Characteristics of Polycarbonate Soft Segment-Based Thermoplastic Polyurethane

Variation of the chemical diffusivity of oxygen and viscosity of an andesite melt with pressure at constant temperature

Thermoplastic polyurethanes (TPUs) are versatile polymers presenting a broad range of properties as a result of their countless combination of raw materials—in essence, isocyanates, polyols, and chain extenders. This study highlights the effect of two different chain extenders and their combination on the structure–property relationships of TPUs synthesized by reactive extrusion. The TPUs were obtained from 4,4-diphenylmethane diisocyanate (MDI), polyester diols, and the chain extenders 1,4-butanediol (BDO) and dipropylene glycol (DPG). The BDO/DPG ratios studied were 100/0, 75/25, 50/50, 25/75, and 0/100 wt.%. The TPUs were characterized by size exclusion chromatography (SEC), Fourier-transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), small-angle X-ray scattering (SAXS), UV–vis spectroscopy, and physical-mechanical properties. The results indicate that DPG promotes compatibility between rigid (HS) and flexible (SS) segments of TPUs. Consequently, increasing DPG content (>75 wt.%) reduced the organization of the rigid segments and the degree of phase separation, increasing the polydispersity of the interdomain distance and the transparency in the UV–visible spectrum of the TPUs. Furthermore, increasing DPG content also reduced the amount of hydrogen bonds present in the rigid phase, reducing or extinguishing its glass transition temperature (TgHS) and melting temperature (Tm), and increasing the glass transition temperature of the flexible phase (TgSS). Therefore, increasing DPG content leads to a deterioration in mechanical properties and hydrolysis resistance.

Rational design of biodegradable thermoplastic polyurethanes for tissue repair

The poor cryogenic performance of thermoplastic polyurethanes (TPU) severely restricts their extensive application in low‐temperature fields as elastomers. Chain extenders are one of the adjustable items for TPUs to optimize cryogenic performance. In this contribution, three cyclic amine homologs of imidazoline, piperazine and 2‐methylpiperazine are selected as bi‐functional chain extenders. The corresponding TPU elastomers, TPU‐IM, TPU‐PP, and TPU‐2P with identical soft segments, are synthesized by the prepolymer method. All TPUs' structure, morphology and thermodynamic properties were investigated. The results showed that the cyclic amine structure embedded in TPU hard segment can effectively promote microphase separation through hydrogen‐bonded crosslink and polar aggregation on the molecular scale, achieving a glass transition temperature (Tg) as low as −103.9°C for resisting low temperatures. The mechanical properties also demonstrated a 23‐fold improvement compared to the control TPU‐BD. The elastomer TPU‐PP possessed the best all‐around performance with an ideal Tg of −98.4°C and tensile strength of 18.1 MPa. We believe that these TPUs will have potential applications in cryogenic engineering.

Two types of biodegradable polyurethanes (PUs) were synthesized from methylene di-p-phenyl-diisocyanate (MDI), polycaprolactone diol (PCL-diol), and chain extenders of either butanediol (BD) or 2,2'-(methylimino)diethanol (MIDE). The effects of two types of chain extenders on the degradation, mechanical properties, hydrophilicity, and cytophilicity of PUs were evaluated. In vitro degradation studies showed that PU containing MIDE has a higher degradation rate than PU synthesized using BD as a chain extender. Mechanical testing on dry and wet samples demonstrated that PU containing MIDE has a much higher elongation in the elastic region than PU containing BD. PU containing MIDE is more hydrophilic and retains more liquid during in vitro culture. Furthermore, preliminary cytocompatibility studies showed that both types of degradable PU are nontoxic, and fibroblasts adhere better and proliferate faster on MIDE containing PU than BD containing PU. To compare the cytocompatibility and degradation behaviors of the synthesized PU with existing FDA approved biocompatible material, polylactide (PLA), with a similar degradation rate, was used as negative control. Two types of PU were shown to have similar cytocompatibility and degradation behaviors as those of the PLA material. To verify the effectiveness of the cytotoxicity assay, latex was used as a positive control. Latex samples showed toxicity to cultured cells as expected. In conclusion, by changing the type of chain extender used during the synthesis of degradable PUs, the degradation rate, mechanical properties, hydrophilicity, and cytophilicity can be adjusted for different tissue engineering applications.

PLA and TPU were melt-blended to form shape memory bio-based blends with or without post-annealing effect. To the authors’ best knowledge, this is the first work to discuss the annealing effect on the PLA-based SMP blends. Annealed TPU showed regularly fractured surfaces unlike the macro-phase segregated domains for non-annealed TPU. After 3 h-annealing treatment, spherulites were observed for PLA, but not for TPU. The crystallinity of PLA increased, close to 3-fold increment, for annealed blends in comparison with non-annealed blends. The shape memory behaviors of PLA/TPU blends predeformed under three different predeformation temperatures (25, 80, 120 °C) were investigated. The annealing effect was helpful in enhancing the shape fixing ratio of the PLA/TPU (60/40) blend at high predeformation temperature of 120 °C in comparison with 25 °C. However, the suitable selection of the optimum predeformation temperature at 80 °C outweighed the annealing effect to attain the high shape fixing ratio, even in the case of non-annealed blends. The annealing effect often increased the perfection of crystal domains/interfaces and the larger crystal sizes, which would be detrimental to the molecular extensibility. The overall annealing effect on the shape recovery ratios were quite effective for both PLA/TPU blends of 80/20 and 60/40 without sacrificing the shape fixing ratios at the optimum predeformation temperature of 80 °C, attributing to the increased crystallinity of PLA and homogenized phase domains of TPU. Particularly, the annealing treatment did significantly increase the recovery ratio of the blends, more than 2-fold increment, especially for PLA/TPU (60/40) blend. At both lower or higher predeformation temperatures, the stress concentration between the increased crystalline domains and amorphous regions tended to dominate the annealing effect, leading to a negative contribution to the shape recovery processes.

Chapter 40 - Liquid Crystal Polymer

Influence of thermoplastic polyurethane (TPU) and printing parameters on the thermal and mechanical performance of polylactic acid (PLA) / thermoplastic polyurethane (TPU) polymer

The fracture and failure behavior of in-situ polymerized polyamide-12 (PA-12) belends prepared by reactive extrusion were studied in instrumented highspeed (v = 1.2 m/s) impact bending tests using the linear elastic fracture mochanics approach. PA-12 was polymerized in presence (up to 9 wt.-%) of ethylene/butyl acrylate copolymers (E/BA) of varying BA content and melt viscosity. From the tests performed en injection molded specimens at ambient temperature and -40°C, respectively, the fracture toughness (K d ) and initiation fracture energy (G d,i ) were derived. K d was less sensitive to either testing temperature of E/BA type and content. G d,i , on the other hand, went through a maximum at m temperature and monotonously increased at T = -40°C as a function of modifier centent. E/BA with higher melt viscosity and lower polarity (lower BA content) performed better than the lower melt viscosity, higher polarity E/BA counter-part. The dominant failure modes and their change both with temperature and modifier content were studied by fractography and discussed.

This study investigates the influence of using multifunctional epoxy Joncryl ADR 4468 chain extender (CE) on the properties of various polylactide (PLA)/thermoplastic polyurethane (TPU) (75 wt/25 wt) blend systems. The blends were based on two different TPU grades with ether‐ and ester‐based soft segment as the dispersed phase (i.e., TPUether and TPUester) and an amorphous and a semicrystalline PLA grades as the matrix (i.e., aPLA and scPLA). PLA appeared to be more compatible with the TPUester, which caused the enhancement of the impact strength and strain at break values of the blends more remarkably. The dynamic rheological experiments also confirmed that the CE revealed a better reactivity with TPUester than TPUether. This further enhanced the interfacial compatibility between the PLA and TPUester and thereby dramatically improved the impact strength and ductility of the PLA/TPUester blends, specifically those with 0.5 wt% CE. Meanwhile, aPLA as the matrix reflected the TPUs toughening effect more efficiently than scPLA. This was due to the possible shrinkage caused by the crystallization of scPLA matrix, which could deteriorate the interfacial interactions between the phases in the corresponding blends.

Enhanced foaming ability of thermoplastic polyurethane by crystallization during mold-opening foam injection molding with supercritical N2 as blowing agents

To address the shortcomings of large porosity and insufficient mechanical properties of skeletonized Thermoplastic polyurethane (TPU) fabrications during the preparation of composite materials by selective laser sintering (SLS) technology. In this paper, SiO2@Si3N4ws‐GPTMS core‐shell structure filler was successfully prepared by first synthetically growing silicon dioxide (SiO2) nanospheres on the surface of silicon nitride whiskers (Si3N4ws) in situ by sol–gel method, and then modified with silane coupling agent Silane coupling agent (GPTMS). Then the filler was incorporated into the inner and outer surfaces of TPU skeletonized structural parts by vacuum dip coating using a water‐based polyurethane (PU) coating post‐treatment enhancement method, and the surface coating coating of TPU skeletonized structural parts was achieved by warming and curing. This composite filler coating structure greatly improved the mechanical properties of the SLS parts (tensile strength of 20.3 MPa and elongation at break of 338.9%, 163% higher tensile strength, 17.7% higher elongation at break, and 672% higher rebound dimension compared with the pure TPU sintered parts). In addition, the thermal stability of the SLS sintered parts was improved, which greatly enhanced the application of the sintered manufactured parts prepared by SLS technology in the field of rebound‐absorbing artificial wear.

Thermoplastic poly urethane (TPU) is a diblock copolymer which naturally phase segregates into thermodynamically incompatible hard (H) and soft (S) segments. The size of the segments and their spatial distribution can significantly affect the microstructure and mechanical properties of the material. In this paper, we investigated the effect of duration of exposure to ultrasound on the solution prior to film formation on the final film properties. The response variable for the study was primarily mechanical properties of the TPU thin films fabricated via a solution route utilizing tetra hydro furan as a solvent. The times of sonication were varied between 30 min and 90 min, while all films were fabricated at average thickness of 20 ± 5 μm. The mechanical tests have been conducted at two different displacement rates of 5 and 10 mm/min. Our results indicated that (relative to untreated TPU) ultrasound tends not to deteriorate the fracture strength, strain and yet improve the fracture toughness. We attribute these results to subtle events at the H and S segment/domain levels. To further understand these microstructural variations, we conducted differential scanning calorimetry scan tests between 25 °C and 200 °C at 5 °C/min on untested and tested TPU samples of all types. This data showed a delicate sonication time dependent trend and has been interpreted in conjunction with our mechanical test data. Transition temperatures, enthalpies, and specific heat capacities have been computed for these cases.

The synergistic effect of organic montmorillonite and thermoplastic polyurethane on properties of asphalt binder

The viability of siloxane-based thermoplastic polyurethane (TPU) nanocomposites as a new insulation material for implantable and electrically active medical devices is investigated. We show that manipulating and controlling the specific interactions between the TPU segments and the engineered nanofiller greatly varies the TPU properties. The incorporation of dual modified organofluoromica as the nanofiller successfully enhanced the tensile strength, toughness and tear strength of the TPU. This is due to the presence of dual surfactants, which form regions of higher and lower surface energy on the layered silicate surface, thus enabling molecular interactions between the organofluoromica and both the hard and the soft TPU segment populations. We show that the addition of a second choline-based modifier with reactive –OH functionality may lead to the formation of positively charged TPU chain end groups as a result of trans-urethanization reactions during high temperature compounding, thus introducing labile "grip-slip-grip-slip" interactions between the TPU and the nanofiller. These molecular interactions assist in achieving a reduced level of stiffening, while at the same time enhance the toughening mechanism. The increase in the creep resistance and retardation in the stress relaxation of the TPU provides evidence that the dual modified organofluoromica also serves to enhance the dimensional stability of the TPU.