Influence Of Hard Segment Content Research Articles

Influence of hard segment content and soft segment length on the microphase structure and mechanical performance of polyurethane-based polymer concrete

Understanding the structure–property relationship of polyurethane (PU) binders is of critical importance in the construction engineering applications. A series of rapid room temperature-curable PU binders were prepared using polyoxypropylene glycol as the soft segments, along with polymethylene polyphenylene isocyanate and 4,4′-methylene-bis(2-chlorobenzenamine) as the hard segments. This work investigated the influence of the hard segment content (40 wt%, 45 wt%, and 50 wt%) and the soft segment molecular weight (1000 g/mol, 2000 g/mol, 3000 g/mol, and 4000 g/mol) on the microphase structure of the PU binders. Their influence on the compressive behaviors, flexural behaviors, impact strengths, and slant shear strengths of the PU-based polymer concretes was also investigated. Structural characterization revealed that increasing either the hard segment content or the larger soft segment molecular weight effectively enhanced hydrogen bonding as well as microphase separation. Our results also demonstrated that a higher hard segment content resulted in better mechanical performance and shorter pot life. In addition, the PU-based polymer concrete using 2000 g/mol polyoxypropylene glycol reached optimal mechanical performance when the hard segment was held constant. Hence, varying the hard segment content and soft segment length can be an effective method to adjust the engineering performance of PU-based polymer concrete.

Influence of Hard Segment Content and Diisocyanate Structure on the Transparency and Mechanical Properties of Poly(dimethylsiloxane)-Based Urea Elastomers for Biomedical Applications.

The effect of hard segment content and diisocyanate structure on the transparency and mechanical properties of soft poly(dimethylsiloxane) (PDMS)-based urea elastomers (PSUs) was investigated. A series of PSU elastomers were synthesized from an aminopropyl-terminated PDMS (: 16,300 g·mol−1), which was prepared by ring chain equilibration of the monomers octamethylcyclotetrasiloxane (D4) and 1,3-bis(3-aminopropyl)-tetramethyldisiloxane (APTMDS). The hard segments (HSs) comprised diisocyanates of different symmetry, i.e., 4,4′-methylenebis(cyclohexyl isocyanate) (H12MDI), 4,4′-methylenebis(phenyl isocyanate) (MDI), isophorone diisocyanate (IPDI), and trans-1,4-cyclohexane diisocyanate (CHDI). The HS contents of the PSU elastomers based on H12MDI and IPDI were systematically varied between 5% and 20% by increasing the ratio of the diisocyanate and the chain extender APTMDS. PSU copolymers of very low urea HS contents (1.0–1.6%) were prepared without the chain extender. All PSU elastomers and copolymers exhibited good elastomeric properties and displayed elongation at break values between 600% and 1100%. The PSUs with HS contents below 10% were transparent and became increasingly translucent at HS contents of 15% and higher. The Young’s modulus (YM) and ultimate tensile strength values of the elastomers increased linearly with increasing HS content. The YM values differed significantly among the PSU copolymers depending on the symmetry of the diisocyanate. The softest elastomer was that based on the asymmetric IPDI. The elastomers synthesized from H12MDI and MDI both exhibited an intermediate YM, while the stiffest elastomer, i.e., that comprising the symmetric CHDI, had a YM three-times higher than that prepared with IPDI. The PSUs were subjected to load–unload cycles at 100% and 300% strain to study the influence of HS morphology on 10-cycle hysteresis behavior. At 100% strain, the first-cycle hysteresis values of the IPDI- and H12MDI-based elastomers first decreased to a minimum of approximately 9–10% at an HS content of 10% and increased again to 22–28% at an HS content of 20%. A similar, though less pronounced, trend was observed at 300% strain. First-cycle hysteresis among the PSU copolymers at 100% strain was lowest in the case of CHDI and highest in the IPDI-based elastomer. However, this effect was reversed at 300% strain, with CHDI displaying the highest hysteresis in the first cycle. In vitro cytotoxicity tests performed using HaCaT cells did not show any adverse effects, revealing their potential suitability for biomedical applications.

Influence of chemical structure of hard segments on physical properties of polyurethane elastomers: a review

Hard segments of polyurethanes (PUs) are generally formed from diisocyanate and diol. Diol can be replaced with triol and thiol. These chemical structures of hard segments strongly affect not only a microphase separated structure but mechanical properties of resultant PUs. In this review, we focus on the relationship between chemical structure like symmetry and bulkiness of diisocyanate and mechanical properties of PU. Then, influence of hard segment content, incorporation of 1,1,1-trimethylol propane with trifunctional groups, and alkyldithiol was reviewed mainly on trans-1,4-bis(isocyanatomethyl) cyclohexane-poly(oxytetramethylene) glycol-based PU.

Organogelation of self-assembling segmented poly(urethane acylsemicarbazides) and their dye adsorbing properties

Segmented poly(urethane acylsemicarbazides) carrying aromatic groups in the hard segments were synthesized by two step polymerization technique using commercially available, cost effective raw materials. The resulting polymers with specific ratios of NCO/OH were found to gel organic solvents like dimethylformamide, dimethylacetamide and N-methylpyrrolidone and their corresponding gels were thermoreversible. Tuning of the gelation behaviour and gel properties have been achieved by varying the polyol molecular weight (polypropylene glycol - 1000 and 2000) and NCO/OH ratio. Influence of hard segment content on the gel-sol transition as studied by DSC showed that increasing hard segment content led to stronger gelator-gelator interactions and hence higher Tgel. Broad tanδ peaks of films of xerogels reflected a network kind of structure due to physical crosslinks in the self-assembled state in DMA analysis. The films of xerogels of PPG1000 based gelators exhibited higher tensile strength but lower elongation compared to PPG2000 based gelators. Viscoelastic nature of the supramolecular elastomeric gels was confirmed by dynamic oscillatory studies and stability of the gel was found to increase with increase in hard segment content. H-bonding between the urethane moieties as confirmed by IR spectroscopy and hydrophobic interactions between the PPG units in the soft segments lead to a phase separated structure. Hence phase separation induced gelation mechanism has been proposed and supported by SEM images and XRD data. Both the gelators and xerogels had capability of adsorbing crystal violet from their aqueous solutions and desorbing in organic solvents like acetone and methanol.

Synthesis of PPG-TDI-BDO polyurethane and the influence of hard segment content on its structure and antifouling properties

Abstract Polyurethane have good anti-protein adsorption properties, could be used as an antifouling material. In this study, a type of polyurethane antifouling coating was prepared using 2,4-toluene diisocyanate and 1,4-butanediol as the hard segment and polyether polyols as the soft segment. The influence of hard segment content on the chemical structure, mechanical properties, and surface properties of the coatings was investigated. Subsequently, the antifouling performance of the polyurethane coatings was investigated by benthic diatom adhesion and panel tests. The results showed that coating H40 (polyurethane coating with a hard segment content of 40 wt.%) exhibited the best antifouling property. The antifouling performance of the coatings was further examined by evaluating the surface changes occurring in the polyurethane coatings during immersion in seawater. In situ diiodomethane contact angle measurements were performed to monitor such changes. The oil contact angle results were consistent with the results of the panel test. The oil contact angle and antifouling property are both determined by the surface roughness, which is determined by the level of microphase separation in the polyurethane coatings.

The influence of 2,4-toluene diisocyanate content on the intrinsic self-healing performance of polyurethane at room-temperature

A new kind of polyurethane was synthesized using 2,4-toluene diisocyanate (TDI) as the hard segment and polyether polyols as the soft segment. The influence of hard segment content on the self-healing ability of polyurethane was investigated by testing tensile strength and elongation healing rates after contact together for one week. Tensile test results indicate that the intrinsic healing capability of the polyurethane at room temperature decreased with an increasing hard segment content, and was lost when it reached fifty percent. Fracture morphologies of polyurethane were observed by confocal laser scanning microscopy, showing that roughness increased with an increasing hard segment content due to increased cross-link density and restraining of segment motion. The self-healing capability of this TDI polyurethane can be attributed to reversible H-bonds and to the mobility of the soft segment at room temperature. Segment mobility is a prerequisite of being able to self-heal.

Structure–property behavior of moisture-cure polyurethane wood adhesives: Influence of hard segment content

One-part moisture-cure polyurethane (PUR) wood adhesives and the effects of hard phase content were studied at three levels: liquid prepolymer, cured neat film, and cured adhesive bondline. Three PURs were prepared from polymeric methylenebis(phenylisocyanate) and poly(propylene glycol) with variable hard phase content (53.5–72.5%). At the prepolymer level, increasing hard phase content increased intermolecular interactions, liquid viscosity, and the soft phase glass transition temperature. When cured as neat films, greater hard phase content caused higher hard phase softening temperature, and greater quantities of hydrogen-bonded urea structures. When bonded within wooden dual cantilever beams, adhesive penetration and bondline thickness varied appreciably. Regardless of these many differences, the measured mode-I fracture toughness was rather insensitive to the adhesive hard phase content. This suggested that a critical hard phase content had been exceeded such that a variety of bonding variables became ineffectual. It was hypothesized that wood bonding performance is compromised when the PUR hard segment content exceeds about 51%, near the composition when the hard phase becomes continuous in the dual-phase PUR morphology. It was suggested that morphological effects should be studied for wood-bonding polyurethanes having hard segment contents near about 50%, near the composition associated with phase inversion or with the loss of a co-continuous morphology.

The influence of hard segment content on mechanical and thermal properties of polycarbonate-based polyurethane materials

Aliphatic segmented polyurethanes were prepared by one-step procedure in catalytic reaction between polycarbonate diol, hexamethylene-diisocyanate and 1,4-butandiol (as chain extender). The hard segment content TS was varied (17, 24, 30 and 42 wt. %) by changing the ratio of starting compounds. The soft segment is made from flexible aliphatic polycarbonate diol, while hard segments consist of chain extender and diisocyanate component. In order to study the hydrogen bonding formation and phase separation, Fourier transform infrared spectroscopy (FT-IR) was used. Wide angle X-ray scattering (WAXS) was performed to determine a degree of crystallinity and to investigate the phase behavior of prepared elastomers. The effect of TS content on mechanical properties (tensile strength, elongation at break and hardness) was tested. Thermal behavior of prepared novel polycarbonate-based polyurethanes was investigated using differential scanning callorimetry (DSC). It was determined that the elastomer which contains the highest amount of urethane groups in its structure (TS content of 42 wt. %) exhibits the most pronounced phase separation and the highest degree of crystallinity. All prepared polyurethanes exhibit high elongation at break (over 700%). The glass transition temperature Tg of prepared samples was in the temperature region from ?39 to ?36?C, and it was found to be slightly influenced by the soft segment content. The enthalpy of chain segments relaxation in diffused region between hard and soft domains (detected in the temperature range from 35 to 55 ?C) was decreased with the increase of hard segment content. The multiple melting of hard segments (connected with the dissruption of physical crosslinks) appeared above 100 ?C. It was found that the melting enthalpy linearly increases with the increase of urethane group content. Sample with 42 wt. % of TS has the highest value of melting enthalpy (41.5 J/g).

Influence of the chemical structure of PUR prepolymers on thermal stability

The thermal stability of adhesives for load-bearing construction has been one of their key parameters since engineered wood products were introduced in timber construction. In the case of one-component moisture-curing polyurethane (1C PUR) adhesives, knowledge about relationships between their chemical structure and the resulting bonding properties is limited, especially under high-temperature conditions. In this study the structure–property relationships of 1C PUR prepolymers were analyzed in the temperature range from 20 to 200 °C by means of mechanical and rheological tests. NCO-terminated urethane prepolymers were prepared from systematically varied MDI and polyether mixtures. The structural parameters investigated were the urea and urethane group content, cross-link density, ethylene oxide content and the adjustment of functionality via NCO or polyether component. Bonded wood joints were tested for their tensile shear strength and polymer films were analyzed by means of DMA and DSC. The results revealed a significant influence of hard segment content and cross-link density on the thermal stability of the prepolymers. Not all parameters that affect the film properties significantly influence bonding.

Properties of shape memory polyurethane used as a low-temperature thermoplastic biomedical orthotic material: influence of hard segment content

A series of PCL-based shape memory polyurethanes was synthesized via bulk pre-polymerization. Their thermal, mechanical properties, shape memory properties, softening and hardening processes were investigated by the experimental approach and made comparison with a commercially available orthotic material. The cytotoxicity of the low-temperature thermoplastic polyurethane was tested. The results suggest that the soft segment phase of the shape memory polyurethanes has a melting transition at about 36–46°C, which makes them possible low-temperature thermoplastic materials. The hard segment phase has a two-fold effect on the shape memory polyurethane as a low-temperature thermoplastic orthotic material: increasing tensile mechanical strength at room temperature, which enables it to be used in circumstances where high tensile strength is required; and reducing low-temperature malleability and fixity ratio, which make it difficult to fabricate orthortic devices. To obtain a shape memory polyurethane with excellent low-temperature thermoplastic properties for orthopaedical surgical use, the hard segment content should not be above 22 wt%. At last, a prototype wrist orthosis was easily fabricated at 60°C with hand using a shape memory polyurethane with 16 wt% hard segment content. Cytotoxicity tests indicate that the wrist orthotic material is not cytotoxic.