Antal Boldizar

Prehydrolyzed Cellulose as Reinforcing Filler for Thermoplastics

Abstract This paper presents the results of an experimental study of the mechanical properties of composites consisting of prehydrolyzed cellulose and thermoplastic matrices. The main feature of prehydrolyzed cellulose fibres is a high degree of brittleness, permitting the fibres to be finely comminuted in the shear field of normal compounding and processing machinery. Such an effect can be anticipated to improve the homogeneity and the mechanical parameters of the moulded samples. In the present work, this has been demonstrated with PP, HDPE and PS containing varying amounts of prehydrolyzed cellulose of different origin (bleached pulps). The tests were done on injection moulded samples. The compounding method (Buss-Kneader vs. twin-screw extruder) had only minor influence on the results. Theoretical assessment of the modulus values using the Tsai–Halpin equation gave somewhat lower values than those recorded on experimental samples. This was interpreted in terms of the disintegration of the cellulose co...

Simulated recycling of post-consumer high density polyethylene material

Abstract Post-consumer high density polyethylene (HDPE) was examined by a test procedure consisting of repeated cycles of alternating extrusion and subsequent accelerated thermo-oxidative ageing. The material studied was collected from a real waste stream of HDPE bottles. The effect of addition of a commercial re-stabiliser was also studied. The material was evaluated in terms of mechanical and chemical properties, such as elongation at break, tensile strength, melt flow rate, oxygen induction temperature and molar mass distributions. The results show that after simulated recycling the HDPE material still has considerable resistance against thermal degradation. Upon an additional period of accelerated ageing the stability of the material was still high. The presence of re-stabiliser, introduced during extrusion in the simulated recycling procedure, increased the resistance to subsequent thermo-oxidative ageing. However, significant crosslinking and/or molecular enlargement were found.

An analysis of the composition and metal contamination of plastics from waste electrical and electronic equipment (WEEE)

The compositions of three WEEE plastic batches of different origin were investigated using infrared spectroscopy, and the metal content was determined with inductively coupled plasma. The composition analysis of the plastics was based mainly on 14 samples collected from a real waste stream, and showed that the major constituents were high impact polystyrene (42 wt%), acrylonitrile-butadiene-styrene copolymer (38 wt%) and polypropylene (10 wt%). Their respective standard deviations were 21.4%, 16.5% and 60.7%, indicating a considerable variation even within a single batch. The level of metal particle contamination was found to be low in all samples, whereas wood contamination and rubber contamination were found to be about 1 wt% each in most samples. In the metal content analysis, iron was detected at levels up to 700 ppm in the recyclable waste plastics fraction, which is of concern due to its potential to catalyse redox reactions during melt processing and thus accelerate the degradation of plastics during recycling. Toxic metals were found only at very low concentrations, with the exception of lead and cadmium which could be detected at 200 ppm and 70 ppm levels, respectively, but these values are below the current threshold limits of 1000 ppm and 100 ppm set by the Restriction of Hazardous Substances directive.

On PVT and Rheological Measurements of Polymer Melts

Abstract The relation between PVT and rheological measurements of several polymer melts including polyethylenes, polypropylene, polystyrene, poly(methyl methacrylate), and polycarbonate has been taken into investigation. Pressure-temperature dependent viscosities, determined on rotational and backpressure-modified capillary rheometers, were fitted through the Carreau-Yasuda model. PVT data was analyzed by the help of the Simha-Somcynsky equation of state (SS EOS). The thermodynamical parameters of the SS EOS were connected to constant-stress viscosity (experimental) and zero-shear viscosity (extrapolated). The Doolittle relationship was modified into the form of η = exp(C1 ln(h′h)). The relation was employed and tested for the data evaluation. It proved to be a good tool for linearization of PVT and rheological data.

Processing and Water Absorption Behavior of Foamed Potato Starch

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.

Processing and Properties of Expanded Starch Materials

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.

On the stress-strain behavior of thermoplastic starch melts

Abstract 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 appeared to promote the drawability of the melt.

Antimony leaching in plastics from waste electrical and electronic equipment (WEEE) with various acids and gamma irradiation

There has been a recent interest in antimony since the availability in readily mined areas is decreasing compared to the amounts used. It is important in many applications such as flame retardants and in the production of polyester, which can trigger an investigation of the leachability of antimony from plastics using different acids. In this paper, different types of acids are tested for their ability to leach antimony from a discarded computer housing, made of poly(acrylonitrile butadiene styrene), which is a common plastic type used in electrical and electronic equipment. The acid solutions included sodium hydrogen tartrate (0.5M) dissolved in either dimethyl sulfoxide or water (at ca. 23°C and heated to ca. 105°C). The metal content after leaching was determined by inductively coupled plasma optical emission spectroscopy. The most efficient leaching medium was the heated solution of sodium hydrogen tartrate in dimethyl sulfoxide, which leached almost half of the antimony from the poly(acrylonitrile butadiene styrene). Gamma irradiation, which is proposed to improve the mechanical properties in plastics, was used here to investigate the influence of antimony leaching ability. No significant change in the amount of leached antimony could be observed.

Melt processing of wood cellulose tissue and ethylene-acrylic acid copolymer composites

Abstract The difficulty of feeding cellulose fibers together with the polymer into the melt processing equipment is a serious disadvantage for the production of cellulose-containing composites on a large scale. In the present work, a continuous method of feeding cellulose in the form of a tissue into a twin-screw extruder through an opening downstream of the extruder cylinder was studied. With this method, composites with different fiber contents were obtained. The tissues used were one made mainly of softwood fibers and another mainly of hardwood fibers. In order to better understand how to improve the fiber dispersion by melt mixing, a second extrusion was performed with a single screw extruder with a barrier-flighted screw and also with the twin-screw used to compound the tissue with the polymer. The compounds produced were then injection molded into test bars. The test bars containing the softwood tissue exhibited some fiber aggregates also after a second extrusion, whereas no fiber aggregates were observed in samples made with the tissue containing hardwood fibers and two passes through the twin screw. The fiber length was in general reduced by each melt processing stage and the shortest fiber length was observed after two extrusions with the twin-screw and injection molding. The tensile modulus increased with increasing fiber content. A higher stiffness was obtained with more softwood fibers in the tissue whereas more hardwood fibers gave a higher tensile strength and greater elongation at break.

Barrier Screw Compounding and Mechanical Properties of EAA Copolymer and Cellulose Fiber Composite

Abstract The difficulty of feeding cellulose fibers and thermoplastics into the extruder or injection molding machine is addressed, this being a serious problem in the production of cellulose fiber composites for industrial applications. Agglomerates consisting in cellulose fibers and ethylene-acrylic acid copolymer (EAA) with different cellulose contents and different fiber lengths were processed with two different screws in order to better understand how the dispersion of the fibers can be improved by melt extrusion. A conventional screw with a compression ratio of 4:1 and a screw with barrier flights were used at different screw rotation speeds. The fiber length and fiber content were measured and microscopic analyses were performed in order to estimate the number and size of the cellulose fiber aggregates in the final composites. It was concluded that the barrier screw was more effective than the conventional screw in breaking up the fiber aggregates and dispersing the fibers. More but smaller cellulose aggregates were observed when the barrier screw was used, and the reduction of length was significantly greater for long than for short fibers. In contrast to that was expected, the samples containing the shorter fibers had better mechanical properties, probably due to a better dispersion of the fibers.