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Abstract: The calorimetric characteristics, the flammability, the thermal stability and the microhardness of polyethylene high density/clay nanocomposites (HDPE/clay) have been studied by differential scanning calorimetry, thermogravimetry, determination of limiting oxygen index and microhardness tests. The nanocomposites have been compatibilized by ethylene–acrylic acid copolymer (EAA), acrylic acid grafted HDPE (HDAA) and maleic anhydride grafted HDPE (HDMA). The clay was montmorillonite Cloisite 15A. The influence of the presence and the type of the compatibilizers on the properties of the nanocomposites has been evaluated. The results have shown that the thermal stability, the reduction of the flammability and the microhardness of HDPE/clay nanocomposites, compatibilized by HDAA and HDMA are higher than those for nanocomposite compatibilized by EAA. Moreover, the presence and the type of compatibilizer have negligible effect on the characteristics of the HDPE phase transitions. These results have been interpreted by the better clay dispersion and higher level of clay exfoliation in the presence of compatibilizers HDAA and HDMA, than those in the presence of EAA compatibilizer. [Copyright &y& Elsevier]

Abstract: The non-isothermal and isothermal crystallization of nanocomposites based on poly(ethylene-co-acrylic acid) copolymers having different concentration of acrylic acid and different molar mass, their Zn ionomer and ethylene–glycidylmethacrylate copolymer as matrices and organically modified montmorillonite as a nanofiller have been investigated. The influence of the presence and the concentration of clay on the kinetic parameters of non-isothermal and isothermal crystallization of the matrix polymer has been evaluated. The melting properties of the isothermal crystallized samples have been also studied. The addition of 5 or 10wt% clay to the matrices of the polar polymers leads to a change in the mechanism of non-isothermal and isothermal crystallization. The growth of the polyethylene spherulites changes from three- to two-dimensional when the lamellar silicate is added. Moreover, the isothermal overall crystallization rate increases in the presence of clay due to the increased nucleation rate and unchanged or decreased crystal growth rate. The results have been interpreted by the influence of the intercalated structure of nanocomposites on the crystallization behavior of the polymers under non-isothermal and isothermal conditions. [Copyright &y& Elsevier]

Abstract: The study deals with the effectiveness of maleic anhydride grafted styrene-b-ethylene-co-propylene copolymer (SEPMA) as compatibilizer precursor (CP) for blends of low density polyethylene (LDPE) with polyamide-6 (PA). The CP was produced by grafting MA onto SEP in the melt. The specific interactions between the CP and the blends components have been investigated through characterizations of the binary LDPE/CP and PA/CP blends. The compatibilizing efficiency of the MA-grafted SEP, as revealed by the thermal properties and the morphology of the compatibilized blends, has been shown to be excellent. The morphology, as well as the mechanical properties of the compatibilized with SEPMA 75/25 w/w and 25/75 w/w LDPE/PA6 blends have been compared with those of the blends compatibilized with maleic anhydride functionalized HDPE sample (1-HDPE-g-MA) and with a commercial maleic anhydride grafted styrene-b-(ethylene-co-1-butene)-b-styrene copolymer (SEBSMA1). The results show that the strong compatibilizing efficiency of SEPMA is comparable with that of SEBSMA1, while 1-HDPE-g-MA exhibits a slightly lower activity, particularly for the blends, in which PA is the matrix phase. [Copyright &y& Elsevier]

Abstract: The paper presents differential scanning calorimetry and electron microscopy of the fractionated crystallization and polydispersity of the dispersed PA6 phase in compatibilized LDPE/PA6 75/25 w/w blends. The compatibilizers used were (i) an acrylic acid functionalized polyethylene, Escor 5001 (EAA); (ii) an ethylene–glycidylmethacrylate copolymer, Lotader GMA AX8840 (EGMA); (iii) a polystyrene–poly(ethylene–butylene)–polystyrene triblock copolymer comprising 2wt.% maleic anhydride grafts, Kraton FG 1901X (SEBS-g-MA). The compatibilizer SEBS-g-MA has the strongest reduction effect upon the size of PA-6 droplets. Its implementation provides the best fractionated crystallization. The fractionated crystallization has not been observed for the blend compatibilized with EGMA. The results show that the degree of compatibilization could be evaluated qualitatively by the progress of the fractionated crystallization. So, the three compatibilizers could be rated according to their effectiveness as follows: SEBS-g-MA>EAA>EGMA. The self-nucleation experiments have demonstrated that the lack of active nuclei in the finely dispersed PA6 droplets is the determining factor for the fractionated crystallization at high supercooling, and not the considered absolute particle size. The measurement of the Vickers microhardness of the compatibilized blends confirms that the compatibilizing activity of SEBS-g-MA and EAA is stronger than that of EGMA. [Copyright &y& Elsevier]

The interfacial tension of the uncompatibilized and compatibilized blends of low density polyethylene (LDPE) and polyamide 6 (PA6) has been measured by the breaking thread method. Different types of compatibilizer precursors have been used: poly(ethylene-co-acrylic acid) (Escor 5001, by Exxon) having 6 wt% concentration of acrylic acid; an ethylene-acrylic acid zinc ionomer (Iotek 4200); a triblock copolymer with polystyrene end blocks and a rubbery poly(ethylene–butylene mid block (SEBS) (Kraton G 1652); and SEBS-g-MA (Kraton FG 1901X) with 2 wt% maleic anhydride. The compatibilizing efficiency of the different types of the compatibilizer precursors towards the blends has been evaluated quantitatively by the values of the interfacial tension obtained. It has been shown that Iotek and SEBS-g-MA posses the highest compatibilizing efficiency, demonstrated by the strongest decrease of the interfacial tension and the dimension of the droplets of the dispersed phase. Contrary, SEBS almost does not influence the interfacial tension and the size of the particles. Hence, it possesses the lowest compatibilizing activity towards the blends. The compatibilizer Escor displays an activity lower than that of Iotek and SEBS-g-MA, but it is higher than that of SEBS. [Copyright &y& Elsevier]

The Vickers microhardness of PET-based liquid crystalline copolyesters has been investigated. The copolyesters have been synthesized by transesterification of PET with equimolar amounts of sebacic acid (S) and hydroquinone (Q) (or 4,4′-dihyroxybiphenyl (B)) and with varying amounts of 4-hydroxybenzoic acid (H). The variation of the Vickers microhardness of PET-S-Q-H and PET-S-B-H liquid crystalline polyesters with the composition have been interpreted by the microstructure of the materials. The increase in the concentration of 4-hydroxybenzoic acid (H) in both types of copolyesters leads to an increase in intermolecular distance and to enlargement of the domain size. This, on its, turn, leads to a decrease in the materials'' microhardness. The effect that the mixing time of the reactive blends of equimolar amounts of PET and poly(phenylene sebacate) (PQS) PET/PQS has upon the microhardness values has been also studied. The variation of the microhardness of PET/PQS blends prepared for different mixing times follows the same tendency as that of the melting enthalpy (i.e. the degree of crystallinity). Both parameters have lower values with the longer mixing time. The decreased crystallinity during the transreaction results into materials having higher creep rate under load. [Copyright &y& Elsevier]

Microhardness tests, water absorption and thermogravimetric measurements have been performed on blends of low density polyethylene (LDPE) with different molar mass and polyamide 6 (PA6) compatibilized with 2 pph poly(ethylene-co-acrylic acid) (Escor 5001 by Exxon). The negative deviation of Vickers microhardness from the additivity has been interpreted by changes in the crystallinity of the blend components. The hardness values of the compatibilized blends that are lower than those of the corresponding uncompatibilized blends have been explained by the decrease of the degree of crystallinity of PA6 phase in the presence of Escor. The molar mass of LDPE almost does not influence on the hardness values. The lower water absorption of the compatibilized blends, caused by the formation of a copolymer between PA6 and the compatibilizer leads to microhardness values of the wet compatibilized blends higher than those of the corresponding uncompatibilized blends. The thermogravimetric measurements demonstrate that the thermal stability of blends increases in the presence of 2 pph Escor 5001. The results confirm the compatibilizing efficiency of Escor 5001 towards LDPE/PA6 blends in a wide composition range. [Copyright &y& Elsevier]

Abstract: The flammability, microhardness and transparency of nanocomposites based on poly(ethylene-co-acrylic acid) copolymers having different concentration of acrylic acid and different molar mass, their Zn ionomer and ethylene-glycidylmethacrylate copolymer as matrixes and on organically modified montmorillonite as a nanofiller have been investigated. The presence and the increase in the content of the clay lead to the increase in the limiting oxygen index and to significant reduction of the burning rate of all materials. The results from the Vickers microhardness measurements have shown that the addition of the clay to matrixes of polar functionalized polyethylenes leads to a significant increase in the microhardness of the materials, while the creep constant does not decrease significantly. The UV spectra show that the light transmittance of the materials does not change significantly in the presence of the clay, i.e., the nanocomposite films preserve the polymer transparency. The results have been interpreted by the intercalated structures of the nanocomposites investigated. [Copyright &y& Elsevier]

Abstract: Polymer/organoclay nanocomposites based on an ethylene–acrylic acid copolymer (EAA), a high-density polyethylene (HDPE) grafted with maleic anhydride (HDMA) and HDPE/HDMA blends with 80/20 and 50/50wt/wt composition have been studied by thermogravimetry in nitrogen and air atmospheres. The following parameters have been determined from the thermogravimetric (TG) and differential thermogravimetric (DTG) curves of the samples: T 10, T 50, T max, the degree of conversion at 450°C and the residue. The study of the non-isothermal degradation kinetics of the neat polymers and their nanocomposites has allowed the determination of the activation energy of degradation, the rate of degradation and the reaction order. The analysis of all parameters has led to the conclusion that in the presence of clay, the thermal stability in nitrogen atmosphere decreases, while the thermal stability in air increases. Moreover, the effect of clay on the degradation behavior of the polymer matrix is more pronounced for the nanocomposites having fully exfoliated structure than that of the nanocomposites containing intercalated clay stacks. The results have been interpreted by the better dispersion of the clay layers in the exfoliated nanocomposites, leading to a better barrier effect for the oxygen flow in air and to an increase in the number of clay catalytic sites in nitrogen. [Copyright &y& Elsevier]