Materials Horizons Emerging Investigator Series: Associate Professor Dr Xuhui Zhang, Jiangnan University, China
Abstract
Our Emerging Investigator Series features exceptional work by early-career researchers working in the field of materials science.
Xuhui Zhang is an Associate Professor at the School of Chemistry and Materials Engineering, Jiangnan University. He received his PhD in Materials Processing Engineering (2019) from South China University of Technology. In 2020, he joined Jiangnan University, and his current research interests are focused on the design and preparation of bio-based and biodegradable polymer materials with high performance and multiple functions, and the construction of novel multiphase structures in polymers. He presided over one National Natural Science Foundation, one Jiangsu Provincial Natural Science Foundation and one National Post-doctoral Fund project. So far, he has published more than 40 peer-reviewed papers in Mater. Horiz., ACS Macro Lett., ACS Appl. Mater. Interfaces and other journals, and he has served as a young editorial board member for China Plastics Industry.
Read Xuhui Zhang’s Emerging Investigator Series article ‘Soft–hard dual nanophases: a facile strategy for polymer strengthening and toughening’ ( https://doi.org/10.1039/D3MH01763J ) and read more about him in the interview below:
MH: Your recent Materials Horizons Communication reports the construction of soft–hard dual nanophases in polymers. How has your research evolved from your first article to this most recent article and where do you see your research going in future?
XZ: In consideration of the increasingly serious environmental problems at present, we have long focused our research on bio-based and biodegradable polymer materials and have carried out research work in this field for many years. Polylactic acid (PLA) is an emerging commercial bio-based biodegradable material, and the development of high-performance and multi-functional PLA materials is of great significance for alleviating environmental problems. One of the research hotspots of PLA is to toughen it, but the traditional toughening method for PLA will significantly reduce its rigidity, which is also a long-term dilemma faced by traditional polymer materials; that is, it is difficult to balance high rigidity and high ductility. We first designed a series of starch-based core–shell particles (CSS), which can significantly improve the toughness of PLA while maintaining its rigidity. In recent years, we have tried to develop bio-based plasticizers to optimize the performance of PLA by constructing plenty of H-bonds. We have designed a modified tannic acid (mTA) as a bio-based plasticizer; the mTA is a star-shaped multi-armed plasticizer rich in hydroxyl termini. mTA can be uniformly dispersed in PLA and form multiple H-bonds with the ester groups in PLA. By incorporating mTA at a high concentration, the ductility of PLA can be significantly improved, and excellent UV shielding and fluorescence effects can be conferred on PLA. Unfortunately, the yield strength (a readily available indicator of stiffness) of PLA still decreased slightly (less than 20%). Therefore, we intend to introduce rigid components into the plasticized PLA to improve its rigidity. The construction of a nanoscale dispersion is always pursued in the preparation of polymer composites and polymer blends. The large surface area of a nanoscale dispersion phase helps to form plenty of interface interactions and promotes the transfer of force in the polymer. Polymer crystallization includes two processes, nucleation and crystal growth. The high annealing temperature of the traditional method (usually 110–130 °C) will lead to the rapid formation of micron PLA crystals, which is not conducive to the improvement of PLA ductility. Therefore, we attempted to construct plentiful nanoscale PLA crystals in PLA by reducing the annealing temperature and controlling the annealing time, to greatly improve the rigidity of PLA/mTA composites while maintaining its excellent ductility. After numerous attempts, it has been found that nanoscale PLA crystals can be constructed in PLA by annealing at the initial temperature of cold crystallization for a short time, which significantly improves the rigidity of PLA/mTA while maintaining excellent ductility. What’s more, we unexpectedly found that the dispersion of mTA was also optimized, reaching the nanoscale. Prior to this discovery, we did not think that annealing would optimize the dispersion of mTA, but might make mTA dispersion worse or cause it to migrate out, which is why the short annealing time was designed. By repeatedly confirming and ruling out other possible mechanisms (such as transesterification between mTA and PLA and migration of mTA), we believe that the optimized mTA dispersion originates from the diffusion of mTA into the PLA matrix. The diffusion results from the good fluidity of mTA enabled by the unique star-shaped multi-armed structure, the excellent compatibility between mTA and PLA, and the weak movability of PLA segments. Besides, the segment rearrangement during PLA crystallization also promotes the movement and diffusion of mTA.
Nanostructures can give polymers various excellent properties, such as high strength and toughness, hydrophobicity, transparency, stimulus response and so on. In the future, we will develop multifunctional polymer materials with high strength and toughness based on soft–hard dual nanophases in semi-crystalline polymers and promote their practical applications in industrial production. It is worth emphasizing that the controlled annealing method can be simply achieved via adding an annealing section (such as a high temperature roll) on the basis of the existing processing equipment to achieve the large-scale construction of nanoscale structures, which is of great significance for the practical application in industry.
MH: What aspect of your work are you most excited about at the moment?
XZ: Two aspects excite us. The performance of the dual-nanophase PLA is comparable to that of polypropylene, polycarbonate and polyethylene terephthalate, which are widely used commercial resin materials. The dual-nanophase PLA is expected to replace these petroleum-based resins, which is of great significance for promoting the practical application of PLA. We will strive to work with manufacturers and government to bring this basic research result to the pilot scale and commercial application. Another aspect is the optimization of the dispersion of the annealed plasticizer mTA. It is usually believed that annealing will lead to the deterioration or migration of plasticizer dispersion. Our results showed that controlled annealing can optimize the dispersion of plasticizers with specific structures in the polymer. To a certain extent, this work enriches researchers’ knowledge and related theories on annealing and plasticizer dispersion.
MH: In your opinion, what are the most important questions to be asked/answered in this field of research?
XZ: At present, the most important problem to be answered is how to promote the practical application of bio-based and biodegradable materials. Basic research is an integral part of our transition to commercial scale; however, more problems need to be considered for practical application. The following key issues need to be addressed: firstly, comprehensive performance should be met – the structure and performance of the material should be designed according to the specific application scenario. Secondly, the material should be mass-produced – the preparation of materials should be easy to scale up, and it is best to directly scale production through existing processing equipment to reduce costs. Finally, the research should be innovative – the approach for material production/structure design should advance the viewpoints, methods, or technologies in relevant fields. Our current work has initially solved these problems, but some details need to be further explored and perfected in large-scale application.
MH: What do you find most challenging about your research?
XZ: For semi-crystalline polymers, the construction of nanocrystals by controlled annealing is easy to achieve and easy to understand. Therefore, how to study the dispersion trajectory of plasticizers (especially star-shaped multi-arm plasticizers) during the controlled annealing process is the biggest challenge at present. More advanced characterization methods (preferably visual methods) and related theoretical models need to be developed. This is one of the key tasks in our follow-up work and will prompt us to constantly explore new methods and innovative solutions.
MH: In which upcoming conferences or events may our readers meet you?
XZ: I am very willing to attend academic conferences in related fields, such as China’s Annual Polymer Conference, the Polymer Molding and Processing Conference, and the Asia-Australia Composite Materials Conference. These meetings provide us with valuable opportunities to exchange ideas and research results, and prompt us to collaborate on some more innovative and valuable research.
MH: How do you spend your spare time?
XZ: In my spare time, I take part in various activities to enrich myself and keep my body and mind healthy. I go walking, running and mountain climbing to keep myself energetic. I am also very happy to get together with friends to exchange recent observations, ideas and concepts in academic research to maintain my academic enthusiasm.
MH: Can you share one piece of career-related advice or wisdom with other early career scientists?
XZ: First of all, it is important to communicate with researchers from different disciplines, which is of great significance to maintain academic enthusiasm and stimulate new inspiration. Secondly, it is necessary to maintain curiosity and enthusiasm for scientific research. As scientific research needs a vast investment of energy for thinking and practice, curiosity and enthusiasm are the best driving force. Finally, we should pay attention to the advanced research results and top journals in the field continuously to maintain the perspective of our research.
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