varying degrees of oxidation, as well as graphene oxide (GO) and pristine graphite (PG). Detailed [...]

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 [...]

By surrounding small droplets with a coating, one can obtain micrometer-size capsules (microcapsules), and combine multiple properties into a single system. This technology has allowed the design of advanced and functional materials. Amino resins are composed principally of urea and/or melamine and formaldehyde, and exhibit advantages as wall-forming materials, such as high mechanical strength and chemical resistance. In this review, a general description of the encapsulation process by in situ polymerization of amino resins is given. Characterization methods, and the influence of the physical and design parameters are discussed. A mechanistic description and some of the promising avenues of research are also presented. [ABSTRACT FROM AUTHOR]

This paper focuses on wrinkle development in decorative film laminates during heating operations with the goal to understand their driving factors and develop strategies to overcome such defects. The study looked at temperature and heating rate effects on the wrinkling behavior of a commercial black-out film laminated onto a metal substrate. The 135℃ threshold temperature identified for our film under which no wrinkles formed, related to the stiffness of its different construction layers. Heating rate was also noted by this study to be an important parameter in wrinkling; values between 1℃ and 350℃/min were tested. It was possible to exceed the threshold temperature stated above without wrinkling when the heating rate was sufficiently low (closer to 1℃/min, though less than 50℃/min was often sufficient depending on the final temperature). The heating rate effect is believed to be related to the time-dependent viscoelastic response of the compliant layer in relation to building thermal stresses. [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. POLYM. ENG. SCI., 57:31-43, 2017. © 2016 Society of Plastics Engineers [ABSTRACT FROM AUTHOR]

The adhesion between adhesively bonded polymer film and a metallic sheet substrate in a polymer laminated sheet metal (PLSM) subjected to large deformation, such as in a forming process, is influenced by two deformation-induced factors. These are (i) evolution of surface roughness of metallic substrate with applied strain and (ii) development of residual stress in the polymer adherend (polymer film with a thin uniform adhesive layer on one side) arising from significant differences in the deformation behavior of metal and polymeric components. A new experimental methodology was devised in this study to decouple the effects of substrate surface roughness and residual stress on interfacial peel strength (IPS) of uniaxially deformed PLSMs. This methodology was based on 180° peel testing of PLSM specimens prepared under two different lamination conditions, one involving systematic pre-straining in uniaxial tension of the metallic substrate prior to laminations and the other involving post-lamination pre-straining of the PLSM. The role of pre-strain and peel test speed, for the above laminations conditions, were critically analyzed for their effect on IPS of two differently tailored PLSM systems. The IPS results were attributed to the effect of deformation-induced residual stress and metallic surface roughness. The analysis suggests that IPS is strongly dependent upon the residual stress induced by uniaxial deformation but only marginally on substrate surface roughness depending upon the constituents (film and adhesive) of the adherend. The magnitude of pre-strain was inversely and non-linearly related to IPS for both deformed PLSMs. Peel test speed, on the other hand, showed a more complex behavior in terms of IPS for the two PLSM systems. [ABSTRACT FROM AUTHOR]

The analysis of the experimental peel test data for obtaining the adhesion fracture energy of an adhesively laminated polymer to the sheet metal surface is considered. The experimental results of the 180° peel test on two types of polymer laminated sheet metal at three different peel speeds are analyzed by two methodological approaches in cohesive zone modeling. These approaches are linear-elastic stiffness approach and critical maximum stress approach. Comparing the results of these two approaches reveals the significance of the peel test speed on the interface strength determination for cohesive zone modeling. It is concluded that a “reference” peel speed may exist at which the interface strength is equal to the yield strength of the peel arm material. A constitutive equation has been proposed which relates the interface strength to the peel test velocity by using the reference peel speed and its corresponding peel arm yield strength. [ABSTRACT FROM AUTHOR]