Relative humidity mechanical properties

Properties of Steam-Treated Film, The properties of film treated with saturated steam at 121 for 20 minutes, the moisture content during treatment being 25%, have been examined in more detail. Compared with unmodified film, it has a lower affinity for water, as evidenced by its high water-equilibrated fibrin content of 57 %, as well as lower water sorption at different relative humidities. Several properties of the water-equilibrated film are directly attributable to its high fibrin content. Thus its opacity is quite low (optical density per mm. of 0.1 to 0.2, compared with 3.0 for water-equilibrated unmodified film) but unmodified film at the same fibrin content (Fig. 32) has a comparable opacity (0.5). Also, the stress-strain curve shows a high initial slope, the mechanical character being tough rather than rubbery it closely resembles the curve for unmodified film at the same fibrin content. 

Because the mechanical properties of hydrophilic fibers are critically dependent on moisture regain, it is vital that such fibers be tested under constant conditions of temperature and humidity. Standard conditions used in the textile industry are 65% relative humidity and 21°C (1,2,21,96). ASTM D1909, D2118, and D2720 Hst accepted commercial moisture regain values used in the buying and selling of fibers. 

The figures given in the table are obtained on mouldings relatively free from orientation and tested under closely controlled conditions of temperature, testing rate, and humidity. Changes in these conditions or the use of additives may profoundly affect these properties. Details of the influence of these factors on mechanical properties have been published in the trade literature but Figures 18.11-18.14 have been included to illustrate some salient features. 

Mechanical properties at 21°C, 65% relative humidity, using 60% minute strain rate)... 

MCC, lactose, calcium phosphate dibasic, and mannitol were selected as common tableting diluents and were evaluated as received from their vendors. These materials are summarized in Table 2. Each material is available from several vendors with multiple grades. Three grades within each excipient were selected for their diverse range of physical and mechanical properties (3). These materials typically comprise 5% to 70% of a formulation. The samples were stored at environmentally controlled laboratory conditions of 20 2°C and 40% 10% relative humidity. 

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