Abstract

We report (1) successful extraction and characterization of cellulose from northern hemisphere green macroalgae Ulva lactuca (Ulva fenestrata) collected along the Swedish west coast and cultivated indoors under controlled conditions, followed by (2) its utilization in the production of lignin-free cellulose nanofibrils (CNF). Cellulose was extracted by sequential treatment with ethanol, hydrogen peroxide, sodium hydroxide, and hydrochloric acid, yielding a cellulose-rich insoluble fraction. The extracted cellulose was disintegrated into CNF using a mechanical homogenization process without any further enzymatic pre-treatments. In addition, regenerated cellulose was prepared. XRD characterization of the CNF showed characteristic peaks for the cellulose I allomorph and confirmed that the nanofibrils were semicrystalline with a crystallinity index of 48%. Regenerated cellulose was mostly amorphous with an XRD pattern indicating the presence of the cellulose II allomorph. The cellulose fractions were essentially free from inorganic substances and thermally stable up to around 260 °C. Structural mapping with CP-MAS ¹³C-NMR sustains the cellulose content of CNF and regenerated cellulose, respectively, yet ion chromatography identified the presence of 10–15% xylose in the fractions. Optotracing was used as a novel and non-disruptive tool to selectively assess the polysaccharide composition of the cellulose fractions and produced CNF aiming to shed light on this hitherto non-resolved origin of xylose in Ulva cell wall matter. Fluorescence excitation and emission spectra of a panel of 4 oligothiophenes identified and verified the presence of cellulose and sustain the conclusion that the isolated fractions consist of cellulose intertwined with a small amount of a xylose-containing glucan copolymer.

Graphic abstract

摘要

我们报告（1）从北半球绿色大型藻类Ulva lactuca（Ulva fenestrata）纤维素的成功提取和表征）收集于瑞典西海岸，并在受控条件下在室内种植，然后（2）将其用于生产不含木质素的纤维素纳米原纤维（CNF）。通过依次用乙醇，过氧化氢，氢氧化钠和盐酸处理来提取纤维素，得到富含纤维素的不溶级分。使用机械均质化方法将提取的纤维素分解为CNF，无需任何进一步的酶预处理。另外，制备了再生纤维素。CNF的XRD表征显示了纤维素I同种异形体的特征峰，并证实了纳米原纤维是半结晶的，其结晶度指数为48％。再生的纤维素大部分是无定形的，具有XRD图谱，表明存在纤维素II同种异形体。纤维素级分基本不含无机物质，并且在高达260°C的温度下具有热稳定性。使用CP-MAS进行结构映射¹³ C-NMR分别维持CNF和再生纤维素的纤维素含量，但是离子色谱法鉴定出馏分中存在10-15％的木糖。光学示踪被用作一种新颖且无干扰的工具，以选择性地评估纤维素级分的多糖组成，并生产了CNF，旨在阐明迄今未解决的木糖在Ulva细胞壁物质中的来源。一组4个低聚噻吩的荧光激发光谱和发射光谱确定并验证了纤维素的存在，并得出以下结论：分离出的馏分由纤维素与少量含木糖的葡聚糖共聚物缠绕在一起组成。

图形摘要