Preparation of lignin-based polyelectrolyte film and its mechanical properties

ObjectiveThe industrial waste lignin was modified to prepare trimethyl-lignin quaternary amine salt (TLQA). The polyelectrolyte film was prepared by compounding TLQA with carboxymethylated polyvinyl alcohol (CMPVA) which was the modified product from polyvinyl alcohol. The influence of different factors on the mechanical properties of polyelectrolyte films was analyzed, and the structure and thermal stability of the films were characterized. The results will provide theoretical basis for the application of lignin-based polyelectrolytes in sustained release, plastic film and packaging.

MethodFirst, quaternization of lignin and carboxymethylation of polyvinyl alcohol were carried out respectively to prepare cationic and anionic polyelectrolytes. With formaldehyde cross-linking agent and polyvinyl alcohol film-forming agent, TLQA/CMPVA reaction film was prepared by a casting method. The structure, morphology and thermal properties of polyelectrolyte films were characterized by FTIR, SEM and TG.

ResultThe molality of R₄N⁺ of TLQA was 1.81mmol/g, and that of —COO^- of CMPVA was 0.62 mmol/g. The optimum conditions to prepare film of best mechanical properties were as follows: the total solid content of polyelectrolyte crosslinked film was 10%, polyvinyl alcohol accounted for 30% of the solid content, TLQA and CMPVA accounted for 70% of the solid content (mass ratio of TLQA to CMPVA was 3:7), and formaldehyde mass fraction was 3.88%, pH 9. Elongation-at-break (EB) and tensile strength (TS) of TLQA/CMPVA reaction film were 222.13% and 6.80 MPa, respectively. The surface of reaction film was smooth and the section was uneven, while the surface of blend film was rough. The ether bond was formed in TLQA/CMPVA reaction film. The thermal stability of TLQA/CMPVA reaction film increased after formaldehyde crosslinking.

ConclusionWith polyvinyl alcohol film-forming agent and formaldehyde cross-linking agent, TLQA/CMPVA reaction film with good slow-release performance and improved thermal stability can be obtained by the modification of lignin and polyvinyl alcohol.