Development of Sustainable Hierarchical Bio-composites for Industrial Applications

自然界产生了许多具有优异机械性能和多种应用潜力的分层复合材料（例如，木材，其结合了具有不同结构和功能的分层不同的微米和纳米级组分，图1a）。利用废物和可再生资源设计和开发此类材料将是迈向可持续和更绿色世界的重要一步，并可在不同工业应用中大大取代木基产品（减少毁林）和不可再生合成产品（减少环境影响）。最近由葡萄牙米尼奥大学的Rana博士监督的研究显示，使用市售微晶纤维素开发的分层复合材料2取得了令人鼓舞的结果。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，农业废物衍生的纳米级NC和可再生聚合物基质。该项目有以下目标/工作包：1）从农业废物中提取纳米纤维素：将使用物理方法从农业废物中提取纳米纤维素，例如高压均质结合超声波处理。不同的工艺参数（例如，均质器的速度/压力、超声处理时间、温度等）将进行优化，以获得具有一致结构、尺寸和结晶度的NC，并使工艺产率最大化。2)将纳米纤维素分散到生物基聚合物树脂中：使用超声处理将NC分散在生物树脂中。含有不同NC重量%的悬浮液并在不同的条件下（时间和温度）制备的，将进行表征（使用TEM，光学显微镜，UV-Vis等）。3）植物纤维表面的纳米化处理：利用植物纤维与聚合物之间形成的弱界面，通过等离子体处理对其表面进行纳米化处理，改善纤维/生物树脂基体的界面。4)分层复合材料的制造和表征：分层复合材料将通过用NC分散树脂浸渍植物纤维（使用压缩成型）并随后固化它们来开发。然后测试它们的密度、吸湿性、强度和刚度、动态力学性能、抗冲击和耐火性、热膨胀和降解等。5）工艺参数的优化：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.