Melting-point temperature paraffins

I. Bake the glass slide with tissue sections approximately 5°C above the melting point temperature of paraffin in the oven for 15 min for improving the tissue section adhesive. The melting point temperature of paraffin depends on the specific paraffin product used. 

While tissue is in xylene, gradual infiltration with paraffin is carried out. For tissues of a small size, 2 to 3 hr of paraffin infiltration is adequate. For large tissues (5-10 mm), overnight infiltration is required. The temperature during infiltration must not be higher than 4° above the melting point of paraffin (54-58°C). 

Evaporation Retardants. Small molecule solvents that make up the most effective paint removers also have high vapor pressure and evaporate easily, sometimes before the remover has time to penetrate the finish. Low vapor pressure cosolvents are added to help reduce evaporation. The best approach has been to add a low melting point paraffin wax (mp = 46-57° C) to the paint remover formulation. When evaporation occurs the solvent is chilled and the wax is shocked-out forming a film on the surface of the remover that acts as a barrier to evaporation (5,6). The addition of certain esters enhances the effectiveness of the wax film. It is important not to break the wax film with excessive bmshing or scraping until the remover has penetrated and lifted the finish from the substrate. Likewise, it is important that the remover be used at warm temperatures, since at cool temperatures the wax film may not form, or if it does it will be brittle and fracture. Rapid evaporation occurs when the wax film is absent or broken. 

Matthews-Akgerman The free-volume approach of Hildebrand was shown to be valid for binary, dilute liquid paraffin mixtures (as well as self-diffusion), consisting of solutes from Cg to Cig and solvents of Cg and C o- The term they referred to as the diffusion volume was simply correlated with the critical volume, as = 0.308 V. We can infer from Table 5-15 that this is approximately related to the volume at the melting point as = 0.945 V, . Their correlation was vahd for diffusion of linear alkanes at temperatures up to 300°C and pressures up to 3.45 MPa. Matthews et al. and Erkey and Akger-man completea similar studies of diffusion of alkanes, restricted to /1-hexadecane and /i-octane, respectively, as the solvents. 

It has been shown" that branched polymers have lower melting points and viscosities than linear polymers of the same molecular weight. The viscosity of the silicone fluids is much less affected by temperature than with the corresponding paraffins (see Figure 29.2). 

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. 

The branched polymer has lower density, Melting point, stiffness, surface hardness, etc. These properties are due to branching. The polymer possesses excellent electrical insulating property. The polymer can be considered as a high molecule weight paraffin and is inert. At room temperature, it is insoluble in all solvents. At high temperature it dissolves in hydrocarbon and alogenates hydrocarbons. 

Paraffin wax is a solid crystalline mixture of straight-chain (normal) hydrocarbons ranging from 20 to 30 carbon atoms per molecule and even higher. Wax constituents are solid at ordinary temperatures [25°C (77°F)], whereas petrolatum (petroleum jelly) does contain both solid and liquid hydrocarbons. The melting point of wax is not always directly related to its boiling point, because wax contains hydrocarbons of different chemical structure. 

The monodisperse fragmentation process can be extended to produce monodis-perse solid particles [156], The general strategy consists of performing the emulsification in conditions such that the dispersed phase is in the liquid state, and to solidify the drops either by a temperature quench or through polymerization. The microscopic image in Fig. 1.29 illustrates this possibility. It corresponds to solid paraffin oil dispersed in water at room temperature. The emulsification was performed in the liquid state, at a temperature above the melting point of the... 

CST of nonhydrocarbons, if any, with each solvent in Table I are placed below those of the hydrocarbons, and in alphabetical order. Again melting points or critical temperatures, etc, are given when pertinent. These serve to explain the use of <, since the actual CST are often not attainable. For paraffin wax the melting point may be merely a characterization. 

Joyce (29) developed the wax method of spray-particle-size measurement to a high degree of perfection during 1942 to 1946. His technique is based upon the observation that paraffin wax, when heated to a suitable temperature level above its melting point, corresponds closely, in the significant characteristics of viscosity and surface tension, with jet fuel. 

Notes. (1) The safest and most satisfacory bath liquids are the highly stable and heat-resistant Silicone oils. A cheaper alternative is medicinal paraffin it has a low specific heat, is non-flammable and is non-corrosive, but it can only be safely heated to about 220 °C above this temperature it begins to decompose and becomes discoloured. Concentrated sulphuric acid has been suggested for use as a melting point bath fluid but is not recommended. 

Petroleum and the majority of petroleum products are liquids at ambient temperature, and problems that may arise from solidification during normal use are not common. Nevertheless, the melting point is a test (ASTM D-87 and D-127) that is widely used by suppliers of wax and by the wax consumers it is particularly applied to the highly paraffinic or crystalline waxes. 

Paraffin wax is not a true wax, but a purified mixture of high-molecular-weight alkanes with melting points well above room temperature. The true waxes are long-chain esters, discussed in Chapter 25. 

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