Can someone help me understand why cellulose acetate butyrate is more hydrophobic than cellulose acetate?
I prepared nanofibers by electospinning of both polymers and both have initially the same contact angle, but after some time (10 mins) the water manages to enter the cellulose acetate nanofiber mat and contact angle changes from 130 to 90 but for CAB no such contact angle decrease is observed?
I know hydrophobicity of CA is dependant on the degree of acetylation and because obtaining DS of 3 is practically impossible, there will always be some hydroxyl groups which can be the reason water gets into it over time. I am not completely sure about CAB, its chemical nature, why is it so hydrophobic, strangely there is not much scientific lit on CAB? Is there a reason for this?
You can find an answer from their structural differences. The macromolecule is more hydrophobic when its hydroxyl groups are substituted by the functional groups with a more longer carbon chain. They prevent water-penetration to the inner pores.
You can find an answer from their structural differences. The macromolecule is more hydrophobic when its hydroxyl groups are substituted by the functional groups with a more longer carbon chain. They prevent water-penetration to the inner pores.
Nodirali is correct. The acetate group just has -CH3 while the butyrate is -CH2CH2CH3. Longer groups
like hexanoate or octanoate would be even more nonpolar.
Cellulose acetate has on average one acetate per cellulose repeat unit (anhydroglucose). Cellulose diacetate (secondary cellulose acetate) has two acetates and is less hydrophilic. Cellulose triacetate (Tricell) is again less polar and soluble in dichloromethane for example.
Cellulose acetate butyrate (CAB) and cellulose acetate propionate (CAP) contain the more hydrophilic butyrate and propionate groups. These latter two cellulose derivates show better film forming capability in coatings and inks; perhaps a surface tension effect. CAB and CAP tend to exhibit lower viscosity solutions hence their use in coatings and inks where high concentration is preferred but application viscosity will be restricted by the coating machinery.
After film forming hydrophobic groups will tend to align at the surface as the films equilibrate, to minimise the surface tension (or surface free energy). CAB and CAP were used as coating on the cloth covered wings of early aircraft; however subsequently cellulose triacetate was found to be a better alternative.
Dear sir,
Here when we talk about butyrate group it is a short-chain fatty acid group.
A fatty acid, consists of one carboxyl group at the end of a linear hydrocarbon containing at least four carbon atoms. Because hydrocarbon chains are nonpolar, fatty acids with long hydrocarbon chains are mainly hydrophobic (insoluble in water) despite having one polar functional group.
Source: HSDB
Record Name: n-BUTYRIC ACID
URL: https://toxnet.nlm.nih.gov/cgi-bin/sis/search/r?dbs+hsdb:@term+@rn+@rel+107-92-6
Source:
https://dlc.dcccd.edu/biology1-3/lipids
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