Development of Sustainable Hierarchical Bio-composites for Industrial Applications

自然界产生了许多层次复合材料（例如木材，它结合了层次不同的微观和纳米级成分，具有不同的结构和功能，图1a），具有优异的机械性能和多样化的应用潜力1。利用废物和可再生资源设计和开发这种材料将是朝着可持续和更绿色的世界迈出的重要一步，并且可以在不同工业应用中大大取代木材产品（减少森林砍伐）和不可再生合成产品（减少环境影响）。在葡萄牙米尼奥大学的Rana博士的指导下，最近的一项研究显示，利用市购微晶纤维素开发的分层复合材料取得了令人鼓舞的成果。受这一初步工作的启发，该博士项目旨在开发分层生物复合材料（图1b），以工程方式结合微尺度可再生植物纤维，农业废弃物衍生的纳米级NC和可再生聚合物基质。项目目标/工作包如下：1)从农业废弃物中提取纳米纤维素：采用高压均质结合超声处理等物理方法从农业废弃物中提取纳米纤维素。将优化不同的工艺参数（如均质机的速度/压力、超声时间、温度等），以获得结构、尺寸和结晶度一致的NC，并最大限度地提高工艺收率。2)将纳米纤维素分散到生物基聚合物树脂中：利用超声波将NC分散到生物树脂中。在不同条件（时间和温度）下制备不同NC wt.%的悬浮液，对其分散质量和稳定性进行表征（使用TEM，光学显微镜，UV-Vis等），并选择最佳条件进行复合开发。3)植物纤维表面的纳米表面工程：由于植物纤维与聚合物形成弱界面，将采用等离子体处理技术对其表面进行纳米工程处理，以改善纤维/生物树脂基质界面。4)层次化复合材料的制备和表征：层次化复合材料将通过用NC分散树脂浸渍植物纤维（采用压缩成型）并随后固化来开发。然后测试它们的密度，吸湿性，强度和刚度，动态机械性能，抗冲击和防火性，热膨胀和降解等。5)工艺参数优化：在最后阶段，将分析所有实验结果，以找出最佳的加工条件，以最大限度地提高性能。

Nature produces numerous hierarchical composites (e.g. wood which combines hierarchically different micro and nano-scale components with different structures and functions, Fig. 1a) with excellent mechanical performance and diverse application potential1. Design and development of such materials using waste products and renewable resources would be an important step towards a sustainable and greener world, and can greatly replace the wood-based products (reducing deforestation) and non-renewable synthetic products (reducing environmental impacts) in different industrial applications. Recent research supervised by Dr. Rana at University of Minho, Portugal showed promising results with hierarchical composites developed using commercially available microcrystalline cellulose2. Inspired by this preliminary work, this PhD project aims to develop hierarchical bio-composites (Fig. 1b) combining, in an engineered way, micro-scale renewable plant fibers, agricultural waste derived nanoscale NC and a renewable polymeric matrix. The project has the following objectives/work packages: 1) Extraction of nanocellulose from agricultural waste: NC will be extracted from agricultural waste using physical methods such as high-pressure homogenization combined with ultrasonication treatment. Different process parameters (e.g. speed/ pressure of homogenizer, ultrasonication time, temp, etc.) will be optimized to obtain NC with consistent structure, size and crystallinity and to maximize the process yield. 2) Dispersion of nanocellulose into a bio-based polymeric resin: NC will be dispersed within the bio-resin using ultrasonication process. Suspensions containing different NC wt.% and prepared at different conditions (time and temperature) will be characterized (using TEM, optical microscope, UV-Vis, etc.) for dispersion quality and stability and the best conditions will be selected for composite development.3) Nano surface engineering of plant fiber surface: As plant fibers form weak interfaces with polymers, their surface will be nano-engineered using plasma treatment to improve fiber/bio-resin matrix interface. 4) Fabrication and characterization of hierarchical composites: Hierarchical composites will be developed by impregnating plant fibers with NC dispersed resin (using compression molding) and subsequently curing them. They will be then tested for density, moisture absorption, strength and stiffness, dynamic mechanical properties, impact and fire resistance, thermal expansion and degradation, etc.5) Optimization of process parameters: At the final stage, all experimental results will be analyzed to find out the optimum set of processing conditions for maximizing performance.