Pentti Järvelä

Multicomponent compounding of polypropylene

The simultaneous compounding of polypropylene with several mineral fillers was investigated. The mineral fillers were selected on the basis of their size and shape which was spherical (glass beads), sheet-like (mica) or fibrous (wollastonite). In addition, one filler with a considerably smaller particle size (fly ash) was selected. The results of single components were as expected. In multicomponent compounding, the best mechanical properties were attained by the simultaneous use of two or more fillers. This was true for all mechanical properties. In the light of the results, it is evident that the need for a matrix polymer and other fillers can be reduced by the use of a filler with a small particle size without impairing the mechanical properties of the composite. It seems that multicomponent compounding yields somewhat better properties than single-component mineral compounding of thermoplastics. In practice, multicomponent compounding is possible using the same process as for single-component compounding.

Melt rheological properties of polypropylene-maleated polypropylene blends. I. Steady flow by capillary

Melt rheological properties of blends of polypropylene (PP) and PP grafted with maleic anhydride (PP-g-MA) are studied using a capillary rheometer. A pseudoplastic flow behavior is observed. The pseudoplasticity of the melt reduces with an increase of PP-g-MA content and/or temperature. The PP-g-MA component in the blend acts as decreasing melt viscosity, especially in the lower shear rate region, while the addition of PP-g-MA to PP does not cause obvious increase of die swell ratio.

Natural fiber-based reinforcements in epoxy composites processed by filament winding

Single natural fibers have rather high mechanical properties; especially, Young’s modulus can be as high as for E-glass fibers. However, the good properties of natural fibers are not exploited efficiently in existing applications. Continuous fibers are required for high-performance applications. Filament winding is a method to produce aligned technical composites which have high fiber content. This work studied the mechanical properties of natural fiber yarn-reinforced composites. Flax and viscose fiber tubular composite samples were produced by filament winding and their properties were compared with the properties of E-glass fiber composites. The flax fiber yarn could be wound to produce a relatively stiff composite tube but poor adhesion between the matrix and fibers affected the properties. The properties of the E-glass fiber composites were superior in comparison to the flax fiber composites. However, the results from the split disk tensile test were competent, although they were only 25–29% of the properties of the E-glass fiber composites. Water absorption and impact strength were notably the weakest properties of the flax fiber composites. The viscose yarn could be wound into a composite tube but the composite was too brittle for machining specimens. In order to develop the structural natural fiber composites, the adhesion and the wet-out of the fibers should be improved.

Methodology for determining the degree of impregnation from continuous glass fibre prepreg

Abstract A procedure to determine the degree of impregnation from melt-impregnated polypropylene/glass fibre prepreg has been developed. The prepeg sample is moulded in an embedding agent, ground and coloured with colouring agent penetrating to the space between unimpregnated fibres. The sample is studied with an optical microscope and transillumination is used. Unimpregnated fibres are calculated individually. Moulding the specimens with embedding agent, grinding and preparing the specimens with colouring agent, postgrinding, study of the specimens and the calculations to determine the degree of impregnation are described.

Dynamic mechanical and mechanical properties of polypropylene/poly(vinyl butyral)/mica composites

Three-component composites consisting of polypropylene (PP) matrix, poly(vinyl butyral) (PVB) modifier, and mica filler at various ratios of matrix to modifies and a constant mica content (30 wt %) were prepared by using two different kinds of PVB, viz., PVB and PVB-P. By correlating with the morphology, the dynamic mechanical and mechanical properties of the composites are studied in detail. PVB component in PP/PVB/mica composites cannot display a reinforcing effect to PP/mica binary composites, while impact strength of the composites are reduced further. It associates with incompatibility between PP and PVB, and as well as higher glass transition temperature of PVB. For PP/PVB-P/mica composites, stiffness decreases and, meanwhile, impact strength increases when PVB-P content is 7 wt %. The improvement of impact strength on PP/mica binary composites at the composition is due to a little affinity between the PP matrix and the plasticizer of PVB-P. Moreover, a minor amount of PP-g-MA in the 63/7/30 PP/PVB/mica composites only acts as an adhesion promoter.

Effect of viscose fabric modification on the mechanical and water absorption properties of composites prepared through vacuum infusion

Viscose fabric-reinforced unsaturated polyester composites were successfully prepared through vacuum infusion process. Unidirectional viscose fabric was modified by two different organosilane coupling agents and by acetylation treatment. The main objective was to study the influence of fabric treatment on the mechanical and water absorption properties of the composites. Flexural, tensile and impact properties of composites were studied. The results from mechanical testing of composites pointed out that 3-aminopropyltriethoxy silane treatment increased the flexural and impact strengths of the composites with respect to untreated fabric composite. The impact strength of 3-aminopropyltriethoxy silane-treated fabric composites almost doubled compared to the value of untreated fabric composite. Among all the composites under study, those with fabrics treated by 2 vol% 3-aminopropyltriethoxy silane in ethanol/water (95:5) solution exhibited significant improvement in water uptake resistance. An unsaturated polyester gelcoat and topcoat were applied as the outer surface on the composites with untreated fabric. This was done in order to investigate the visual surface appearance and evaluate the gelcoat and topcoat effect on water absorption after accelerated water immersion test. The regenerated cellulose fibre as reinforcement shows high potential to be used as an alternative for natural bast fibres, especially, when toughness of material matters. Chemical treatment of regenerated cellulose fibres could result in improvement in properties of polymer composites, considering that the appropriate treatment method is selected for the corresponding fibre–matrix system.

Coating plywood with a thermoplastic

This work presents a method for the surfacing of wood sheets such as plywood with melt processable thermoplastic using extrusion coating. The method uses a direct coating of the plywood with a very hot low-viscosity coating. During the coating, the pressure of the melt is kept as low as possible. These factors produce a very high mechanical adhesion between the coating and the wood. In addition, the coating method uses a tool for preventing the formation of holes in the surface by the penetration of air expanding and water evaporating from the wood pores through the coating. In this work the method was applied to coating plywood with a copolymer of polypropylene. The adhesion between the wood and the polypropylene was improved by blending the polypropylene with maleated polypropylene wax. The experiments showed that the method produces sound and smooth polypropylene coated plywood. Addition of a modifying agent improves the adhesion between the polypropylene and the wood.

Polyamide 6/wollastonite composites: Strength properties and their dependence on humidity and temperature

The use of wollastonite as a reinforcement for polyamide 6 (PA 6) composites was evaluated using various mechanical test methods. The results suggest that wollastonite acts as a reinforcement for PA 6 at concentrations in the range 25 to 40 wt%, because it increases strength, stiffness and impact strength. Increases of 20 to 200% in these properties were obtained for these wollastonite concentrations. This reinforcing effect was observed when the composite was not exposed to any humidity or temperature treatment; such treatments were found to cause a deterioration in interfacial adhesion as concluded from scanning electron microscopy observations. In conclusion it seems that the present surface treatment system of the wollastonite may be improved and so better the long-term properties of PA 6/wollastonite composites in severe conditions. The short-term tests, however, show that the wollastonite reinforces PA 6, i.e. increases the strength, stiffness and impact strength when it is not exposed to any humidity or temperature treatments.

A method to measure the fusion strength between expanded polystyrene (EPS) beads

Cellular polystyrene (EPS) is the most commonly used cellular thermoplast whose main applications are insulation and packages. One of its new applications is core material in building elements, and this poses higher requirements for strength. This is particularly evident in self-supporting roof elements. This study presents a method for determining the fusion strength between beads in cellular polystyrene and the dependence of this strength on processing. This method has also enabled us to determine the adhesion of cellular polystyrene beads to other materials, such as glass fibre, and it allows measurement of the fusion strength between EPS beads without the influence of porosity. Fusion strength was found to have a characteristic behaviour. It has an absolute upper limit, and fusion forces approximate this limit asymptotically as heating time is prolonged (this increase is dependent on the energy content of the steam).

Mechanical strength and thermal stability of magnesium silicate filled polypropylenes

Mineral fillers are widely used to improve the mechanical properties of polypropylene, but at the same time they may cause some degradation of polymer, especially if the stabilization is insufficient. Two different kinds of silicate minerals, talc and serpentinite, were used as fillers for homo- and copolypropylene, and their influence on mechanical properties and degradation was investigated. The mechanical properties of filled polypropylene were tested at room temperature using tensile and impact tests. GC-MS technique was used to characterize the degradation of compounds. The results revealed differences in the mechanical properties: talc filled polypropylene had higher tensile strength, rigidity and impact strength properties than serpentinite filled. The oxidation stability of filled polypropylene measured by the oven method showed lower values in the case of serpentinite filled polypropylene. In the beginning of pyrolysis there was no significant difference between talc and serpentinite filled polypropylene in the formation of degradation products, as was observed by GC-MS. In a slightly higher temperature and longer incubation time PP-serpentinite compound started to form more small molecular weight degradation products than PP-talc due to stronger catalytical effects of the serpentinite surfaces. The characterization methods used here provided us new information to understand the role of mineral fillers in degradation processes. The results of DSC measurement yielded information on the effects of the filler crystallization and thermal degradation. Talc, for example, was shown to be better nucleation agent than serpentinite for PP.