Wax Blends as Tunable Encapsulants for Soil-Degradable Electronics

Abstract

Printed biodegradable electronics potentially enable the monitoring of various soil parameters at a high spatial density while minimizing cost and waste. A tunable degradable encapsulant is a critical component in a soil-degradable electronic device, as it acts to delay the ingress of water, microbes, and other agents responsible for degradation of underlying functional materials. Here, blends of beeswax and commercial soy wax are presented as tunable biodegradable encapsulant materials for transient soil sensors. Using differential scanning calorimetry, we first show that the blends of the two waxes have limited miscibility, which enables programming of degradation times. Laboratory degradation tests in soil revealed that the longevity of encapsulated devices can be controlled by the ratio of the component soy and beeswax, with up to 100 days with 100% beeswax and less than 10 days with the addition of 25% soy wax by mass. Thicker coatings of 1.6 mm of 10% soy wax in beeswax blends are shown to protect devices for 12 weeks. Additionally, melt-processed beeswax encapsulants are used as a simple method to delay the degradation of otherwise rapidly biodegradable materials, such as wooden stakes, that could be used to house soil-degradable electronic devices.

Wirelessly Powered Sensing Fertilizer for Precision and Sustainable Agriculture

“…Coating sensor devices with natural waxes not only prevents moisture, but also reduces biodegra-dation rates(Figures S3 and S4, Supporting Information). Coating materials such as natural waxes eventually biodegrade, [60][61][62] and it is crucial to consider the coating material selection and coating thickness depending on the set lifetime. It is not necessary to collect degradable sensors after use; therefore, they can be tilled with the soil following crop harvesting.…”

A Transient Printed Soil Decomposition Sensor Based on a Biopolymer Composite Conductor

“…Printed conductive traces comprising a PLA binder have been shown to degrade rapidly in an enzyme solution while staying relatively stable in water [25] and water-soluble traces encapsulated in wax blends have been shown to act as fuses whose failure in soil is easily discernible from failure in wet sand or aqueous solutions. [26] As with methods such as the TBI, monitoring the decomposition of certain materials can shed light on the microbial activity of soil. In that same vein, here we propose that printed biodegradable conductors, comprising the soil-degradable polymer, poly(3hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) as a binder, can act as in situ microbial activity or decomposition sensors (see Figure 1) by monitoring its conductivity with low-cost wireless electronics.…”

“…Printed conductive traces comprising a PLA binder have been shown to degrade rapidly in an enzyme solution while staying relatively stable in water [ 25 ] and water‐soluble traces encapsulated in wax blends have been shown to act as fuses whose failure in soil is easily discernible from failure in wet sand or aqueous solutions. [ 26 ]…”

Degradable π-Conjugated Polymers

“…Sensors can be built into food packaging, − alerting consumers about the quality of the food they consume and preventing food waste (Figure ). Other future applications include environmental monitoring, − where nutrient and humidity levels can be monitored remotely, implantable energy storage devices, , or on-demand drug delivery with integrated biosensors − for targeted release of medicines (Figure ). As these technological advancements evolve, a question arises: what is the fate of these devices once they are no longer needed?…”