Luigi Torre

On the physical dimensions of the Avrami constant

In this note, some discrepancies in the utilization of the Avrami model adopted for the crystallization modelling of advanced semicrystalline thermoplastic matrices are pointed out. In particular, the correct representation of the kinetic constants as a function of the isothermal crystallization temperature is discussed. In fact, Avrami analysis of isothermal crystallization data leads to the computation of kinetic constants characterized by physical dimensions depending on the calculated Avrami index. The representation on a single plot of these kinetic constants is not formally correct, and therefore a modification of the Avrami expression must be adopted.

Thermal stability of P(HB-co-HV) and its blends with polyalcohols

The thermal stability of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) [P(HB-co-HV)] and its blends with poly(propylene glycol)s (PPGs) and castor oil (CO) is reported. The study includes the determination of the degradation kinetics of these materials and the analysis of the effects of the degradation on the mechanical properties and crystallization behavior. Spectroscopy (1H-NMR, FTIR), differential scanning calorimetry (DSC), thermogravimetry, and tensile testing techniques are used for the experimental analysis. A chain-scission degradation mechanism is confirmed by the formation of vinyl groups. Two temperature ranges are investigated. In the range closest to the melting point, 100–200°C, where the blend does not exhibit weight reduction, a fast and sensible loss of molecular weight and tensile strength was detected. The second temperature range, 200–400°C, is characterized by mass loss by pyrolysis. In this range, different kinetic models of the degradation process are proposed. Polyalcohol addition produces opposite effects, while the addition of PPG enhances the degradation of P(HB-co-HV). When CO is added, the thermal stability of the blend increases. Mechanical properties of the blends before and after degradation were determined. The tensile modulus increases at the first step of degradation and decreases with the degradation time.

Short- and long-term degradation of polymer-based composites

Abstract The thermal stability of high-performance thermoplastic matrix composites is studied by thermogravimetric analysis. The study is focused on the degradation behavior, under different environments, of continuous carbon-fiber-reinforced composites with poly(ether-ether ketone) (PEEK) matrix. The experimental results are analyzed by two different methods. In one method a phenomenological kinetic model is developed and compared with the degradation behavior measured in isothermal and constant heating conditions. In the second method, a simple correlation is presented to describe the onset of the degradation at long times and under normal service conditions. Both approaches give similar results and confirm the good thermal stability of PEEK matrix/carbon fiber composites at high service temperatures.

Processing and properties of recycled polypropylene modified with elastomers

Abstract This work presents a study of the processability and the characterisation of blends of recycled polypropylene (PP) with two different elastomers. The aim of the work was to demonstrate that the introduction of an elastomeric phase could improve the properties of recycled PP without changing the processing characteristics of the blends in terms of viscosity and temperature. The study was carried out using thermal analysis, thermomechanical analysis and rheological measurements. The rheological analysis of blends of recycled PP and elastomeric additives showed that, despite the different rheological behaviour of the added elastomers, the properties of the blends were dominated by the thermoplastic (PP) phase. A thermogravimetric analysis of the selected blends allowed the calculation of the parameters related to the thermal degradation of such materials and the main results indicated that there were no significant differences between virgin and recycled PP in terms of behaviour at high temperatures. Furthermore, the blending of recycled PP with elastomers did not result in a significant change in thermal degradation behaviour. Crystallisation studies showed that blending polypropylene with elastomers influenced the rate and amount of crystallisation, which increased at low additive concentrations and then decreased at a higher elastomer content. Thermomechanical analysis showed the immiscible character of the blends. The mechanical properties of the blends were affected by the concentration of elastomer, which also influenced the crystallinity of the material.

Study of the Crystallization of an Aromatic Poly-ether-ketone (PK99) by Calorimetric and X-ray Analysis

An analysis of the crystallization behaviour of a new poly(aryl-ether-ether-ketone-ketone), PK99, by differential scanning calorimetry (DSC) and wide-angle X-ray diffraction (WAXD) is presented. Isothermal crystallization TG were obtained in the whole range between the glass transition temperature (Tg) and the melting temperature (Tm) as a consequence of the slow crystallization kinetics stemming from the closeness of these transitions. The calorimetric results, compared with WAXD data, were applied to determine the theoretical melting temperature and crystallization enthalpy. The DSC and WAXD data were combined in order to calculate the total amount of the crystallizable fraction of the polymer, and a model was proposed to explain the difference between the fractions of crystallinity observed with these techniques. The thermal and X-ray data were also correlated with different lamellar morphologies arising from the crystallization conditions. Finally, DSC experiments on the crystallized sample were used to detect the presence of a rigid amorphous phase which does not relax at Tg.

PHENOLIC MATRIX NANOCOMPOSITES BASED ON COMMERCIAL GRADE RESOLS SYNTHESIS, CHARACTERIZATION AND COMPARISON WITH MICROCOMPOSITES

Polymer layered silicate nanocomposites based on a commercial grade resol were produced using a simple, low labor cost mechanical approach, providing an effective alternative to the more traditional technique based on the use of the intercalative polymerization of phenol and formaldehyde monomers. The matrix was a resol diluted in methanol. The selected nanoclay was Cloisite® 30B. Two kind of nanocomposites were studied: the first one prepared at a nanoclay percentage equal to 5% and, the second one, produced at 20% nanoclay percentage. Finally, a comparison between these nanocomposites and a blend loaded with 20% of micrometric silica, was performed. The produced materials were studied by means of X‐ray diffraction, SEM and thermogravimetric analysis. The first nanocomposite showed a good degree of dispersion as well as distribution of the nanoclay platelets. SEM images even showed that high loaded nanocomposite exhibited a morphology very similar to a porous media. According to thermogravimetric analysi...

Processing and Characterization of Nano-biocomposites Based on Mater-Bi® with Layered Silicates

The development of new nano-biocomposites has been one of the main research areas of interest in polymer science in recent years, since they can combine the intrinsic biodegradable nature of matrices with the ability to modify their properties by the addition of selected nano-reinforcements. In this work, the addition of mineral nanoclays (montmorillonites and sepiolites) to a commercial starch-based matrix is proposed. A complete study on their processing by melt-intercalation techniques and further evaluation of the main properties of nano-biocomposites has been carried out. The results reported show an important infl uence of the nano-biocomposites morphology on their fi nal properties. In particular, the rheological and viscoelastic characteristics of these systems are very sensitive to the dispersion level of the nanofi ller, but it is possible to assess that the material processing behaviour is not compromised by the presence of these nano-reinforcements. In general, both nanofi llers had a positive infl uence in the materials fi nal properties. Mechanical performance shows improvements in terms of elastic modulus, without important limitations in terms of ductility. Thermal properties are improved in terms of residual mass after degradation and low improvements are also observed in terms of oxygen barrier properties. ® , nanoclays, melt intercalation, characterisation

Science and Technology of Polymer Composites

The polymeric matrix and its interaction with a reinforcing phase, in the form of continuous or discontinuous high strength and stiffness fibers, is one of the major controlling factors in the processing and property characteristics of composites. Although traditionally the matrix has been thought to play a passive role in composite performance and development with major emphasis being placed on the fiber properties alone, the demanding recent uses of composites require that polymeric matrix plays an increasingly important role in composite performance.