Ammonium chloride, potassium iodide, etc.Pharmaceutical excipientsAfter moisture absorption, they are prone to deliquescence and liquefaction. Dry extracts, etc., become sticky and hard after moisture absorption. Powders such as proteins, starch, sodium chloride, and PVP have reduced flowability after moisture absorption, and even deliquesce and agglomerate. The results show that powders after moisture absorption have five kinds of binding forces: mechanical entanglement, three-dimensionality, electrostatic attraction, free liquid, and solid bridges.

After moisture absorption, drugs easily form hydrates, and trace amounts of water can cause them to change from amorphous to hydrated. Powder-likePharmaceutical excipientsMoisture absorption significantly affects operations such as tableting. When the relative humidity is greater than 50%, tartaric acid is difficult to compress, and ranitidine and citric acid are difficult to extrude. Gelatin absorbs moisture, softens, swells, and dissolves. Microcrystalline cellulose and anhydrous lactose show no change in appearance after moisture absorption, but will affect the final quality of the preparation.

For drug or preparation powders,Pharmaceutical excipientsThe results of hygroscopicity studies are as follows:

① As the particle size of the powder decreases, the moisture absorption rate increases. At 25℃, the moisture absorption rate of three kinds of Coptis powder increases with time. The moisture absorption rate of nanopowder is the highest, the conventional powder is the lowest, and the micropowder is in the middle.

② The results show that the increase in the specific surface area of the powder, the crystal defects and amorphous morphology on the powder surface increase its hygroscopicity. When exposed to water vapor, the amorphous substance will reabsorb water to form crystals, thereby releasing excess water.

③ Hygroscopicity affects powder-likePharmaceutical excipientsFlowability. The powder has high flowability, but the surface tension changes after moisture absorption. At the same time, due to the action of capillary force, the attraction between particles increases, and the flowability decreases. If the hygroscopicity continues to increase, the flowability will increase, and the adhesion will decrease. However, when the powder is pressed, it is easy to form a connecting bridge between the powders, which is easily glued together and impacted.

④Pharmaceutical excipientsSuppliers believe that the effect of the hygroscopicity of different powders on flowability is different. The smaller the flowability, the greater the adhesion. Some hygroscopicity has a great influence on flowability, such as sucrose, sodium chloride and potato starch, while others have little or no effect on flowability, such as alginate, gum arabic and Aspergillus niger gum.