Hot-melt viscosity

If polymer A has a hydrogenated rubber block, it will be nearly impossible to tackify, will have very high hot melt viscosity, and might be sticky at elevated... 

Paraffin waxes do not differ much in viscosity, a typical viscosity being 3 + 0.5 cSt at 99°C (210°F). Microcrystalline wax is considerably more viscous and varies over a wide range, 10-20 cSt at 99°C (210°F). Some hot melt viscosities exceed 20,000 cSt at 177°C (350°F). 

Typically, if oil absorption is low, the filler does not change the hot melt viscosity much. Because of this, oil absorption test is often used to characterize the effect of fillers on rheological properties of filled plastics. 

Ability to absorb oil, 101, 124, 129 Aluminum trihydrate, 129 Biodac , 101, 129 Calcium carbonate, 129 Hot melt viscosity, effect on, 129 Kaolin, 129 Mica, 129... 

Hindered amine light stabilizer (HALS), 533 Hindered amines, 526 Hindered phenolic antioxidant, 528 Hindered phenolic compounds, 526 Hollow deck boards, 2, 36, 267, 212, 213, 280 Cross-sections, density, 212, 213 Ribs, 212, 213 Hollow boards, 36 hollow profiles, 229 Homopolymers, 57, 67 Honeywell A-C 950P, 189 Hot melt viscosity, 104, 129, 131 Hot tub (on a deck), 15, 289 Deflection of a deck, under, 290 Dimensions, 289 load, 15... 

Hot-Melt Chemical Families. EVA copolymers are the cheapest hot-melt adhesives and are used in the greatest quantities. Typical properties of these adhesives include sufficient strength between ca. 30 and 50 °C, but limited upper service temperature of 60 - 80 °C, low hot-melt viscosity, and low creep resistance under load with time. Most EVA-based hot-melt adhesives are used to bond paper, fabrics, wood, and some thermoplastics. 

Polybutylene polymers slow oystallization rates are helpful in forming hot-melt adhesives with long open times [67]. Besides the hot-melt viscosity, lap shear strength, T-peel, and open time, the shear adhesion failure temperature (SAFT) of the bonded substrate is an inqxntant noperty for evaluating the effectiveness of the adhesive. The polymer MFI plays an inqxntant part in determining the surface tenqterature at whidi shear adhesion fidlure could occur, as can be seen from Fig. 9.75. The top curve represents the SAFT test results with a 0.5-kg load, whereas the bottom curve shows test results with a 1-kg... 

Viscosity ( C) Thermoplastic Hot-Melts - Viscosity, in Pa.s (Pascal.seconds), at stated temperature. Temperatures given are generally related to processing temperatures, where available they are the upper and lower temperatures of the stated usage range. 

Figure 15 Hot melts viscosity, consistency and hardness versus temperature.

Styrenic block copolymers (SBCs) are also widely used in HMA and PSA appHcations. Most hot melt appHed pressure sensitive adhesives are based on triblock copolymers consisting of SIS or SBS combinations (S = styrene, I = isoprene B = butadiene). Pressure sensitive adhesives typically employ low styrene, high molecular weight SIS polymers while hot melt adhesives usually use higher styrene, lower molecular weight SBCs. Resins compatible with the mid-block of an SBC improves tack properties those compatible with the end blocks control melt viscosity and temperature performance. 

Rosin, modified rosins, and derivatives are used in hot-melt adhesives. They are based primarily on ethylene—vinyl acetate copolymers. The rosin derivative is used in approximately a 1 1 1 concentration with the polymer and a wax. The resin provides specific adhesion to the substrates and reduces the viscosity at elevated temperatures, allowing the adhesive to be appHed as a molten material. 

Low viscosity cellulose propionate butyrate esters containing 3—5% butyryl, 40—50% propionyl, and 2—3% hydroxyl groups have excellent compatibihty with oil-modified alkyd resins (qv) and are used in wood furniture coatings (155). Acetate butyrate esters have been used in such varied apphcations as hot-melt adhesive formulations (156), electrostatically spray-coated powders for fusible, non-cratering coatings on metal surfaces (157—159), contact lenses (qv) with improved oxygen permeabiUty and excellent wear characteristics (160—162), and as reverse-osmosis membranes for desalination of water (163). 

Another major area of use is in the field of adhesives. The main attractions of the material are the absence of a need for mastication, easy solvation of the polymer, which is supplied in a crumb form, the production of low-viscosity solutions and high joint strength. In conjunction with aromatic resins they are used for contact adhesives whilst with aliphatic resin additives they are used for permanently tacky pressure-sensitive adhesives. In addition to being applied from solution they may be applied as a hot melt. 

To produce mouldings from polystyrene with minimum strain it is desirable to inject a melt, homogeneous in its melt viscosity, at a high rate into a hot mould at an injection pressure such that the cavity pressure drops to zero as the melt solidifies. Limitations in the machines available or economic factors may, however, lead to less ideal conditions being employed. 

Pot life is several hours versus several days for conventional non-reactive hot melts. A good reactive urethane is one which exhibits a viscosity rise of less than 10%/h. The slow increase in viscosity with urethane adhesives is due to chain extension via the slow reaction of the active hydrogen of the urethane groups with... 

Hot melt aerylie polymers for UV cure are generally of lower moleeular weight than their solution counterparts in order to maintain an aceeptable application viscosity. Consequently more crosslinks are needed to produce a complete network and thus peel and tack suffer to some degree. Nonetheless, several UV curable materials have been commercialized for PSA tapes and labels. 

Hot melt viscometer. Simple bob in cup viscometers are available which measure viscosity at various temperatures. Fortunately, hot melts are — almost without exception — Newtonian at their application temperatures, so shear rate is not critical. 

In most cases, the allophanate reaction is an undesirable side reaction that can cause problems, such as high-viscosity urethane prepolymers, lower pot lives of curing hot-melt adhesives, or poor shelf lives of certain urethane adhesives. The allophanate reaction may, however, produce some benefits in urethane structural adhesives, e.g., additional crosslinking, additional modulus, and resistance to creep. The same may be said about the biuret reaction, i.e., the reaction product of a substituted urea linkage with isocyanate. The allophanate and biuret linkages are not usually as thermally stable as urethane linkages [8]. 

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