The fulvic acid (FA) was prepared with Xinjiang local weathered coal by HNO3 oxidation technology

and then quaternary fulvic acid (QFA) was synthesized with FA.The QFA intercalated saponite (QFA-saponite) was prepared with saponite by ultrasonic intercalation.Poly(lactic acid) (PLA)/QFA-saponite nanocomposites were in situ polymerized with D

L-lactide and QFA-saponite and with stannous octoate as the catalyst.The effects of polymerization time

polymerization temperature

the addition amount of catalyst and QFA-saponite on the molecular weight of PLA were investigated by orthogonal experiment

respectively.The optimum conditions were as follows:polymerization time was 12 h

the addition amount of stannous octoate was 3 wt%

polymerization temperature was 150 ℃ and the addition amount of QFA-saponite was 2 wt%

respectively.Under the optimum conditions

the molecular weight of PLA/QFA-saponite nanocomposites was 95300.FTIR analysis showed that the quaternary ammonium ions were introduced into fulvic acid.The structure of QFA-saponite was characterized by X-ray diffraction (XRD).It was shown that QFA-saponite had co-existence structure with intercalation and partial exfoliation

and its basal spacing was 1.57 nm

which was increased by 0.17 nm compared with that of saponite.The structure of PLA/QFA-saponite nanocomposites was investigated by XRD

polarized optical microscopy (POM) and thermal gravimetric analysis (TGA)

respectively.The results showed that exfoliated PLA based nanocomposites were obtained by in situ polymerization

and QFA-saponite significantly improved the crystallinity properties and thermal stability of PLA.Antibacterial experiments showed that QFA-saponite had antibacterial and sterilization properties against Escherichia coli

Bacillus subtilis

Aspergillus and Penicillium.Meanwhile

PLA/QFA-saponite nanocomposites also had good antibacterial properties.