Moisture absorption prediction

Figure 3.3(a) shows the predicted moisture absorption through the thickness of a carbon fibre laminate [5] after 3 days in 96% RH at 50 C. This illustrates the timescale of the diffusion process. Thus it can take 13 years in a composite laminate of thickness 12 mm before saturation is reached. In service, materials are subjected to variations in temperature and kinetic processes such as diffusion follow the Arrhenius law ... 

Figure 11.4 shows that an increased concentration of plasticizer reduces the hardness of cellulose acetate parts. Figure 11.5 shows that the potential moisture absorption must be accounted for to predict real properties of products in their normal performance conditions. Water acts as co-plasticizer and changes properties of the product depending on the amount of equihbrium moisture absorbed. 

Correlation coefficients were calculated between moisture determined by oven drying and moisture estimated by the InfraAlyzer 400 (R =. 97, tot. 0.99). Averaged SECs of 0.12% are acceptable (Table 20.7). The results obtained for the prediction sets are comparable with those of the calibration sets. The calibration procedure resulted in three to six filters giving significant information including the most significant filter for moisture absorption at 1940 nm. 

Another consideration in modeling the uptake of moisture by adhesives is that the uptake behavior can be different in absorption and desorption and can change with number of sorption cycles. This is illustrated in Fig. 31.13b. It can be seen that the rate of moisture absorption and the equilibrium moisture content increase from the first to second absorption cycle, although there is little difference between the second and third absorption cycles. Desorption is faster than absorption and more closely resembles Fickian diffusion. Mubashar et al. (2009b) proposed a method of incorporating the moisture history effects illustrated in Fig. 31.13b in a finite element-based predictive methodology. 

Q The most detailed studies were reported by Hermansson and Akesson ( , 41) and Hermansson (42) in which the properties of a soy isolate, caseinate, WPC, and model test systems of additive and lean beef or pork were studied. Solubility, swelling, and viscosity (properties reviewed as related to water absorption) were correlated with moisture loss in the raw systems. In cooked systems, the best predictability of meat texture as affected by additive was a statistical model that included the functional properties of swelling and gel strength of protein additive dispersions. 

The stability of toxicant-carrier combinations used in pesticide wettable powder formulations cannot be easily predicted by evaluating various properties of the carrier. Several types of synthetic calcium silicates and their modifications were evaluated for malathion stability and other properties. The carriers were evaluated for pH (slurry), pK (surface acidity), moisture content, absorptive capacity, and/or ion exchange capacity. These properties were correlated with actual malathion stabilities as measured at 40° C. storage for 1, 2, 3, and 7 months. The carrier properties evaluated did not offer a simple means of predicting compatibility in the variety of carriers tested. 

Figure 12.4 depicts the comparison of the measured moisture uptake history for the laminate with NOVA-3D predictions. In general, the model prediction agrees reasonably well with test data over the 112 day period used for this comparison, especially during the absorption cycles. Figure 12.5 shows the predicted evolution of the in-plane stress at the exposed laminate surface with hygrothermal cycling. The increase in in-plane tensile... 

It must be concluded that NIR is not applicable to the prediction of flour baking quality and is of limited use for measurement of ash. However, it may be used on a routine basis for measurement of protein, moisture, starch damage, water absorption, particle size, and color. 

NIR transmission spectroscopy and thermogravimetric analysis (TGA) were used to predict diffusion of water into polyamide 6,6 samples immersed in water at varied temperatures and time. The diffusion was time dependent. The absorption curves were fitted by the use of a time-dependent surface concentration and a water-concentration-dependent diffiisivity. The water diffusivity decreased non-linearly and the activation energy of diffusion increased from 24 to 58 kJ mol with decreasing temperature. The accuracy and feasibility of this method was similar to conventional TGA methods, however FT-NIR provided the possibility of monitoring the moisture concentration on-line and non-destructively [112]. 

The study had three objectives first, changes in NIR spectra were correlated to the time aspirin tablets spent in the hydrator (the calibration had a correlation coefficient of 0.95 and SEE of 18.8 h) second, a calibration was developed for the prediction of tablet salicylic acid content (the researchers ensured that prediction of salicylic acid was based on changes in salicylic acid concentration, and not some related process, such as absorption of moisture, by evaluation of loadings spectra from principal component analysis of the data. The HPLC-determined salicylic acid levels ranged from 0.36 to 1.66 mg, and the NIR method allowed prediction of the degradant with a standard error of 144 mg) and third, the mass of water absorbed by the tablets was determined by NIR spectroscopy. 

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