Selective laser sintering (SLS) is a desirable method for fabricating human motion detecting sensors as it can produce a complex shape with different materials that are machinable to specific applications. The bottleneck in the SLS processing of sensors is the preparation of a material that is both flexible and conductive. In this study, carbon nanotubes (CNTs) were selected as a conductive nanofiller and dispersed into a flexible thermoplastic polyurethane (TPU) polymer matrix to prepare TPU/CNT composites for SLS processing pressure sensors. CNTs were first oxidized to prevent them from aggregating in the TPU matrix. TPU/CNT composites were prepared via solution blending and ball milling methods, and the dispersion of the CNTs in the composites was observed by scanning electron microscopy. The thermal properties of TPU/CNT composites with different CNT content were measured, and processing parameters used in the SLS were determined based on differential scanning calorimetry measurements. SLS-processed TPU/CNT composites were prepared with different conductivity and piezoresistive properties. Percolation theory and piezoresistive performance results proved that a 0.25 wt% CNT-containing TPU/CNT composite showed the best pressure sensing ability, and it was successfully used as a sensor to detect plantar pressure distribution in a human foot.

In order to explore the effect of printing parameter configurations on the forming performance of Digital Light Processing (DLP) 3D printed samples, printing experiments were carried out on the enhanced adhesion and efficient demolding of DLP 3D printing devices. The molding accuracy and mechanical properties of the printed samples with different thickness configurations were tested. The test results show that when the layer thickness increases from 0.02 mm to 0.22 mm, the dimensional accuracy in the X and Y directions increases first and then decreases, while the dimensional accuracy in the Z direction decreases, and the dimensional accuracy is the highest when the layer thickness is 0.1 mm. The mechanical properties of the samples decline with an increasing layer thickness of the samples. The mechanical properties of the 0.08 mm layer thickness are the best, and the tensile, bending, and impact properties are 22.86 Mpa, 48.4 Mpa, and 35.467 KJ/m², respectively. Under the condition of ensuring molding accuracy, the optimal layer thickness of the printing device is determined to be 0.1 mm. The analysis of the section morphology of samples with different thicknesses illustrates that the fracture of the sample is a river-like brittle fracture, and there are no defects such as pores in the section of samples.

In order to recycle agricultural and forestry waste and reduce the cost of materials, energy consumption and CO₂ emission of the laser sintering process, herein, a sustainable and low-cost walnut shell/Co-PES composite (WSPC) is developed as a feedstock for laser sintering technology. Laser sintering experiments are performed to study the formability of WSPC. Through single layer sintering, the optimal mixture ratio of walnut shell powder and Co-PES was determined, which is 1 : 4 by weight. Moreover, the microstructure and dispersity of walnut shell particles in the WSPC prototype were examined via scanning electron microscopy (SEM). In addition, it is shown that the WSPC parts have good forming accuracy and mechanical properties. The tensile strength, bending strength and impact strength of the WSPC parts are 6.0801 MPa, 9.6759 MPa and 0.8102 kJ m⁻², respectively. In order to improve the strength of the WSPC parts, their internal pores were filled with infiltrating wax through post-processing. The result shows that the density of the WSPC parts considerably increases and their average tensile strength, bending strength and impact strength increase to 6.5879 MPa, 11.0822 MPa and 0.9504 kJ m⁻², respectively.

A novel forming method of enhanced adhesion-efficient demolding integration is proposed to solve the problems of weak adhesion between the initial forming layer and the printing platform as well as the excessive stripping force at the bottom of the liquid tank when the printing platform rises. Therefore, a digital light processing (DLP) 3D printing forming device equipped with a porous replaceable printing platform and a swing mechanism for the liquid tank is manufactured and verified by experiments. The experimental results show that the porous printing platform can enhance the adhesion between the initial forming layer and the printing platform and improve the demolding efficiency of the forming device. In addition, the pull-out design of the printing platform plate reduces the maintenance cost of the forming device. Therefore, the device has a good application prospect.

To alleviate resource shortage, reduce the cost of materials consumption and the pollution of agricultural and forestry waste, walnut shell composites (WSPC) consisting of walnut shell as additive and copolyester hot melt adhesive (Co-PES) as binder was developed as the feedstock of selective laser sintering (SLS). WSPC parts with different ingredient proportions were fabricated by SLS and processed through after-treatment technology. The density, mechanical properties and surface quality of WSPC parts before and after post processing were analyzed via formula method, mechanical test and scanning electron microscopy (SEM), respectively. Results show that, when the volume fraction of the walnut shell powder in the WSPC reaches the maximum (40%), sintered WSPC parts have the smallest warping deformation and the highest dimension precision, although the surface quality, density, and mechanical properties are low. However, performing permeating resin as the after-treatment technology could considerably increase the tensile, bending and impact strength by 496%, 464%, and 516%, respectively.

Agricultural and forestry wastes are used as materials for selective laser sintering (SLS) to alleviate resource shortage, reduce the pollution of the environment, lower the cost of materials, and improve the accuracy of parts produced by SLS. However, the mechanical properties of wood–plastic parts are poor, and thus they cannot be applied widely. In order to improve the mechanical properties of wood–plastic parts, a new type of walnut shell polymer composite (WSPC) was prepared by a polymer mixing method and was used to produce parts via SLS. Additionally, the dimensional accuracy, morphologies, density, and mechanical properties of the WSPC parts were studied. The results showed that the addition of a small amount of copolyamide (Co-PA) powder could effectively improve the mechanical properties and decrease the density of the WSPC parts. By increasing the amount of Co-PA powder and decreasing that of copolyester (Co-PES) powder, the mechanical properties first increased, then decreased, and finally increased again; in addition, the density first decreased then increased. By increasing the preheating temperature, the mechanical properties and density of the WSPC parts were enhanced.