Jiangsu Co-Innovation Center of Efficient Processing and Utilization of Forest Resources, Jiangsu Key Lab of Biomass-Based Green Fuel & Chemicals, College of Chemical Engineering , Nanjing Forestry University , Nanjing 210037 , China.
ACS Nano. 2019 Mar 26;13(3):2927-2935. doi: 10.1021/acsnano.8b07235. Epub 2019 Feb 4.
High yield (>85%) and low-energy deconstruction of never-dried residual marine biomass is proposed following partial deacetylation and microfluidization. This process results in chitin nanofibrils (nanochitin, NCh) of ultrahigh axial size (aspect ratios of up to 500), one of the largest for bioderived nanomaterials. The nanochitins are colloidally stable in water (ζ-potential = +95 mV) and produce highly entangled networks upon pH shift. Viscoelastic and strong hydrogels are formed by ice templating upon freezing and thawing with simultaneous cross-linking. Slow supercooling and ice nucleation at -20 °C make ice crystals grow slowly and exclude nanochitin and cross-linkers, becoming spatially confined at the interface. At a nanochitin concentration as low as 0.4 wt %, highly viscoelastic hydrogels are formed, with a storage modulus of ∼16 kPa, at least an order of magnitude larger compared to those measured for the strongest chitin-derived hydrogels reported so far. Moreover, the water absorption capacity of the hydrogels reaches a value of 466 g g. Lyophilization is effective in producing cryogels with a density that can be tailored in a wide range of values, from 0.89 to 10.83 mg·cm, and corresponding porosity, between 99.24 and 99.94%. Nitrogen adsorption results indicate reversible adsorption and desorption cycles of macroporous structures. A fast shape recovery is registered from compressive stress-strain hysteresis loops. After 80% compressive strain, the cryogels recovered fast and completely upon load release. The extreme values in these and other physical properties have not been achieved before for neither chitin nor nanocellulosic cryogels. They are explained to be the result of (a) the ultrahigh axial ratio of the fibrils and strong covalent interactions; (b) the avoidance of drying before and during processing, a subtle but critical aspect in nanomanufacturing with biobased materials; and (c) ice templating, which makes the hydrogels and cryogels suitable for advanced biobased materials.
提出了一种通过部分脱乙酰化和微流处理实现高得率（>85%）和低能耗的未干燥海洋生物质解构方法。该过程得到了具有超高轴向比（高达 500）的壳聚糖纳米纤维（纳米壳聚糖，NCh），这是生物衍生纳米材料中轴向比最大的一种。纳米壳聚糖在水中（ζ-电位= +95 mV）具有胶体稳定性，并且在 pH 变化时会产生高度缠结的网络。通过冷冻和解冻时的冰模板化以及同时的交联作用形成了粘弹性强的水凝胶。在-20°C 下的缓慢过冷和成核使冰晶缓慢生长，并将纳米壳聚糖和交联剂排除在外，在界面处受到空间限制。在纳米壳聚糖浓度低至 0.4wt%的情况下，形成了具有高粘弹性的水凝胶，其储能模量约为 16 kPa，与迄今为止报道的最强壳聚糖衍生水凝胶相比，至少大一个数量级。此外，水凝胶的吸水率达到 466 gg。冷冻干燥有效地生产出密度可在很宽范围内（0.89 至 10.83 mg·cm）进行调节的冷冻气凝胶，以及对应的孔隙率在 99.24%至 99.94%之间。氮气吸附结果表明具有大孔结构的吸附和解吸循环是可逆的。从压缩应力-应变滞后环中记录到快速的形状恢复。在 80%的压缩应变之后，在负载释放时，冷冻气凝胶迅速且完全地恢复。这些和其他物理性能的极值以前在壳聚糖或纳米纤维素冷冻气凝胶中均未达到过。这被解释为以下因素的结果：（a）纤维的超高轴向比和强共价相互作用；（b）在纳米制造过程中避免了在处理前后的干燥，这是生物基材料的一个微妙但关键的方面；（c）冰模板化，使水凝胶和冷冻气凝胶适用于先进的生物基材料。
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