Fabrication of New Thermoplastic Polyurethane Elastomers with High Heat Resistance for 3D Printing Derived from 3,3-Dimethyl-4,4′-diphenyl Diisocyanate

Supersoft Norbornene-Based Thermoplastic Elastomers with High Strength and Upper Service Temperature

With over 6 million tons produced annually, thermoplastic elastomers (TPEs) have become ubiquitous in modern society, due to their unique combination of elasticity, toughness, and reprocessability. Nevertheless, industrial TPEs display a tradeoff between softness and strength, along with low upper service temperatures, typically ≤100 °C. This limits their utility, such as in bio-interfacial applications where supersoft deformation is required in tandem with strength, in addition to applications that require thermal stability (e.g., encapsulation of electronics, seals/joints for aeronautics, protective clothing for firefighting, and biomedical devices that can be subjected to steam sterilization). Thus, combining softness, strength, and high thermal resistance into a single versatile TPE has remained an unmet opportunity. Through de novo design and synthesis of novel norbornene-based ABA triblock copolymers, this gap is filled. Ring-opening metathesis polymerization is employed to prepare TPEs with an unprecedented combination of properties, including skin-like moduli (<100 kPa), strength competitive with commercial TPEs (>5 MPa), and upper service temperatures akin to high-performance plastics (≈260 °C). Furthermore, the materials are elastic, tough, reprocessable, and shelf stable (≥2 months) without incorporation of plasticizer. Structure-property relationships identified herein inform development of next-generation TPEs that are both biologically soft yet thermomechanically durable.

Thermomechanically stable supramolecular elastomers inspired by heat shock proteins

Supramolecular polymers are usually thermomechanically unstable, as their mechanical strength decreases drastically upon heating, which is a fatal shortcoming for their application. Herein, inspired by heat shock proteins (HSPs) which enable living organisms to tolerate lethal high temperatures, we design an HSP-like response to impart a supramolecular elastomer with high thermomechanical stability. The HSP-like response relies on the reversible hydrolysis of boronic acid and the tunable association strength of boron dative bonds. As the temperature increases, the boronic acid dehydrates and transforms into boroxane. The boroxane, acting as a heat shock chemical, prevents the disintegration of the supramolecular network through formation of multiple and stronger dative bonds with imidazole-containing polymers, thereby enabling the material to retain its mechanical strength at high temperatures. Such chemical transformation and network change induced by the HSP-like response are fully reversible during the heating and cooling processes. Moreover, due to the dynamic nature of the supramolecular network, the elastomer possesses recycling and self-healing abilities.

In vitro biocompatibility evaluation of a heat-resistant 3D printing material for use in customized cell culture devices

Additive manufacturing (3D printing) enables the fabrication of highly customized and complex devices and is therefore increasingly used in the field of life sciences and biotechnology. However, the application of 3D-printed parts in these fields requires not only their biocompatibility but also their sterility. The most common method for sterilizing 3D-printed parts is heat steam sterilization-but most commercially available 3D printing materials cannot withstand high temperatures. In this study, a novel heat-resistant polyacrylate material for high-resolution 3D Multijet printing was evaluated for the first time for its resistance to heat steam sterilization and in vitro biocompatibility with mouse fibroblasts (L929), human embryonic kidney cells (HEK 293E), and yeast (Saccharomyces cerevisiae (S. cerevisiae)). Analysis of the growth and viability of L929 cells and the growth of S. cerevisiae confirmed that the extraction media obtained from 3D-printed parts had no negative effect on the aforementioned cell types, while, in contrast, viability and growth of HEK 293E cells were affected. No different effects of the material on the cells were found when comparing heat steam sterilization and disinfection with ethanol (70%, v/v). In principle, the investigated material shows great potential for high-resolution 3D printing of novel cell culture systems that are highly complex in design, customized and easily sterilizable-however, the biocompatibility of the material for other cell types needs to be re-evaluated.

3D-Printed Soft Pneumatic Robotic Digit Based on Parametric Kinematic Model for Finger Action Mimicking

A robotic digit with shape modulation, allowing personalized and adaptable finger motions, can be used to restore finger functions after finger trauma or neurological impairment. A soft pneumatic robotic digit consisting of pneumatic bellows actuators as biomimetic artificial joints is proposed in this study to achieve specific finger motions. A parametric kinematic model is employed to describe the tip motion trajectory of the soft pneumatic robotic digit and guide the actuator parameter design (i.e., the pressure supply, actuator material properties, and structure requirements of the adopted pneumatic bellows actuators). The direct 3D printing technique is adopted in the fabrication process of the soft pneumatic robotic digit using the smart material of thermoplastic polyurethane. Each digit joint achieves different ranges of motion (ROM; bending angles of distal, proximal, and metacarpal joint are 107°, 101°, and 97°, respectively) under a low pressure of 30 kPa, which are consistent with the functional ROM of a human finger for performing daily activities. Theoretical model analysis and experiment tests are performed to validate the effectiveness of the digit parametric kinematic model, thereby providing evidence-based technical parameters for the precise control of dynamic pressure dosages to achieve the required motions.

Mechanical and wear behaviour of PEEK, PTFE and PU: review and experimental study

Soft polymers such as polyether ether ketone (PEEK), polyurethane (PU) and polytetrafluoroethylene (PTFE) have gained significant research interest in the last few decades owing to their excellent material properties which can be harnessed to meet the demands of various applications such as biomedical implants and accessories, insulation panels to cooking utensils, inner coating material for non-stick cookware etc. In the present study, we provide a comprehensive review on the mechanical and tribological behaviour of PEEK, PU and PTFE polymers. Samples of these materials were also fabricated and the experimentally obtained tensile strength, flexural strength, wear rate and coefficient of frictions were ascertained with values reported in literature. It is highlighted that coefficient of friction of polymers were highly dependent on the surface texture of the polymer’s surface; where an uneven surface exhibited higher coefficient of friction. Perspectives for future progress are also highlighted in this paper.

Controllable Design and Preparation of Hydroxyl-Terminated Solution-Polymerized Styrene Butadiene for Polyurethane Elastomers with High-Damping Properties

Vibration and noise are ubiquitous in social life, which severely damage machinery and adversely affect human health. Thus, the development of materials with high-damping performance is of great importance. Rubbers are typically used as damping materials because of their unique viscoelasticity. However, they do not satisfy the requirements of different applications with various working conditions. In this study, the advantages of the high loss factor of styrene butadiene rubber (SBR) are combined with the strong designability of polyurethane. Hydroxyl-terminated solution-polymerized styrene butadiene rubbers (HTSSBRs) with different structures are prepared using anionic polymerization. HTSSBRs are then used as the soft segment during the synthesis of temperature-tunable high-damping performance polyurethane (HTSSBR-polyurethane (PU)). The prepared HTSSBR-PUs with different structures exhibit excellent loss performance, a maximum loss factor (tan δ_max ) of above 1.60, and an effective damping performance over a wide temperature range compared to traditional SBR and polyurethane. Therefore, this work offers an effective method for the design of damping materials with adjustable properties. This article is protected by copyright. All rights reserved.

Biobased and Recyclable Polyurethane for Room-Temperature Damping and Three-Dimensional Printing

Petroleum-based polymer materials heavily rely on nonrenewable petrochemical resources, and damping materials are an important category of them. As far as green chemistry, recycling, and damping materials are concerned, there is an urgent need for renewable and recyclable biobased materials with high damping performance. Thus, this study designs and synthesizes a series of polylactic acid-based thermoplastic polyurethanes (PLA-based TPUs) composed of modified polylactic acid polyols, 4,4'-diphenylmethane diisocyanate, and 1,4-butanediol. PLA-based TPUs, as prepared, display excellent mechanical properties, damping performance, and biocompatibility. Otherwise, they can be used for three-dimensional printing (3D printing). Under multiple recycling, the overall performance of PLA-based TPUs is still maintained well. Overall, PLA-based TPUs, as designed in this article, show a potential application in damping materials under room temperature and personalized shoes via 3D printing and could realize resource recycling and material reuse.

Optical, Structural, and Dielectric Properties of Composites Based on Thermoplastic Polymers of the Polyolefin and Polyurethane Type and BaTiO3 Nanoparticles

In this work, new films containing composite materials based on blends of thermoplastic polymers of the polyurethane (TPU) and polyolefin (TPO) type, in the absence and presence of BaTiO₃ nanoparticles (NPs) with the size smaller 100 nm, were prepared. The vibrational properties of the free films depending on the weight ratio of the two thermoplastic polymers were studied. Our results demonstrate that these films are optically active, with strong, broad, and adjustable photoluminescence by varying the amount of TPU. The crystalline structure of BaTiO₃ and the influence of thermoplastic polymers on the crystallization process of these inorganic NPs were determined by X-ray diffraction (XRD) studies. The vibrational changes induced in the thermoplastic polymer's matrix of the BaTiO₃ NPs were showcased by Raman scattering and FTIR spectroscopy. The incorporation of BaTiO₃ NPs in the matrix of thermoplastic elastomers revealed the shift dependence of the photoluminescence (PL) band depending on the BaTiO₃ NP concentration, which was capable of covering a wide visible spectral range. The dependencies of the dielectric relaxation phenomena with the weight of BaTiO₃ NPs in thermoplastic polymers blends were also demonstrated.

Relationship between Photoelasticity of Polyurethane and Dielectric Anisotropy of Diisocyanate, and Application of High-Photoelasticity Polyurethane to Tactile Sensor for Robot Hands

Eight types of polyurethane were synthesized using seven types of diisocyanate. It was found that the elasto-optical constant depends on the concentration of diisocyanate groups in a unit volume of a polymer and the magnitude of anisotropy of the dielectric constant of diisocyanate groups. It was also found that incident light scattered when bending stress was generated inside photoelastic polyurethanes. A high sensitive tactile sensor for robot hands was devised using one of the developed polyurethanes with high photoelasticity.

Research of TPU Materials for 3D Printing Aiming at Non-Pneumatic Tires by FDM Method

3D printing technology has been widely used in various fields, such as biomedicine, clothing design, and aerospace, due to its personalized customization, rapid prototyping of complex structures, and low cost. However, the application of 3D printing technology in the field of non-pneumatic tires has not been systematically studied. In this study, we evaluated the application of potential thermoplastic polyurethanes (TPU) materials based on FDM technology in the field of non-pneumatic tires. First, the printing process of TPU material based on fused deposition modeling (FDM) technology was studied through tensile testing and SEM observation. The results show that the optimal 3D printing temperature of the selected TPU material is 210 °C. FDM technology was successfully applied to 3D printed non-pneumatic tires based on TPU material. The study showed that the three-dimensional stiffness of 3D printed non-pneumatic tires is basically 50% of that obtained by simulation. To guarantee the prediction of the performance of 3D printed non-pneumatic tires, we suggest that the performance of these materials should be moderately reduced during the structural design for performance simulation.