Victor Jayme Roget Rodriguez Pita

Effect of Weathering and Accelerated Photoaging on PET/PC (80/20 wt/wt%) Melt Extruded Blend

In this study we investigated the natural weathering of a catalyzed blend of poly(ethylene terephthalate)/polycarbonate PET/PC (80/20wt/wt%). The results were compared to the accelerated photoaging tests. The specimens were characterized by wide angle X-ray diffraction (WAXD), optical microscopy (OM), thermogravimetry (TG/DTG), medium infrared spectroscopy (FT-IR) and stress-strain analysis. The OM analysis revealed the coexistence of at least three phases – one rich in PET (matrix), the other rich in PC (dispersed droplet) and an interfacial region between them, made of PET/PC copolymer (compatibilizing agent) produced in situ. The TG/DTG curves showed that UV radiation acted mainly on the PET-rich phase and the PET/PC copolymer. The OM and TG/DTG results indicated that the degradation of the compatibilizing agent has had a critical effect on the mechanical properties. For both types of aging (natural and accelerated), the PET’s carbonyl index decreased with the exposure time. The FT-IR results corroborated what was seen in the OM images, showing that the PET phase acts as a shield against the PC degradation. Under accelerated aging, the mechanical properties decreased abruptly - mainly the stress-strain at yield and break - due to the degradation of the in situ compatibilizing agent.

Thermal Degradation Behavior, Permeation Properties and Impact Response of Polyethylene/Organo-montmorillonite/(Ethylene Methacrylic Acid) Ternary Nanocomposites

Through this work we explored the effect of melt compounding a commercial grade of HDPE with organoclays of different precedence using EMAA as compatibilizing agent on the thermal behavior, barrier properties and biaxial impact response of composites. Morphology was examined by XRD and TEM. Crystalline structure was examined by DSC. Thermal behavior was evaluated by TGA. Barrier properties to low-molecular-weight penetrants were experimentally determined employing a gravimetric technique. Mechanical properties under impact conditions were evaluated by instrumented puncture tests. Intercalated nanocomposites were obtained. Throughout the thermal degradation of the nanocomposites in oxidant atmosphere a charring process of the PE, which is normally a non-char-forming polymer, was observed. The addition of OMMT improves barrier properties due to its contribution to tortuosity path and to the reduction of molecular mobility. Impact properties were only slightly reduced by nanocomposite formation. Results demonstrate that EMAA did not improve exfoliation, but it enhanced polymer–organoclay interactions giving rise to better thermal and permeation properties, without detriment of impact response.

Preparation, Physical and Mechanical Characterization of Montmorillonite/polyethylene Nanocomposites

In this paper, we report the preparation of polyethylene composites with organically modified montmorillonite. Three different Na+-montmorillonites were modified in order to obtain organoclays and two grades of high-density polyethylene were used as composite matrices. All composites were prepared by melt blending, and their physical and mechanical properties were thoroughly characterized. The extent of clay platelet exfoliation in the composites was confirmed by X-ray diffraction (XRD). Mechanical properties under static and impact conditions were evaluated to assess the influence of the reinforcement on the properties of polyethylene.

Processamento de amido de milho em câmara de mistura

Corn starch/water mixtures at compositions of 70:30, 80:20 and 90:10 (w/w %) were submitted to processing at 90oC and different rates (20, 40, 80 and 100rpm) in an internal mixer (Rheomix 600), equipped with counter-rotating roller type rotors. The effect of the water content and of the rotation rate on the starch processing was investigated by torque and temperature curves given by the in-line Rheocord 9000 torque rheometer. Viscosity measurements, carried out in a Rapid Visco Analyser (RVA), and optical microscopy analysis were performed on the processed samples to complement the rheometry data. The results indicated that the water content and the rotation rate had a significant effect on the characteristics of the processed starch samples. For compositions with 10 and 20% (w/w) water contents and processed at 80 and 100rpm, degradation was observed at a larger extent. For compositions in which water had been added at a 30% (w/w) content, its plastifying property contributed to minimize degradation caused by mechanical and thermal inputs. In these cases, the granular structure of starch was largely preserved.

Effect of the Organoclay Preparation on the Extent of the Intercalation/Exfoliation and the Barrier Properties in Polyamide-6/Montmorillonite Nanocomposites

This paper shows the importance of the clay surface chemistry in the preparation of nanocomposite materials. An Argentinean montmorillonite was used for preparing two modified clays. The filosilicate was intercalated with a quaternary ammonium salt derived from ε- caprolactam to obtain an organofilic material. The other modification was introduced by mixing the clay with hexadecyl trimethyl ammonium chloride. Thus, the polyamide 6 ability in dispersing clays was applied to prepare composites with the intercalated clays. The polyamide 6/clay dry composites with 3 wt % of filler were prepared by melt processing in a mixer chamber. Composites of polyamide 6/organoclay were characterized by X-ray diffraction, transmission and scanning electron microscopy and thermogravimetry. The barrier properties were determined by cyclohexane pervaporation. The results show that the dispersion and degree of delamination depend on a proper chemical treatment and the clay content influences the polyamide 6 nanocomposites solvent pervaporation resistance.

Water vapor permeability and tensile properties of poly(l-lactic acid)/synthetic mica nanocomposites prepared by melt blending

Poly(L-lactic acid)/synthetic mica (Somasif) nanocomposites were obtained by melt blending in a mixing chamber according to a factorial experimental design and considering the following variables: temperature, rotor speed, nanofiller concentration and residence time. Relatively high degree of dispersion was attained by the melt processing which generates poly(L-lactic acid)/synthetic mica nanocomposites with particle size even in the order of 40 nm. The tensile properties and the water vapor permeability of these nanocomposites were evaluated. The introduction of synthetic mica into neat poly(L-lactic acid) decreased the water vapor permeability by about 50%. The variables which most affected the tensile properties were the mixing time and clay concentration, but the levels studied or the degree of intercalation/exfoliation were insufficient to significantly improve the tensile properties of poly(L-lactic acid)/somasif mica nanocomposites.

Processability, morphology and thermal behavior of poly(lactic acid)/synthetic mica nanocomposites obtained by melt blending

Poly(lactic acid)/synthetic mica nanocomposites were obtained by melt blending in an internal mixer in an investigation designed by experimental factorial planning. The results indicated that low speeds and temperatures favoured intercalation. In the range of concentrations tested (3–7 wt%), the added mica did not act as a nucleating agent, and it produced no significant change in the thermal properties of the poly(lactic acid). The thermogravimetric analyses suggested that temperatures below 190℃ and short mixing times (<10 min) promoted better dispersion of the synthetic mica in the matrix nanocomposite.