Schott H
School of Pharmacy, Temple University, Philadelphia, PA 19140.
J Pharm Sci. 1992 May;81(5):467-70. doi: 10.1002/jps.2600810516.
The swelling limit or equilibrium swelling of semicrystalline or cross-linked polymers and of their gels upon immersion in liquids has been investigated extensively. Few studies, however, have dealt with the kinetics of swelling. Theoretical considerations, based on diffusion-controlled swelling, show that first-order kinetics do not apply, even though deviations during the initial and even middle stages of the swelling process may be relatively small. Extensive studies of swelling rate and equilibrium swelling of supported and unsupported gelatin films have been published. Diffusion was always fast. After it was completed, the rate of swelling was controlled by stress relaxation in the amorphous portion of the polymer network. The rate equations for this process, which also apply to regenerated cellulose, are shown to represent second-order kinetics with respect to the remaining swelling capacity. The following interpretation for the applicability of second-order kinetics to the swelling of semicrystalline polymers, such as gelatin and cellulose, is given. The rate of swelling is assumed to be directly proportional to the percent swelling capacity still available at a given time and to the total internal specific boundary area enclosing those sites capable of swelling that have not yet become hydrated and swollen at that time. The latter, in turn, is also directly proportional to the percent unrealized swelling capacity.
半结晶或交联聚合物及其凝胶在浸入液体时的溶胀极限或平衡溶胀已得到广泛研究。然而，很少有研究涉及溶胀动力学。基于扩散控制溶胀的理论分析表明，即使在溶胀过程的初始阶段甚至中间阶段偏差可能相对较小，但一级动力学并不适用。关于负载型和非负载型明胶膜的溶胀速率和平衡溶胀已有大量研究发表。扩散总是很快。扩散完成后，溶胀速率由聚合物网络无定形部分的应力松弛控制。该过程的速率方程（也适用于再生纤维素）表明，相对于剩余溶胀能力，其呈现二级动力学。对于二级动力学适用于明胶和纤维素等半结晶聚合物溶胀的情况，给出了以下解释。溶胀速率假定与给定时间仍可用的溶胀能力百分比以及包围那些尚未水合和溶胀的可溶胀位点的总内部比表面积成正比。而后者又与未实现的溶胀能力百分比直接成正比。
