Starch humidity

Fig. 36.—Changes in electromagnetic wave damping, A, as a function of starch humidity at various pressures. Three potato-starch varieties are denoted by three different point patterns. (Reprinted with permission from M. Boruch, S. Brzezinski, and A. Palka, Acta Aliment. Pol., 11 (1985) 115-124.)...

Zeleznak and Hoseney [47] found that the glass transition temperature of wheat starch with 13-18.7% moisture varies between 30 and 90 C and that Tg is likely to be lower than room temperature if the starch humidity increases above 20%. Van Soest et al. [48] determined a Tg value of 5 C for extruded potato starch with 14% moisture content, whereas at higher moisture content the Tg could not be determined. Shogren showed that the glass transition temperature for starch with 7-18% moisture content ranged from 140 to 150 C [49, 50]. 

The choice and combinations of different size components must take account of many factors if optimum results are to be obtained. Much has been published regarding the optimisation of size formulations in relation to desizing processes [177-183]. Cotton warp yarns sized with starch are normally woven at high humidity (80% and above) to keep yarn breakages low, as the starch film is brittle at low humidity. It has been shown [183], however, that improved weavability at moderate relative humidity (e.g. 65%) can be obtained using (a) starch/acrylamide or hydroxyethyl starch at not less than 15% add-on or (b) poly(vinyl alcohol), which gave excellent results even at a low add-on of 5-6%. 

Addition of acrylamide to starch improved the performance of cotton yarn more than acrylamide alone, but addition of poly(vinyl alcohol) to starch lowered the performance of the yarn compared with poly(vinyl alcohol) alone. Overall, taking into account economic considerations, stringent pollution requirements and the needs of desizing, the singlecomponent hydroxyethyl starch showed optimum acceptability for weaving performance at moderate relative humidity. 

The sorption of water by excipients derived from cellulose and starch has been considered by numerous workers, with at least three thermodynamic states having been identified [82]. Water may be directly and tightly bound at a 1 1 stoichiometry per anhydroglucose unit, unrestricted water having properties almost equivalent to bulk water, or water having properties intermediate between these two extremes. The water sorption characteristics of potato starch and microcrystalline cellulose have been determined, and comparison of these is found in Fig. 11. While starch freely adsorbs water at essentially all relative humidity values, microcrystalline cellulose only does so at elevated humidity values. These trends have been interpreted in terms of the degree of available cellulosic hydroxy groups on the surfaces, and as a function of the amount of amorphous material present [83]. 

Fig. 12 Percent weight gain associated with the exposure of tablet formulations to 80% relative humidity at 40°C. Formulation A (0) was essentially a 1 11 blend of the drug entity and microcrystalline cellulose, while formulation B ( ) was essentially 1 5.5 5.5 drug-microcrystalline cellulose-starch.

The range of application of shear cell testing methodology is seen in Tables 2-6. Table 3 relates the flow properties of mixtures of spray-dried lactose and bolted lactose. These mixtures, in combination with the excipients tested, cover a broad range of flow. Tables 4 and 5, for example, show lot to lot variations in the flow properties of several materials, and Table 6 shows the variation in flow properties of bolted starch, sucrose, and phenacetin at different relative humidities (RH). Figure 8 presents the yield loci of sucrose at four different consolidation loads. Also shown in the figure are the shear indices determined at each consolidation load. 

In the homogenous mixture of Starch and Polyvinyl alcohol (PVA), 30 % of plasticizer was mixed to make Pure blend. Then 10 % cellulose was mixed into above mixture followed by removal of extra water gave Cellulose-Reinforced starch-PVA blends. The different proportions of Fly ash were mixed into mixture of Cellulose-Reinforced starch-PVA blends to get various fly ash inserted Cellulose-Reinforced starch-PVA blends. Solubility, swelling behaviour and water absorption studies of Fly ash blends were measured at different time intervals at relative humidity of 50-55%. The insertion of Cellulose into starch-PVA blend decreases the solubility of blends due to the hydrophobicity of cellulose, but the solubility further increases by insertion of Fly ash into starch-PVA matrix that indicating the mechanical stability enhancement of blends. The water absorption behaviour of fly ash blends increases rapidly upto 150 min and then no change. The optimum concentration of Fly ash into Cellulose-Reinforced starch-PVA blend was 4%. 

The used tablet ingredients were a-lactose monohydrate (Ph.Eur grade, 100 mesh), rice starch (Ph.Eur. grade) and magnesium stearate (Ph.Eur. grade). Before use the magnesium stearate was sieved through a 210 im sieve. Prior to use, the materials were stored at 20 1 °C and 45 5% relative humidity (RH) for at least one week. 

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 ... 

Tablets prepared with dicalcium phosphate dihydrate increased in crushing strength due to increasing temperatures (A,sir(s) ). The relative humidity had a negative effect on the SIR of crushing strength of the tablets prepared with dicalcium phosphate dihydrate, except for the tablets prepared with potato starch. Also a significant interaction between the temperature and relative humidity effect was seen (A3,sir(S) 0), indicating that the effect of the relative humidity on the SIR of crushing strength of dicalcium phosphate dihydrate tablets depended on the level of temperature and vice versa.

Of the tablets prepared with sodium starch glycolate, only the 6-lactose/sodium starch glycolate combination was influenced by all three adjustable factors (Table 8.8). Moreover, the effect of the relative humidity depended on the level of the temperature as well as the level of the disintegrant concentration and vice versa. 

Figure 8.4 Storage to Initial Ratio of crushing strength (SIR(S)) off-lactose/potato starch tablets, as a function of storage temperature (°C) and storage relative humidity (%RH)...

Each combination behaves differently after storage. In all cases there was an effect of the starch concentration (y i sir(d) is significant). In most cases the relative humidity as well as the interaction between the relative humidity and the disintegrant concentration plays a role in the disintegration time of tablets prepared with either lactose. The dicalcium phosphate dihydrate/rice starch combination is influenced very strongly by the three factors studied. This combination is not suitable for use in tropical countries. Neither is the combination of B-lactose and crospovidone. 

Altieri, P. A. Tessler, M. M. (1996). Water Humidity Resistant Starch Foams, U.S. Patent 5,554,660. 

Note A, stearic acid B, magnesium stearate C, AEROSIL 380 D, lactose E, LUDIPRESS F, corn starch G, AVICEL PH 101 H, methylcellulose I, ethylcellulose J, EUDRAGIT RSPM K, mannitol L, relative humidity M, temperature N-W, pseudo variables. (+) is high level and (-) is low level. 

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