Setting the Optimal Laser Power for Sustainable Powder Bed Fusion Processing of Elastomeric Polyesters: A Combined Experimental and Theoretical Study

Additive manufacturing (AM) of polymeric materials offers many benefits, from rapid prototyping to the production of end-use material parts. Powder bed fusion (PBF), more specifically selective laser sintering (SLS), is a very promising AM technology. However, up until now, most SLS research has been directed toward polyamide powders. In addition, only basic models have been put forward that are less directed to the identification of the most suited operating conditions in a sustainable production context. In the present combined experimental and theoretical study, the impacts of several SLS processing parameters (e.g., laser power, part bed temperature, and layer thickness) are investigated for a thermoplastic elastomer polyester by means of colorimetric, morphological, physical, and mechanical analysis of the printed parts. It is shown that an optimal SLS processing window exists in which the printed polyester material presents a higher density and better mechanical properties as well as a low yellowing index, specifically upon using a laser power of 17–20 W. It is further highlighted that the current models are not accurate enough at predicting the laser power at which thermal degradation occurs. Updated and more fundamental equations are therefore proposed, and guidelines are formulated to better assess the laser power for degradation and the maximal temperature achieved during sintering. This is performed by employing the reflection and absorbance of the laser light and taking into account the particle size distribution of the powder material.

Melt Spinning of Flexible and Conductive Immiscible Thermoplastic/Elastomer Monofilament for Water Detection

In many textile fields, such as industrial structures or clothes, one way to detect a specific liquid leak is the electrical conductivity variation of a yarn. This yarn can be developed using melt spun of Conductive Polymer Composites (CPCs), which blend insulating polymer and electrically conductive fillers. This study examines the influence of the proportions of an immiscible thermoplastic/elastomer blend for its implementation and its water detection. The thermoplastic polymer used for the detection property is the polyamide 6.6 (PA6.6) filled with enough carbon nanotubes (CNT) to exceed the percolation threshold. However, the addition of fillers decreases the polymer fluidity, resulting in the difficulty to implement the CPC. Using an immiscible polymers blend with an elastomer, which is a propylene-based elastomer (PBE) permits to increase this fluidity and to create a flexible conductive monofilament. After characterizations (morphology, rheological and mechanical) of this blend (PA6.6CNT/PBE) in different proportions, two principles of water detection are established and carried out with the monofilaments: the principle of absorption and the short circuit. It is found that the morphology of the immiscible polymer blend had a significant role in the water detection.

Powder Surface Roughness as Proxy for Bed Density in Powder Bed Fusion of Polymers

Powder bed fusion of polymers is becoming increasingly adopted by a variety of industries to tailor the strength, weight and functionality of end-use products. To meet the high standards of the modern manufacturing industry, parts built with powder bed fusion require consistent properties and to be free of defects, which is intrinsically connected to the quality of the powder bed prior to melting. The hypothesis of this work is that the roughness of the top surface of an unmelted powder bed can serve as a proxy for the powder bed density, which is known to correlate with final part density. In this study, a laser line scan profilometer is integrated onto the recoater arm of a custom powder test bench, which is able to automatically create layers of powder. A diverse group of polymers was investigated including polyamide 12 (PA12), polyamide 11 (PA11), polypropylene (PP), and a thermoplastic elastomer (TPU) under different recoating speed in order to increase the variance of the dataset. Data analytics were employed to compare roughness to measured powder bed density and a statically significant correlation was established between them.

Effect of Ground Tire Rubber on Mechanical Properties of Low Density Polyethylene

This research explores the effect of ground tire rubber (GTR) on the mechanical properties of LDPE. This thermoplastic-elastomer blend sets the composition of ground tire rubber and low-density polyethylene (LDPE/GTR). The blend was prepared in different proportions and was processed in a compression molding machine. The optimum operating conditions of the blend set to be 220℃ temperature and pressure varied from 150-200 bars. Different parts per hundred rubber (phr) samples were obtained under these conditions, including 1 phr, 2 phr, 3 phr, 4 phr, and 5 phr. After that, the mechanical properties of the blend were examined concerning various compositions. Different testing methods were used to determine the mechanical properties of the thermoplastic-elastomer blend, which include tensile strength, flexural strength, and Izod impact. The results obtained from these tests show that tensile strength and modulus decreases by increasing the rubber content. However, impact strength and percentage elongation increase by increasing the rubber content. This enhancement in impact and percentage elongation may be suitable for the applications in gymnasium mat and automobile industry.

Bacterial Adhesion on Prosthetic and Orthotic Material Surfaces

Prosthetic and orthotic parts, such as prosthetic socket and inner sides of orthoses, are often in contact with human skin, giving bacteria the capability to adhere and form biofilms on the materials of those parts which can further cause infections. The purpose of this study was to determine the extent of bacterial adhesion of Staphylococcus aureus and Staphylococcus epidermidis on twelve different prosthetic and orthotic material surfaces and how roughness, hydrophobicity, and surface charge of this materials affect the adhesion. The roughness, contact angle, zeta potential of material surfaces, and adhesion rate of Staphylococcus aureus and Staphylococcus epidermidis were measured on all twelve prosthetic and orthotic materials, i.e., poly(methyl methacrylate), thermoplastic elastomer, three types of ethylene polyvinyl acetates (pure, with low-density polyethylene and with silver nanoparticles), silicone, closed-cell polyethylene foams with and without nanoparticles, thermo and natural cork, and artificial and natural leather. The greatest degree of adhesion was measured on both closed-cell polyethylene foams, followed by artificial thermo cork and leather. The lowest adhesion extent was observed on ethylene-vinyl acetate. The bacterial adhesion extent increases with the increasing surface roughness. Smaller deviations of this rule are the result of the surface’s hydrophobicity and charge.

Effects of POE and Carbon Black on the PTC Performance and Flexibility of High-Density Polyethylene Composites

High-density polyethylene (HDPE)/carbon black (CB) is widely used in positive temperature coefficient (PTC) composites. In order to expand its applications to fields that need good flexibility, polyolefin elastomer (POE) was incorporated into HDPE/CB composites as a secondary thermoplastic elastomer phase to provide flexibility. The effects of POE and CB content on the PTC performance and flexibility were investigated. Micro morphology and crystallization behavior are closely related to PTC properties. SEM was conducted to reveal phase morphology and filler dispersion, and DSC was conducted to research crystallization behavior. The results show that the incorporation of 18 wt.% POE can decrease the percolation threshold of conductive carbon black from 22.5 wt.% to 16 wt.%. When the CB content is 30 wt.%, the room temperature resistivity gradually increases with the increasing content of POE because of the barrier effect of POE phase, and the PTC intensity is gradually enhanced. Meanwhile, the PTC switching temperature shifts down to a lower temperature. The incorporation of 18 wt.% POE significantly increases the elongation at break, reaching an ultrahigh value of 980 wt.%, which means great flexibility has been achieved in HDPE/POE/CB composites. This work provides a new method of fabricating PTC composites with balanced electrical and mechanical properties.