Reversibly Crystalline Nanoparticles from Cellulose Alkyl Esters via Nanoprecipitation

Abstract

Nanoparticles (NPs) from biopolymers, in particular polysaccharides, attract much attention but they are rarely systematically investigated in comparison to NPs from synthetic polymers. In this report, stable aqueous suspensions of NPs from cellulose alkyl esters with different alkyl chain lengths (cellulose stearoyl, lauroyl, and caproyl ester) and degrees of substitution (DS) are fabricated via nanoprecipitation. Their properties are investigated in terms of the average size, surface charge and polarity, temperature‐responsive crystalline structure, and dry‐state morphology, in relationship with the chemical compositions of cellulose esters. Generally, the average diameters of NPs increase with higher DS and longer alkyl chains length, but the surface hydrophobicity decreases with longer alkyl chain length. The presence of the crystallizable stearoyl groups along polymeric backbones renders polymeric NPs with reversibly temperature‐responsive property. The NPs from cellulose stearoyl esters (CSE) with stearoyl groups of high contents (DS of 1.3 and 3) and poly(vinyl stearate) can be altered between more crystalline, solid nanospheres, and amorphous, liquid nanodroplets without the loss of their stability by changing the temperature. In comparison, NPs from CSE with a low DS of 0.3, cellulose lauroyl and caproyl ester contain only slightly ordered structure.