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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.

Plastics is a group of materials commonly encountered on a daily basis by many people. They have enabled rapid, low-cost manufacturing of products with complicated geometries and have contributed to the weight reduction of heavy components, especially when produced into a foamed structure. Despite the many advantages of plastics, some drawbacks such as the often fossil-based raw-material and the extensive littering of the material in nature, where it is not degraded for a very long time, needs to be dealt with. One way to address at least one of the issues could be to use polymers from nature instead of fossil-based ones. Here, a β-glucan concentrate originating from barley was investigated. The concentrate was processed into a foam by hot-melt extrusion, and the processing window was established. The effect of different blowing agents was also investigated. Water or a combination of water and sodium bicarbonate were used as blowing agents, the latter apparently giving a more uniform pore structure. The porous structure of the foamed materials was characterized mainly by using a combination of confocal laser scanning microscope and image analysis. The density of the samples was estimated and found to be in a similar range as some polyurethane foams. A set of 3D parameters were also quantified on two selected samples using X-ray microtomography in combination with image analysis, where it was indicated that the porous structure had a pre-determined direction, which followed the direction of the extrusion process.

Hydroxyazetidinium salts were used to surface-modify cellulose nanocrystals (CNC) by grafting the salts onto the sulphate ester groups on the CNC surfaces. The grafting was confirmed by ζ-potential measurements and by the thermal degradation behaviour of the modified CNC. The thermal stability (onset of degradation) of the CNC was improved by the surface modification (almost 100 °C). Composites containing surface-modified or unmodified CNC (0.1, 1.0 and 10 wt%) with an ethylene-based copolymer as matrix were produced by compression moulding. The thermal stability of the composites was not, however, markedly improved by the surface grafting onto the CNC. It is suggested that this is due to a degrafting mechanism, associated with the alkaline character of the system, taking place at high temperatures. Model experiments indicated, however, that this did not occur at the conditions under which the composites were produced. Furthermore, in the case of a reference based on pH-neutralised polymeric system and modified CNC, an upward shift in the onset of thermal degradation of the composite was observed. The addition of the CNC to the polymer matrix had a strong influence of the mechanical performance. For example, the tensile modulus increased approximately three times for some systems when adding 10 wt% CNC. The surface grafting of the hydroxyazetidinium salts appeared mainly to affect, in a positive sense, the yield behaviour and ductility of the composites. The results of the mechanical testing are discussed in terms of interactions between the grafted units and the matrix material and between the grafted groups.

During the past century, plastics have become a natural element in our every-day life. Lately however, an awareness about the fossil origin and often non-degradable nature of many plastics is rising. This has resulted in the emergence of some bio-based and/or biodegradable plastics, often produced from renewable resources. One possible candidate for bioplastics production could be found in cellulose. This paper aims at contributing information regarding a cellulose derivative, which could possibly be used in foamed plastics applications. Therefore, the reduction of the chain-length of a methyl ethyl hydroxyethyl cellulose (MEHEC), assessed by size exclusion chromatography, and the effect of chain-length on the foaming behaviour were studied. The foaming was accomplished with a hot-mould technique using aqueous polymer solutions. The generated steam was here used as the blowing agent and important parameters were polymer concentration and solution viscosity. The density of the produced foams was assessed and was in some cases comparable to that of commodity foams. It was found that reducing the chain-length enabled an increase of the initial polymer concentration for the foaming process. This is believed to be beneficial for creating more structurally stable foams of this type.

The extensional viscosity is an important rheological characteristic of polymer melts. It is however not as frequently reported on as the shear viscosity. The extensional viscosity is of special interest when considering polymeric materials for foaming and film blowing processes. Here, the extensional (and shear) viscosity along with the melt strength and the tensile properties of the corresponding solid film of a β-glucan concentrate are reported on. A capillary viscometer equipped with a hyperbolic die, yielding a contraction flow, was used to assess the extensional viscosity of the aqueous β-glucan compound at room temperature and at elevated temperatures (110 and 130 °C). In general, the extensional viscosity as well as the shear viscosity decreased with increasing deformation rate. The influence of two different amounts of added water (40 and 50%) was also examined. As expected, both types of viscosities decreased with increasing temperature. It is suggested that gelatinization of the starch fraction in the concentrate at 110 and 130 °C contributes to temperature dependence of the viscosity. To some extent, this is supported by light microscopy and confocal scanning laser microscopy studies of the microstructure of the materials. The results reported here indicate that the β-glucan concentrate might, after some modifications, be used as a complement to fossil-based polymers and processed by conventional manufacturing techniques.

Cellulose nanocrystals (CNC) were surface modified by grafting azetidinium salts onto the sulphate ester groups on the cellulosic surfaces. The modified CNC were characterized using NMR, FTIR spectroscopy, conductometric titration and measurement of the ζ-potential. Thermal gravimetrical analysis revealed that the onset temperature for the thermal degradation was shifted upwards by almost 100 °C as a result of the surface grafting. The rheological properties of dispersions based on unmodified and modified CNC were evaluated in detail. Two solids contents were studied; 0.65 and 1.3 wt%. In general, the grafting of the salts significantly increased the shear viscosity at a given shear rate as well as the storage and loss moduli of the dispersions. The CNC concentration at the gel point (network formation) decreased in a corresponding manner when the nanocellulosic particles were surface modified. This may be associated with pronounced hydrophobic attractive interactions between the grafted substituents.

The rheological properties of aqueous suspensions based on three different nanocelluloses were compared. One system was obtained via acid hydrolysis (thus yielding crystalline nanocellulose, CNC) and the other two from mechanical shearing, but from different origins and subjected to different pretreatments. Of the latter two, one was considered to be a rather typical cellulose nanofibril (CNF) suspension whereas the other was a kind of intermediate between CNF and CNC. All three nanocellulose elements differed in dimensions as evident from transmission electron microscopy and atomic force microscopy. With regard to the length of the fibrils/particles, the three nanocelluloses formed three distinct groups with lengths between 200 and slightly more than 800 nm. The three cellulosic elements were also subjected to a TEMPO-mediated oxidation yielding a similar carboxylate content in the three systems. Furthermore, the TEMPO-oxidized elements were grafted with poly(ethylene glycol) (PEG). The amount of grafted PEG was about 35 wt%. The shear viscosity, the storage modulus and the loss modulus of suspensions of the unmodified, the TEMPO-oxidized and the grafted nanocelluloses were determined at room temperature and the solids content of the suspensions was varied between 0.7 and 2.0 wt%. It was concluded that the rheological properties varied significantly between the suspensions depending on the dimensions of the cellulosic elements and their surface characteristics. In this context, the length (or the aspect ratio) of the particles played a very important role.

Plastics are a material group which have revolutionized the materials industry during the past century. However, the often fossil origin and littering of the material is problematic. Therefore, this study aims at exploring natural polymers, such as cellulose derivatives and hemicelluloses from different botanical origins, and demonstrate the possibility to use these polymers in a foaming application. The hemicelluloses were chemically treated in order to enhance their performance and foams with ratios as high as 4:1 of hemicellulose and the cellulose derivative, respectively, were successfully produced by a hot-mould foaming technique. The foams were found to be thermally stable up to about 280 °C. The chemical modifications were confirmed by Fourier transform infrared (FTIR) spectra and the foams were evaluated with regard to their liquid absorption capacity as well as their density. After 1 min the best foam absorbed 12.5 g/g of liquid and after 30 min soak time and centrifugation the foams had absorption capacities between 2 and 5 g/g. All foams exhibited densities below 0.1 g/cm3. In both the absorption test and density evaluation, the foams produced from mainly hemicellulose performed in a similar way as the reference foams based only on the cellulose derivative, which is considered an impressive result since cellulose is often reported to have superior properties to hemicelluloses.

The large-scale surface modification of cellulose nanocrystals (CNC) was carried out to produce CNC-containing composites, in a scale of 3 kg, using industrial-scale melt processing techniques such as twin-screw extrusion and injection moulding. Two different polymer matrices, ethylene-acrylic acid copolymer (EAA) and low-density polyethylene (LDPE), were reinforced with 10 wt% unmodified cellulose nanocrystals (CNC) or surface-treated CNC, where a 2-hydroxyproyl-N-diallyl group had been grafted onto the sulphate half-ester groups on the CNC surfaces. This was achieved by mixing an aqueous CNC dispersion and the polymer pellets directly in the twin-screw extruder followed by a second dry compounding step prior to shaping by injection moulding. The injection-moulded materials were characterized with respect to their mechanical properties and thermal stability. The addition of 10 wt % CNC resulted in all cases in an increase in the yield strength and stiffness by 50–100%, most significantly for the EAA based composites. There were indications of the presence of a stable interphase and a percolating network in the EAA-based materials, according to dynamic-mechanical measurements. A reduction in thermal stability was observed for the melt-processed samples containing diallyl-modified CNC and discoloration in the EAA based samples.

Foamed materials are gaining an increased interest due to their good mechanical properties in relation to their low densities and an increased industrial demand can be expected. A few less attractive issues can however be associated with commodity foamed products. For instance the raw-material often originates from non-renewable, fossil-based, sources. Furthermore, degradation in nature is slow, therefor the disposed product is burned or end up in landfills. One possibility to reduce the impact on nature could be to produce foams from natural polymers such as starch or cellulose. In this study the possibility to produce foams from hydroxypropyl methylcellulose (HPMC) with water as blowing agent, by continuous extrusion, was investigated. A pre-study using a capillary viscometer, batch-extruder, was conducted to evaluate the foamability of HPMC. Due to promising results further experiments were conducted with a single-screw extruder. The goal was to find an adequate processing window for foaming. It was concluded that HPMC could successfully be foamed by continuous extrusion, although a careful tailoring of the processing parameters was required. Crucial parameters were here the temperature, pressure and residence time distribution in the extruder. Regions of the extruded foams were examined using optical and scanning electron microscopy and HPMC foams with a density in the range of that of fossil-based polymeric foams could be produced.

Composite fibres with a matrix of poly(ethylene glycol) (PEG) and cellulose nanofibrils (CNF) as reinforcing elements were produced using a capillary viscometer. Two types of CNF were employed: one based on carboxymethylated pulp fibres and the other on TEMPO-oxidized pulp. Part of the latter nanofibrils was also grafted with PEG in order to improve the compatibility between the CNF and the PEG matrix. The nominal CNF-content was kept at 10 or 30 weight-%. The composite fibres were characterized by optical and scanning electron microscopy in addition to dynamic mechanical thermal analysis (DMTA). Evaluation of the storage modulus indicated a clear reinforcing effect of the CNF, more pronounced in the case of the grafted CNF and depending on the amount of CNF. An interesting feature observed during the DMTA-measurements was that the fibrils within the composite fibres appeared to form a rather coherent and load-bearing network which was evident even after removing of the PEG-phase (by melting). An analysis of the modulus of the composite fibres using a rather simple model indicated that the CNF were more efficient as reinforcing elements at lower concentrations which may be associated with a more pronounced aggregation as the volume fraction of CNF increased.

© BME-PT. The effect of adding carbon black on the electrical and rheological properties of graphite nanoplatelets/poly(ethylene- butyl acrylate) copolymer composites produced via melt or solution mixing was studied. By adding a small amount of low- or high-structured carbon black to the nanocomposite, the electrical percolation threshold decreased and the final conductivity (at higher filler contents) increased. The effect on the percolation threshold was significantly stronger in case of the high-structured carbon black where replacing 10 wt% of the total filler content with carbon black instead of graphite nanoplatelets reduced the electrical percolation threshold from 6.9 to 4.6 vol%. Finally, the solution mixing process was found to be more efficient leading to a lower percolation threshold. For the composites containing high-structured carbon black, graphite nanoplatelets and their hybrids there was a quite reasonable correlation between the electrical and rheological percolation thresholds.

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.

A multi-angle spectrophotometer was used to measure the CIELab coordinates L∗, a∗ and b∗ in different angles relative to the incident light. The specimens used were acrylonitrile-butadiene-styrene injection-molded plaques in different colors and with different surface textures. Variations in the coordinates when changing the measuring angle depended on the color and the texture. In general, however, smooth (glossy) surfaces were measured to be darker and of higher chroma than textured surfaces and as the gloss of the surfaces decreased (due to texturing), the lightness of the surfaces increased and the absolute values of a∗ and b∗ decreased over the range of measuring angles (not too close to the specular reflection angle). A psychometric study involving a human test panel was used as a complement to the measurement. The agreement between the measurements and this study cannot be said to be satisfactory, unless the variation in the color coordinates was quite clear. Possible reasons are discussed.

The processing conditions and the mould design are important parts of the powder injection moulding (PIM) process. In the present work, the mould filling phase of the process has been studied in situ with a special mould equipped with a sight glass using a high speed camera. Effects of features such as the mould temperature, the melt temperature, the surface roughness of the mould cavity, the gate dimensions, the mould design and the flow rate on the filling behaviour were demonstrated. In particular it was noted that a rougher mould surface to some extent facilitated the filling of the mould. The mould temperature, the nominal melt temperature and the flow rate affected the position of weld lines via the cooling of the feedstock and the corresponding change of the melt viscosity. The experimentally determined weld-line positions were compared with predictions from numerical simulations performed with the commercial software Moldex3D. The agreement between the experiment and the prediction was in most cases quite fair or good. The in situ observation of the mould filling also provided the possibility to study how the gate dimensions and the flow rate influenced the jetting behaviour.

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

Powder injection moulding (PIM) is an important and accepted industrial technique for net shaping of precision components which can have a rather complex geometry. In order to meet the imposed, often rather strict, requirements with regard to dimensional accuracy, it is important to have an adequate knowledge and control of the rheological behaviour and the related processing properties of the powder/polymer melt (feedstock). Such a knowledge is furthermore of crucial importance in numerical simulations of the PIM-process. In the present work, a model system, consisting of steel powder, poly(ethylene glycol) and wax, is used in order to illustrate how the viscometric properties as well as thermal properties, such as the conductivity and the specific heat, of the system can be related to the corresponding properties of the polymeric binder system. In a similar way, the pvT (pressure-volume-temperature)-behaviour of the model system is analysed and discussed. The pvT-behaviour, which has not been extensively reported on for PIM-feedstocks, is considered to be of significant relevance for controlling the outcome of the injection moulding process.

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.

Hydroxypropylated and oxidised potato starch (HONPS) was used together with glycerol and water to produce thermoplastic starch. The amount of glycerol was kept constant at 22 parts by weight per 100 parts of dry starch. The thermoplastic starch was converted into films/sheets using three different processing techniques; casting, compression moulding and film blowing. The last two methods represent typical thermoplastic conversion techniques requiring elevated processing temperatures. By means of size-exclusion chromatography, it was found that compression moulding and film blowing led to some degradation of high-molecular weight amylopectin as well as of high-molecular weight amylose-like molecules. The degradation was significantly less pronounced for the cast films. The morphology of the specimens was quite complex and phase separations on different levels were identified. In the cast films and, to a lesser extent, in the compression-moulded specimens, a fine network structure could be distinguished. Such a structure could however not be ascertained in the film-blown material and this is discussed in terms of the thermo-mechanical treatment of the starch materials.

Thermoplastic starch materials are often based on a combination of starch, glycerol and water. In the present study, two potato starch grades were employed; a native (natural) grade and an oxidised and hydroxypropylated grade of the native material, in order to produce the thermoplastic material. The primary aim of the study was to identify possible routes for film blowing thermoplastic starch on a laboratory scale by a suitable choice of processing conditions, amount of glycerol and moisture content. With an appropriate combination of these parameters, the thermoplastic material based on the modified starch could be film blown in a satisfactory manner. Film blowing of material based on the natural starch was significantly more difficult. The difficulties encountered were mainly related to a sticky surface of the film, insufficient tenacity and foaming. The processing window for thermoplastic starch (related to film blowing) is briefly outlined and discussed.

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.

Different grades of starch, glycerol, and water were blended in order to produce a series of thermoplastic starch materials. The starch grades used included native potato starch and modified grades of native potato starch, high amylose potato starch, and amylopectin potato starch. The modification of the latter three grades involved hydroxypropylation and oxidation. The main focus of the study was on the stress-strain properties or the drawability of the thermoplastic starch melts at 120° or 140°C. At these temperatures, the ultimate strain of the starch materials was found to be significantly lower than that of a high-density polyethylene reference at 180°C. In general, the strain at break of the melts based on the native potato starch and the modified native potato starch tended to increase when increasing the glycerol content (and the corresponding amount of water) but decreased as the melt temperature was increased from 120° to 140°C. The chemical modification of the native potato starch appe...

Thermoplastic starch was prepared by mixing native high amylose potato starch and normal potato starch in a Buss co-kneading extruder at starch to glycerol ratios of 100:45 and 100:30. The materials were also conditioned to different moisture contents at different relative humidities at 23 °C. After the mixing, the compounds were extruded into sheets with a Brabender laboratory extruder. The thermoplastic high amylose materials exhibited a higher melt viscosity than the normal potato starch materials when conditioned at 53% relative humidity. Increasing the moisture content in HAP from 27% to 30% (by weight) lowered the melt viscosity to the same level as that of normal potato starch with a moisture content of 28%. In general, the high amylose materials were more difficult to extrude than the thermoplastic material based on normal starch. The main extrusion problems encountered with the high amylose starch were unstable flow, insufficient melt tenacity and clogging of the die. By increasing the moisture content, increasing the compression ratio of the screw and increasing the rotation rate of the screw, the problems were reduced or eliminated. However, only with a starch to glycerol ratio of 100:45 was an acceptable extrusion result obtained. Extruded sheets of such high amylose materials had a stress at break of about 5 MPa at room temperature and 53% relative humidity, whereas the corresponding value for normal potato (thermoplastic) starch was 3 MPa. The elongation at break was also higher in the case of the high amylose material. The results are discussed in terms of residual crystallinity of the starch materials.

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

Adding plate-like pigments such as talc or kaolin clay to a styrene-butadiene (SB) dispersion before coating paperboard on a pilot scale resulted in a coated material with improved water vapour barrier properties. Addition of paraffin wax further significantly reduced the water vapour permeability. A limited study was also performed using poly(vinyl alcohol) (PVA) as the matrix material and a similar result was obtained. In addition to the barrier properties, the surface characteristics (gloss, roughness, surface energy and chemical composition) and the printability of the coated substrate were evaluated. In general, it was found that the properties of the coated material were improved if the surface of the base substrate was smoothened prior to coating by a suitable surface treatment such as hot calendering or precoating. Such a treatment gave a more homogeneous coating film on the substrate. A comparison of the experimental results with the prediction of models for the effect of impermeable particles on the vapour permeability indicated that the pigments were not optimally dispersed (or oriented) in the coating layer. There is thus room for improvement. In a further series of experiments, nanoclays were incorporated into the coating layers. Exfoliation of the silicate layers was indicated in laboratory coating experiments using SB, but not on the pilot-scale coated materials. Thus no significant effects on the barrier properties were observed for such coated specimens. With PVA as the matrix polymer and low contents of the nanoclay, a marked decrease in the water vapour permeability took place, indicating a more pronounced exfoliation.

Paperboard was coated on a pilot scale using aqueous dispersions of styrene–butadiene (SB) copolymers in order to improve its surface characteristics (including printability) and barrier properties with regard to the transmission of water vapour. Coating the paperboard with the dispersion in two steps gave a smoother surface with a remarkable increase in gloss. The printing properties of the smoother double-coated surface were slightly better than those of the single-coated surface. Paraffin wax added to the latex dispersion reduced the water vapour transmission rate (WVTR) but had a negative effect on the printability of the board. The effect of two commonly used surface treatment techniques (corona and plasma at atmospheric pressure) on the printing and barrier properties of dispersion-coated (containing wax) paperboard was evaluated. A fairly intense corona treatment led to an undesirable increase in the WVTR-value. A less intense corona treatment preserved the WVTR-value to a great extent, but the printability remained at an unsatisfactory level. With plasma treatment, the water vapour barrier was not impaired, and the printability of the plasma-treated dispersion-coated (wax-containing) substrate was good. It is suggested that a better result using corona treatment may be obtained by optimising the power and controlling the time between the treatment and the printing, although this was not investigated here.

In our recent work, it was shown that the rate of filling during injection moulding did not significantly affect the tensile and impact properties of recovered and virgin polypropylene, whereas significant changes in the properties were observed after ageing at 100 °C. The purpose of the present work was to extend the former study to include the effects of processing and ageing on surface-appearance-related properties, in particular the gloss. In-mould rheology and gate-seal analyses were performed in order to select the filling and post-filling processing windows, respectively. The influences of filling rate, holding and cooling times on the gloss measured in the gate area and at the far end of the moulded specimens were evaluated. The mould used had an embossed surface giving test plaques with a matte appearance. The results showed that the gloss varied by about 30 to 40% within the filling window obtained by in-mould rheology. The slight gloss difference between the two PP-grades noted at the lowest injection speed vanished with increasing filling rate. Gloss differences were observed between the gate area and the far end of each processed moulding, again at the lowest injection speed. The materials processed at a high filling rate exhibited a fairly constant gloss as the holding time increased regardless of the position of the analysed region, whereas a more significant decrease was noted in the case of the mouldings processed at the low filling rate. The cooling time had a negligible effect on the gloss in comparison to the effect of filling rate. Ageing at 100 °C for 240 h increased the gloss level, especially at the far end of the moulding, but only for specimens manufactured at the lowest filling rate. Roughness measurements with a profilometer showed that the gloss development during processing and ageing was related to the topographical matching between the developing polymer surface and the mould topography.

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

Polymer dispersions can be used for coating paper products in order to e.g. enhance their barrier properties. The influence of characteristics such as the degree of cross-linking (the gel content), glass transition temperature and degree of carboxylation of styrene–butadiene (SB) latex polymers on the mechanical properties and water vapour permeability of the corresponding polymer coating films at room temperature has been investigated. The storage modulus in the rubbery region increased markedly with increasing degree of cross-linking and the blocking (sticking tendency) towards adjacent paper substrates was in general somewhat lower at higher cross-link densities. There was also a tendency for the water vapour permeability to decrease somewhat with higher degrees of cross-linking. The degrees of carboxylation were quite low for the studied SB-dispersions and it had only a minor influence on the mechanical performance and barrier properties of the films. Reducing the glass transition temperature significantly below room temperature had a negative effect with regard to the blocking/sticking tendency of the polymer and on the water vapour permeability. On the other hand, a glass transition temperature significantly above room temperature resulted in a coating film with microcracks that caused a marked deterioration in the physical properties. These films were rather brittle with a low elongation at break. All the polymer films were also characterised using scanning electron microscopy, contact angle measurements and ESCA (electron spectroscopy for chemical analysis).

Desired savings in energy, raw materials and processing in the manufacture of coated papers may lead to the development of processes with reduced usage of water. One proposed process, the dry surface treatment (DST) for pigment-coating of paper has been studied in a laboratory scale. The treatment involves the application of dry, powdery coating materials on the paper surface and fixation of the deposited layer in a thermomechanical compression and smoothening phase in a heated roll nip. Electrostatic deposition of charged particles enables a non-contact coating application. In the previous studies, the DST-papers produced with two or multi-component powdery materials, that were formed by drying coating suspensions, exhibited coating coverage, surface strength and smoothness similar to commercial coated mechanical reference papers at equal coat weights, but a generally larger pore size of the dry-formed coatings gave higher levels of oil absorption, air permeability and somewhat irregular ink setting properties. This study aims to explore the possibilities to prepare the DST coating particles in a dry state. The eventual target is to obtain coating particles in the size range used in conventional pigment coating and adjust the binder properties, content and distribution in a favourable way with regard to the structure of the coating layer. Synthesis of particulate polymers under water-free conditions in supercritical carbon dioxide is described and performed. Hybrid coating particles, consisting of the pigment and binder together, were prepared and evaluated for their structure and the coating applicability.

It is well known that the properties of a final polymer product are determined not only by the polymer characteristics but also, via process-related structural changes, by the processing technique and by processing conditions such as cooling rate and machine speed. In this study, the influence of the extrusion coating process on the structure and properties of LDPE-, LLDPE-, and m-LLDPE-grades was evaluated. Process variables such as the melt temperature, the draw ratio, the length of the air gap between the die exit, and the laminating nip and the machine speed were studied. The primary interest was in the influence of the process parameters on the degree of orientation and its corresponding impact on the tensile and barrier properties (water vapor transmission rate) of the polymer films. The degree of orientation of the films, assessed by shrinkage measurements, was found to be directly related to the elongational strain rate imposed on the films during the drawing stage of the coating process. Furtherm...

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.