Structure and property relationships in ethylene–vinyl acetate copolymers

Abstract

synopsisThe effects of vinyl acetate content on crystallinity of ethylene-vinyl acetate (E/VA) copolymers were investigated by x-ray diffraction and differential thermal analysis (DTA). The values of these parameters obtained from DTA were found to agree quantitatively with data calculated from x-ray, probability equations, and copolymer theory. The melting points of the crystalline copolymers, and the molar amounts of vinyl acetate to produce a completely amorphous rubber corresponds exactly to that predicted by the Flory theory. The random character expected in E/VA copolymers is thereby confirmed. The physical properties of E/VA copolymers of all ranges of compositions and crystalliiity were determined. Depending directly upon vinyl acetate content, the copolymers changed progressively from highly crystalline polyethylene to semicrystalline polyethylene, a completely amorphous rubber, a soft plastic with a glass transition near room temperature. Properties which were correlated with copolymer composition include: crystallinity, melting point, density, modulus, tensile strength, glass transition, and solubility. Finally, the effect on crystallinity and physical properties of replacing the acetoxy group in E/VA with the smaller, highly polar hydroxyl group (ethylene-vinyl alcohol copolymer) was also investigated. 103 98 77 44 112 113 107 110 Calcd by theory 106.2 97.6 72.0 44.0 100.2 97.6 72.0 44.0 12. L.

Polymorphism and side group location of ethylene copolymers characterized by FTIR and NMR spectroscopy

“…Crystallization perfection will lead to 'blue shift' of the rocking band of the ethylene segments. The higher hydroxyl group content in EVOH copolymers provides more opportunities for hydroxyl groups to be included in the crystalline lattice [7], which in turn causes the crystallization imperfection and the 'red shift' of crystalline bands from 733.8 for EVOH (9) to 730.8 cm 21 for EVOH (28).…”

Combined XPS and contact angle studies of flat and rough ethylene‐vinyl acetate copolymer films

“…Ethylene‐vinyl acetate (EVA) random copolymer is a good example of this class. Nonpolar ethylene monomer (CH 2 CH 2 ) can be readily copolymerized with polar vinyl acetate monomer (CH 2 CHCOOCH 3 ) to yield a range of ethylene‐vinyl acetate (EVA) random copolymers having a wide variety of physical properties 23. When the amount of VA in the copolymer is less than 40 wt %, the copolymer is referred to EVA, poly (ethylene‐ co ‐vinyl acetate), which is widely used as a hot melt adhesive and electrical insulator.…”

“…EVA copolymers are less polar than polyvinyl acetate (PVAc) homopolymer, which is mainly produced by emulsion homo‐ and copolymerization to be used in adhesive and surface coating industries 24. The incorporation of the polar VA comonomer units into a polyethylene backbone chain has many effects to change the final copolymer properties: Crystallinity, tensile yield strength, surface hardness, melting point of the polyethylene decreases and density, impact strength, optical clarity, glass transition temperature, gas permeability, coefficient of friction, and solubility in organic solvents increases with the increase in VA content 23, 25. Polar VA causes a corresponding change in compatibility with other suitable polymers and resins.…”

Reusable dry adhesives based on ethylene vinyl acetate copolymer with strong adhesion

“…Assuming the contact radius equals the radius of microstructures, a = R , hence the unit pull‐off pressure P c of a single pillar can be expressed as equation: where E * is the reduced elastic modulus and γ * is the effective work of adhesion per area . Since the microstructure size is same and the surface energies for EVA and PDMS are in the same order of magnitude, the larger adhesion of EVA samples should mainly attribute to the relatively larger Young's modulus (~48 MPa) compared with PDMS (~0.75 MPa), which may interpret the one‐magnitude‐order adhesion difference with a rough estimation . Conversely, the adhesion forces for three typical dry adhesive samples were tested with first 50 cycles, namely T‐shaped EVA, cylinder‐shaped EVA, and T‐shaped PDMS dry adhesives.…”