On the Cold Drawing of Poly-Ether-Ether-Ketone (PEEK) Tubes

AbstractThe mechanical behaviour commonly referred as cold drawing (CD) is a phenomenon that occurs once the yield point is reached, in a thermoplastic material subjected to a uniaxial tensile test at constant strain rate. In effect, after yielding the sample undergoes a neck in its cross-sectional area, which then propagates along the entire useful length of the sample while the applied force remains constant. This phenomenon occurs in amorphous or semi-crystalline materials in a wide range of temperatures below the glass transition temperature. Understanding this phenomenon involves knowing what deformation mechanisms operate and how they are related to the morphology of the material. In this work, on one hand, the mechanical response of poly-ether-ether-ketone (PEEK) thermally aged at 25 and 135°C for 30 day is measured. In previous researches PEEK aged at 130 and 135°C undergoes cold drawing when subjected to a tensile strain rate of 1,7 10-3 s-1 at 25°C. In addition, the average stress and the ultimate elongation of the plateau depend on the temperature and the duration of the annealing. On the other hand, wide angle X ray diffraction, density measurements, differential thermal analysis, shape memory analysis and complex impedance measurement allow determine changes in the amorphous and crystalline phases due to thermal aging and cold drawing effects

Lavandin essential oil combined with the biopolymer PHBV, poly(3-hydroxybutyrate-co-3-hydroxyvalerate), for wound treatment

In this work, poly(3-hydroxybutyrate-co-3-hydroxyvalerate), PHBV, was combined with lavandin essential oil (LavEO), from Lavandula hybrida grown in Argentina. Linalool (36%), linalyl acetate (29%) 1,8-cineole (6%) and camphor (6%) were its main compounds as analyzed by GC-MS. PHBV is a biodegradable copolyester from a bacterial source; PHBV porous scaffolds have been shown to be suitable for fibroblast and keratinocyte proliferation [1,2] and thus for skin regeneration. In addition, LavEO exhibits strong anti-inflammatory and antibacterial activity, what improves wound healing [4,5]. Purified monoterpenes and entire EOs have been combined with other biopolymers for different applications but scarcely for wound healing and never previously with PHBV [6]. PHBV porous membranes, 100-200 µm thickness, containing LavEO at 2, 4 or 8% m/m were obtained by an emulsion-solvent evaporation method. LavEO-PHBV membranes did not show cytotoxicity when tested on NIH/3T3 fibroblasts (according to the ISO 10993-5 standard). SEM membrane analysis showed, in all cases, a high level of porosity, ̴ 20% of the surface. Keratinocytes (KC) adhesion and proliferation were evaluated with the HaCaT cell line. Membranes containing 2 or 4% of LavEO, allowed KC proliferation of the same level as that of PHBV membrane controls. However, cells neither adhered to nor proliferated on membranes with 8% LavEO although their hydrophobicity, estimated by the contact angle, was similar to that of 4%-LavEO membranes. The reduction in the elastic modulus–determined by the dynamic mechanical analysis–due to the presence of LavEO, suggests its plasticizer effect (control E=305±10 MPa; 8%-LavEO membrane E=150±20 MPa). According to these results, 2 or 4% LavEO-PHBV membranes seem as a promising treatment, especially in the case of infected and chronic wounds, often arrested at the inflammatory phase

Non-Linear Effects in the Snoek Relaxation of Nb-O

Internal friction peaks measured as a function of temperature or frequency have been associated to non-linear processes only after studying how the amplitude of the applied stress affects the relaxation process. Here it is demonstrated that the partial derivative of the internal friction with respect to the frequency at constant temperature is a useful tool to determine that non-linear effects are involved. This analysis applied to actual data of the Snoek relaxation in Nb-O, reveals that at high interstitial contents non-linear effects appear

On the Frequency Dependence of the High Temperature Background

The high temperature background (HTB) damping in metals and alloys has been measured mostly as a function of temperature. These data were described by several empirical expressions proposed in the literature. In the present work, HTB in pure Mg and in two alloys (Zry-4 and Cu-5at.%Au), measured with a torsion pendulum with variable moment of inertia, are analyzed on considering a new treatment of the data. This analysis provides an useful tool to determine whether a damping process is linear or not

Anomalous Behaviour of the Zener Relaxation in Cu-Au

Measurements of the Zener relaxation in single crystals of Cu-18at.%Au and Cu3Au are presented. In the 18at.% alloy only one internal friction peak is observed at low frequencies (of the order of 1 Hz). This peak is only slightly wider than a Debye's peak. An additional hump appears at intermediate frequencies (of the order of 60 Hz). The Zener peak in the Cu3Au alloy is accompanied by an additional maximum produced by the order-disorder transition. A measurement of the derivative of the damping with respect to the frequency through the use of a pendulum with variable moment of inertia shows that non-linear effects are present in the Zener relaxation in both alloys

Dislocation Relaxation Processes due to Kink Migration

The interpretation of the Bordoni relaxation and of related relaxation phenomena in terms of the thermally activated, stress-assisted formation of kink pairs on dislocation lines is well established on assuming that the migration of kinks along dislocation lines is described by a high kink mobility µk. This assumption, however, is not valid if the activation enthalpy for kink migration, Hm, is comparable with or even larger than the formation enthalpy of kink pairs or if even when small compared with the formation energy of kinks, Hm is larger than the lowest thermal energies accessible in internal friction experiments. In those cases not only migration but also annihilation and trapping of thermal kink pairs may produce internal friction peaks. The difference-differential equations governing the thermal kink pairs evolution along dislocation lines under the action of a homogeneous applied shear stress are set up and their time-dependent solutions characterized by a set of relaxation times. It is shown how to obtain, from these solutions, the internal friction spectrum under conditions that are experimentally realized. Quantitative descriptions of geometrical kink migration and kink pair evolution are compared with selected experimental results