| 1. |
- Agde Tjernlund, Jessica, et al.
(författare)
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Influence of molecular weight on strain-gradient yielding in polystyrene
- 2004
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Ingår i: Polymer Engineering and Science. - : Wiley. - 0032-3888 .- 1548-2634. ; 44:10, s. 1987-1997
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Tidskriftsartikel (refereegranskat)abstract
- Experimental observations have indicated that the presence of strain gradients has an influence on the inelastic behavior of polymers as well as in other materials such as ceramics and metals. The present study has experimentally quantified length-scale effects in inelastic deformations of the polymer material polystyrene (PS) with respect to the molecular length. The experimental technique that has been used is nano-indentation to various depths with a Berkovich indenter. The hardness has been calculated with the method by Oliver and Pharr, and also by direct measurements of the area from atomic force microscopy. The experiments showed that the length-scale effects in inelastic deformations exist in polystyrene at ambient conditions. The direct method gave a smaller hardness than the Oliver-Pharr method. It was also shown that the length-scale parameter according to Nix and Gao increases with increasing molecular weight. For high molecular weights above a critical value of entanglement, there was no pertinent increase in the length-scale parameter. The length-scale parameter for strain-gradient plasticity has a size of around 0.1 μm for polystyrene.
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| 2. |
- Arino, I., et al.
(författare)
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On the relation between surface texture and gloss of injection-molded pigmented plastics
- 2005
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Ingår i: Polymer Engineering and Science. - : Wiley. - 0032-3888 .- 1548-2634. ; 45:10, s. 1343-1356
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Tidskriftsartikel (refereegranskat)abstract
- 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 degrees, 60 degrees and 85 degrees, 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 degrees and 60 degrees 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 degrees 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.
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| 3. |
- Arino Marine, Ruth, 1980, et al.
(författare)
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Processing and mechanical properties of thermoplastic composites based on cellulose fibers and ethylene-acrylic acid copolymer
- 2012
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Ingår i: Polymer Engineering and Science. - : Wiley. - 0032-3888 .- 1548-2634. ; 52:9, s. 1951-1957
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Tidskriftsartikel (refereegranskat)abstract
- The melt processing and the tensile mechanical properties of composites consisting of 30 wt% softwood kraft pulp cellulose fibers and ethylene-acrylic acid copolymer (EAA) with 7% acrylic acid content were studied. The compounding techniques used were extrusion mixing performed with a single screw extruder and elongation dispersive mixing performed with the injection-molding machine. All blends were injection-molded in a final step. Fiber length, fiber content, and mechanical properties were measured and the number and the size of the fiber aggregates were determined by microscopy analysis. It was concluded that two passes of elongation dispersive mixing had a beneficial effect on the mechanical properties, which could be related to the fewer and smaller amounts of aggregates. The different types of processing performed had a small or insignificant effect on the fiber length since the fiber lengths measured were within the same range as that of the starting material. POLYM. ENG. SCI., 52:1951-1957, 2012. © 2012 Society of Plastics Engineers Copyright © 2012 Society of Plastics Engineers.
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| 4. |
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| 5. |
- Boz Noyan, Ezgi Ceren, 1990, et al.
(författare)
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A comparison between laboratory-scale and large-scale high-intensity washing of flexible polyethylene packaging waste
- 2024
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Ingår i: Polymer Engineering and Science. - 0032-3888 .- 1548-2634. ; 64:4, s. 1877-1886
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Tidskriftsartikel (refereegranskat)abstract
- Sorted flexible polyethylene packaging waste was washed on a laboratory scale at both 25 and 40°C with water alone, with water and added NaOH, and with water and added detergent. The washed materials were then compounded using a twin-screw extruder and injection molded. The results were compared with those for an unwashed and a large-scale high-intensity sample washed with NaOH at 70–80°C. An intensive washing combined with high temperature gave a lower extensibility both in the molten and solid states presumably because of a greater degradation of the recycled material. Washing with NaOH resulted in the lowest strain-at-break in both the melt and solid states, whereas washing with water alone or with a detergent gave similar strain-at-break levels. The melt strength, the stiffness and tensile strengths at room temperature, and the thermal properties were less affected by the washing procedure. Although the final properties seem to be useful in general there were still some trade-offs between the washing condition and the degradation. While these results were expected, the influence of washing parameters on final product, for example, injection molded sample, has to our knowledge not been shown before especially regarding the mechanical properties. Highlights: Post-consumer flexible polyethylene packaging waste was studied with a focus on washing conditions. The influence of washing conditions on thermal, rheological, and mechanical properties of recycled samples was investigated. High-intensity washing at high temperature caused significant degradation of the material, this was to our understanding shown for the first time.
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| 6. |
- Camacho, W., et al.
(författare)
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NIR, DSC, and FTIR as quantitative methods for compositional analysis of blends of polymers obtained from recycled mixed plastic waste
- 2001
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Ingår i: Polymer Engineering and Science. - : Wiley. - 0032-3888 .- 1548-2634. ; 41:9, s. 1626-1635
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Tidskriftsartikel (refereegranskat)abstract
- Methods for the determination of the composition of two binary blends in mixtures of recycled polymeric materials were analyzed and compared. Recycled polypropylene/polyethylene (PP/HDPE) and recycled poly(acryl-butadiene-styrene) and polypropylene(ABS/PP) were used to develop and validate the methods. Diffuse reflectance near infrared spectroscopy (NIRS) offers high sensitivity and ease of operation and a possibility to perform multivariate data analysis. In comparison, differential scanning calorimetry (DSC) and Mid-IR which are commonly used for this purpose require certain sample preparation and are indeed time consuming. In addition, the low sensitivity of these two methods to concentrations lower than 1% wt makes their application in quality control of recycled polymers inappropriate. NIR can be used for estimating the composition of the recyclate on-line in only a few seconds, no sample preparation is required, and high precision is achieved. We obtained a root mean square error of prediction (RMSEP) equal to 0.21% wt in the interval from 0-15% wt of PP in HDPE and a RMSEP equal to 0.91% wt in the interval 0-100%. For blends of PP/ABS a RMSEP of 0.74% wt in the range 0-100% and 0.32% wt in the range 0-15% wt PP was calculated. Most of the variation in the spectral data with respect to the polymer blend composition for all the studied blends were explained by two principal components (PC). The optimal number of factors (PC) was determined by cross-validation analysis.
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| 7. |
- Claesson, Johan, et al.
(författare)
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Masked edge effects when measuring diffusion coefficients with the cup method
- 1994
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Ingår i: Polymer Engineering and Science. - : Wiley. - 1548-2634 .- 0032-3888. ; 34:10, s. 821-826
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Tidskriftsartikel (refereegranskat)abstract
- When diffusion coefficients are measured with the cup method, the exposed area is often less than the area of the sample. Because of this masking effect the measured diffusion coefficient is overestimated. The present article presents simple formulas based on two-dimensional analytical solutions to correct for this in cylindrical cup samples. Different cases of anisotropical diffusion are dealt with. The error in the analytical solutions is determined by numerical computer simulations.
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| 8. |
- Flodberg, G., et al.
(författare)
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Barrier properties of blends based on liquid crystalline polymers and polyethylene
- 2000
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Ingår i: Polymer Engineering and Science. - : Wiley. - 0032-3888 .- 1548-2634. ; 40:9, s. 1969-1978
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Tidskriftsartikel (refereegranskat)abstract
- Blends of an extrusion-grade polyethylene and two different liquid crystalline polymers of Vectra type were prepared by melt mixing using poly(ethylene-co-methacrylic acid) as compatibilizer. Oxygen and water vapor permeability, transparency and welding strength of compression molded and film blown specimens were studied. The compression molded blends showed gas permeabilities conforming to the Maxwell equation assuming low permeability liquid crystalline polymer spheres in a high permeability polyethylene matrix One of the liquid crystalline polymers with suitable rheological properties formed a more continuous phase in the film blown blends and a substantial decrease in oxygen and water vapor permeability was observed in these blends. The compression molded blends with 50% liquid crystalline polymer and some of blow molded blends showed very high gas permeabilities. It is believed that voids forming continuous paths through the structure were present in these samples. The blends showed significantly higher opacity than pure polyethylene.
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| 9. |
- Flodberg, G., et al.
(författare)
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Barrier properties of injection molded blends of liquid crystalline polyesters (Vectra) and high-density polyethylene
- 2003
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Ingår i: Polymer Engineering and Science. - : Wiley. - 0032-3888 .- 1548-2634. ; 43:5, s. 1044-1057
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Tidskriftsartikel (refereegranskat)abstract
- Blends of an extrusion-grade high-density polyethylene and two liquid crystalline copolyesters (LCP; Vectra A950 and Vectra RD501) were prepared by melt mixing and injection molding, and the. morphologies and oxygen permeabilities of the blends were assessed. Scanning electron microscopy revealed that the LCP was present in the blends as mixed oriented bands and small spheres at low LCP contents (4-9 vol%), Whereas blends with more than 18 vol% LCP showed LCP lamellae of macroscopic lateral size (mm). Scanning electron microscopy revealed a two-dimensional continuity of the LCP domains in the disc plane due to radial shear deformation and circumferential stretching of the melt leaving the central gate of the disc-shaped cavity. The oxygen permeability, diffusivity and solubility decreased with increasing LCP content of the blends. The decrease in permeability with respect to polyethylene was significant (46%-55%) already at 9 vol% LCP. At 27 vol% LCP, the decrease with respect to polyethylene, was 92% for the Vectra A950 blend and 98% for the Vectra RD501 blend. These blends showed a greater decrease in diffusivity (86%-92%) than in solubility (39%-76%) with respect to polyethylene, which showed the very pronounced effect of the LCP lamellae on the geometrical impedance factor. Microvoids were present in all the blends despite the use of a very high injection pressure (180 MPa) but their impact on the oxygen permeability was negligible for the Vectra. RD501 blends and relatively small for the Vectra A950 blends.
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| 10. |
- Forsgren, Lilian, 1990, et al.
(författare)
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Injection Molding and Appearance of Cellulose-Reinforced Composites
- 2019
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Ingår i: Polymer Engineering and Science. - : John Wiley and Sons Inc.. - 0032-3888 .- 1548-2634. ; 60:1, s. 5-12
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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