Maria Jesús Sanchis

Films of carrageenan (KC) and glycerol (g) with different contents of chitin nanowhiskers (CHW) were prepared by a solution casting process. The molecular dynamics of pure carrageenan (KC), carrageenan/glycerol (KCg) and KCg with different quantities of CHWs as a filler was studied using dielectric relaxation spectroscopy. The analysis of the CHW effect on the molecular mobility at the glass transition, T_g, indicates that non-attractive intermolecular interactions between KCg and CHW occur. The fragility index increased upon CHW incorporation, due to a reduction in the polymer chains mobility produced by the CHW confinement of the KCg network. The apparent activation energy associated with the relaxation dynamics of the chains at T_g slightly increased with the CHW content. The filler nature effect, CHW or montmorillonite (MMT), on the dynamic mobility of the composites was analyzed by comparing the dynamic behavior of both carrageenan-based composites (KCg/xCHW, KCg/xMMT).

A report on the syntheses, thermal, mechanical and dielectric characterizations of two novel polymeric acrylic materials with azide groups in their pendant structures is presented. Having the same general structure, these polymers differ in length of oxyethylene units in the pendant chain [-CONH-CH₂CH₂-(O-CH₂CH₂)_nN₃], where n is 1 (poly(N-(2-(2-azidoethoxy)ethyl)methacrylamide), PAzMa1) or 2 (poly(N-2-(2-(2-azidoethoxy)ethoxy)ethyl)methacrylamide), PAzMa2), leading with changes in their dynamics. As the thermal decomposition of the azide group is observed above 100 °C, dielectric analysis was carried out in the temperature range of −120 °C to 100 °C. Dielectric spectra of both polymers exhibit in the glassy state two relaxations labelled in increasing order of temperature as γ- and β-processes, respectively. At high temperatures and low frequencies, the spectra are dominated by ohmic conductivity and interfacial polarization effects. Both, dipolar and conductive processes were characterized by using different models. Comparison of the dielectric activity obtained for PAzMa1 and PAzMa2 with those reported for crosslinked poly(2-ethoxyethylmethacrylate) (CEOEMA) was performed. The analysis of the length of oxyethylene pendant chain and the effect of the methacrylate or methacrylamide nature on the dynamic mobility was analysed.

Understanding the thermal behaviour of lignin is crucial in order to realise its valorisation as an engineering polymer. Two hardwood lignins, organosolv (OSL) and chemically modified kraft lignin (ML) have been chosen to represent important classes of renewable and abundant raw materials. The relationship between ionic mobility and viscosity in OSL and ML has been studied. The rheological results have been interpreted in terms of the competitive processes of thermal plasticisation and stiffening through crosslinking. Results show that with OSL, crosslinking proceeds relatively rapidly, and this is consistent with its more reactive structure. Higher molecular weight (M_w) influenced the melt stability as cross-linking kinetics was reduced and this was attributed to the reduction of chain ends available for cross-linking reactions. Scanning calorimetry has shown that both materials are glassy and pass through the glass transition between 100 °C and 115 °C, with the higher molecular weight modified material having a slightly higher T_g. Both lignins show pronounced maxima in the Gram–Schmidt plots for methane or methanol around 400 °C. However, a significant difference between the materials is observed with the detection of a strong carbonyl peak in the evolution products of the ML, which is attributed to the scission of the hydroxypropyl substituent present in the ML structure. The differences in the degradation processes are further reflected in the dielectric properties of the partially degraded materials where loss maxima occur at different temperatures and show different degrees of frequency dependence. An important observation is the difference in conductivity, where higher values for OSL are attributed to the cross-linking between adjacent benzene rings, whereas with the ML, a lower conductivity is associated with intrinsically less conductive intermolecular linkages. These results demonstrate that the thermal decomposition of the two lignins follows significantly different paths at the molecular level. With the more reactive OSL, it appears to be the case that there is a greater tendency to form direct ring to ring crosslinks and this is very significant for the properties of the intended end product.