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Modification Tutorial of EVA

2022-03-18 Page view : 57 views

Ethylene-vinyl acetate copolymer, abbreviated as EVA, is a plastic composed of non-polarity, crystalline vinyl monomers and non-crystalline vinyl acetate (VA) monomers. EVA’s flexibility, toughness, stress crack resistance, transparency, and compatibility with fillers are better than polyethylene (PE). EVA can be made into various products through molding processes such as extrusion.

Through the blend modification technology, the performance of EVA can be effectively improved, and the scope and adaptability of its application can be expanded. In order to let everyone understand the blending and modification of EVA, Xiaobian has compiled relevant materials for everyone to read.

Factors influencing EVA performance.

01. Effect of VA Content on EVA Performance

The impact of VA content on the performance of EVA is mainly reflected in two aspects.

① Va side groups destroy the crystalline region formed by the polyethylene chain segment, with the increase of VA content, the crystallinity of EVA gradually decreases, when the VA content continues to increase to 40% to 50%, EVA copolymer becomes a completely random structure;

② Since VA is a polar group, with the increase of VA content, the polarity of EVA becomes larger, so that many of its properties have changed, such as tensile strength, heat deformation resistance, chemical corrosion resistance and other properties have decreased, while the permeability friction coefficient, environmental stress crack resistance and other properties have improved.

02. Effect of Molecular Weight Distribution on EVA Performance

EVA lining

EVA with a wide molecular weight distribution, long chains are easier to tangle with each other than short chains, and long chain molecules can absorb most of the deformation energy and show a higher elastic response, so EVA with a wider molecular weight distribution has a large viscosity when subjected to less shear action, which is not easy to flow, but is easier to flow. In actual processing and production, this viscosity/shear relationship due to different molecular weight distributions will have some impact on the selection of EVA raw materials.

In addition, when the molecular weight of EVA increases, the thermal weld strength, melt viscosity, deflection, stiffness, stress fracture resistance and so on of EVA are improved.

03. Infact of Branching Degree of Molecular Chains on EVA Performance

EVA Mould

Compared with EVA and PE molecules, EVA disrupts the original crystallization state due to the introduction of short branches composed of polar groups in the branched chains of molecules, so that EVA tends to “plasticizing effect”, increasing the distance between polymer molecular chains, thereby reducing the crystallinity of the polymer, making EVA softer and more elastic than PE; the spatial steric hindrance of CH3COO-group formation on the EVA molecular chain makes the crystallinity and glassing temperature different from that of low-density polyethylene (LDPE). The thermal stability, aging and other physical and mechanical properties of EVA are also affected.

Modification Method of EVA

01. Fill Modified

Magnesium Hydroxide Filler

Filling is a simple and effective polymer modification method, which can not only maintain the advantages of the polymer itself, but also use the compounding effect to improve the defects, to achieve the goal of improving the comprehensive performance of the polymer. At present, the filling modification of EVA has a trend towards nano-functionalization and filler surface modification technology.

① Filling EVA with hydrotal rocks (LDHs) can improve the bending strength of EVA.

②Filling EVA with magnesium hydroxide (Mg(OH)2) can improve the thermal stability of EVA, improve tensile strength and processing fluidity.

③ The modification of EVA hot melt adhesive with ferric oxide (Fe3O4) particles can improve the adhesion of hot melt adhesive and improve its melt fluidity within a certain range.

④ NANO-SiO2 with a volumetric filling fraction of 4% can maximize the tensile strength of EVA/SiO2 composite materials.

The types of fillers applied to EVA filler modification are further increasing, but there are still many problems in filler modification, how to improve the dispersion of fillers in EVA matrix, etc. The resolution of these issues helps to further improve the performance of EVA.

02. Blending Modification

Blending and modifying EVA can optimize the combination of the properties of different polymers, so that EVA can obtain new properties and improve the performance of a certain aspect. Blending EVA with other polymers with good compatibility is an important aspect of EVA modification research in recent years.

① When 15% EVA-g-MAH is added to the EVA/halogen-free flame retardant copoly polyester (P-PET) blend system, its compatibility, process flow and flame retardancy can be improved.

② In the EVA/high-density polyethylene (HDPE) blending system, when the HDPE content is 15%, the mechanical properties of the spinning and blended fibers are the best.

③ In the EVA/NBR blend system, the highest thermal decomposition temperature can be obtained by adding oxidized diisobenzotride (DCP).

With the development of the third generation of polymer alloy technology, such as interpenetrated polymer network technology, dynamic vulcanization technology, reaction extrusion technology, molecular composite technology, etc., more and better comprehensive performance EVA blending materials will be developed to meet the requirements of various engineering technologies for materials.

03. Other Modifications

In addition to the traditional research on filling and blending modification of EVA, there has also been great research progress in chemical grafting and crosslinking of EVA in recent years, which has laid a good foundation for the development of more varieties of EVA products.

① Benzoyl peroxide (BPO) is used as a crosslinking agent to improve the shape recovery rate of the material.

② EVA-g-PU polymer was obtained by melting grafting method, which obtained better tensile strength and elongation at break than raw materials. And the addition of PU prepolymers can also effectively improve the thermal stability performance of EVA.

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