First, the research background
Due to the accumulation of pollution and the loss of valuable resources, materials that are not recycled at the end of their life create a huge environmental and economic burden. Given the rapidly increasing turnover of electronics, e-waste containing toxic substances and precious metals is an urgent environmental, safety and economic issue. However, the recyclability of electronic products rarely becomes the design criterion, and existing recycling procedures lead to secondary contamination and insufficient recycling of valuable parts. Transient electronics are programmed to have an operating life and on-demand conversion. The stimulus response can be designed in a protective layer to control the life of the device. A combination of stimuli including heat, ionic substances, and ultraviolet light needs to be used to degrade several layers. Despite the success of these multilayer materials in electronics, their complexity can increase disposal costs and pose an obstacle to recycling e-waste from existing infrastructure. Embedding enzyme nanoclusters into plastics allows for programming the degradation of polyester under industrial composting conditions. Integrating these new developments into composites could be an ideal entry point for achieving sustainable printed electronics and reducing e-waste.
2. Research results
Due to the rarity and toxicity of heavy metal components, the energy costs and environmental burden of e-waste are comparable to those of plastic waste. Recently, the research group of Professor Xu Ting of the University of California, Berkeley reported on the recyclable conductive composite materials used in printed circuits, which are formulated from polycaprolactone (PCL), conductive fillers and enzyme/protective agent nanoclusters. Circuits can be printed with flexibility (fracture strain ≈80%) and conductivity (2.1×104 S m-1). At the end of their useful life, these composites are degraded by soaking in warm water with a programmable incubation period. Approximately 94% of the functional fillers can be recycled and reused, with similar equipment performance. After storing at room temperature for at least 7 months and continuously operating at voltage for one month, the printed circuit remains functional and degradable. This study provides composite designs for recyclable and easily handlable printed electronics for applications such as wearable electronics, biosensors, and soft robotics. The research work was published in advanced materials, an international top journal, under the title "Conductive Ink with Circular Life Cycle for Printed Electronics".
3. Graphic and text courier
Figure 1. Recovery mechanism of RHP/BC-Lipasenp nanocluster printed circuits
Figure 2. The degradation performance of RHP/BC-Lipasenp nanodispersible PCL adhesives is affected by the molecular weight of RHPs
Degradable composites can provide an opportunity to design conductive inks to fabricate flexible electronic circuits (Figure 1). When formulated using conductive fillers, biodegradable polymer binders and enzymes, the composite ink has mechanical strength, tensile strength of about 6.3 MPa, mechanical flexibility of about 80% fracture strain, conductivity of about 2.1×104 S m-1. Printed circuits at the end of their life are degraded by immersion in warm water, and degradation rates and latency can be programmed by heat treatment. Metal fillers were collected and reused, no loss of function was observed. In the absence of humidity control, at room temperature, after 7 months of storage at 3 V and 1 month of continuous operation, the circuit remains fully functional and degradable. In addition, the process is optimized to be compatible with commercially derived enzymes without purification, an important step towards scalable equipment manufacturing.
Figure 3. E-waste collection
Figure 4. Degradation test at voltage
Figure 5. 3D printing applications
This ink can be printed on a variety of substrates such as glass, rubber, live plants, and biodegradable polyester (Figure 4). Since the printed material is designed to be mechanically flexible and electrically conductive, its mechanical deformation can be detected by monotonic conductivity changes in cyclic tensile tests (1000 times and 1 cycle s-1). The composite can also be manufactured using hot melt extrusion. In this work, the ink is prepared by melting the blended PCL/RHP/BC-Lipasenp and 79.8 wt% Ag flakes for less than 5 min at less than 60 °C, followed by extrusion using a syringe without using any organic solvent. The filaments of molten extrusion also exhibit good electrical conductivity and degrade when immersed in warm water.
4. Conclusions and Outlook
The unrefined BC-Lipase/RHP complex was added to the Ag/PCL composite to make a biodegradable electronic ink. When immersed in warm water, the embedded enzyme catalyzes hydrolytic degradation of the film and the PCL chain in the printed state. This RHP-assisted enzymatic depolymerization makes it easy to separate electronic components and recover functional particles even after months of storage and use under environmental conditions. In addition, temperature and post-heat treatment can be used to regulate the rate of polymer degradation after direct ink writing. Since warm water is the primary source of degradation and recycling, the proposed approach is more sustainable and potentially more cost-effective than using toxic and expensive organic solvents to recycle e-waste consisting of multiple components. These new biodegradable, recyclable, conductive, flexible and printable materials can be applied to many electronic devices as a cornerstone for the development of environmentally friendly, recyclable electronics.
5. Literature
Literature Links:
https://onlinelibrary.wiley.com/doi/10.1002/adma.202202177
Literature sic:
Pay attention to the public account [material PLUS], reply to the background "ink", you can get the original text of the literature.