M. Jesús Fernández

THERMAL DECOMPOSITION OF COPOLYMERS FROM ETHYLENE WITH SOME VINYL DERIVATIVES

The thermal degradation of ethylene-vinyl acetate (EVA), ethylene-vinyl-3,5-dinitrobenzoate (EVDNB) and ethylene-vinyl alcohol (EVAL) copolymers have been studied using differential thermal analysis (DTA) and thermogravimetry (TG) under isothermal and dynamic conditions in nitrogen. Thermal analysis indicates that EVA copolymers are thermally more stable than EVDNB samples. The degradation of the copolymers considered occurs as an additive degradation of each component polyethylene (PE) and poly(vinyl acetate) (PVA), poly(vinyl-3,5-dinitrobenzoate) (PVDNB) or poly(vinyl alcohol) (PVAL). The apparent activation energy of the decomposition was determined by the Kissinger and Flynn-Wall methods which agree well.

Synthesis, characterization and properties of telechelic hybrid biodegradable polymers containing polyhedral oligomeric silsesquioxane (POSS)

In this work, telechelic POSS-containing inorganic–organic hybrid poly(L-lactic acid) (POSS–PLLA) and ditelechelic POSS-containing hybrid poly(e-caprolactone) (POSS–PCL–POSS) were synthesized by click coupling between alkyne moiety-functionalized POSS and azide end-functionalized PLLA and bis-azide end-functionalized PCL. Characterization of the POSS-containing hybrid polymers was performed using FTIR, 1H and 13C NMR spectroscopy. The study of the effects of covalent POSS incorporation on the polymer thermal and surface properties was undertaken using differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and water contact angle measurement. In all synthesized hybrids, the glass transition temperature (Tg) increased and crystallization was retarded with the incorporation of a POSS moiety at the chain ends of PLLA and PCL compared to that of neat homopolymers. Covalent end-capping by POSS disrupted the crystallization of PCL and PLLA. POSS moieties, attached to both ends of PCL, crystallized in the polymer matrix prior to PCL crystallization from the melt. The thermal and thermal oxidative stability of the polymers enhanced significantly after incorporation of the POSS moiety. Static contact angle measurements revealed that the POSS-containing polymers displayed a significant enhancement in surface hydrophobicity.

Thermal degradation of copolymers of styrene and 4-nitrostyrene

The thermal degradation of styrene-4-nitrostyrene copolymers (SNS) has been studied using differential thermal analysis (DTA) and thermogravimetry (TGA) under isothermal and dynamic conditions in dynamic nitrogen. The apparent activation energy of the degradative process was determined following several methods of thermogravimetric analysis. The stability decreases as the nitrostyrene content in the copolymer increases. Fourier-transform infra-red spectroscopy has been used to analyze the degradation products at various degrees of conversion.

Study on the effect of graphene and glycerol plasticizer on the properties of chitosan-graphene nanocomposites via in situ green chemical reduction of graphene oxide

Unplasticized and glycerol plasticized chitosan/graphene (CS/GS) nanocomposites were synthesized via in situ chemical reduction of graphene oxide sheets (GO) with l-ascorbic acid (L-AA) as reductant by solution casting. The reduction of GO with L-AA was investigated to establish the optimal amount of reductant required to produce chemically reduced graphene sheets (GS). The combine effect of both nanofiller and glycerol on the structure, thermal, mechanical, and electrical properties of CS/GS nanocomposite films was evaluated. Materials were characterized by FT-IR, NMR, UV-Vis, XPS, XRD, Raman, SEM, TEM, and TGA. The results showed that GS sheets were homogeneously dispersed throughout the CS matrix, and that interactions between CS and the surface of GS took place. When compared with neat CS, nanocomposites showed a decrease in the crystallinity, better thermal stability under oxidative atmosphere, and improved mechanical properties, while maintained the thermal properties of CS under inert conditions. Combined use of glycerol and GS led to substantially enhanced mechanical properties. The electrical conductivity was increased with increasing GS loading in nanocomposite. This study demonstrates how CS/GS nanocomposites performance properties can be tailored by controlling GsS and plasticizer content.

Thermal degradation of styrene-2,4-dinitrostyrene copolymers

The thermal degradation of styrene-2,4-dinitrostyrene copolymers (SDNS) has been studied using differential thermal analysis (DTA) and thermogravimetry (TGA) under isothermal and dynamic conditions in dynamic nitrogen. The apparent activation energy of the degradative process was determined following several methods of gravimetric analyses. The stability decreases as the mole fraction of dinitrostyrene in styrene-dinitrostyrene copolymers increases. Fourier-transform infrared spectroscopy has been used to analyze the degradation products at various degrees of conversion.