1 Introduction

The investigation into regenerated polymers aligns with the internationally advocated principle of promoting environmentally friendly energy conservation [1,2,3]. Among these, regenerated polyethylene terephthalate (rPET) stands out as the most significant category of regenerated polymers [4]. However, its current applications still primarily remain traditional. The exploration of potential value-added functional utilization for rPET has emerged as a new focal point. With the rapid advancement of wearable electronics, there has been a significant surge in interest in flexible sensors. This is primarily attributed to their extensive potential applications in various fields, such as human healthcare monitoring [5,

$$W = \frac{{W_{1} - W_{2} }}{A}$$

where W1 refers to the weight after scratch coating process, W2 refers to the pristine weight of control sample, and A refers to the surface area of the original sample.

2.4 Characterization

Morphology Scanning electron microscopy (FE-SEM, JEOLJSM-840, Japan) and stereo microscope were operated with an EHT of 3.0 kV and a work distance of 8.0 mm to observe the surface and cross section morphology of G/WPU and explore the interface combination of components.

Chemical structure and thermal stability Chemical structure of rPET fabrics before and after scratch coating was measured through Fourier transform infrared spectroscopy (FTIR, Nicolet 5700, Thermo Electron Corporation, USA). The test wavenumber range of nanometer powder was 400–4000 cm−1 with a resolution 0.4 cm−1.

The thermogravimetric analyzer (TG209 F1, Netzsch, Germany) was employed for thermogravimetric analysis (TGA) in nitrogen atmosphere with a heating rate of 10 °C/min across a temperature range of 30–800 °C. The thermal stability of composite fabrics was determined by analyzing the TGA and derivative thermogravimetry (DTG) curves.

Physical properties test Mechanical measurements of fabrics were tested at room temperature using a fabric strength tester (YG026Q). All samples were placed in a standard environment (temperature 25 °C, moisture 65%) for a duration of 24 h to mitigate the potential influence of moisture on the mechanical properties. The dimensions of fabric sample were cut as 80 mm long, 20 mm wide and 5 mm thick. The constant stretching rate was set as 100 mm/min, and the initial distance between the two clips as 50 mm.

Water vapor permeability test In order to assess the breathability of textile sensor, it was placed on top of a beaker filled with hot water, allowing unobstructed passage of water vapor through the fabric. The ASTM E96 inverse cup standard [40] was used to accurately measure its breathability by exploring the water vapor transmittance (WVT) rate. Specifically, the textile sensor was exposed to a temperature of 38 °C, relative humidity of 50%, and wind velocity of 1 m⋅s−1. The WVT rate was calculated as following:

$${\text{WVT rate}} = \frac{{m_{1} - m_{2} }}{S} \times 24$$

where m1 represents the initial weight of beaker, m2 represents the final weight of beaker, and S represents the test area.

Sensing and electrothermal performance test The composite fabrics were connected to the circuit to measure the sensing performance via a sourcemeter (Keithley 2450, USA). In addition, the Joule heating behavior of the composite fabrics (dimensions of 2 × 1 cm2) were incorporated into a circuit connected with a DC bias power source under 1–20 V for thermotherapy. Unless otherwise stated, each experiment was conducted at an ambient temperature of 25 °C and a humidity of 50%.