Semi-conductive polymer composites are used in a wide range of sensors, measurement devices. This paper discusses the development of a model and a new theoretical formulation for predicting piezoresistive behavior in semi-conductive polymer composites including their creep behavior and contact resistance. The relationship between electrical resistance and force applied to the piezoresistive force sensor can be predicted by using the proposed theoretical formulation. In order to verify the proposed formulation, the piezoresistive behavior of Linqstat, a carbonfilled polyethylene, was modelled mathematically. In addition, some experimental tests such as Thermo Gravitational Analysis and Scanning Electron Microscopy have been performed on Linqstat to find the volume fraction and size of carbon particles which are essential for modeling. In addition, on a fabricated force sensor using Linqstat, a the force vs. resistance curve was obtained experimentally which verified the validity and reliability of the proposed formulation.

Star-shaped and comb-like poly(L-Lactide)s (PLA) are produced by employing multifunctional initiators, and hyperbranched structure is prepared using a cyclic co-monomer with hydroxyl group. FTIR, size exclusion chromatography, and H-NMR techniques are employed to characterize the synthesized polymers, validating the formation of desired structures with chain lengths above the critical length for entanglement. After characterization of the synthesized polymers, the effect of branching on PLA properties is investigated by comparing the crystallization and rheological behavior of branched PLAs to those of a linear commercial grade. Differential scanning calorimetry and optical microscopy observations reveal a remark-able improvement in PLA crystallization due to the nucleation role of branching points. Moreover, synthesized polylactides exhibit strain hardening behavior during elongational viscosity measurements by a sentmanat extension rheometer platform. Significant improvements in crystallization and elongational rheology behavior of the synthesized polymers support the achievement of branched polymer structures.

This study was aimed at improving the process rheology of polylactide (PLA) melts by means of two strategies. First, PLAs of different branched structures, i.e., star shaped, comblike, and hyper branched, were synthesized and blended with a linear grade analog. Shear and extensional flow rheometry tests were performed on pure materials and their blends to evaluate their rheological properties. It was shown that the presence of branched poly(L-lactide) (PLLA) increased the shear thinning, shear and extensional viscosity, and elastic modulus of linear PLLA at the same time; the star shaped PLLA providing the most significant change. Second, poly(D-lactides) (PDLA) with similar molecular architectures were synthesized to have a double branching effect. In addition to the presence of branched architecture, physical cross-links due to the stereocomplex formation exist between PLLA and PDLA chains. Based on the rheological characterizations in shear and extensional mode, a greater improvement in PLA melt rheological properties was observed for blends containing stereocomplex structure as compared to linear/branched enantiopure blends. V C 2015 The Society of Rheology. [http://dx.

This work was done with the aim to solve an important environmental issue regarding poly (ethylene terephthalate), (PET) wastes. Samples of recycled PET (r‐PET) were reinforced with 10 to 30 wt% modified short glass fibers (SGF) through a melt mixing process in an internal mixer and their performance were assessed and compared with those of commercial glass reinforced PET through investigation of their rheology, morphology, thermal, and mechanical properties. It was found that the mechanical properties of the glass reinforced r‐PET composites in most cases were comparable or even higher than those of the commercial grades. The impact strength of the 30 wt% SGF filled r‐PET composite was about 30% higher than the commercial grades. This led to a conclusion that the PET wastes can be successfully converted to easily moldable thermoplastic materials by incorporation of 30 wt% SGF having a good balance of properties. Through investigation of rheological and morphological properties the optimum conditions for the best reinforcement performance were determined. The r‐PET with 30 wt% glass fiber content showed the highest level of orientation and improved interaction with the r‐PET matrix while having an acceptable flow behavior and processability. In spite of significant fiber breakage during the melt mixing process, leading to about 20 times reduction in the fiber aspect ratio, the composites maintained their good mechanical properties and showed a shear thinning behavior at high shear rates. The incorporated glass fibers acted as nucleating agents and improved the crystallization rate of r‐PET leading to an overall increase in the crystallinity. POLYM. COMPOS., 2009. © 2008 Society of Plastics Engineers

No abstract