Thermally expandable cellulose-based microspheres having low expansion temperatures

Thermally expandable microspheres comprising a polymeric shell surrounding a single hollow core, wherein the single hollow core comprises a C4 to C12 iso-alkane blowing agent, and the polymeric shell comprises a carboxylate-functionalised cellulose, wherein the thermally expandable microspheres have a temperature at which expansion starts, TStart, of from 89° C. to 128° C.,

• wherein the polymeric shell further comprises a polymer shell enhancer in the form of a crosslinker or a hydrogen bond donor,
• wherein if the cross-linker is utilized, the crosslinker is 1,2,4,5-benzenetetracarboxylic acid dianhydride (PMDA) or benzophenone tetracarboxylic dianhydride (BPDT);
• wherein a molar ratio of polymerizable functional groups of the crosslinker to functional groups suitable for crosslinking of the carboxylate-functionalised cellulose is from 0.3/1 (mol/mol) to 1.2/1 (mol/mol);
• wherein if the hydrogen bond donor is utilized, the hydrogen bond donor is 1,2,3,4-butanetetracarboxylic acid (BTCA), 1,2,4,5-benzenetetracarboxylic acid (PMA), or citric acid;
• wherein an amount of the hydrogen bond donor is from 10 to 20 wt %, the wt % being based on the total weight of the polymer shell enhancer and the carboxylate-functionalised cellulose;
• wherein the carboxylate-functionalised cellulose is a cellulose acetate propionate (CAP) having a number average molecular weight (Mn) in the range of from 2,000 to 30,000 Da or a cellulose acetate butyrate (CAB) having a number average molecular weight (Mn) in the range of from 2,000 to 30,000 Da;
• wherein the microspheres have a TMA density of from 22 to 127 g dm−3;
• and
• wherein an amount of the C4 to C12 iso-alkane blowing agent present in the microspheres after four weeks of storage is at least 70% and up to less than 100% of a weight of the original amount of the C4 to C12 iso-alkane blowing agent present in the microspheres.