Review of Recent Developments of Glass Transition in PVC Nanocomposites

This review addresses the impact of different nanoadditives on the glass transition temperature (Tg) of polyvinyl chloride (PVC), which is a widely used industrial polymer. The relatively high Tg limits its temperature-dependent applications. The objective of the review is to present the state-of-the-art knowledge on the influence of nanofillers of various origins and dimensions on the Tg of the PVC. The Tg variations induced by added nanofillers can be probed mostly by such experimental techniques as thermomechanical analysis (TMA), dynamic mechanical analysis (DMA), differential scanning calorimetry (DSC), and dielectric thermal analysis (DETA). The increase in Tg is commonly associated with the use of mineral and carbonaceous nanofillers. In this case, a rise in the concentration of nanoadditives leads to an increase in the Tg due to a restraint of the PVC macromolecular chain’s mobility. The lowering of Tg may be attributed to the well-known plasticizing effect, which is a consequence of the incorporation of oligomeric silsesquioxanes to the polymeric matrix. It has been well established that the variation in the Tg value depends also on the chemical modification of nanofillers and their incorporation into the PVC matrix. This review may be an inspiration for further investigation of nanofillers’ effect on the PVC glass transition temperature.

Membranes for Cation Transport Based on Dendronized Poly(epichlorohydrin-co-ethylene oxide). Part 1: The Effect of Dendron Amount and Column Orientation on Copolymer Mobility

Dendronized polyethers give rise to columnar LC structures which can successfully act as cation transport materials. Therefore, we prepared two different materials, based on Poly(epichlorohydrin-co-ethylene oxide) (PECH-co-EO) grafted with methyl 3,4,5-tris[4-(n-dodecan-1-yloxy)benzyloxy] benzoate, containing 20% or 40% modified units, respectively. The obtained polymers were characterized by differential scanning calorimetry (DSC), X-ray diffraction and optical microscopy between crossed polars (POM) and compared to the unmodified PECH-co-EO. In order to reach efficient transport properties, homeotropically oriented membranes were prepared by a fine-tuned thermal annealing treatment and were subsequently investigated by dynamic mechanical thermal analysis (DMTA) and dielectric thermal analysis (DETA). We found that the presence of the dendrons induces a main chain partial crystallization of the polyether chain and coherently increases the polymer Tg. This effect is more evident in the oriented membranes. As for copolymer orientation upon annealing, the cooling rate and the annealing temperature were the most crucial factors. DMTA and DETA confirmed that grafting with the dendron strongly hinders copolymer motions, but did not show great differences between unoriented and oriented membranes, regardless of the amount of dendrons.

Effect of Dendritic Side Groups on the Mobility of Modified Poly(epichlorohydrin) Copolymers

The macromolecular dynamics of dendronized copolymer membranes (PECHs), obtained by chemical modification of poly(epichlorohydrin) with the dendron 3,4,5-tris[4-(n-dodecan-1-yloxy)benzyloxy] benzoate, was investigated. In response to a thermal treatment during membrane preparation, these copolymers show an ability to change their shape, achieve orientation, and slightly crystallize, which was also observed by CP-MAS NMR, XRD, and DSC. The phenomenon was deeply analyzed by dielectric thermal analysis. The dielectric spectra show the influence of several factors such as the number of dendritic side groups, the orientation, their self-assembling dendrons, and the molecular mobility. The dielectric spectra present a sub-Tg dielectric relaxation, labelled as γ, associated with the mobility of the benzyloxy substituent of the dendritic group. This mobility is not related to the percentage of these lateral chains but is somewhat hindered by the orientation of the dendritic groups. Unlike other less complex polymers, the crystallization was dismantled before the appearance of the glass transition (αTg). Only after that, clearing transition (αClear) can be observed. The PECHs were flexible and offered a high free volume, despite presenting a high degree of modifications. However, the molecular mobility is not independent in each phase and the self-assembling dendrons can be eventually fine-tuned according to the percentage of grafted groups.

Starch behaviour in potato at temperatures close to cellular membrane breakdown

A combined thermal analysis (including a dynamic mechanical analysis and a dielectric thermal analysis) was applied to the cortex tissues of long-stored potatoes in the temperature range of 30-90°C, with the constant air relative humidity of 90%. Two heating rates, i.e. 1°C min−1 and 0.5°C min−1, were used for temperature scanning. The obtained results were found to differ in the inspected temperature range, indicating either a different mode of drying or differences in the starch gelatinization mechanism, the latter being usually controlled by water availability in contact with starch in both tests. The observed results indicate new possibilities in the cooking strategies that are usually applied to potatoes.

THERMAL AGING STUDY OF BIODEGRADABLE POLYMER MATERIALS BY DIELECTRIC THERMAL ANALYSIS

Two different studies of the thermal aging of polyesters based on lactic and glycolic acidswere compared. Thermal degradation of poly(L-lactic acid) (PLLA), poly(L-lactic acid-co-glycolicacid) (PLLGA) and poly(DL-lactic acid-co-glycolic acid) (PDLGA) was studied by the dielectricthermal analysis (DETA). The aging was performed at 37C in vacuum oven. The dielectric featuresi.e., dielectric permittivity,, dielectric losses,, and phase lag, tg , were determined by PL-DETAcontaining a parallel plate capacitance cell, from the room temperature to 80, 150, and 180  C,at the heating rates of 2 and 3 Cmin-1. Dielectric scans were obtained at a frequency of 1 kHz anda.c. signal of 200 mV. Different behavior of PLLA, PLLGA, and PDLGA during degradation wasobserved. As the aging of PDLGA proceeds, dielectric losses shift to the lower temperatures,indicating existence of lower molecular weights.  - T, and tg  - T dependences of PLLGA, as wellas those for PLLA show two simultaneous processes occurring, crystallization and degradation.