Vinicius Pistor

Microstructure and crystallization kinetics of polyurethane thermoplastics containing trisilanol isobutyl POSS

The synthesis of thermoplastic polyurethanes (TPU) from the reaction of a NCO group-containing prepolymer and 0, 1.14, 1.71, and 2.28 wt% of trisilanol isobutyl polyhedral oligomeric silsesquioxane (POSS) was carried out in an instrumented batch mixer. The samples were characterized by thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), X-ray diffraction (XRD), and scanning electron microscopy (SEM). SEM analysis shows that the incorporation of POSS promoted strongly aggregation through physical interactions (formation of POSS-rich domains). Modifications in the TPU microstructure and the reduction in the crystal size were observed in the XRD diffractograms. The incorporation of POSS equally altered the TPU crystallization, and samples bearing higher concentrations of POSS formed two distinct types of crystalline structures. The kinetics of crystallization showed that nucleation strongly depends on the balance between TPU crystal formation and POSS-rich domains.

Degradation kinetics of ethylene propylene diene terpolymer residues devulcanized by microwaves

The reclaiming of elastomer residues is one of the main problems of recycling materials. In this work, the efficiency of devulcanization of recycled ethylene propylene diene terpolymer (EPDM) was determined by subjecting the elastomer samples to 2, 3 and 4 min of microwaves exposure. Scanning electron microscopy and thermogravimetric analysis using different heating rates to determine the kinetic degradation parameters according to the Flynn–Wall–Ozawa and Criado methods were studied. The results obtained showed that up to 4 min devulcanization exposure period, the degradation temperature of EPDM did not exceed. Microwaves exposure caused modifications in the morphology and reduction in activation energy values upon increased samples exposure period. Degradation mechanisms were altered, mainly for the 4-min exposure period, where the nucleation mechanism shifts to diffusion, suggesting that the microwave method was able to promote the breakage of the elastomeric three-dimensional network.

Thermal and Mechanical Characterization of a Terpolymer Mixture of Devulcanized Recycled Ethylene-Propylene-Diene and Low-density Polyethylene

In this study, mixtures of low-density polyethylene (LDPE) and the recycled elastomeric terpolymer ethylene-propylene-diene (EPDM-r) were obtained. The EPDM-r was incorporated as obtained by the manufacturer (vulcanized) and also after being submitted to a devulcanization process using microwaves. The mixtures were obtained with the use of bis(α, α-dimethylbenzyl) peroxide. The elastomeric residue was characterized by gel content and scanning electron microscopy, before and after the devulcanization process. The mixtures obtained were characterized by thermogravimetric analysis, differential scanning calorimetry, and mechanical tests for resistance to traction and impact. The results of the analysis of the residues showed that the devulcanization process reduced significantly the gel content of the elastomer. The mixtures obtained demonstrated that the incorporation of vulcanized EPDM-r reduced the crystallization and fusion enthalpies, while conserving the crystallization and fusion characteristics of the thermoplastic. The mixtures showed a reduction in the deformation and traction strength; however, the incorporation of devulcanized EPDM-r led to a significant increase in the elasticity modulus values and the resistance to impact in relation to the pure LDPE.

Influence of Processing Conditions on Productivity, Thermal and Rheological Properties of Reprocessed Low Density Polyethylene

Abstract The market for recycled thermoplastic polymers is undergoing a sharp increase, although recyclate polymers are regarded as materials with inferior properties when compared to the virgin material. This study investigates the behavior of non-contaminated scraps of low density polyethylene (LDPE) from the plastic packaging industry after single processing stage, in terms of the productivity and the thermal and rheological properties. The LDPE used was reprocessed on a single-screw extruder (Miotto) of 90 mm screw diameter and L/D = 25. Three screw speeds (80, 90 and 100 min−1) were investigated at three processing temperatures (200, 250 and 300°C). The reprocessed materials were characterized by thermogravimetric analysis TGA, parallel plates rheometry and productivity. The results obtained by TGA showed a typical range of polyolefin degradation (350 to 450°C). The viscoelastic properties did not show significant changes in relation to the rheological behavior. Increasing the temperature and screw speed promoted a productivity gain of approximately 30%. This suggests that under the conditions studied it is possible to reprocess this material with good productivity ensuring its thermal, mechanical and rheological properties.

Thermal and Rheological Properties of Poly(ethylene-co-vinyl acetate) (EVA) Nanoclay

Poly(ethylene-co-vinyl acetate) (EVA) is a copolymer of utmost importance in nanocomposite applications. Clay dispersed in an EVA matrix was tested using different types of clays with hydrated silicate layers. Several observations have led to the unexpected physical point of view of (clay/polymer) interaction. Due to the polar nature of the acetate group, a strong interaction would be expected when using a polar group-bearing surfactant such as organophilic modified montmorillonite (OMMT – 30B). Through research using techniques that explore the rheology in the molten state, it was evident that a stronger interaction is possible for nonpolar group-modified organophilic clays. This strong interaction is the result of a complex environment of physical entanglements that show a pseudo-solid behavior among the nanoclay dispersed in the EVA matrix. In this chapter, we will emphasize the influence of processing and type of organic modifier in natural organophobic clay (Cloisite® Na+) dispersed in an EVA matrix. The characterization techniques will be discussed by the study of melt state rheology and thermal behavior of these materials. The relaxation phenomena and creep compliance behavior as well as a correlation between the processing and final properties are detailed for EVA and OMMT nanocomposites.

Influence of Functionality of Polyhedral Oligomeric Silsesquioxane (POSS) Dispersed in Epoxy Resin for Application in Hybrid Coating

The present study aimed to characterize the structure of nanocomposites obtained from the incorporation of three different polyhedral oligomeric silsesquioxane (POSS) in an epoxy resin. glycidylisobutyl-POSS, triglycidylisobutyl-POSS and glycidyl-POSS were added (5% by weight) in an epoxy matrix, diglycidyl ether of bisphenol-A (DGEBA), through a sonication process. The nanocomposites were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and dynamic mechanical analysis (DMA). The XRD analysis presented a characteristic peak of POSS. The incorporation of glycidylisobutyl-POSS showed a significant increase in the value of glass transition temperature (Tg), being also the most effective in terms of dispersion. It should also be noted that glycidyl-POSS presented a greater influence on the thermal stability.

Influence of two different molecular weight epoxy resins on the glass transition of composites manufactured with expanded graphite

Developing composites of epoxy resins containing graphite is important for technological and scientific research. The applications of these systems in electronic devices have been seen as a promising research field. To contribute to this field, we evaluated the influence of exfoliated graphite dispersed in two resins with different molecular weights (Mw). The glass transition was estimated by dynamic-mechanic analysis (DMA) and the modulated differential scanning calorimetry (MDSC). We calculated the parameters of the phantom model, Williams–Landel–Ferry (WLF) and Vogel–Fulcher–Tumman (VFT) equations, and the parameters correlated with the Angell fragility. The results demonstrated a strong influence of the Mw on the glass transition and its crosslinking density. A more homogeneous system with lower fluctuations of potential energy was achieved with higher Mw resin suggesting advantageous for the structural stability of crosslinking.

Influence of stabilizer additives on thermochromic coating for temperature monitoring

Compounds based on smart materials are functional structures that can be used as thermochromic sensors for temperature monitoring in equipment such as pipelines, motors, and heat exchangers. We developed thermochromic coatings based on 1,3,3-trimethylindolino-β-naphthopyrylospiran acrylic polyurethane with and without 2-(2H-benzotriazol-2-yl)-4,6-ditertpentylphenol photostabilizer additives and antioxidant butylated hydroxytoluene and applied them on stainless-steel plates by the spray lay-up method. The samples were analyzed using a weathering chamber with UVA and UVB radiation to monitor their degradation process, revealing complete degradation of the coating without antioxidant and photostabilizer, leading to loss of its thermochromic characteristic.