The effect of co-spray drying with polyethylene glycol 4000 on the crystallinity and physical form of lactose

The effect of spray drying lactose alone and in the presence of polyethylene glycol 4000 was investigated. Lactose was added to distilled water to give concentrations of 10, 20, 30 and 40g/100ml at room temperature and each spray dried in turn. Identical samples were prepared to which polyethylene glycol (PEG) 4000 was added (12% by weight of lactose) prior to spray drying. Microcalorimetric and X-ray diffraction studies showed that spray drying lactose solutions produced completely amorphous material due to rapid solidification during the spray drying process, whereas lactose suspensions yielded partially crystalline products due to crystalline material that remained in suspension. However, all the PEG/lactose (12%w/w) co-spray dried products were found to be crystalline. It can be inferred that the solidification rates of the lactose in the presence of PEG must have been slower than that of lactose alone which allowed PEG and lactose to crystallize. The PEG/lactose products that were spray dried from solution consisted of alpha-anhydrous, alpha-monohydrate, beta-lactose and PEG extended chain polymorph, whereas those formed from suspension PEG/lactose samples consisted of only alpha-anhydrous, alpha-monohydrate and extended chain PEG crystals. PEG probably caused the more concentrated lactose suspensions to crystallize slowly due to the strong hydrogen bonding between PEG and water, which allowed growth on the alpha-lactose seed crystals.