Research On The Preparation And Properties Of EVOH/Inorganic Nanocomposites

The expansion of industrial and economic activities results in a continuous demand for new, low-cost materials able to meet increasingly stringent conditions. Polymers are commonly admixed with a variety of both natural and synthetic compounds to improve their performance. Inorganic components used for this purpose are called"fillers"and give rise to"filled polymers"with greater mechanical strength or impact resistance, or reduced electrical conductivity or permeability to gases, such as oxygen, and moisture. In these conventional materials, there is a distinct macroscopic separation between the organic and the inorganic phase without any significant interactions between them. Microscopic dispersion is the most that can be achieved by treating the surface of the inorganic material. Nano-composites, on the other hand, constitute a new class of materials with an ultra-fine phase dispersion (e.g. of clay) of the order of a few nanometers that endows them with unique properties not shared by conventional materials and offers new technological and economic opportunities. Nano-composites can be classified depending on the shape of the nano-filler. Particles are characterized by a three-dimensional nano-size distribution whereas in nano-tubes or whiskers nano-size is limited to two dimensions in space. Finally, in the case of phyllosilicates (e.g. clay) single silicate layers with one-dimensional nano-size can be dispersed in the polymer.The modified matrix in this paper is ethylene vinyl alcohol copolymer (EVOH). EVOH is a thermoplastic resin related to polyvinyl alcohol (PVOH) with improved extrudability and water resistance while maintaining most ofPVOH's advantages: gas barrier, oil resistance, and transparency. EVOH is produced by complete hydrolysis of vinyl acetate groups present in the random copolymer. A high degree of hydrolysis is required (over 99wt %). A particular EVOH composition range is required to achieve good barrier properties, that is, 25–45 mol % ethylene content. If the ethylene content is more than 50 mol %, EVOH is not a high barrier resin, owing to characteristic higher oxygen transmission coefficient values. On the other hand, EVOH is hygroscopic, and thus for practical applications, reduction of oxygen barrier properties owing to moisture absorption cannot be neglected. A wide variety of polymers can be employed in a filmed multilayer structure along with EVOH. Such multilayered structure should conform to EVOH under various processing conditions such as blow molding, thermoforming, and orientation. EVOH offers innovative food-packaging technology owing to reduced oxygen permeability. An outstanding characteristic of EVOH is its high level of hydrogen bonding and the retention of crystallinity in all copolymer compositions, despite the irregularity and non-stereospecificity of the vinyl alcohol segments distributed in the EVOH copolymer chain. This behavior is a result of dense chain packing of the copolymer components, because only small spatial interruptions in EVOH occur owing to the relatively small volume of the hydroxyl groups. Therefore, the randomness of the hydroxyl groups does not have a significant effect on crystallinity reduction as in other random copolymers. Mechanical properties of EVOH depend on the ethylene content. Increasing the ethylene content from 25 to 45mol% leads to strength and modulus decreasing. Elongation increases and impact strength decreases with increase of ethylene content. Presumably, with variation of the ethylene content, the cohesive intermolecular hydrogen bonds and crystallinity are changed, thus affecting chain flexibility. So far, reports on the modification of EVOH are all limited to the filling of layered silicate into the polymer, and there is no record on EVOH based composites filled with spherical nano-particles.Our research group has researched on radiation effect of ethylene-vinyl alcohol copolymers (EVOH). On the basis of this work, my work focuses on theresearch on the preparation, characterization and radiation effect of EVOH/inorganic nano-composites. Using EVOH-56(VA content 56mol%) and EVOH-68(VA content 68mol%) as matrix and different nano-particles as the filler, different kinds of nano-composites were prepared by melt blending. Tensile tests, FTIR and X-Ray were used to characterize the mechanical properties, rheological properties and morphological structure in order to research and compare the following contents: 1. Effects of nano-particles with different chemical structures on the properties of nano-composites. 2. Effects of nano-particles with different interface structures on the properties of nano-composites. 3. Effects of nano-particles with different aggregation statuses on the properties of nano-composites. 4. Effects of matrixes with different VA contents on the properties of nano-composites. 5. Effect of radiation on the properties of nano-composites. The main results of this work are as followings:1. Effects of nano-particles with different chemical structures, interface structures and aggregation statuses on the properties of nano-composites were researched and discussed using models of interaction among phases of composites and structures of MMT nano-composites. Results show that the less is the parameter B in the model of interaction among phases of composites-TPT equation, the better the interaction among phases of composites, the smaller the adhesion degree of the systems, and the better the mechanical properties of the composites. The value of B of EVOH-56/nano-TiO2 composite is higher than that of EVOH-56/nano-ZnO composite, and so are the mechanical properties. The mechanical properties of treated nano-particles filled composites are better than those untreated nano-particles filled composites. The elongation at break of ZQ-602 coupler treated nano-TiO2 filled composite is higher than that of YGO-1203 coupler treated nano-TiO2 filled composite. Nano-fillers with different aggregation structures have different interaction styles with matrixes, but they exhibit almost the same mechanical properties.2. The value of B of EVOH-56/nano-TiO2 is higher than that of EVOH-68/nano-TiO2 composite, and so are the mechanical properties. The valueof B of EVOH-56/nano-ZnO is higher than that of EVOH-68/nano-ZnO composite, and so are the mechanical properties. The mechanical properties of EVOH-56/MMT composites are generally lower than those of EVOH-68/MMT systems. But the elongation at break of EVOH-56/MMT composite has increased to 200% of neat matrix.3. After radiation, the mechanical properties of all the samples were discussed. It is found that mechanical properties of irradiated nano-composites based on EVOH-68 decrease dramatically, while the mechanical properties of irradiated nano-composites based on EVOH-56 improve at low radiation doses and decrease at high radiation doses, and in general have small changes. For nano-composites with different nano-fillers, different systems have different reactions to radiation. EVOH-56/nano-ZnO system exhibits better endurance to radiation than EVOH-56/nano-TiO2 system. At the irradiation doses of 10M,20M and 60M, The mechanical strength of EVOH-56/ZQ602/nano-TiO2 system improves more than EVOH-56/YGO-1203/nano-TiO2 system. At different irradiation doses, EVOH-56/nano-ZnO system, EVOH-56/nano-TiO2 system, EVOH-56/nano-SiO2 system and EVOH-56/nanoMMT system have different mechanical property trends. However, the mechanical strength of EVOH-56/nanoMMT system improves most, increasing to 140% of neat matrix at the irradiation dose of 20M.