Harmless and degradable mineral plastics, zhejiang University team’s new achievements help green China

2022-06-01 0 By

Plastic is an important artificial material, because of its unique flexibility, plasticity and durability, almost permeate into every aspect of modern life.The main material of plastics today is organic polymers.On the one hand, the covalent bond of carbon elements in the polymer structure leads to the multifunctional properties of plastics.On the other hand, these covalent bonds also give polymer plastics a durability that makes them difficult to degrade under natural conditions.Currently, due to limitations in recycling technology, only about nine percent of plastic can be manually recycled after use, while a large amount is dumped into the environment.Therefore, developing natural and recyclable alternatives to plastic is an urgent task for materials scientists.In the earth’s crust, there is a high abundance of geological minerals that can spontaneously participate in geological cycles and are part of nature.Is it possible to make mineral-based plastics that are sustainable?Recently, scientists at Zhejiang University prepared a mineral-dominated plastic using inorganic ion polymerization and biomimetic mineralization.This plastic has similar flexibility to traditional plastics, and has better hardness and thermal stability than ordinary plastics, and can be dissolved in natural simulation conditions, residual minerals can be returned to nature through geological cycle, the realization of harmless treatment.The paper, titled “A Flexible and Degradable Hybrid Mineral as A Plastic Substitute,” was published in Advanced Materials,Professor Rui-kang Tang and Researcher Zhaoming Liu from the Department of Chemistry, Zhejiang University served as corresponding authors.The main difficulty in preparing mineral-dominated plastics is to eliminate the brittleness of inorganic Materials.In polymer chemistry, chain structure endows polymers with flexibility, and high cross-linking degree of cross-linking network makes polymer materials rigid.This relationship also applies to inorganic materials: the crystalline bulk phase consists of ions connected to each other by ionic bonds, forming a rigid network.We can define ionic crosslinking as the number of ions connected to each other, which is similar to the crosslinking degree in polymer chemistry.Therefore, the degree of ion crosslinking makes the crystal structure rigid and brittle.Reducing the degree of ion crosslinking in inorganic minerals can improve the flexibility of minerals.For example, a polymer-induced liquid precursor (PILP) system that uses a large number of polymers to achieve steric hindrance between inorganic minerals can improve the flexibility of the resulting material.However, to develop mineral-dominated plastics, simply adding lots of polymers is not feasible.It is concluded that the reduction of ion crosslinking degree in mineral structure is the key to improve mineral flexibility during the preparation of mineral-dominated plastics.Calcium phosphate (CaP) is a natural geological mineral with excellent mechanical properties, biocompatibility, biodegradation and environmental protection.In addition, Caps can easily form ionic oligomers and can be prepared on a macro scale.Recent findings by the authors suggest that inorganic ion oligomers can be used as precursors for mineral preparation by “making inorganic materials as polymer materials”.In previous work, this process was dominated by the cross-linking and polymerization of inorganic ion oligomers (defined as inorganic ion polymerization), resulting in the formation of an ion network that maintains the inherent brittleness of minerals.In the process of biological mineralization, organic matter can control inorganic growth to achieve controllable preparation of minerals.Previous studies by the authors have shown that polyvinyl alcohol (PVA, rich in hydroxyl groups) and sodium alginate (SA, rich in carboxyl groups) can strongly interact with CaP ion oligomers.Therefore, PVA and SA are ideal biomimetic polymers for regulating the inorganic ion polymerization process of CaP ion oligomers.Based on the above work, we prepared CaP ion oligomers as precursors, and used PVA and SA as biomimetic organic molecules to control the inorganic ion polymerization of CaP oligomers.Under the regulation of PVA and SA, the CaP oligomer undergoes bionic mineralization and produces flexible CaP nanofibers with periodic structural defects.Interestingly, the authors found that CaP nanofibers, which have periodic structural defects, have lower ionic crosslinking than hydroxyapatite (HAP).As a result, CaP nanofibers become flexible and achieve high curvature.These CaP nanofibers are further layered and assembled into networks and bulk materials, named composite minerals (HMs) due to their mineral composition and low organic polymer content.HMs exhibit plastic-like flexibility and toughness and can be molded into different shapes.Even HM samples with a high mineral content of 81.7wt% can be bent to 90 degrees without brittle fracture.At the same time, their mineral composition gives them greater hardness and thermal stability.The HM sample with mineral content of 81.7wt% had high Young’s modulus (19.52±1.04 GPa) and high hardness (0.78±0.07 GPa).Traditional CaP composites cannot have such high mineral content and maintain structural integrity.Additionally, it is noteworthy that HM samples with mineral content of 81.7wt% retained their original structural integrity after being roasted in a butane blowtorch flame at about 1300°C for 2 minutes.At the same time, HMs can be degraded under natural simulation conditions, and the residual minerals are the same as natural minerals, which can participate in geological cycle.The authors show that mineral-based HMs have similar properties to plastics and are more environmentally friendly, making this material a suitable alternative to traditional plastics to mitigate current plastic pollution.In addition, the raw materials prepared by HMs are readily available, and the production of HMs is simple and economical, ensuring the potential of large-scale industrial production of the material.At the moment of green China construction, the author’s work is of great significance and impact on the fundamental treatment of plastic pollution.- End – reference:1. Yu, Y., Guo, Z., Zhao, Y., Kong, K., Pan, H., Xu, X., Tang, R. and Liu, Z. (2022), A flexible and degradable hybrid mineral as a plastic substitute. Adv. Mater. Accepted Author Manuscript 2107523. https://doi.org/10.1002/adma.202107523