In material-sensitive recycling of crushed reclaimed rubber materials, which is achieved by admixing the recycled rubber with new rubber matrices, a drop is noted in the mechanical value level of elastomers. This drop is due to deficient grafting of the recycled rubber with the fresh rubber matrix. To improve grafting quality, the particle surfaces are modified chemically in different ways following a comprehensive morphological and chemical characterization of select types of rubber powder. Grafting with maleic anhydride and grafting of reactive silane-based coupling agents following epoxidation or hydroxylation have shown themselves to be the most promising methods. The criterion applied to evaluate the suitability and effects of the surface modification is the level of or the observable changes in the material's mechanical properties, such as, for example, fracture stress and dynamic modulus.

Compounds of powder rubber based on NR/CB were produced by using the twin-screw extruder equipped with well-designed screw configuration. A significant increase of the output was achieved with increasing screw speed at moderate mixing temperatures, while retaining good material properties. In addition the development of the degree of dispersion, Mooney-viscosity and temperature along the extruder screw was studied. Several configurations of the latter were tested at constant parameters. A high mixing quality could be reached by one extrusion zone with appropriate mixing elements. Two extrusion concepts are proposed for the simplification of the continuous mixing process of powder rubber.

Based on the mentioned Powder Rubber system the fundamental technical questions concerning the present raw material concept, the production of the products as well as their characterization and physicochemical properties are discussed. For the application the attention directs next to the use of the material in the today's internal mixer and thereby to the acquirement of advantages in processing (e. g. reduction of mixing time and energy) as well as the improvement of the in rubber data. Finally a summary is given concerning the investigations carried out till now and the results received when using the products in a continuous mixing process.

Improved thermoplastic materials have been produced by application of cellulose II, microcrystalline cellulose or hemicellulose from renewable resources by simple extrusion with polypropylene and adding a small amount of a compatibilizer, or without a compatibilizer. Investigations were carried out on these materials and in addition on pure cellulose acylates by dynamic mechanical and thermal measurements. Good adhesion between cellulose and polypropylene was detected and a shift of the usable range of the materials to higher temperatures was observed. A correlation function between microscopic structural parameters and macroscopic properties of the cellulose derivatives has been introduced.

The solubility behavior of various elastomer additives, i.e. processing promoters (PRMs) was studied in EPDM, NBR and PP by using thermoanalytical and dynamic-mechanical methods. Binary rubber/thermoplastic blends containing selected PRM types were then investigated with regard to phase morphology, compatibilization and related final properties. The incorporation of some additives resulted in significant effects on the physical characteristics of the mixtures. It was demonstrated that the PRMs act as effective homogenizing agents, contributing to considerably improved dispersion and compatibility of the blend components.

The development of a continuous mixing process for natural rubber (NR) powder rubber compounds using the twin screw extruder is proposed, using an appropriate screw configuration taking advantage of the various types of screw elements used for conveyance and dispersive and distributive mixing. A further target of the study was a significant increase in the output, while retaining a good quality of process behaviour and material properties. Within the given limits of machine capacity, a gradual increase of the feed rate was successfully achieved with increasing screw speed at clearly moderate mixing temperatures. A markedly high degree of dispersion of filler of >95% was obtained for all compounds produced by varying the process parameters. Consistently, rheological and mechanical measurements revealed only negligible to weak differences between the sample properties. For comparison of results, compounds based on NR in both bale and powder form were prepared by the discontinuous mixing process. (C) 2001 IoM Communications Ltd.

Thermal, morphological and dynamic mechanical properties of polypropylene (PP)–cellulose fibre (CF) composites were investigated. Two types of CF and a compatibilizer were used. Calorimetric measurements exhibited an increase in the crystallization temperature and crystallinity of the PP component. This is attributed to the nucleating effects of the fibre surfaces, resulting in the formation of transcrystalline regions observed by an optical method. The dynamic mechanical spectra of the composites revealed an increase in the stiffness and a reduction in the damping values with an increasing CF content. The results are consistent with morphological observations, which verify an improved interfacial adhesion between fibre and matrix. The effects of drawing on the structure and physical properties of PP–CF composites were also studied. Increasing draw ratio, the melting peak of PP component was shifted to higher temperatures suggesting a constrained melting, and the uniaxial elastic modulus was considerably enhanced. The biggest influence was observed for the samples of PP–spun cellulose and the lowest for neat PP. In addition to the fibrillar structure of the oriented PP, the highly CF orientation and the efficient compatibilization in composites are responsible for the effects observed in the drawn samples.

The thermal and viscoelastic properties of polypropylene (PP)/cellulose as well as PP/Xylan composites were investigated by differential scanning calorimetry (DSC) and dynamic mechanical thermoanalysis (DMTA). Morphological aspects were available by using polarizing light microscopy and scanning electron microscopy (SEM). Three types of fillers were incorporated in PP: xylan fillers (XL), cellulose microfibers (CM) and short fibers of spun cellulose (CS). The compatibilizer maleic anhydride modified PP (MAPP) was added to the composites. The crystallization temperature and crystallinity of PP apparently increased in the presence of all fiber types. The cellulose fiber surfaces act as nucleating agents for PP, resulting in the formation of transcrystalline regions around the fibers. The DMTA spectra of PP/filler composites revealed a significant increase in the stiffness and a remarkable decrease of the damping values. This effect was stronger for PP/CS than for the other composites. The results verify that improved compatibility and interfacial adhesion between fiber and matrix markedly contribute to an improvement of the mechanical properties.

The thermal behavior and dynamic mechanical properties of isotactic polypropylene (PP) and reactor blend PP/ethylene-propylene copolymer (EPM), reinforced with different amounts of short glass fibers (GF) and/or polyester fibers (PETF), were investigated by differential scanning calorimetry (DSC) and dynamic mechanical thermoanalysis (DMTA) of imposed tensile load on rectangular film specimens. DSC measurements exhibited an increase of the crystallization temperature of PP in the presence of fibers, but indicated no change in its percentage of crystallinity. DMTA spectra revealed an increase in the stiffness and a decrease of the damping with increasing GF content. The positions of the primary relaxations of PP and EPM did not change, but a significant broadening of the α-relaxation in the crystalline phase was observed, due to the induced reinforcement and interfacial interactions. The addition of PETF to PP enhanced its damping values at low temperatures and promoted the α-transition. The DMTA behavior was studied in dependence on the preconditioning and the frequency excitation. Heat treatment changed the characteristics of the β-relaxation of PP, due to enhanced molecular motion of the polymer segments. The variation of frequency affected the secondary relaxations considerably and, in the presence of GF, the glass transitions. For the different relaxations, activation energies from peak shift and loss peak areas were determined. Experimental data of loss peaks were fitted to phenomenological equations. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 63: 1143–1154, 1997

The physical behavior of isotropic and oriented samples of an isotactic polypropylene (iPP)/ethylene–propylene–copolymer (EPM) reactor blend was studied by performance of dynamic mechanical measurements over a wide temperature range (DMTA). The influence of thermal history and drawing procedure was examined. The results showed that with increasing draw ratio the uniaxial elastic modulus of the material was considerably enhanced, whereas the intensity and strength of the amorphous relaxations of both components were reduced. At a certain draw ratio, the glass transtions of iPP and EPM phenomenologically merged and appeared as a single relaxation. The crystalline relaxation of iPP emerged with increased draw ratio at higher temperatures and was better seperated and easier to detect. The effects observed were attributed to the orientation of the crystallites in a fibrillar structure and to the restricted molecular mobility in amorphous regions. Measurements by differential scanning calorimetry (DSC) and x-ray diffraction of several drawn samples were performed to determine the effects of drawing on the melting behavior and the crystal orientation in the semicrystalline polymer. For comparison, some results of analogous studies on neat isotactic PP are presented and discussed. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 35: 1439–1448, 1997