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Composite materials based on an ethylene-acrylic acid (EAA) copolymer and 20 wt% cellulose fibers were compounded by two runs in a twin-screw extruder. The composite material with cellulose fibers (CF) and a reference of unfilled EAA were injection molded into plaques using three different temperature profiles with end zone temperatures of 170°C, 200°C, and 230°C. The injection molded samples were then characterized in terms of their mechanical properties, thermal properties, appearance (color and gloss), and surface topography. The higher processing temperatures resulted in a clear discoloration of the composites, but there was no deterioration in the mechanical performance. The addition of cellulose typically gave a tensile modulus three times higher than that of the unfilled EAA, but the strength and strain at rupture were reduced when fibers were added. The processing temperature had no significant influence on the mechanical properties of the composites. Gloss measurements revealed negligible differences between the samples molded at the different melt temperatures but the surface smoothness was somewhat higher when the melt temperature was increased. In general, addition of the cellulose to the EAA reduced the gloss level and the surface smoothness. POLYM. ENG. SCI., 2019. © 2019 Society of Plastics Engineers.

Polyvinylidene fluoride (PVDF) fibers with a high amount of phase crystal structure were prepared by melt spinning. With this technique, the cold drawing process is critical and efficient when aiming for a high amount of phase. During the cold drawing process, more than 80% of the originally formed phase crystal structure was converted into the phase structure. In addition, the incorporation of 0.01 wt % of amino-modified double wall carbon nanotube (NH2-DWCNT) could further enhance the phase content in the PVDF fibers. FTIR and DSC studies showed that the addition of NH2-DWCNT to PVDF fibers could increase both the total crystallinity and phase fraction in PVDF. The addition of nanoclay was found to be less efficient in this respect

Acrylonitrile-butadiene-styrene copolymers (ABS) are known to be sensitive towards ageing which can lead to color changes, primary interest in this study. The color changes were expressed in terms of the CIELAB color system. ABS plaques were subjected to heat ageing and artificial weathering. Uncolored ABS and dark gray colored specimens were employed. The pigmented ABS plaques were also imposed with different surface textures. In general, the uncolored material suffered from the most severe discoloration and the artificial weathering produced the strongest effect. For both types of specimens, a clear yellowing took place. Both the pigment system and the surface texture affected the color development during the ageing test. The latter can be of significant importance in certain applications when components with different surface textures are placed adjacent to each other. The surface micro-hardness increased with increasing ageing time and its change followed that of the discoloration. Chemical changes of the surface layers were characterized by FTIR and were in accordance with results reported in the literature; i.e., an increase of the bands associated with carbonyl groups with increasing ageing time and a decrease of the bands associated with the polybutadiene phase clearly indicated chemical degradation due to ageing treatments.

Surface defects associated with manufacturing processes can severely impair the appearance of polymeric products. These defects can be enhanced with ageing (time, UV-light, heat and weather conditions). In the present contribution, the interest is focused on the defects generated during injection molding of elastomer-modified polymers that are often used in the automotive sector to produce interior and exterior components. In particular, defects denoted as “flow marks” or “tiger stripes” were investigated. Two different grades of elastomer-modified polypropylene (PP)-containing mineral fillers were studied here before and after heat ageing for 9 weeks at a constant temperature of 95°C. Although injection moldings are one of the grades that did not exhibit any flow marks, moldings of other PP-grade showed such defects and they were enhanced after the ageing process. The properties and structure of the glossy and the dull bands (as well as the effect of the thermal ageing) have been assessed by several characteristics such as microhardness, nanohardness, crystallinity, and surface composition. An increase in surface hardness was noted after the ageing treatment as a consequence of increased crystallinity. Dull and glossy bands also exhibited different values of the nanohardness, glossy bands were harder, and the dull bands appeared to be less crystalline. The surface composition of glossy and dull regions was slightly different; the surface regions of the glossy areas contained higher amounts of filler particles. The effect of the ageing on the striped appearance is furthermore discussed in relation to possible depletion of the stabilizer system. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

The production of injection-molded parts free from surface appearance defects is of great importance in the manufacturing of high-quality products. A particular surface defect which occurs on components manufactured from an acrylonitrile-butadiene-styrene copolymer (ABS) is here described. The defect has been called ghost marks and is characterized by a local change in gloss or lightness which is only visually detectable in certain viewing angles and conditions of illumination. By means of scanning electron microscopy, small-scale deformations of the surface texture were observed in the area of the defect which in turn alters the light scattering properties of the surface. The light scattering properties were evaluated by means of a multiangle spectrophotometer. The holding pressure during the injection molding process was shown to play a significant role in the formation of the ghost marks possibly imposing forces causing the deformation of the surface texture. The deformations may also occur from nonuniform thermal surface shrinkage during cooling. The type of texture and wall thickness also influences the occurrence of ghost marks.POLYM. ENG. SCI., 2012. © 2011 Society of Plastics Engineers.

Melt spinning of conductive polymer composites (CPCs) is coupled with some difficulties such as a decrease of conductivity upon drawing and a reduced spinnability with increasing filler concentration. Applying bicomponent technology may provide the possibility to produce fibers from CPCs with a high filler concentration. A pilot-scale bicomponent melt spinning set-up was used to produce core/sheath fibers with fiber titers between 13 and 47 dtex. The sheath material was polyamide 6 (PA6) or polypropylene (PP) and the core material was a CPC. Two CPCs were used, polypropylene (PP) with carbon black (CB), denoted by PP/CB, and polyethylene (PE) with multiwalled carbon nanotubes (MWNT), denoted by PE/MWNT. The results showed that both materials could be used with a filler concentration of 10 wt % to obtain melt draw ratios up to 195. The volumetric fraction of core material in the bicomponent structure was 28%. A heat treatment of PP/CB fibers restored the conductivity to the level of the undrawn material, corresponding to an increase in conductivity by a factor 5. The same heat treatment had a positive effect on the conductivity of PE/MWNT fibers although the conductivity was not restored.

Conducting polymeric materials prepared from immiscible blends, such as polypropylene (PP)/polystyrene (PS), together with carbon black (CB), are known to have a relatively high electrical conductivity, because of a selective distribution of CB (double percolation). Melt spinning of immiscible blends containing CB has, however, not been extensively reported on previously. An immiscible 1:1 blend of PP and PS to which 4 wt% CB was added exhibited a very low melt draw-down ratio at rupture compared wit PP with the same content of CB. By adding 5 wt% SEBS (styrene-ethylene-butene-styrene block copolymer), the ultimate melt draw-down ratio increased about 10 times, which made the material more suitable for melt spinning. As-extruded samples of the immiscible blends (with CB) did not have higher electrical conductivities than PP/CB. A heat treatment increased the conductivity of immiscible PP/PS/CB composites, and longer treatment times and higher temperatures promoted the conductivity. POLYM. ENG. SCI., 2011. © 2011 Society of Plastics Engineers

Fibers produced by melt spinning of conductive polymer composites are attractive for several applications; the main drawback is however reduced processability at high filler concentrations. Carbon ...

Starch foams were prepared from four types of potato starch using two-step extrusion with an intermediate conditioning step at 53% relative humidity in order to control the moisture content. The moisture content was the driving force for the expansion during the second extrusion. The second extrusion was performed with two different dies in order to achieve differences in porosity of the materials. Glycerol in combination with water was used as plasticizer for the starches. The rheological properties of the melts and the moisture content of the starch materials prior to the expansion were determined. The porosity of the expanded structures was characterized using environmental scanning electron microscopy imaging and density measurements. The absorption capability of the starch-based foams was investigated using aqueous NaCl solutions, and the water uptake of thin starch-based films from humid air was also evaluated. Foams prepared from amylopectin potato starch were found to exhibit the highest porosity, the lowest density, and the greatest absorption capability, both from water and from humid air. Not only the density but also the absorption capability was influenced by the porosity level. © 2010 The Author(s).

The concept of contrast gloss and its relation to visually perceived gloss was examined for textured polymeric specimens. The specimens were injection-molded plaques manufactured in three different polymers (acrylonitrile-butadiene-styrene copolymer, polypropylene, and a blend of polycarbonate and acrylonitrile-butadiene-styrene copolymer). A contrast gloss factor was determined from the reflectance data obtained with a conventional multiangle spectrophotometer. To evaluate the visual impression of gloss of the specimens a psychometric study was performed. The contrast gloss factor corresponded well with the visual assessment of the gloss and it was able to discern the visual differences between several specimens not significantly discriminated by their gloss values. These latter gloss values were obtained with a conventional glossmeter measuring specular gloss. In correspondence with the visual assessments and practical experience, the relation between the contrast gloss factor and the specular glossmeter measurements was found to depend on the type of polymer used. When evaluating gloss of specimens varying in color, the contrast gloss factor corresponded well with the visual assessments. This was in contrast to the specular glossmeter measurements which ranked the specimens essentially in the opposite order. © 2010 Society of Plastics Engineers.

A premium appearance is essential for many polymeric products and for this reason surface defects associated with the manufacturing process, e.g. injection molding, are detrimental. In this study, the interest is focussed on defects arising during injection molding of such elastomer-modified polymers that are often used in the automotive sector to produce interior and exterior components. In particular, defects denoted as "flow marks" or "tiger stripes" were investigated. These defects appear on the surface of the injection-molded components, especially if long flow lengths are involved and consist of alternating glossy and dull bands. Here an attempt was made to elucidate to what extent some important rheological properties of the polymer melts influence the generation of such flow marks. Hence, the flow properties, mainly in shear; of three different grades of elastomermodified polypropylene containing mineral fillers were correlated to their propensity for defect generation. In summary, it was noted that a higher melt elasticity, as reflected in pressure losses during flow through a capillary, the degree of die swell and to some extent the dynamic-mechanical behavior, leads to less severe flow marks or retards the formation of such defects. Elongational draw-down experiments also indicated a more stable flow in the case of the melt that exhibited the highest elasticity. Furthermore, subjecting the measured flow behavior to a Mooney analysis, the results obtained pointed to that wall-slip in itself is not a primary cause for the appearance of the type of flow marks studied here. © 2010 Wiley Periodicals, Inc.

A stereographic scanning electron microscopy (SEM) technique combined with a filtering procedure was used to characterize the surface topography of injection- molded polymeric plaques to improve the understanding of the relation between surface texture and gloss of deliberately textured and quite rough surfaces. The specimens, having small differences in surface topography and gloss, were produced by using two mold cavities with slight differences in surface texture and three different polymers. Small differences in gloss were also achieved by changing the processing conditions. All specimens exhibited a very low gloss. A stereographic image of the textured surface was constructed from two SEM micrographs of the same area, but differing slightly in viewing angle. From this image, descriptors characterizing the surface topography could be evaluated, in the present study the root-mean-square roughness and a lateral correlation length. The results indicated that small differences in gloss in the low gloss region could to a significant extent be associated with small-scale variations in the surface topography. The EM method used might provide a useful tool for identifying the length scale at which the surface pattern or irregularities has a strong effect on the appearance of polymeric low-gloss surfaces. © 2010 Society of Plastics Engineers.

The relation between color and gloss of injection-molded plastic specimens was evaluated by means of a 45°/0° geometry spectrophotometer and a glossmeter. The specimens were plaques having one smooth, glossy field and one rougher, textured region made of two different polymeric materials (acrylonitrile-butadiene-styrene and polypropylene) in a range of colors. A significant influence of the lightness L* of the specimens on the measured gloss of the textured field, with a low gloss appearance, was found. This can probably be attributed to a contribution from bulk scattering, which is linked to the reflectance from within the specimen. The influence of texture on the measured color of the plaques was assessed by evaluating the color difference between the smooth field and the more textured area on the specimens. When the surface was textured, the color changed; in general it became lighter and less saturated. The magnitude of the change depended on the color of the material. The darker the material was, the larger was the increase in lightness L* as the surface became rougher. The shift in chroma C* was determined not only by the saturation but also by the lightness of the specimens. Darker specimens exhibited a larger decrease in chroma when the surface was textured. The change in the measured color caused by increasing the surface roughness could be predicted in a satisfactory manner using a model developed for xerographic printing paper. © 2009 Wiley Periodicals, Inc. Col Res Appl, 34, 291–298, 2009

Expanded starch materials are prepared from normal potato starch (NPS) and amylopectin potato starch (PAP) using two-step extrusion with an intermediate conditioning in order to control the moisture content. The moisture content is the driving force for the expansion during the second extrusion. The effect of two different plasticizers, urea and glycerol, are compared with regard to the foaming ability in the presence of wheat gluten, acting as a processing aid. Melt strength, moisture content, and elongation at break of the melt of the starch materials prior to expansion are evaluated. The expanded structures are characterized using environmental scanning electron microscopy and density measurements. The water absorption capability of the starch-based foams is also investigated. The processing of starch is facilitated by the addition of gluten and the properties of the foam are improved. The fraction of small cells in the foams is increased and the foam exhibits an improved water absorption ability. PAP in this case is found to be a more suitable raw material than NPS for preparing starch-based foams.

The effect of an imposed texture on the gloss of injection-molded polymeric surfaces was evaluated as well as the way in which these properties are visually perceived. Specimens having small differences in surface topography were produced using two mold cavities with slight differences in texture and three different polymers. The texture and gloss were characterized using laser profilometry, gloss measurements, and by means of psychometric evaluations. The measured surface topography parameters and gloss were determined mainly by the texture of the mold surface and the gloss also by the processing conditions. Variations in surface topography due to differences in the rheological properties of the polymer melts were, in most cases, too small to be reflected in the measurements. The visual assessments of the texture and the gloss of specimens from the same cavity were in fair agreement with the measurements, although the observers could discern differences between some specimens not revealed by the measurements. When the specimens molded in the two cavities differing significantly both in gloss and texture were compared, the agreement between the measured topography parameters and the perceived roughness was poorer. It is suggested that higher gloss of a textured surface enhances the perception of a higher roughness.

Polypropylene (PP) or, in some cases, poly (lactic acid) (PLA) were compounded with cellulosic fibres. The amount of fibres used was in the range 10–30 vol % and, in case of PP, a series of compounds was prepared with a minor amount of maleated PP as a compatibiliser. This matrix was denoted MAPP. Before compounding the polymers and the fibres, undelaminated bentonite (industrial scale) or delaminated clay (nanoclay) was deposited on the fibres in different amounts to improve the dispersion of the fibres in the polymer matrix, i. e., to avoid detrimental fibre bundles. The PP-based compounds were either extruded or injection moulded, whereas the PLA-compounds were only injection moulded. The mechanical properties were primarily evaluated for the injection moulded specimens. In general, the fibres had a strong effect on the mechanical behaviour of the materials, especially in the case of PLA and MAPP. Treating the fibres with undelaminated clay or nanoclay improved to some extent the dispersion of the fibres and the mechanical performance of the composites, but further optimization of the function of the mineral in this respect is probably required. The combination of the mineral treatment with a debonding agent appeared to be an interesting route here. With such a combination, a visually very good dispersion of the fibres in the PP-based matrix could be obtained, partly at the expense of the mechanical performance. The compounding of the cellulosic fibres with PP led in this case to a marked decrease in the fibre length. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2008

The influence of processing parameters such as screw geometry, temperature profile, and screw speed on the electrical properties of hybrid composites consisting of graphite nanoplatelets and carbon black in ethyl butyl acrylate was studied. Two different screws were used to compound the hybrid composites at two different temperatures and two different screw speeds. A beneficial effect was noted with regard to the electrical properties when adding nanoplatelets to the filler system. The cause could be a synergistic effect due to the difference in particle shape of the two fillers. Lower percolation thresholds were obtained with the conventional screw due to less breakage of the graphite nanoplatelets compared to the barrier screw. No significant changes of the electrical properties were observed when changing the temperature profiles or the screw speeds. Furthermore, the melt viscosity of the compounds was not appreciably affected at the rather low filler contents used here.

© 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 42255. © 2015 Wiley Periodicals, Inc. Melt spinning at semi-industrial conditions of carbon black (CB) containing textiles fibers with enhanced electrical conductivity suitable for heating applications is described. A conductive compound of CB and high density polyethylene (HDPE) was incorporated into the core of bi-component fibers which had a sheath of polyamide 6 (PA6). The rheological and fiber-forming properties of a low-structured and a high-structured CB/HDPE composite were compared in terms of their conductivity. The low-structured CB gave the best trade-off between processability and final conductivity. This was discussed in terms of the strength of the resulting percolated network of carbon particles and its effect on the spin line stability during melt spinning. The conductivity was found to be further enhanced with maintained mechanical properties by an in line thermal annealing of the fibers at temperatures in the vicinity of the melting point of HDPE. By an adequate choice of CB and annealing conditions a conductivity of 1.5 S/cm of the core material was obtained. The usefulness of the fibers for heating applications was demonstrated by means of a woven fabric containing the conductive fibers in the warp direction. By applying a voltage of 48 V the surface temperature of the fabric rose from 20 to 30°C.

The effect of surface texture on the pass/fail colour tolerance region was estimated using acrylonitrile–butadiene–styrene injection-molded plaques in three different colours and with different surface textures. Variations in the measured colour coordinates due to differences in texture for three selected colours were observed using the specular component excluded mode (SCE) of the spectrophotometer. Such variations could not, however, be clearly distinguished in the specular component included mode. The colour tolerance regions were assessed through a combination of colour measurement and a psychometric study involving 35 observers. The limits of acceptance of colour differences varied substantially with the surface texture. In some cases, the observers accepted a larger colour difference for the textured than for the smooth surface, whereas in other cases, the reverse situation was noted. Thus, no general conclusion regarding the influence of texture on the tolerance region can be drawn, since the acceptable differences were colour- and/or surface texture-dependent. In the case of textured surfaces, measurements made in the SCE mode of the spectrophotometer appear to be more meaningful for assessing perceived colour differences and tolerance regions. © 2006 Wiley Periodicals, Inc. Col Res Appl, 32, 47–54, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/col.20284

The effects of processing conditions on appearance characteristics of injection-molded mineral-filled polypropylene (compounded with pigments giving differing intensities of a beige color) have been studied; characteristics studied included gloss, color, and texture. A mold cavity embossed with smooth, fine, and coarse surface patterns was used. In-mold rheology and gate-seal analysis were used to select the filling and postfilling processing parameters. Interest was focused on the effects of filling rate, holding pressure, and mold temperature on the appearance characteristics, and a significant influence of these processing conditions on the gloss and color was found. For all the surface patterns examined, a better replication of the mold texture was obtained with a low melt viscosity at a high shear rate (high injection speed or short injection time) and a high mold temperature. This gave a higher gloss in the smooth surface regions and a lower gloss in the textured regions. An increase in the holding pressure had an effect similar to but smaller than increasing the filling rate or mold temperature. The gloss (or surface topography) had a significant effect on the color; an increase in gloss was associated with an increase in the color coordinate b* and a decrease in the lightness L*. POLYM. ENG. SCI. 45:1557–1567, 2005. © 2005 Society of Plastics Engineers

The relation between the surface topography of injection-molded plastic objects with deliberately imposed textures and their gloss, measured by means of a conventional glossmeter at incident angles of 20°, 60°, and 85°, was investigated. A modification of the general scalar Kirchhoff approximation, which accounts for geometrical features of the glossmeter, is used to describe the experimental gloss values of the textured surfaces. The agreement between the measured and the calculated values for incidence angles of 20° and 60° confirms the usefulness of the approach, though several of the textured surfaces used here are too rough for the Kirchhoff theory to be strictly valid. A poorer agreement, however, was noted at higher incidence angles (85° in this case). For very smooth surfaces (without any texture), the classical Bennett-Porteus theory could in many cases describe the gloss level with sufficient accuracy. The influence on the measured gloss of the polymer material (in terms of its refractive index) and the color of the injection-molded object is also discussed. Light beige specimens in three different polymeric materials (acrylonitrile-butadiene-styrene, acrylonitrile-butadiene-styrene/polycarbonate blend, and polypropylene) as well as three acrylonitrile-butadiene-styrene products with different colors were used. The refractive index of the polymer had no major influence on the measured gloss. The gloss level increased slightly with increasing lightness of the specimens, which can be associated with an increased contribution from the bulk scattering. However, the surface texture governed most of the gloss variations. POLYM. ENG. SCI., 45:1343–1356, 2005. © 2005 Society of Plastics Engineers

The printability of paper in flexography is largely dependent on the topographical characteristics of the substrate. Topography imaging instruments make it possible to obtain three-dimensional scans of paper surfaces that can be further used to calculate valuable quality parameters. The primary aim of the work described in this thesis has been to identify and isolate structural properties of the paper surface which significantly influence the ink distribution during printing and limit the subsequently attainable print quality.OptiTopo is an optical imaging technique which provides precise and fast topographic scans of both printed and unprinted paper surfaces. The potential and limitations of the technique have been evaluated. The optical requirements on the substrate for an accurate and precise topographic scan were determined. Detail-rendering was substantially improved using a custom-designed restoring filter, and a new enhanced spatial resolution range was established. A combination of further algorithm improvements made it possible also to obtain reflectance-factor-calibrated intensity images of scanned printed surfaces.Serious deficiencies affecting the quality of flexographic prints may appear in the form of local unprinted areas (UCA) in a full-tone print, generally caused by incomplete ink transfer. An algorithm detecting and quantifying local uncovered area was developed, tested and successfully integrated with the OptiTopo instrument. A UCA occurrence frequency distribution, indicating the percentage of the uncovered area at a certain topographical elevation, was calculated for different prints. The topographic characteristics of the uncovered areas clearly indicate that surface depressions are the primary cause of uncovered areas in flexographic printing.Four different predictive models based on topography thresholding were proposed and tested using two independent quality judgement criteria. These quality indices took into account both the amount and location of the predictions. A deeper understanding of the topographical features governing UCA occurrence was established with a proposed ink bridging effect. The total risk of non-ink-covered areas in flexography printing due to topographical features was estimated.The overall influence of paper topography on the flexography printability of full-tone areas was studied and its importance for the ink distribution assessed. The impacts of printing plate hardness, printing pressure, anilox cylinder volume and substrate roughness were quantified. Two typical flexography patterns were identified and their origin discussed: sub-millimetre elongated structures and millimetre-scale blotches.

The influence of the physical and chemical characteristics of a paper substrate coated with a thin homogeneous film of poly(vinyl alcohol) (PVA) has been investigated. Some of the paper specimens were temperature-gradient (TG) calendered (at high temperatures) before pilot-scale coating. Two different paper grades differing in structure and sizing formulation were used. For one of the grades, the high-temperature calendering had a slight effect on the chemical composition of the paper surface as evaluated by electron spectroscopy for chemical analysis. For the other grade, no such effect was noted. In the former case, it was suspected that the sizing in the paper substrate degraded and, as a consequence, that volatile hydrocarbons evaporated from the surface. The slight change in surface chemistry had no significant direct effect on the homogeneity of the applied polymer film. The results indicated that the surface roughness of the substrate was the governing factor. The low surface roughness obtained by TG-calendering was beneficial for the homogeneity and barrier properties. In one series of experiments, some of the paper substrates (uncalendered and calendered) were corona-treated before PVA-coating. This treatment greatly increased the wettability of the surface by water. In general, the corona treatment improved the homogeneity and the barrier properties (grease resistance, air permeability and water vapour transmission) of the applied film. The surface smoothness was clearly important also for the corona-treated papers.

The effect of the concentration of a colorant (masterbatch) and the surface texture on the color of an opaque injection-molded plaque is experimentally described by means of the spectral reflectance and the CIELAB coordinates. It was noted that the surface texture had a marked influence on the experimental results and on the perceived color. The relation between the color of these pigmented plastic plaques and intrinsic physical material properties, such as light absorption and scattering coefficients, is described by means of the Kubelka-Munk equation for pigment/ paste mixtures. The concentration dependence of this Kubelka-Munk equation for different masterbatch-polymer mixtures can be modeled in terms of the color of the individual constituents using a fitting parameter. Further experiments were carried out which indicated that the fitting parameter had a physical meaning. The effect of the surface texture on the optical appearance of the plaques can also be accounted for by this parameter.

The purpose of this study was to provide experimental evidence of the separation of the polymer components at different scales during conventional processing. This was achieved by characterizing the surface and the bulk (cross section) of moldings manufactured with a high-flow grade and a low-flow grade of commercial polystyrene by the time-of-flight secondary ion mass spectrometry (TOF-SIMS) analytical technique. Owing to the geometric constraints of the mold used, a weld was also obtained. Different surface spectra were observed for the two molded polystyrenes. The surface of the high-flow grade moldings showed the spectral features of low-molar polyolefin (paraffin) contaminants, whereas the bulk was dominated by polystyrene. Spectra from both the surface and the bulk of the low-flow grade moldings were characteristic of polystyrene. Mold-filling effects on the surface composition were observed in the flow front region of molded short-shots of the low-flow grade. The spectral changes indicated the abundance, in the surface, of the high end of the molar-mass distribution of the material during the mold filling process. Two-dimensional maps of the secondary ions from the low-flow grade also showed an occasional alkali contamination, preferentially along the notch of the weld.

The aim of this work is to evaluate routes to upgrade recycled engineering plastics, especially mixed plastics with acrylonitrile–butadiene–styrene copolymers (ABS) as the major component. A core-shell impact modifier was successfully used to improve the impact strength of blends of ABS and ABS/polycarbonate (PC) blends recycled from the automotive industry. However, the presence of other immiscible components like polyamide (PA), even in small amounts, can lead to a deterioration in the overall properties of the blends. A styrene–maleic anhydride (SMA) copolymer and other commercial polymer blends were used to promote the compatibilization of ABS and PA. The core-shell impact modifier was again found to be an efficient additive with regard to the impact strength of the compatibilized ABS/PA blends. The results obtained with fresh material blends were quite promising. However, in blends of recycled ABS and glass-fiber-reinforced PA, the impact strength did not exhibit the desired behavior. The presence of poorly bonded glass fibers in the blend matrix was the probable reason for the poor impact strength compared with that of a blend of recycled ABS and mineral-filled PA. Although functionalized triblock rubbers (SEBS–MA) can substantially enhance the impact strength of PA, they did not improve the impact strength of ABS/PA blends because the miscibility with ABS is poor. The possibilities of using commercial polymer blends to compatibilize otherwise incompatible polymer mixtures were also explored giving promising results. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 2535–2543, 2002

The aim of this investigation was to evaluate the possibility of mechanically recycling blends of ABS with minor amounts of semicrystalline engineering plastics, such as polyamide, poly(ethylene terephthalate), and poly(butylene terephthalate). Compatibilizers and a core–shell impact modifier were incorporated into the blends in order to improve the mechanical properties. The toughness values, measured by the J-integral method, and the Charpy impact strength did not always exhibit consistent results, due to the significant difference in deformation rate and in fracture mechanism. The formation of co-continuous structures in the blends were noted and discussed. The fibrillation in the fracture surface contributed to the toughness as measured by the J-integral method. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 2435–2448, 2002

The influence on the adhesion to some metal surfaces and the damping properties of various modified styrene-ethylene/butylene-styrene (SEBS) materials was evaluated. Modification of the different phases of the SEBS with resins was shown to have a large effect on the damping properties of the polymers, which were evaluated by dynamic mechanical analysis (DMA). A small amount of maleic anhydride grafted onto the EB block was found to lead to a significant improvement in the adhesion of the polymer to some metal surfaces without affecting the damping properties of the polymers. The results of the DMA tests on the polymers were used to calculate the composite loss factor (CLF) for a steel laminate, which consisted of two steel plates with a polymeric layer in between, according to the theory proposed by Ross, Ungar, and Kerwin. The calculated results were compared with the measured CLFs determined in vibrating beam tests (VBTs). The agreement between the calculated and measured values was quite fair, provided that the DMA values used for the calculations were recalculated to the actual higher frequencies used in the VBTs, using the time–temperature superposition principle. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 2865–2876, 2001

The dynamic viscoelasticity was investigated for isoprene rubber (IR) composites filled with untreated and chemically treated cellulose fibers. Mercerization and benzylation were employed as chemical treatments. Bleached kraft pulp and cellulose powder were used as cellulose fillers. By mixing cellulose fillers, the dynamic modulus E′ of IR composites was improved, especially above the glass transition temperature. Benzylation of cellulose fibers reduced E′ of IR composite, while mercerization increased it. A tan δ peak was observed at about −33°C at 110 Hz along with a shoulder peak at about −16°C for the IR composites. The intensity of the tan δ peak decreased when mixed with cellulose fillers. The shoulder peak next to the main peak could be separated assuming a Gaussian type equation; log E″ = D exp { −C[(1sol;T) − (1/T0)]2} where D is the maximum value of log E″ vs. 1/T curve, T0 is the maximum temperature, and C is a parameter to determine the width of the Gaussian function. From the Arrhenius plot of the frequencies against 1/T0, the apparent activation energies were calculated as 220–235 kJ/mol for the shoulder peak (α1 process) and ca. 180 kJ/mol for the main peak (α2 process). The α2 process is caused by the glass transition of the rubber matrix. The α1 process is assigned as the molecular motion of the rubber matrix strongly restricted by the fiber element.

The dynamic-mechanical properties of high density polyethylene filled with 20% by volume of untreated glass spheres or glass spheres treated with a silane-based coupling agent were studied as a function of temperature and imposed tensile deformation. The coupling agent used is capable of providing covalent bonding between the polymeric matrix and the glass spheres. It is assumed that an interphase region is formed in the matrix around each filler particle with properties depending on the surface treatment of the filler, but different to that of the bulk matrix. It is shown how the mechanical loss factor can be used to characterize the properties of the interphase region and the degree of adhesion between the two phases, as affected by the surface treatment. We suggest that these kinds of measurements can be valuable when determining the effectiveness of various surface treatments of filler particles from a mechanical point of view.

High pressure injection molding of HDPE with relatively high molecular weight is known to give products with significantly increased modulus and strength. The extent of this improvement is reduced when the thickness of the molded sample increases. The present paper is an account of experiments with varying mold filling rates and gate geometries. After choosing proper gating and then optimizing the filling rate, thick samples with tensile moduli previously characteristic of thinner samples have been obtained. The modulus data are supplemented by measurements of the melting point of the normal and high-strength HDPE structures at different locations in the molded test bars. Corresponding crystallinity data are also included. The structure of the samples appears to provide some guidance in interpreting the observed modulus variations.

The mechanical properties of clay-based pigmented coating films bonded with a series of carboxylated styrene–butadiene latex binders have been investigated. The in-plane tensile strength and the elongation at rupture increased with increasing amount of polymeric binder. It is suggested that this is due to an improvement in stress transfer through the structure. The mechanical behavior of the films was furthermore found to be strongly related to the properties of the polymeric binder at the usage temperature. In torsional pendulum experiments an increase in the glass transition temperature of the polymeric binder was observed when it was incorporated in the coating film. This is interpreted as being the result of a decrease in the segmental mobility of the polymer molecules due to the presence of the clay particles, i.e., due to the interaction between the clay pigments and the binder. The interaction was, however, less noticeable in experiments using an NMR (nuclear magnetic resonance) technique. If the clay was replaced by calcium carbonate, a strong interaction, as measured using NMR, was observed between CaCO3 and the styrene–butadiene polymer, although the in-plane mechanical strength and ductility were reduced. A structural model accounting for some of the observed differences in mechanical behavior between clay-based and CaCO3-based coating films is suggested.

The build-up of internal stresses in injection molded parts is due to the combined effect: of a low thermal conductivity (diffusivity) of normal polymer melts and their rapid cooling in the mold cavity. The present paper shows that increasing the thermal diffusivity of the polymer by the addition of relatively small amounts of metallic fillers resulted in a substantial reduction in the internal stress level. The filler content was of the order of a few percent by volume. The average internal stress (σi) was determined by a stress relaxation method. The modulus, tensile strength, and other mechanical properties of the samples were not influenced by the filler addition. The impact strength, however, decreased sharply, as no adhesion pro-motors were used. The observed improvements in mold shrinkage, thermal shrinkage, hardness, and stress-cracking tendency could be related to a decreased σi level. In comparative experiments with other fillers (MgO, glass powder), a good correlation was found between the σi level and the thermal diffusivity of the filler.

Dry-formed networks of cellulose fibers, produced with a laboratory device, have been impregnated with aqueous solutions of poly(vinyl alcohol) or solutions of poly(vinyl acetate) in acetone. In both cases, the strength and stiffness of the networks increase several times compared with the unmodified structure. When aqueous solutions are used, it appears that a minimum amount of poly(vinyl alcohol) is required (ca. 2 wt %) to increase the strength appreciably, but when poly(vinyl acetate) dissolved in acetone is used, as a binder, the strength improves even at the lowest level of polymer addition. For the systems studied here, the elongation at rupture increased with increasing polymer concentration. In most cases, the amount of polymer in the network structure was less than 10 wt %. Some results from impregnations using other polymeric systems, e.g., latices, are also reported.

The mechanical properties, i.e., the tensile strength, tensile modulus, elongation at rupture, and tensile energy absorption (work of rupture), of a dry-formed network of cellulose fibers are shown to be substantially improved by impregnation of the network with organic solutions of poly(vinyl acetate) (PVAC). With the exception of the tensile strength, the improvement of the mechanical properties in the dry state is, however, dependent not only on the polymer content, but also on the interaction between the solvent and the cellulose fibers constituting the network. A solvent which interacts strongly with cellulose produces a stiffer and less ductile network than a more inert liquid. It is suggested that this effect is the result of a change in the cellulose network structure itself. The solvents used in this study were methanol, acetone, ethyl acetate, chloroform, and toluene.

The stress–relaxation behaviors of molybdenum (Mo) and polyethylene are compared, especially with regard to the role played by the internal stress level, in the relation F = 0.1(σ0 − σi). Here F is the maximum slope in the inflexion region of stress vs. In time curves (σ vs. ln t), σ0 is the initial stress, and σi is the internal (equilibrium) stress. Despite a significant difference in σi in the two materials, this relation was obeyed in both cases. The data for Mo are for room temperature and 90 K; those for low and high density polyethylene for room temperature only. Some of the data are reevaluated results of earlier measurements. The shape of the σi(ϵ) curves is reminiscent of the σ(ϵ) behavior for both Mo and polyethylene. The implications of the results for interpretation of the relaxation process in terms of current theoretical concepts is discussed.

High-pressure injection molding (nominal pressure 500 MPa) is known to substantially improve the mechanical properties of high-density polyethylene of a high molecular weight (HMWPE). This work shows that if the mold is equipped with an exit cavity, the tensile modulus and strength of HMWPE-bars molded is further improved at high pressure levels. The maximum values of the stiffness and strength (thin bars, 1 mm) obtained with the exit chamber is about 12 GPa and 260 MPa, respectively. The improvement due to the exit cavity is of the order of 30 percent for the tensile strength for thicknesses lower than 4mm, while the modulus increases about 1 to 1.5 GPa for bars with thicknesses between 1 and 6 mm. The orientation of the melt during the filling of the mold was also found to have an influence on the mechanical properties of the HMWPE bars.

During creep deformation many polymeric materials exhibit small cracklike zones, crazes. In the literature it is reported that crazing will not occur if the strain is kept under a critical value, specific for each material. This fact has importance in avoiding rupture. In this work a uniaxial theory is put forward that is based on a creep law describing the buildup of internal stress and on the Kachanov damage law. Crazing is here regarded to be a stage in the damage accumulation process, the final stage of which is rupture. Relations among the critical strain, the corresponding critical stress, and the minimum stress leading to creep rupture are derived. Some conditions that are necessary for the critical strain concept to work are formulated.

In dry-formed polymer-bonded networks of cellulose fibers and in other types of nonwovens, the fiber-polymer joint is considered to be the primary factor determining the ultimate properties of the network structure. In an attempt to develop a model describing the joint failure, the well-known fiber pullout test has been applied to a system consisting of regenerated cellulose fibers and three different polymer matrices: a styrene–acrylate copolymer, poly(vinyl alcohol), and high density polyethylene. For each system, the interfacial bond strength was evaluated. The results are, to some extent, discussed in relation to the mechanical behavior of dry-formed networks bonded with similar polymeric materials. It is suggested that both the interfacial properties and the cohesive strength of the polymer binder are of importance for the mechanical strength of the bonded network.

Sulfur- and peroxide-cured natural rubbers (NR) reinforced with short fibers of cellulose and carbon black have been studied with respect to water absorption, crosslink density, tensile strength, and the dependence of the dynamic storage modulus on strain amplitude. The results indicate that there is bonding between fiber and matrix even in the absence of a specific bonding system.