Effect of stereo-complexation on crystallization behavior and barrier properties of poly-lactide.

The unique stere-complex crystal formed by poly(ʟ-lactide)/poly(ᴅ-lactide) (PLLA/PDLA) has a significant impact on properties of poly-lactide materials and is considered an effective means to improve the barrier properties of poly-lactide (PLA). In this work, poly-lactide films with different aggregate structures were prepared and the relationship of aggregate structure and barrier properties were explored. The results show that the crystal structure including crystallinity and crystal forms can be controlled by adjusting the isothermal crystallization time and crystallization temperature during the molding process. PLLA/PDLA composite films contain both homochiral crystallites and stereo-complex crystallites, and there is a synergistic crystallization effect between the two of them, which provides the composite films with high crystallinity and excellent barrier properties. Compared to the PLLA with homochiral crystallites, the PLLA/PDLA composite film with only stereo-complex crystallites exhibits higher barrier properties. The linear correlation between the crystallinity and the barrier properties is weak due to the changes in crystallization behavior and then the structure of poly-lactide caused by stereo-complexation. The linear correlation between the crystallinity and the barrier properties of the blend film is strong in the low crystallinity but weak at high crystallinity. Compared to homochiral crystallites, stereo-complex crystallites exhibits lower crystallinity dependence. It has been proven that different crystal forms have different design ideas for preparing high-barrier films, but the stereo-complexation resulting from the intermolecular forces between PLLA and PDLA having complementary chemical structure, is an effective method for enhancing the barrier performances of poly-lactide sustainably.

Preparation and properties of O-chitosan quaternary ammonium salt/polyvinyl alcohol/graphene oxide dual self-healing hydrogel.

A simple method had been developed through O-chitosan quaternary ammonium salt (O-HACC), polyvinyl alcohol (PVA) and graphene oxide (GO) to prepare O-HACC/PVA/GO dual self-healing bacteriostatic hydrogels. Then the hydrogels and materials were characterized by FT-IR, X-RD, 1H NMR, SEM and TG. The hydrogel's compressive strength, equilibrium swelling and bacteriostatic efficiency were systematically studied. The research results showed that the maximum equilibrium swelling rate of hydrogel was 720%, the maximum compressive strength was 1500 Pa, and could self-heal within 12 h. In addition, the hydrogel could effectively inhibit E. coli and S. aureus, and also showed a good release behavior for bovine serum albumin (BSA). The CCK-8 method proved that the hydrogel was non-toxic to murine fibroblasts and could promote cell proliferation and growth to a certain extent. This research has potential significance for the application of self-healing hydrogel materials in the field of biomedicine.

Hydroxypropyl chitosan-based dual self-healing hydrogel for adsorption of chromium ions.

A facile, environmentally benign approach had been developed for the preparation of dual self-healing and adsorption hydrogel through hydroxypropyl chitosan (HPCS), polyacrylamide (PAM) and polyvinyl alcohol (PVA). The self-healing capability of the hydrogels without any external stimulus was ascribed to dynamic Schiff-base bonds, borate bonds and hydrogen bonds, while the adsorption capacity of hydrogels came from the protonated amino group effect at a specific pH. It was demonstrated that the HPP DN hydrogel had a maximum equilibrium swelling ratio of 643% and a maximum compressive strength of 267 kPa. The weight loss of HPP DN hydrogel was 14.26% lower than that of HPCS/PAM single network hydrogel, furthermore, HPP DN hydrogel could achieve self-healing within 10 h. Due to the large number of active groups, the adsorption capacity of Cr6+ reached 95.31 mg/g. It could adsorb in a wide pH range of 1 to 6, and could describe by pseudo-first-order kinetic model and Langmuir adsorption isotherm model, which would provide a new idea for the adsorption and removal of heavy metal ions. In short, the prepared HPP hydrogel had dual self-healing ability, adsorption capacity and mechanical strength, which would make it a promising candidate for long-life adsorbent.