Monitoring the Thermal Gelation of Cellulose Ethers in situ Using Attenuated Total Reflectance Fourier Transform Infrared Spectroscopy

Abstract

In this work attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy was used to probe the thermal gelation behavior of aqueous solutions of hydroxypropyl methylcellulose (HPMC), specifically thermal gelation and accompanying precipitation. Cloud point measurements are usually evaluated through turbidity in dilute solutions but the method cannot readily be applied to more concentrated or highly viscous solutions. From the ATR-FTIR data, intensity changes of the nu(CO) band marked the onset of gelation and information about the temperature of gelation and the effect of the gel structure on the water hydrogen bonding network was elucidated. Changes in the relative intensities of bands associated with the methoxyl groups and hydrogen-bond-forming secondary alcohol groups indicated that hydrophobic polymer chain interactions were involved in the gelation process. The dominance of inter-molecular H bonding over intra-molecular H bonding within the cellulose ether in solution was also observed. The ATR-FTIR data was in good agreement with measurements of turbidity conducted on the same systems. The work indicates significant potential for the use of ATR-FTIR for the investigation of gelation and cloud point measurements in viscous cellulosic formulations.

Cellulose-Derivatives-Based Hydrogels as Vehicles for Dermal and Transdermal Drug Delivery

“…Although the gelation of MC has been extensively studied by various analytical techniques (NMR, differential scanning calorimetry, IR attenuated total reflectance spectroscopy, small-angle neutron scattering, static and dynamic light scattering, and rheology) and the researchers have proposed different gelation mechanisms, the specific molecular interactions that govern this process is still unclear. However, the results of various studies, which were in good agreement one with another, indicated several factors and/or phenomena which play an important role in the gelation of MC [24,[51][52][53][54][55][56][57][58][59][60][61][62][63][64]:…”

“…Thus, the additives that impart a solubilizing effect (i.e., ethanol, propyleneglycol, PEG 400) raise the gel point of HPMC, whereas the additives that exhibit a coagulant effect (i.e., glycerol, sorbitol, and most electrolytes) lower the gel temperature. In the past decade, numerous studies on thermoreversible gelation behavior of HPMC solutions have been carried out [22][23][24][25][26].…”

“…Usually, the watersoluble cellulose derivatives form hydrogels in the concentrations of 1-10% (by weight), depending on the polymerization degree. The gelation of cellulose ether derivatives has been extensively studied for decades and numerous of these studies have been reviewed in several scientific journals and books [24,[39][40][41][42][43][44][45][46][47].…”

Calculation of conformations and vibrational spectra of a monomeric fragment of the 2,6-carboxymethyl cellulose molecule

“…In [1,2], in an investigation Table 3. The lines join the frequencies of normal vibrations for different conformers with comparable modes of vibration.…”

Sustained Release Pellets Based on Poly(N-Isopropyl Acrylamide): Matrix and In Situ Photopolymerization-Coated Systems

“…Most temperature-sensitive polymeric excipients have a LCST too high to be useful for this purpose (e.g., cellulose ethers above 418C). 7 By contrast, poly(Nisopropyl acrylamide), PNIPA, exhibits the LCST at around 338C, 8 which is not significantly altered by saliva components or gastrointestinal fluids. 9 Owing to its LCST, PNIPA cross-linked hydrogels undergo intense volume phase-transitions.…”