Strain induced crystallization and reinforcement were studied for poly(isoprene)s from the following sources: Ziegler–Natta catalysis, hevea brasiliensis (HNR), taraxacum kok-saghyz (TKS), known as the russian dandelion, partenium argentatum (GR), known as guayule. Two HNR samples were studied, with high (HNR-H) and low (HNR-L) molar mass. Investigated guayule samples were: as isolated from the latex (GR-R) and after extraction with acetone (GR-P). All of the samples had weight average molar mass higher than 1.5 × 10⁶ Da. TKS was found to be the most stereoregular sample, with undetectable amounts of stereoerrors. Wide angle X-Ray diffraction patterns were collected on samples, unstretched after processing and during stretching, up to 5 as the strain ratio. Quasi-static tensile measurements were performed. HNR and GR-P exhibited rubber crystallinity already in the undeformed state and the orientation of their crystalline phase remained low also for the highest strain ratios. GR-R and TKS were amorphous at low strain and developed highly oriented crystalline phases under stretching. TKS developed extraordinary mechanical reinforcement under stretching: stresses at large elongations were much higher than those obtained with HNR. It is thus shown that the formation of highly oriented crystalline phases brings large mechanical reinforcement.

In conclusion, an amorphous NR sample from a natural source, such as TKS, which has high molar mass and does not contain non rubber components which could act as plastifiers, is able, under stretching, to develop crystallinity and a high degree of axial orientation. Crystallization occurs at high strain ratio, when the chains are prevailingly aligned. The biosynthesis of TKS is likely to play a strategic role, as it promotes the chain end crosslinking of the polymer chains.

The isothermal and non-isothermal crystallization behaviour of composites of a poly(propylene) (PP) and multi-walled carbon nanotubes (MWCNTs) were investigated using Differential Scanning Calorimetry (DSC). An Avrami analysis was used to study the isothermal crystallization kinetics of unfilled PP and composites of PP with MWCNT loadings up to 2 (w/w). The value of the Avrami exponent (n) was greater than 2 for all samples, confirming the primary stage of crystal growth is a three-dimensional phenomenon. The activation energy (ΔE), determined using an Arrhenius type expression, for the isothermal crystallization of PP increased from 87 kJ for unfilled PP to 228 kJ on incorporation of 2 (w/w) MWCNTs to PP. An attempt was made to model the non-isothermal crystallization kinetics of composites of PP and MWCNTs using a range of mathematical models, including the Jeziorny extended Avrami equation, Ozawa equation, Cazé and Chuah average Avrami exponents, and a combined Avrami/Ozawa approach. The Jeziorny extended Avrami approach confirmed that the non-isothermal crystallization of MWCNT filled PP is clearly a two-stage process. Fitting of the Ozawa model was shown to be not valid and both the Cazé and Chuah average Avrami approaches were ineffective as neither took in to account the effects of secondary crystallization. Only the combined Avrami/Ozawa method successfully modelled the two-stage crystallization of composites of PP and MWCNTs. The activation energy (ΔE) for the non-isothermal crystallization of PP on addition of MWCNTs increased with increasing MWCNT content, up to as high as 726 kJ.

A scaling relation of the electric conductivity behavior of high-density polyethylene (HDPE) composites loaded with carbon black (CB) and carbon fibers (CF) was studied. The results demonstrated, the curves of the scaled current density (J_sc) versus the scaled electric field intensity (E_sc) and the curves of a scaled conductivity (σ_sc) versus J_sc and E_sc were linear in a bi-logarithmic coordinate system. There was a scaling relationship between the nonlinear electrical conductivity properties of the HDPE conductive composites; the HDPE/CB conductive composites satisfied an excessive degree relation, while the HDPE conductive composites reinforced with CF did not strictly satisfy a hyperscaling relation due to the CF weakening the nonlinear electric conductivity behavior of these composite. In addition, the introduction of the ethylene-vinyl acetate copolymer (EVA) into these composites was helpful to disperse the CB in the HDPE matrix, leading to presenting obviously linearity in a bi-logarithmic coordinate system.