Ethylene-vinyl acetate copolymer melting range

This type of adhesive is generally useful in the temperature range where the material is either leathery or mbbery, ie, between the glass-transition temperature and the melt temperature. Hot-melt adhesives are based on thermoplastic polymers that may be compounded or uncompounded ethylene—vinyl acetate copolymers, paraffin waxes, polypropylene, phenoxy resins, styrene—butadiene copolymers, ethylene—ethyl acrylate copolymers, and low, and low density polypropylene are used in the compounded state polyesters, polyamides, and polyurethanes are used in the mosdy uncompounded state. 

According to the chemical structure of the hot-melt adhesive polymers (polyamide resins, saturated polyester, ethylene vinyl acetate copolymers, polyurethanes), the processing temperatures range between 120 and 240 °C. 

The most widely used thermoplastic polymer is the ethylene—vinyl acetate copolymer, which is obtainable in a wide range of molecular weights as well as in a variety of compositions. Often flexibilizers or plasticizers are added in order to improve both the mechanical shock resistance and the thermal properties of the adhesive. Polybutenes, phthalates, and tricresyl phosphate have been used as plasticizers. Tackifying agents can also be added. Because hot-melt adhesives are frequendy ethylene-based, they are subject to oxidation if, as in a typical situation, the adhesive sits in an applicator for long periods before use. Thus, antioxidants such as hindered phenols are often used, as are fillers. Fillers are added to opacify or to modify the adhesive s flow characteristics, as well as to reduce cost. Wax is also a very important component. Wax alters surface characteristics by decreasing both the liquid adhesive s surface tension and its viscosity in the melt. Upon solidification, however, the wax acts to increase the strength of the adhesive. Both paraffin and microcrystalline wax are used (see Waxes). 

Near-infrared diffuse reflectance spectra were measured by use of a rotating drawer for pellets of 12 kinds of ethylene-vinyl acetate copolymers with vinyl acetate comonomer varying in the 7-44 wt% range. An attempt was made to predict the melting points of these copolymers. The potential of near-infrared spectroscopy with that of Raman spectroscopy in the discrimination of copolymers and the prediction of their properties was given. 23 refs. 

Water-based dispersions or emulsions such as polyvinyl acetate, acrylics, polyvinyl chloride and polyvinyl alcohol with plasticizers and tackifiers. In addition, this range can include urea formaldehyde and phenolic adhesives, resins, natural adhesives produced from starch, dextrin, casein, animal glues (see Polyvinyl alcohol in adhesives, Phenolic adhesives single-stage resoles. Phenolic adhesives two-stage novolacs. Animal glues and technical gelatins) and rubber latex (see Emulsion and dispersion adhesives). Solvent-free 100% solids such as polyurethane. Hot melt adhesives include Ethylene-vinyl acetate copolymers, polyolefins, polyamides, polyesters with tackifiers and waxes. More recent additions include cross-linkable systems. 

The product mix of autoclave and tubular reactors are similar in terms of LDPE homopolymers (0.910-0.935 g/cc) and some specialty grades of polyethylene such as ethylene/vinyl acetate copolymers up to about 30 wt% vinyl acetate (VA). However, the autoclave process provides higher levels of vinyl acetate (40 wt%) in ethylene/VA copolymers and additional specialty grades of polyethylene such as ethylene/methyl acrylate, ethylene/acrylic acid and ethylene/n-butyl acrylate. Polyethylene molecular weight can be varied over a wide range with the high-pressure process, with Melt Index values (I ranging from 0.15 to 40. 

The EVA is prepared by controlled hydrolysis of ethylene vinyl acetate copolymer. For most food applications, VA ranging from 5 to 20% is recommended. The EVA has good flexibility (better than LDPE), excellent toughness at low temperatures and heat seal-ability. As the melting temperature is low, it has to be processed at relatively lower tem-... 

As adhesives based on ethylene-vinyl acetate copolymers cover a very wide range of applications, they are used in large quantities. In the case of higher demands on the bond, polyamide- or polyolefin-based hot-melt adhesives are recommended. Highest... 

Early hot melt adhesives were based on ethyl cellulose and animal or hide glues. These were later replaced by synthetic resins such as polyamides and ethylene-vinyl acetate copolymers. More recently a new class of compounds, referred to as block copolymers because of their unique chemical structure, have emerged. These latter compounds are copolymers of styrene and butadiene, isoprene, or ethylene-butylene which tend to widen the flexibility property range of hot melt adhesives. They probably represent the fastest growing segment of the hot melt adhesives market at the present time. Their primary application is in hot melt pressure sensitive adhesives. Polymers based on other than polyolefin resins are discussed in other chapters in this handbook. 

The ethylene-vinyl acetate copolymers cover a wide range of compositions and melt indices, as shown in Fig. 1. 

Ethylene Copolymers. Ethylene copolymers probably are the most important materials in hot-melt formulations. Ethylene-vinyl acetate and ethylene-ethyl acrylate polymers are very versatile and available in a wide range of grades offering different co-monomer contents and viscosities. The melts are stable and compatible with various modifying resins, waxes, extenders, and fillers. Adhesion to many substrates is good—including the polyolefin plastics, which are difficult to bond with most other types of adhesive unless the surfaces are pre-treated. 

EVA-copolymers are used as sealants. With vinyl acetate contents ranging from 15-40 % these copolymers are particularly applicable for the production of hot melts because of their good compatibility with fillers and other plastics. Ethylene vinyl alcohol copolymer (EVOH) is a plastic with exceptional barrier properties. It is manufactured by saponification of EVA. 

Ethylene-Vinyl Acetate EVA). The addition of vinyl acetate to ethylene imparts flexibility, impact and stress crack resistance, optical clarity, and melt adhesive properties. EVA copolymers are used extensively as hot-melt adhesives, in biomedical applications as drug delivery devices, and as a foam in a broad range of sports equipment. 

The early hot melt adhesives were not strictly definable as rubber-based adhesives. Most rubber polymers such as natural rubber and random SBR are of such molecular weight and structure that they do not melt readily to a workable coating consistency at a temperature below which thermal degradation and decomposition take place. Certain synthetic polymers, however, lend themselves to the formulation of a wide range of hot melt adhesive compositions. Polyamide and polyester resins, ethylene-vinyl acetate (EVA) copolymers, ethylene-ethyl acrylate (EEA) copolymers, low molecular weight polyethylene and amorphous polypropylene, and certain vinyl ethers have found application in hot melt adhesives. These adhesives have found wide use in packaging, industrial, and construction applications. 

A hot melt adhesive is heated to a viscosity of approximately 10 000 cP and can be coated at speeds as high as 800 mpm, typically onto papers and films. Most hot melt coating processes apply either pressure-sensitive adhesives or permanent adhesives. Pressure sensitive adhesives are applied within the converting industry in web width ranges over 2 m with a coating thickness up to approximately 100 g/m. The adhesives include ethylene vinyl acetate (EVA) copolymers, sty-rene-isoprene-styrene (SIS) copolymers, styrene-butadiene-styrene (SBS) copolymers, ethylene ethyl acrylate copolymers (EEA), and polyurethane reactive (PUR) pressure sensitive formulations. 

Specialty waxes include polar waxes for more polar adhesive systems. Examples would be castor wax (triglyceride of 12-hydroxy stearic acid) or Paracin wax N- 2 hydroxy ethyl)-12-hydroxy stearamide) which are used in polyester, polyamide, or with high VA EVA copolymer-based systems. Other common polar waxes are maleated polyethylenes, which are used to improve the specific adhesion of polyethylene-based adhesives, and low molecular weight ethylene copolymers with vinyl acetate or acrylic acid, which are used to improve low temperature adhesion. High melting point isotactic polypropylene wax (7 155°C) and highly refined paraffin wax (7,n 83°C) are used where maximum heat resistance is critical. Needless to say, these specialty waxes also command a premium price, ranging from 2 to 5 times that of conventional paraffin wax. 

Ethylene-copolymer melts generally have a vinyl acetate proportion of approx. 5 to 35% by weight, equivalent to a melt index of Ml216/i9o°c=2 to 500 g/10 min. The melt temperatures in the low-pressure trap range from 160 to 200 °C, depending on the viscosity of the melt. Depending on the polymerization and on the pressure in the low-pressure trap, the melt contains free vinyl acetate (approx. 4000 ppm) in addition to the known ethylene content of... 

The compositions in this article are expressed as percentages by weight.) Bulk polymerization is widely used for polymers of 40-50% VA, and an emulsion process for those over 60% VA. In the intermediate range (15-60%), solution polymerization may be used. Both low (10-40%) and high (60-95%) VA materials have adhesive applications, the former as Hot melt adhesives, the latter as emulsion adhesives (see Emulsion and dispersion adhesives). The term vinyl acetate-ethylene is sometimes used to describe the copolymers rich in VA. 

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