Compressive strength humidity effects

Like conventional glass-ionomers, resin-modified glass-ionomers may improve in strength as they age, which indicates that they, too, undergo slow maturation reactions [25,28]. In a study of compressive strength on early commercial resin-modified glass-ionomer cements, the values shown in Table 7.2 were obtained for specimens stored in air at ambient humidity [25]. Storage in an aqueous solution of sodium chloride or in water masked this effect, for reasons explained in Section 7.5.1. 

The analysis described in this paper can be used to make judgements and estimates of the mechanical behavior of paper materials under transient humidity conditions. Changing moisture content results in altered physical and chemical properties of sheets. One example is the surface electrical resistivity of sheets which is known to be an exponential function of the local moisture content. An analysis of the type shown here allows us to predict the electrical property variation under transient humidity conditions. Another example of the applicability of this analysis is in the compressive strength of paper board. It is known that the compressive strength of paper board decreases sharply with changing moisture contents. An analysis based on the thermal and moisture transport effects can easily identify whether thermal and moisture transients are responsible for accelerated loss in compressive strengths of paper materials. 

Generally, extrusion techniques can be successfully employed for production of starch-based foams. The physical properties of loose-fills, such as density, porosity, cell structure, water absorption characteristics, and mechanical properties, are highly dependent on the raw materials and additives. The mechanical behavior of foamed pellets can be adjusted effectively by controlling the cell structure through use of different additives. At room temperature and 50% relative humidity, some mechanical properties, such as compressive strength or compressive modulus of elasticity, are comparable to those of commercial EPS foams. 

By combination of the data, two large models can be calculated which describe the effects of the four adjustable, standardized variables (temperature, relative humidity, starch concentration and compression load) on the crushing strength (Sg) and the SIR of crushing strength after storage (S1R(S)), respectively ... 

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