P. Pagès

Effects of different treatments on the interface of HDPE/lignocellulosic fiber composites

Abstract We studied the chemical and mechanical characteristics of composites made up of HDPE (high-density polyethylene) and lignocellulosic fibers (in the presence or absence of a coupling agent). Interfacial morphology and esterification reactions between aspen fibers and the coupling agent were analyzed by means of Fourier Transform Infrared Spectrophotometry (FTIR) and Scanning Electron Microscopy (SEM). The variation of absorption in spectral bands (related to water absorption, glycosidic bonds in the cellulose backbone, hydroxyl and vinyl contents, and the formation of ether bonds) was determined in order to assess the influence of the coupling agents as well as the lignocellulosic fiber content. SEM micrographs were used in order to show the “bridge effect”, brought about by the coupling agent between the HDPE matrix and the reinforcement of lignocellulosic fibers. Mechanical properties, such as tensile strength, Young modulus, elongation at breaking point and toughness, were also analyzed. Finally, the differences observed between the various composites studied were explained by some specific adhesion mechanisms (including interdiffusion, adsorption-wettability and chemical bonds).

Artificial aging of high-density polyethylene by ultraviolet irradiation

Artificial aging of high-density polyethylene exposed to UV irradiation, with wavelength close to 350 nm, in the presence of air, has been studied in this paper. Such irradiation is one of the environmental factors which affect most to weather exposed polyethylene. The structural modifications and chemical changes experienced by the polymer by the application of Fourier-transform infrared spectrophotometry (FTIR), mainly polymeric chain breaking, branching and oxidation, have been studied. The variation of crystallinity has also been determined by FTIR. Finally, the evolution of the mechanical properties versus the irradiation time has been closely followed.

Thermogravimetric analysis of polystyrene: Influence of sample weight and heating rate on thermal and kinetic parameters

This article studies the influence of the heating rate and sample weight on the thermal decomposition of polystyrene (first-order kinetics). For this purpose, the kinetic parameters (i.e., frequency factor and activation energy), variables at the maximum decomposition rate (such as conversion, reaction rate, and temperature), as well as some characteristic temperatures have been determined for a series of experiments where the heating rate varies (0.5–11.5 K/min) and also, the sample weight (6.0–25.1 mg). Some mathematical equations have been developed that allow: (1) evaluation of the activation energy of thermal decomposition by different ways and comparing the results obtained; (2) relating different parameters between themselves, such as the heating rate with the temperature at the maximum decomposition rate or the frequency factor with the heating rate and sample weight. Finally, some theoretical explanations of the variation of thermal and kinetic parameters have been proposed.

STUDY OF THE CURING PROCESS OF AN EPOXY RESIN BY FTIR SPECTROSCOPY

The curing process of an epoxy resin of glycidic polyether by Fourier transform infrared spectroscopy has been studied. The influence of the hardener/resin ratio, temperature, and curing time have been determined. This article discusses which bands of the infrared spectrum and what relation of their absorbances are most convenient to monitor the resin-curing process.

Study on polypropylene–polyethylene-based copolymer solidification

In the present work, nonisothermal crystallization is analyzed. Concretely, we study the solidification process of polypropylene–polyethylene-based copolymers by means of differential scanning calorimetry (DSC). Several samples with different additives are subjected to artificial aging processes. The calculation of the specific surface energy, σ, is in good accordance with the results reported in the references. The artificial aging is responsible for a slight increase of σ values (i.e., increase of 1.6 kJ · m−2 for sample A and 0.3 kJ · m−2 for sample B). On the other hand, the σ value of sample B is considerably lower than that of samples A, C, and D (i.e., 17.3 kJ · m−2 for sample B versus an average value of 23.0 kJ · m−2 for the other samples). Microstructure analysis was performed by scanning electronic microscopy (SEM). As shown from the analysis, aging only affects superficial zones because no changes in the morphology of the central zone were detected in the different samples. Sample B shows a different behavior; it was less resistant to fracture. From DSC and SEM measurements, we can state the additive influence on the original sample behavior as well as on the solidification process of polypropylene–polyethylene-based copolymers.

Crystallization kinetics of polypropylene-polyethylene-based copolymers

A crystallization kinetics analysis of several polypropylene-polyethylene (PP-PE), PP-rich copolymers was made by means of differential scanning calorimetry. The crystallization was studied via calorimetric measurements at different cooling rates. Several additives were added to the base material. Some test samples were subjected to artificial ageing processes. A modified isoconversional method was used to describe the crystallization process under non-isothermal conditions. The value of the Avrami parameter was determined for primary and secondary crystallization.

Image Analysis of Elastomer Morphology in Toughened Thermoplastic and Thermoset Resins

A thermoplastic polystyrene-based material with styrene-butadiene-styrene dispersed particles and a thermoset polyester toughened with butadiene-acrylonitrile particles were studied. Photomicrographs of materials that had different proportions of elastomer were processed and the images analysed. The changes in the morphological characteristics were correlated with the fracture toughness and modulus of elasticity.