High-strain slide-ring shape-memory polycaprolactone-based polyurethane

Highly Improved Shape Memory Properties of a PCL-Based Polyurethane via Polylactide Stereocomplexation

In shape memory polymers (SMPs) composed of semicrystalline polymers, their crystallization-melting process and the overall entropic elasticity of the material determine their shape memory behavior. In this work, cross-linked polyurethanes with polycaprolactone (PCL), poly(l-lactic acid) (PLLA), and poly(d-lactic acid) (PDLA) segments were designed, in which four-armed PCL served as the chemical cross-linking and polylactic acid (PLA) crystals acted as physical cross-linking. By adjusting the molecular weight of the four-armed PCL and the type of PLA crystals [homocrystals (HC) and stereocomplex (SC) crystals], the overall cross-linking degree of the material was controlled, and the crystallization behavior, mechanical properties, and shape memory behavior of the material were studied. The results indicated that both physical and chemical cross-linking significantly affect the mechanical properties and shape memory properties of materials. Moreover, polyurethane-contained SC exhibited a higher shape recovery ratio (Rr) and fixation ratio (Rf) than polyurethane-contained HC because SC provided higher entropy elasticity and promoted PCL crystallization. This study provides a method for synergistically enhancing Rf and Rr of SMPs, offering insights into the design of related materials.

Synthesis and characterization of macrodiols and non-segmented poly(ester-urethanes) (PEUs) derived from α,ω-hydroxy telechelic poly(ε-caprolactone) (HOPCLOH): effect of initiator, degree of polymerization, and diisocyanate

Nine different macrodiols derived from α,ω-hydroxy telechelic poly(ε-caprolactone) (HOPCLOH) were prepared by ring-opening polymerization of ε-caprolactone (CL) using three linear aliphatic diols (HO-(CH2) n -OH, where n = 4, 8, and 12) as initiators and catalyzed by ammonium decamolybdate (NH4)8[Mo10O34]. The crystallization temperature (T c) and crystallinity (x i) were relatively high for HOPCLOH species with a long aliphatic chain [-(CH2)12-] in the oligoester. Also, HOPCLOH was the precursor of twenty-seven different poly(ester-urethanes) (PEUs) with various degrees of polymerization (DP) of HOPCLOH and three types of diisocyanates such as 1,6-hexamethylene diisocyanate (HDI), methylene diphenyl diisocyanate (MDI), and 4,4'-methylenebis (cyclohexyl isocyanate) (HMDI). HOPCLOH exhibited the melting temperature (T m) and crystallinity (x i) with a proportional dependency to the degree of polymerization (DP). PEUs showed significant thermal and mechanical properties, which had a direct correlation in terms of the type of DP and diisocyanate. PEUs derived from HDI versus MDI or HMDI exhibited an apparent effect where aliphatic diisocyanate (HDI) induced a significant x i with respect to aromatic and cyclic diisocyanate (MDI or HMDI). The profile of PEUs films according to mechanical properties is mainly a plastic behavior. The chemical nature and properties of HOPCLOH and PEUs were characterized by NMR, FT-IR, GPC, MALDI-TOF, DSC, and mechanical properties.

Towards high performance and durable soft tactile actuators

Soft actuators are gaining significant attention due to their ability to provide realistic tactile sensations in various applications. However, their soft nature makes them vulnerable to damage from external factors, limiting actuation stability and device lifespan. The susceptibility to damage becomes higher with these actuators often in direct contact with their surroundings to generate tactile feedback. Upon onset of damage, the stability or repeatability of the device will be undermined. Eventually, when complete failure occurs, these actuators are disposed of, accumulating waste and driving the consumption of natural resources. This emphasizes the need to enhance the durability of soft tactile actuators for continued operation. This review presents the principles of tactile feedback of actuators, followed by a discussion of the mechanisms, advancements, and challenges faced by soft tactile actuators to realize high actuation performance, categorized by their driving stimuli. Diverse approaches to achieve durability are evaluated, including self-healing, damage resistance, self-cleaning, and temperature stability for soft actuators. In these sections, current challenges and potential material designs are identified, paving the way for developing durable soft tactile actuators.

Polylactide-Based Nonisocyanate Polyurethanes: Preparation, Properties Evaluation and Structure Analysis

This study investigated the successful synthesis and characterization of nonisocyanate polyurethanes (NIPUs) based on polylactide. The NIPUs were synthesized by a condensation reaction of oligomers with hard segments (HSs) and synthesized carbamate-modified polylactic acid containing flexible segments (FSs). The oligomers with HSs were prepared from phenolsulfonic acid (PSA) or a mixture of PSA and hydroxynaphthalenesulfonic acid (HNSA), urea and formaldehyde. The mixing of oligomeric compounds with different amounts of formaldehyde was carried out at room temperature. Obtained NIPU samples with different hard segment content were tested for their mechanical and thermal properties. The tensile strength (TS) of all NIPU samples increased with an increasing amount of HSs, attaining the maximum value at an HS:FS ratio of 1:3. Samples prepared from PSA and HNSA showed higher tensile strength (TS) without significant change in elongation at break compared to the samples based only on PSA. Thermogravimetric analysis data indicated an absence of weight loss for all samples below 100 °C, which can be considered a safe temperature for using NIPU materials. Maximum degradation temperatures reached up to 385 °C. Fourier transform infrared spectroscopy results confirmed the existence of expected specific groups as well as the chemical structure of the prepared polyurethanes. DSC analysis showed the existence of two characteristic phase transitions attributed to the melting and crystallization of hard segments in the NIPU samples.

Shape-memory responses compared between random and aligned electrospun fibrous mats

Significant progress has been made in the design of smart fibers toward achieving improved efficacy in tissue regeneration. While electrospun fibers can be engineered with shape memory capability, both the fiber structure and applied shape-programming parameters are the determinants of final performance in applications. Herein, we report a comparison study on the shape memory responses compared between electrospun random and aligned fibers by varying the programming temperature T _prog and the deforming strain ε _deform . A PLLA-PHBV (6:4 mass ratio) polymer blend was first electrospun into random and aligned fibrous mat forms; thereafter, the effects of applying specific T _prog (37°C and 46°C) and ε _deform (30%, 50%, and 100%) on the morphological change, shape recovery efficiency, and switching temperature T _sw of the two types of fibrous structures were examined under stress-free condition, while the maximum recovery stress σ _max was determined under constrained recovery condition. It was identified that the applied T _prog had less impact on fiber morphology, but increasing ε _deform gave rise to attenuation in fiber diameters and bettering in fiber orientation, especially for random fibers. The efficiency of shape recovery was found to correlate with both the applied T _prog and ε _deform , with the aligned fibers exhibiting relatively higher recovery ability than the random counterpart. Moreover, T _sw was found to be close to T _prog , thereby revealing a temperature memory effect in the PLLA-PHBV fibers, with the aligned fibers showing more proximity, while the σ _max generated was ε _deform -dependent and 2.1-3.4 folds stronger for the aligned one in comparison with the random counterpart. Overall, the aligned fibers generally demonstrated better shape memory properties, which can be attributed to the macroscopic structural orderliness and increased molecular orientation and crystallinity imparted during the shape-programming process. Finally, the feasibility of using the shape memory effect to enable a mechanoactive fibrous substrate for regulating osteogenic differentiation of stem cells was demonstrated with the use of aligned fibers.

Physical Properties of Slide-Ring Material Reinforced Ethylene Propylene Diene Rubber Composites

High-damping rubber composites were prepared by mixing ethylene propylene diene monomer rubber (EPDM) with slide-ring (SR) materials using a two-roll mill, followed by a compression molding technique. SR material has a novel supramolecular structure with unique softness and slidable crosslink junctions. The mechanical strength, thermal stability, compression set property, and damping performance of the composites were investigated. The use of the high damping SR phase dispersed in the EPDM matrix displayed improved physical properties and damping performance compared to those of virgin rubber. As SR content increases in the composites, the damping factor of SR/EPDM blends becomes higher at room temperature. In addition to this, the SR composites showed excellent improvements in the compression set properties. The composites showed a compression set improvement of 35–38% compared to virgin EPDM. These improvements are due to the “pulley effect” of slide-ring materials. Therefore, these materials present a robust platform for making novel elastomer composites for high-performance damping and sealing applications.

Shape memory hierarchical AB copolymer networks

Herein, the novel shape memory hierarchical AB copolymer networks (HAB-CPNs) with heterophase structures were presented, which showed perfect shape fixity and recovery, rapid response, outstanding cycle performance, and high recovery force.

Mechanically and thermo-driven self-healing polyurethane elastomeric composites using inorganic–organic hybrid material as crosslinker

Self-healable, recyclable, and robust polyurethane elastomeric composites by thermally driven Diels–Alder chemistry using inorganic–organic hybrid material as crosslinker.