Shrinkage volumetric

Shrinkage is often different along the lines of flow and perpendicular to them. It is commonly found that an increase in the melt temperature reduces the along-flow shrinkage but increases the shrinkage across the flow . Volumetric shrinkage is, however, virtually unaffected by melt temperature. 

The isobutane makeup x5 was determined by a volumetric reactor balance. The alkylate yield x4 equals the olefin feed xx plus the isobutane makeup x5 less shrinkage. The volumetric shrinkage can be expressed as 0.22 volume per volume of alkylate yield so that... 

Levi, G. and Karel, M. 1995. Volumetric shrinkage in freeze-dried carbohydrates above their glass transition temperature. Food Res. Int. 28, 145-151. 

Moreira, R. and Sereno, A.M. 2001. Volumetric shrinkage of apple cylinders during osmotic dehydration. In Proceedings of the International Congress on Engineering and Food, ICEF 8 (J. Welti-Chanes, G.V. Barbosa-Canovas, and J.M. Aguilera, eds), Vol. 2, pp. 1351-1355. Technomic Publisher, Lancaster, PA. 

The primary resin of interest is epoxy. Carbon-fiber-epoxy composites represent about 90% of CFRP production. The attractions of epoxy resins are that they polymerize without the generation of condensation products that can cause porosity, they exhibit little volumetric shrinkage during cure which reduces internal stresses, and they are resistant to most chemical environments. Other matrix resins of interest for carbon fibers include the thermosetting phenolics, polyimides, and polybismaleimides, as well as high-temperature thermoplastics such as polyether ether ketone (PEEK), polyethersulfone (PES), and polyphenylene sulfide. 

Dental compositions prepared by Bissinger et al. (4) consisting of an aromatic carbosilane component, (IV), and an unsaturated alkenyl or epoxy component, initiator, and filler had a volumetric shrinkage of less than 2 vol% after polymerization. 

Figure 2. External volumetric shrinkage vs. relative vapor pressure for thin Sitka spruce cross sections containing originally different quarter-saturated salt solutions (29)...

Figure 4. External volumetric shrinkage vs. relative vapor pressure for thin white pine cross sections presoaked in different concentrations of sucrose or invert sugar (31). O, water only C, 6.25% sucrose 0, 12.5% sucrose , 25.0% sucrose , 80.0% sucrose 3, 12.5 invert sugar A, 25.0% invert sugar 60.0% invert sugar.

Table 3.6 shows typical percentage volumetric shrinkage for various reactive adhesive systems during cure. One of the reasons for the great acceptance of epoxy resins as adhesive materials is their low degree of shrinkage on cure relative to other reactive adhesives. 

Microstructure evolution in solids formed from a melt is important in processes such as prilling or casting. For example, in aluminum alloy shape casting the final microstructure depends directly on the as-cast microstructure since the only post-casting process is the heat treatment. The micro-porosity formed owing to the combined effects of the volumetric shrinkage upon the solidification of the melt and the precipitation of the dissolved hydrogen affects the final properties of the aluminum alloy. 

If it is hypothesized that the cell cavity remains constant in size as wood changes moisture content it can be shown (JO) that the volumetric shrinkage Shf of a wood of swollen volume specific gravity Gf can be predicted, based on a modification of Equation 8, as in Equation 10. 

Volumetric shrinkage data on other woods have also indicated that the ratio Shf/Gg tends to approximate the fiber-saturation moisture content Mf. For example, a mean ratio was found for Shf/Gg of 27 for 170 Australian woods (33). Data on tropical woods suggest somewhat lower values for this same ratio. The mean value for 140 Indian woods was approximately 20, considerably lower than the values for U.S. woods. This may indicate that tropical woods are less hygroscopic than temperate-zone woods, possibly because of their higher mean extractive contents. 

It is important to appreciate that water molecules do not penetrate a porous cell wall. Rather the dry cell wall expands as water is adsorbed within the non-crystalline regions of the wall and the accompanying volumetric swelling of the cell wall roughly corresponds to the volume of water adsorbed. Conversely when green wood is dried the volumetric shrinkage of the cell wall corresponds to the volume of adsorbed water that is removed. 

Wood only shrinks when water is lost from the cell walls and it shrinks by an amount that is proportional to the moisture lost below fibre saturation point. To a first approximation the volumetric shrinkage is proportional to the number of water molecules that are adsorbed within the cell wall, and that in turn is related to the number of accessible hydroxyls on the cellulose, hemicelluloses and lignin, and to the amount of cell wall material, i.e. the basic density of the wood (Figure 4.2). 

The axial, radial and tangential shrinkages, which together account for the volumetric shrinkage, are directed by features of wood structure that resist shrinkage, e.g. the quantity of ray tissue in the radial direction, or by features of the... 

The volumetric shrinkage to the oven-dry state is determined by measuring the green and oven-dry volume ... 

Figure 4.2. External volumetric shrinkage of 7/8 in. (22 mm) boards of loblolly pine (Stamm, 1964). The dotted lines extrapolate to the shrinkage intersection point, which is an estimate of the fibre saturation point.

Volumetric shrinkage (%) = MC at fibre saturation (%) X basic density x 10 (2)... 

Figure 4.3. External volumetric shrinkage of 106 different North American hardwoods from the green to oven-dry state plotted against their respective basic densities (Stamm, 1964).

---