Soft Block Research Articles

Effect of temperature, rate, and molecular weight on the failure behavior of soft block copoly(ether-ester) thermoplastic elastomers.

Thermoplastic elastomers (TPEs) based on multiblock copolymers are an important class of engineering polymers. They are widely used in many applications where flexibility and durability are required and are seen as a sustainable (recyclable) alternative to thermoset rubbers. While their high-temperature mechanical behavior has received recent interest, few studies have explored their fracture and fatigue behavior. Understanding how the temperature and rate-dependence of the deformation behavior at both a local and global scale influences the fatigue resistance and failure behavior is critical when designing with these materials. In this study, the failure behavior in tensile, fracture, and fatigue of well-characterized, industrially relevant, model block copoly(ether-ester) based TPEEs were evaluated over a wide range of temperatures, deformation rates, and molecular weights. Small changes in temperature or rate are shown to result in a sharp transition between a highly deformable and notch resistant response, to a more brittle and strongly notch-sensitive response. This behavior surprisingly manifests itself as a threshold strain below which the cracks do not propagate in fatigue and increasing deformation rates decreases the materials toughness in fracture tests, whereas in tensile tests the opposite is observed. The change from homogenous to inhomogeneous stress fields for tensile and fracture experiments coupled with the viscoelasticity and strain-dependent morphology of TPEs explains why a different rate dependency is observed. Strain and stress delocalization is key to achieve high toughness. Digital Image Correlation is used to measure the size and time dependence of the process zone. Comparison with micromechanical models developed for soft, elastic, and tough double network gels highlights the dominance of high strain properties for toughness and explains the strong molecular weight dependence. However, to understand the rate dependence, the characteristic times for stress transfer from the crack tip and the time to nucleate failure must be compared. The results presented in this study demonstrate the complex effect of loading conditions on the intrinsic failure mechanisms of the TPE material, and provide a first attempt at rationalizing that behavior.

Tongue laceration in a patient taking antiplatelet agents during transcranial motor-evoked potential monitoring: a case report

BackgroundTranscranial motor-evoked potential (Tc-MEP) monitoring is usually performed during surgeries involving a risk of damaging brain motor areas. However, it involves a risk of bite injuries. We report a case of severe tongue laceration from Tc-MEP stimulation during carotid endarterectomy (CEA) in a patient taking antiplatelet agents.Case presentationA 74-year-old man on antiplatelet therapy was scheduled for CEA under general anesthesia with intraoperative Tc-MEP monitoring. Bite blocks were not inserted. Postoperatively, we observed a tongue laceration with severe bleeding, which was sutured. The difficulties in tongue movement persisted for ≥ 1 month postoperatively.ConclusionsBite injuries during Tc-MEP may induce severe bleeding in patients on antiplatelets. The complications of tongue bite injuries may persist, decreasing the patients’ quality of life. Hence, during Tc-MEP monitoring, it is important to use soft bite blocks and to check the patient’s face and the position of the tracheal tube intraoperatively.

Effect mechanism of block convexity on the shear behaviors of soil-rock mixtures by the developed 3D spherical harmonics-based modeling approach

The effect of block convexity on the shear behaviors of soil-rock mixtures (S-RMs) can be investigated using accurate 3D models constructed with the discrete element method (DEM). Based on the improved spherical harmonics series, a new block geometry modeling approach was proposed for generating 3D blocks with different convexities but the same form and angularity. By introducing tracer particles, a DEM modeling approach was also proposed for generating S-RM models with the same block distribution characteristics and possible block breakage. Numerical direct shear tests were performed on the generated stiff and soft S-RM models with different block convexities. The meso- and the macro-shear behaviors of the S-RMs were analyzed in detail to reveal the effect mechanism of block convexity. The results showed that the breakage degree of soft blocks increased linearly with the block convexity degree. The interlocking degrees of blocks with higher convexities are higher, leading to higher contributions of the blocks to the shear strength and greater block rotation. As the effect of block breakage is more significant, soft blocks with higher convexity degrees contribute smaller to the shear resistance. For S-RMs with higher block convexity degrees, the shear strength of stiff S-RMs is higher owing to their higher block interlocking degrees, while the shear strength of soft S-RMs under high normal stress is smaller due to their higher block breakage degrees. The dilation magnitude is greater for stiff S-RMs while lower for soft S-RMs with higher convexity degrees, owing to the greater effect of block breakage than the rotation behavior. The friction angles of stiff S-RMs with higher block convexity degrees are larger due to their higher block interlocking degrees, while the friction angles of soft S-RMs with lower block convexity degrees are smaller under high normal stress due to their higher block breakage degrees.

Fused Filament Fabrication of Bio-Based Polyether-Block-Amide Polymers (PEBAX) and Their Related Properties

This paper describes the application of poly(ether-block-amide) polymers, so-called Pebax, in fused filament fabrication (FFF). Pebax® is a thermoplastic elastomer (TPE), a copolymer based on rigid polyamide and soft polyether blocks. By variation of the blocks, unique properties such as soft or rigid behaviour are tailored without additional additives and plasticisers. Pebax®Rnew® polyamide blocks are bio-based and made from castor beans that allow the design of sustainable applications. In this study, two types of Pebax were selected, processing parameters were characterised, filaments were extruded and applied to FFF printing, and the final mechanical characteristics were determined. Both types were suitable for FFF processing with improved process stability due to less shear thinning and good mechanical performance. The connection strength between the grades was also described in the design context for complex parts with tailored soft or hard regions. Combining the two materials in one design is a promising concept, and the adhesion strength is close to the strength in the Z-direction of the flexible Pebax®Rnew®35R53 grade.

Polymer elastomer near plastic-to-rubber critical transition produces enhanced elastocaloric effects

Solid-state cooling technology based on elastocaloric effects has shown potential advantages over traditional vapor-compression cooling systems owing to its high energy efficiency and zero greenhouse gas emissions. However, a lack of strategies for improving the elastocaloric activity of polymers remains the main obstacle to their commercialization since the elastocaloric effect was first investigated by J.P. Joule in natural rubber. Herein, we demonstrate that polymer elastomers with molecular chains near molecular-structure-induced plastic-rubber critical transitions exhibit superior elastocaloric activity through reversible conformational changes. As the content of ethyl side groups in the soft block of polystyrene- b -poly(ethylene- co -butylene)- b -polystyrene decreases from 33 to 8 mol %, the adiabatic temperature change increases from −4.3 to −16.3 K, and the isothermal entropy change increases from 38.5 to 173.3 J kg −1 K −1 , which thus shows the highest polymer elastocaloric activity near room temperature. This strategy could promote the commercialization of elastocaloric polymers in solid-state cooling applications. • Polymers near plastic-rubber critical transition show reversible conformations • Over a 3-fold increment in the elastocaloric activity close to room temperature • The lowest limit value of cooling temperature decreased from 275 to 262 K Solid-state cooling technologies are expected to be a net-zero potential alternative to vapor-compression cooling systems. Here, Shixian Zhang et al. demonstrate a strategy to enhance the cooling performance of solid polymers. This strategy could be widely applied in polymer systems to reach polymers’ solid-state cooling.

Using the intact periosteum for horizontal bone augmentation of peri-implant defects: a retrospective cohort study

The objectives of this study were to observe hard tissue changes in guided bone regeneration (GBR) with intact periosteum and soft block deproteinised bovine bone mineral (DBBM), and evaluate whether the result of horizontal bone augmentation varied by initial peri-implant defect depth. Forty patients with a single missing tooth and contained peri-implant defect were categorised into three groups according to their presurgical defect depth (≤ 2, 2–4, and 4–6 mm). Cone-beam computed tomography (CBCT) images were collected and reconstructed preoperatively, postoperatively, and at six months’ follow up. The buccal bone width (BBW -0, -3, -5), alveolar bone width (ABW -0, -3, -5) and volume of augmented area were measured. At the six-month follow up the increase in BBW, ABW at all levels, and in bone volume, was statistically significant (all p < 0.001). No statistical significance in bone dimensions or bone resorption was found among groups (all p > 0.05). Histological analysis detected new bone formation in intimate contact with bone grafts underlying the periosteum. Within the limitations of this study, the insights gained may be of assistance to suggest that comparable and acceptable results of horizontal bone augmentation can be achieved in cases of peri-implant defect depth of ≤6 mm by means of GBR with intact periosteum.

Reconfigurable Soft Robots by Building Blocks.

Soft robots are of increasing interest as they can cope with challenges that are poorly addressed by conventional rigid-body robots (e.g., limited flexibility). However, due to their flexible nature, the soft robots can be particularly prone to exploit modular designs for enhancing their reconfigurability, that is, a concept which, to date, has not been explored. Therefore, this paper presents a design of soft building blocks that can be disassembled and reconfigured to build different modular configurations of soft robots such as robotic fingers and continuum robots. First, a numerical model is developed for the constitutive building block allowing to understand their behavior versus design parameters, then a shape optimization algorithm is developed to permit the construction of different types of soft robots based on these soft building blocks. To validate the approach, 2D and 3D case studies of bio-inspired designs are demonstrated: first, soft fingers are introduced as a case study for grasping complex and delicate objects. Second, an elephant trunk is used for grasping a flower. Third, a walking legged robot. These case studies prove that the proposed modular building approach makes it easier to build and reconfigure different types of soft robots with multiple complexshapes.

Domain Structure, Thermal and Mechanical Properties of Polycaprolactone-Based Multiblock Polyurethane-Ureas under Control of Hard and Soft Segment Lengths.

A series of multiblock polyurethane-ureas (PUU) based on polycaprolactone diol (PCL) with a molecular mass of 530 or 2000 g/mol, as well as hard segments of different lengths and structures, were synthesized by the step-growth polymerization method. The chemical structure of the synthesized multiblock copolymers was confirmed by IR- and NMR-spectroscopy. Differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA) were used to determine the relaxation and phase transition temperatures for the entire series of the obtained PUU. The X-ray diffraction (XRD) method made it possible to identify PUU compositions in which the crystallizability of soft segments (SS) is manifested due to their sufficient length for self-organization and structuring. Visualization of the crystal structure and disordering of the stacking of SS with an increase in their molecular mobility during heating are shown using optical microscopy. The change in the size of the hard phase domains and the value of the interdomain distance depending on the PCL molecular mass, as well as the length and structure of the hard block in the synthesized PUU, were analyzed using small-angle X-ray scattering (SAXS) and small-angle neutron scattering (SANS). The evolution of the domain structure upon passing through the melting and crystallization temperatures of PUU soft blocks was studied using SANS. The studies carried out made it possible to reveal the main correlations between the chemical structure of the synthesized PUU and their supramolecular organization as well as thermal and mechanical properties.

Some Basic Concepts of Neutrosophic Soft Block Matrices

Some Basic Concepts of Neutrosophic Soft Block Matrices

Influence of Interpenetrating Chains on Rigid Domain Dimensions in Siloxane-Based Block-Copolymers.

1H spin-diffusion solid-state NMR was utilized to elucidate the domain size in multiblock-copolymers (BCPs) poly-(block poly(dimethylsiloxane)-block ladder-like poly(phenylsiloxane)) and poly-(block poly((3,3′,3″-trifluoropropyl-methyl)siloxane)-block ladder-like poly(phenylsiloxane). It was found that these BCPs form worm-like morphology with rigid cylinders dispersed in amorphous matrix. By using the combination of solid-state NMR techniques such as 13C CP/MAS, 13C direct-polarization MAS and 2D 1H EXSY, it was shown that the main factor which governs the diameter value of these rigid domains is the presence of interpenetrating segments of soft blocks. The presence of such interpenetrating chains leads to an increase of rigid domain diameter.

Hybrid Ni–Co–Ni Structures Prepared by Magnetophoresis as Efficient Permanent Magnets for Integration into Microelectromechanical Systems

The direct integration of performant permanent magnets (PMs) within miniaturized circuits remains both a scientific and a technological challenge. Magnetophoresis‐driven capillary assembly of hard magnetic nanoparticles is a promising approach to fabricate 3D rare‐earth‐free PMs. However, this process implies the use of soft magnetic blocks to generate the magnetic field gradients required to localize the assembly directly onto silicon substrates. The impact of these soft elements onto the overall magnetic properties is evaluated using Co nanorods as hard material and 150 μm–thick Ni blocks. As expected, the presence of Ni softens the overall properties of the hybrid magnet obtained, but PM properties are preserved for reduced Ni volumes. Magnetic induction as high as 19 mT at a distance of 200 μm is generated by the hybrid Ni–Co–Ni structures, allowing for the electromagnetic actuation of a microelectromechanical resonant sensor.

Sustainable ABA triblock methacrylate copolymers incorporating both high and low Tg terpene-derived monomers

We report the synthesis of novel terpene-based monomers: nopinyl acrylate and methacrylate, from naturally abundant β-pinene. A very high Tg value was observed for poly(nopinyl methacrylate) when synthesised by free radical polymerisation, and well-defined polymers have been produced via RAFT polymerisation. This exciting new high Tg material shows promise as a hard block in thermoplastic elastomers. ABA triblock copolymers have been synthesised which also incorporate a low Tg renewable soft block, poly(tetrahydrogeraniol methacrylate), using a divergent, difunctional RAFT polymerisation method. Initial phase separation behaviour and adhesive properties have been investigated to highlight the potential of these copolymer materials as renewably sourced thermoplastic elastomers.

Renewable low viscosity polyester‐polyols for biodegradable thermoplastic polyurethanes

AbstractIn the transition to renewably sourced, biodegradable polymers, the preparation of low viscosity polyester‐polyols has posed a challenge for renewable polyurethane (PU) development. Low viscosity polyols not only reduce the requirement for high process temperatures but also decrease manufacturing time. In our efforts to incorporate increasing ratios of bio‐based monomers into renewable PUs, we mixed diacids such as even carbon sebacic acid and odd carbon azelaic acid along with a renewable diol. This provided library of 2000 g/mol molecular weight polyester‐polyols, and structures were established by 1H and 13C NMR analysis. The prepared polyester‐polyols offered lower viscosity and enable lower fabrication temperatures to make TPUs, and their structure and material metrics were evaluated. The formation of TPUs is ascertained from FTIR and NMR analysis. The final TPUs displayed good physical and mechanical properties. These TPUs exhibited Tg in the range of −56.5 to −39.7°C, corresponding to TPU soft block structure, and Tm between 98.3 and 105.1°C originating from the hard segment. Prepared TPUs exhibit excellent biodegradation under compost environmental conditions. These TPUs showed up to 57% decrease in molecular weight by GPC analysis after 9 weeks of biodegradation, and respirometer analysis displayed up to 97% biodegradation over 120 days.

3D Printed CO2 -Based Triblock Copolymers and Post-Printing Modification.

We report the facile synthesis and 3D printing of a series of triblock copolymers consisting of soft and hard blocks and demonstrate that alkene pendant groups of the hard block can be covalently modified. The polymers are prepared using a salenCo(III)TFA/PPNTFA binary catalyst system and 1,2-propanediol as a chain transfer agent, providing an efficient one-pot, two-step strategy to tailor polymer thermal and mechanical properties. Thixotropic inks suitable for direct ink write printing were formulated by dissolving the block copolymers in organic solvent and dispersing NaCl particles. After printing, porous structures were produced by removing solvent and NaCl with water to give printed structures with surfaces that could be modified via UV-initiated thiol-ene click reactions. Alternatively, a tetra-thiol could be incorporated into the ink and used for cross-linking to give objects with high solvent resistance and selective degradability.

3D Printed CO2‐Based Triblock Copolymers and Post‐Printing Modification

AbstractWe report the facile synthesis and 3D printing of a series of triblock copolymers consisting of soft and hard blocks and demonstrate that alkene pendant groups of the hard block can be covalently modified. The polymers are prepared using a salenCo(III)TFA/PPNTFA binary catalyst system and 1,2‐propanediol as a chain transfer agent, providing an efficient one‐pot, two‐step strategy to tailor polymer thermal and mechanical properties. Thixotropic inks suitable for direct ink write printing were formulated by dissolving the block copolymers in organic solvent and dispersing NaCl particles. After printing, porous structures were produced by removing solvent and NaCl with water to give printed structures with surfaces that could be modified via UV‐initiated thiol‐ene click reactions. Alternatively, a tetra‐thiol could be incorporated into the ink and used for cross‐linking to give objects with high solvent resistance and selective degradability.

A Fully Coupled Mechano-Electrochemical Model for All-Solid-State Thin-Film Li-Ion Batteries with Non-Porous Electrodes: Effects of Chemo-Mechanical Expansions on Battery Performance and Optimization Strategies for Stress Evolution

A comprehensive and novel mechano-electrochemical coupling model for all-solid-state Li-ion batteries (ASSLBs) is developed, in particular, focusing on the influence of the volume changes caused by ions redistribution in the electrodes on the electrical and mechanical properties of the battery. The mathematical relationship between the partial molar volume and Poisson’s ratio is determined for the condition of zero stress. The roles of the partial molar volumes of cathode and anode, the thickness and Young’s modulus of the spacer are investigated. The results show that the electrode volume changes significantly during the charging and discharging process. Due to the mechanical imbalance, the confined cell generates considerable compressive stress (approximately 0.6 MPa). Reducing the partial molar volume of the anode can not only eliminate the compression stress but augment the capacity. Note that for the ASSLBs containing inorganic (oxide or sulfide) solid electrolytes (SEs), adjusting the material parameters to obtain proper compressive stress instead of a bulky cell holder may be another useful method to overcome the poor interface contact. Finally, by introducing polyurethane foam or other soft blocks with a suitable thickness and Young’s modulus as spacers, the stress of the cell can be reduced by 79.33%.

Water transport in epoxy/polyurethane interpenetrating networks

AbstractDiffusion of water in epoxy–polyurethane (PU) interpenetrating networks was investigated using gravimetry, time‐resolved ATR‐FTIR, and 2D correlation analysis. In this study, the amount of PU component and the length of polyethylene oxide soft block in them were systematically varied to determine their influence on water uptake. The diffusion coefficients were calculated and anomalous water diffusion is well described by the Carter and Kibler model. Water molecules of four different states were identified in the network volume, and sequence of their formation was determined by 2D‐IR spectroscopy. One of them could be confined into free volume (microvoids) or molecularly dispersed with hydrogen‐bonding at cluster formation (bulk dissolved), while the others could be attributed to the bound water forming strong hydrogen bonds with hydrophilic entities of networks. These results were supported by solid‐state 2H NMR data. The influence of water uptake on thermomechanical behavior of epoxy/PU networks was determined. It was shown that the increase of PU content in composites leads to the changes of the effect of water uptake from plasticizing to the anti‐plasticizing as a result of the formation of new networks of interchain hydrogen bonds.

Utility of Chemical Upcycling in Transforming Postconsumer PET to PBT-Based Thermoplastic Copolyesters Containing a Renewable Fatty-Acid-Derived Soft Block.

Thermoplastic copolyesters (TPCs) are important structural components in countless high performance applications that require excellent thermal stability and outstanding mechanical integrity. Segmented multiblock architectures are often employed for the most demanding applications, in which semicrystalline segments of poly(butylene terephthalate) (PBT) are combined with various low T g soft blocks. These segmented copolymers are nearly always synthesized from pristine feedstocks that are derived from fossil-fuel sources. In this work, we show a straightforward, one-pot synthetic approach to prepare TPCs starting from high-molar mass poly(ethylene terephthalate) recyclate (rPET) combined with a hydrophobic fatty acid dimer diol flexible segment. Transesterification is exploited to create a multiblock architecture. The high molar mass and segment distribution are elucidated by detailed size-exclusion chromatography and proton and carbon nuclear magnetic resonance spectroscopy. It is also shown that rPET can be chemically converted to PBT through a molecular exchange, in which the ethylene glycol is substituted by introducing 1,4-butane diol. A series of copolymers with various compositions was prepared with either PET or PBT segments and the final thermal properties and mechanical performance is compared between the two different constructs. Ultimately, PBT-based TPCs crystallize faster and exhibit a higher modulus over the range of explored compositions, making them ideal for applications that require injection molding. This represents an ideal, sustainable approach to making conventional TPCs, utilizing recyclate and biobased components to produce high performance polymer constructs via an easily accessible upcycling route.

Tongue Bite Injury Resulting from Intra-operative Neuromonitoring during Posterior Scoliosis Corrective Surgery Not an Uncommon Complication: Case Report and Literature Review

Tongue bite injuries (TBI) resulting from the use of intra-operative neuromonitoring (IONM) during spinal surgeries are not as uncommon a complication as previously thought, especially when using transcranial motor evoked potential (TcMEP). The incidence of bite injuries ranged from 0.14% to 0.63%, with TBI occurring four times more frequently than lip injuries, and of these, 0.15% of tongue lacerations required surgical repair. Through our literature search, we discovered that these injuries have never been reported in Malaysia; additionally, this is the first incidence encountered by our team. We are reporting a 20-year-old male who sustained a TBI during posterior scoliosis corrective surgery while using TcMEP. We report on its management and reviewed literatures to explain the causes and the recommendations for the prevention of this injury. In conclusion, TBI is an unpleasant complication in spinal surgery related to the use of IONM. Safety precautions need to be taken during surgical preparation, and we propose using two to three soft bite blocks (SBB) to aid in reducing the rate of this complication.

Thermal Fractionation of Ethylene/1-Octene Multiblock Copolymers from Chain Shuttling Polymerization

Ethylene/1-octene statistical multiblock copolymers (OMBCs) consisting of the alternation of crystalline, hard blocks and amorphous, soft blocks, with ≈0.5 and 20 mol % of 1-octene units, respectively, are subjected to thermal fractionation resorting to successive self-nucleation and annealing (SSA). The study is extended to random copolymers (RCs) of high (44 kDa) and low (3.4 kDa) number average molecular mass Mn, mimicking in 1-octene content the crystalline hard blocks and to the OMBC fractions extracted in boiling n-hexane and cyclohexane through a suitable solution fractionation protocol. For all the samples, the melting endotherms are well resolved in a multiplicity of peaks corresponding to the melting of crystals of different thicknesses generated in the SSA protocol that reflect the distribution of the methylene sequence length (MSL) in between consecutive interruptions along the chains. It is shown that, regardless of molecular mass, the MSL distributions of the RC samples are shifted toward greater values than those of the OMBC samples, and that also the shapes of the distributions are different. Since the MSL distribution depends on the frequency and distribution of the defects along the chains, and the defects act as interruption points, the higher fraction of long crystallizable sequences in the RC samples suggests that whereas for the RC samples the interruptions are merely represented by the 1-octene units that are rejected outside the crystals, for the OMBCs, the interruption of the regular methylene sequences belonging to the crystalline hard blocks due to the amorphous soft blocks linked to them should also play a role. Indeed, due to the partial miscibility of the hard and soft blocks, the hard blocks of major length tend to crystallize in a confined environment. This prevents the formation of thicker crystals and induces decrease of the MSL values as well as changes in the shape of the MSL distributions (topological confinement). On the other hand, the hard blocks of shorter length tend to crystallize, crossing the hard block rich regions and causing melting point depression and consequent shift of the MSLs toward lower values with respect to RCs (diluent effect). It is shown that differences in the MSL distribution of OMBCs are the result of the interplay between topological confinement and diluent effect, which in turn reflects differences in the OMBC chain microstructure, that is, differences in the distribution of block length at the inter- and intra-chain level.