Ricardo Vinicius Bof de Oliveira

Caracterização viscosimétrica de nanocompósitos híbridos PS/POSS

Polystyrene (PS) and polyhedral oligomeric silsesquioxanes (POSS) hybrid nanocomposites with different compositions were obtained by reactive melt processing using dicumyl peroxide (DCP) as initiator in the presence or absence of styrene as radical transfer agent. The materials were characterized by viscosimetry by means of gel permeation chromatography (GPC) using triple-detector: light scattering, viscometer and refractive index. PS/POSS samples processed with styrene showed higher weight average molecular weights (Mw) and lower polydispersity indexes (Mw/Mn), as a result of higher PS-POSS conversion (28-40%) and lower PS degradation, as compared to the PS/POSS samples processed without styrene in which the degree of conversion was lower (24-28%). For the PS/POSS solutions in THF, the parameters of the Mark-Houwink-Sakurada equation, α ≅ 0.7 and log K ≅ -3.5 to -3.9, and the values of polymer-solvent interaction parameter, χij ≅ 0.49, were not changed with respect to changes in molecular size. On the other hand, these changes were characterized by a cumulative function of the mass fraction of chains as a function of the root mean square end to end distance ( 01/2).

Influence of glycerol on morphology and properties of polylactide/montmorillonite nanocomposites

The widespread use of polymers from renewable sources is currently unachievable, not only by economic constraints but by the limiting properties of this type of material. Several strategies have been developed to overcome this problem; one of the most extensively explored is the use of nanofillers to improve the biopolymer’s properties such as stiffness, impact strength and gas barrier, amongst others. However, several gaps in understanding the morphology formation of these systems still exist. This study evaluates the use of glycerol as an auxiliary additive during production of polylactide/montmorillonite nanocomposites. In this study, the presence of glycerol seems to influence the nanocomposites’ morphology, influencing the clay exfoliation in some cases, and the mechanical properties. On the other hand, the presence of glycerol seems to induce a greater molecular weight reduction during twin screw extrusion.

Reactive processing of a non-additivated isotactic polypropylene: mechanical and morphological properties on molten and solid states

Isotactic polypropylene (iPP) is a thermoplastic with several desirable properties as it can be modified by additives and processing, making it one of the most versatile and popular polymers. In this context, we present a detailed study of morphological and mechanical properties of non-additivated iPP produced by reactive processing, mainly concerning the effect of controlled radicalar degradation on polymer structure in molten and solid states. Melt rheology and size exclusion chromatography analyses evidenced the reduction on viscosity and moduli in dependence of molecular weight by the addition of commercial peroxide. The behavior in solid state showed that smaller chains of degraded iPP at high temperatures exhibited greater mobility resulting in a more viscous response upon a mechanical loading. Moreover, β-form crystals were suppressed by molecular weight reduction as suggested by X-ray diffraction. This finding suggests that smaller chains have higher mobility, and consequently are less susceptible to shear deformations during processing.

Mistura polipropileno/poliestireno: um exemplo da relação processamento-estrutura-propriedade no ensino de polímeros

Polymer blends remain an important research topic in different areas, in spite of innumerous studies over the years. In particular, mixtures of polypropylene and polystyrene are among the most studied, mainly owing to their low cost and technological relevance. In this work, the students enrolled in the discipline Polymer Processing I (PG24) in the Materials Science Graduate Program (PGCIMAT-UFRGS) produced blends of polypropylene and polystyrene, where all polymer processing steps were performed during lab classes. Then, each student undertook a characterization procedure with a specific technique, which included samples preparation, the analysis itself and discussion of the results. Subsequently, the results were confronted in the classroom, where we sought the correlations. Finally, all students reviewed this article, including suggestions and criticisms. As expected, the mixture of polystyrene and polypropylene formed an immiscible blend. Furthermore, the processing affected the characteristics of the polymers, leading to a reduction in molecular weight, and as a result a drop in its physical properties. In the PP/PS mixtures, phase separation produced PS domains with micrometers in size, and low adhesion to the PP matrix, which explains the loss of mechanical properties.

Polyamide worm gear: manufacturing and performance

The focus of this paper is to establish a characterisation method for seven polyamide (PA) grades to determine the major material to manufacture an automotive worm gear. The composite properties were measured according to the worm gear loadings: tensile strength, Youngs modulus, abrasion and impact resistance. They were also correlated to the PA moisture absorption and its glass fibre (GF) reinforcement. The data from mechanical tests were applied in the finite element analysis (FEA) using the von Mises stress criterion. Before the rig tests of the PA worm gears, the injection process was evaluated, through the capillary rheometry. A higher difficulty to process PA 6/6 30% GF was found, due to its lower apparent viscosity. In the end, the influence of moisture absorption was as decisive to the gears material selection as the GF to the pinion. Thus, the PAs with the best performance were: PA 6 with 30% GF (gear) and with PA 60% GF (pinion).

HIGH-IMPACT PP NANOCOMPOSITES: INFLUENCE OF CLAY CONTENT ON MECHANICAL AND THERMAL PROPERTIES

The preparation of high-impact polypropylene nanocomposites with different organo-montmorillonite (O-MMT) contents by means of meltprocessing was investigated. The nanocomposite properties were evaluated by transmission electron microscopy (TEM), flexural modulus, izod impact strength, dynamic mechanical analysis (DMA), differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). It was noticed that the PP/O-MMT nanocomposites properties were affected by clay content. Exceptional improvements in impact strength were obtained (maximum of 185%) by the use of low O-MMT content. The results showed that higher enhancement on mechanical/thermal properties was obtained by 3 wt.% of O-MMT instead of higher quantities.

Recuperação hidrofóbica de polipropileno tratado por VUV ou plasma

Surface treatments using plasma and vacuum ultraviolet radiation (VUV) were used to introduce oxygen-containing functional groups in samples of polypropylene, in order to modify its wettability. ATR-FTIR, AFM and contact angle (CA) measurements were used to analyze the chemical and physical changes on the PP surface as a function of time. The results showed changes in wettability of the VUV-treated samples mainly due to chemical modification of the surfaces. For plasma-treated samples, aging occurred faster than for the VUV-treated ones. For both treatments, a rearrangement of the polymer chains during aging has probably occurred, with possible crosslinking of surface macromolecules for the VUV-treated samples.