Diisocyanate-Linked Polymers. III. Relationships between the Composition and Ultimate Tensile Properties of Some Polyurethane Elastomers

1962 ◽  
Vol 35 (3) ◽  
pp. 753-775 ◽  
Author(s):  
Thor L. Smith ◽  
Alan B. Magnusson
Keyword(s):  
Tensile Strength ◽  
Chemical Nature ◽  
Average Molecular Weight ◽  
Extension Rate ◽  
Glass Temperature ◽  
Experimental Conditions ◽  
Polyurethane Elastomers ◽  
Ultimate Elongation ◽  
Rate Of Increase ◽  
Ultimate Properties

Abstract The tensile strength and elongation at rupture of elastomers vary markedly with the experimental conditions used in measurement. For example, when measured at a fixed rate of extension, the tensile strength may increase by a factor of 100 or more as the temperature is decreased, and the ultimate elongation may increase concomitantly by a factor of 10 or more and then decrease to a few per cent. The ultimate properties also depend on the chemical nature of the network chains, the degree of crosslinking, and on the regularity of spacing of the crosslinking sites. In addition, those elastomers which crystallize during extension (e.g., vulcanized natural rubber) normally exhibit higher tensile strengths and ultimate elongations than those which do not crystallize (e.g., SBR rubbers). In seeking relationships between the structure and the ultimate properties of elastomers, these various factors which affect ultimate properties must be carefully considered. Previously a study was made of the tensile strength and ultimate elongation of several series of polyether-polyurethan elastomers prepared from polyoxypropylene glycol 2025 (PPG), trimethylolpropane (TMP), and either toluene 2,4-diisocyanate (TDI) or hexamethylene 1,6-diisocyanate (HDI). The structure of these elastomers was characterized by (1) the number of network chains per unit volume ν and (2) the concentration of urethan groups [U]. These parameters could be varied independently over certain ranges by making appropriate changes in the average molecular weight of PPG 2025 through blending it with dipropylene glycol (DPG). The glass temperature Tg of the elastomers increased linearly with [U], the rate of increase being considerably greater for the TDI-linked than for the HDI-linked elastomers. These elastomers apparently did not crystallize upon extension, and their ultimate properties, measured at a fixed extension rate, were found to depend on both [U] and ν. However, when compared in corresponding temperature states, i.e., at equal values of T−Tg, the ultimate properties over a wide temperature range were found to be independent of [U], or approximately so, when [U] was less than about 1.85 moles/kg. Also, the ultimate elongation was observed to be inversely proportional to ν, although the proportionality constant was temperature-dependent. It thus appears that certain elastomers which do not crystallize have ultimate properties which depend not only on ν and Tg but also on the chemical nature of the network chains.

Time and Temperature Dependence of the Ultimate Properties of an SBR Rubber at Constant Elongations

1961 ◽  
Vol 34 (3) ◽  
pp. 897-909
Author(s):  
Thor L. Smith ◽  
Paul J. Stedry
Keyword(s):  
Tensile Strength ◽  
Strain Rate ◽  
Temperature Dependence ◽  
Rate Dependence ◽  
Strain Rates ◽  
Type Specimens ◽  
Stress Strain ◽  
Ultimate Elongation ◽  
Tensile Tester ◽  
Ultimate Properties

Abstract A study was made previously of the temperature and strain rate dependence of the stress at break (tensile strength) and the ultimate elongation of an unfilled SBR rubber. In that study, stress-strain curves to the point of rupture were measured with an Instron tensile tester on ring type specimens at 14 temperatures between −67.8° and 93.3° C, and at 11 strain rates between 0.158×10−3 and 0.158 sec−1 at most temperatures. The tensile strength was found to increase with both increasing strain rate and decreasing temperature. At all temperatures above −34.4° C, the ultimate elongation was likewise found to increase with increasing strain rate and decreasing temperature but at lower temperatures the opposite dependence on rate was observed; at −34.4° C, the ultimate elongation passed through a maximum with increasing rate.

Viscoelastic and Ultimate Tensile Properties of Styrene-Butadiene-Styrene Block Copolymers

1969 ◽  
Vol 42 (5) ◽  
pp. 1257-1276 ◽  
Author(s):  
T. L. Smith ◽  
R. A. Dickie
Keyword(s):  
Tensile Strength ◽  
Block Copolymers ◽  
High Speed ◽  
Extension Rate ◽  
Stress Strain ◽  
Simple Tension ◽  
Ultimate Properties ◽  
Styrene Butadiene Styrene ◽  
Styrene Butadiene ◽  
Butadiene Styrene

Abstract A study was made of the stress—strain and ultimate properties in simple tension of an elastomeric styrene—butadiene—styrene block copolymer (Kraton 101) and also of a similar material (Thermolastic 226) that contains about 35% plasticizer as well as inorganic pigments. Stress—strain data were obtained at crosshead speeds from 0.02 to 20 in./min at temperatures from − 40 to 60° C. The relaxation rate, derived from the data at constant extension rates, was about 8% per decade of time for both materials at temperatures from − 40 to about 40° C and at extensions from about 20% up to 400%. Above − 30° C, the shift factor log aT was found to vary linearly with temperature. These findings indicate that the time and temperature dependence of the mechanical properties results primarily from the plastic (or viscoelastic) characteristics of the styrene domains. The tensile strength for Kraton 101 below 40° C is somewhat greater than 4000 psi, sensibly independent of extension rate and temperature. For the highly plasticized Thermolastic 226, the tensile strength at an extension rate of 1.0 min−1 increases from 2200 psi at 0° C to 3600 psi at − 40° C. Above 40° C for Kraton 101 and above 0° C for Thermolastic 226, the tensile strengths are dependent on extension rate and temperature owing to the increased ductility of the styrene domains. The high strength of these materials results from the uniformly dispersed styrene domains of colloidal dimensions. To obtain a crack of sufficient size to satisfy an energetic criterion for self-sustained high-speed propagation, domains must be disrupted. The plastic characteristics of the domains have a controlling effect on crack growth and thus on the ultimate properties of the materials. The strength and extensibility of other elastomers are considered in relation to those of the block copolymers.

Molecular Theory for the Tensile Strength of Gum Elastomers

1964 ◽  
Vol 37 (4) ◽  
pp. 808-817 ◽  
Author(s):  
F. Bueche ◽  
J. C. Halpin
Keyword(s):  
Tensile Strength ◽  
Creep Curve ◽  
Viscoelastic Properties ◽  
Butyl Rubber ◽  
Molecular Theory ◽  
Creep Response ◽  
Failure Curve ◽  
Ultimate Elongation ◽  
Propagating Crack ◽  
Ultimate Properties

Abstract The tensile strength and ultimate elongation properties of any given amorphous elastomer can be described by a characteristic failure curve. It is shown in this paper that the failure curve can be predicted from a knowledge of the creep curve of the elastomer together with the data from a Mooney-Rivlin plot. The theory relating the ultimate properties to the viscoelastic properties of the elastomer is based upon the idea of a propagating crack, the rate of propagation being limited by viscoelastic mechanisms. Data for the failure curves and creep response for EPR and SBR elastomers are presented and shown to support the theory. Literature data for butyl rubber are also shown to confirm the theory.

The Ultimate Properties of Simple Elastomers

1958 ◽  
Vol 31 (1) ◽  
pp. 19-26 ◽  
Author(s):  
A. M. Bueche
Keyword(s):  
Tensile Strength ◽  
Shear Strength ◽  
Theoretical Approach ◽  
Major Part ◽  
Large Mass ◽  
University Of Wyoming ◽  
Ultimate Elongation ◽  
Ultimate Properties ◽  
Similar Theory

Abstract The ultimate properties of polymers are very poorly understood. A large mass of practical data is available but at present there seem to be no molecular theories for its correlation or for use as a guide in obtaining new data. In the following pages a theoretical approach to the ultimate properties of simple crosslinked elastomers will be described. The treatment will be limited to the tensile strength and ultimate elongation at temperatures high enough so that crystallinity and the viscous work during extension are negligible. The theory can be extended to cover compressive or shear strength with relatively little effort. The incorporation of the effects of viscosity and crystallinity will require somewhat more work. (After the completion of the major part of this work I learned that Prof. F. Bueche, University of Wyoming, has developed a somewhat similar theory for the tensile strength of viscous elastomers.)

Studies on fluorescence of cellulosics

Holzforschung ◽  
2007 ◽  
Vol 61 (5) ◽  
pp. 504-508 ◽  
Author(s):  
Alain Castellan ◽  
Reinaldo Ruggiero ◽  
Elisabete Frollini ◽  
Ludmila A. Ramos ◽  
Christine Chirat
Keyword(s):  
Solid State ◽  
Microcrystalline Cellulose ◽  
Woody Plants ◽  
Average Molecular Weight ◽  
Homogeneous Medium ◽  
Fluorescence Emission ◽  
Excitation Wavelength ◽  
Experimental Conditions ◽  
Fluorescence Emission Spectra ◽  
Cotton Linters

Abstract Steady-state fluorescence emission spectra of various celluloses were measured at an excitation wavelength of 320 nm. Various spectra recorded in the solid state were compared: (1) ECF bleached papers made of hardwood, the anhydroglucose units of which were chemically modified at C1 and C6 or C2 and C3 positions with carboxylic groups; (2) microcrystalline cellulose; (3) cotton linters; and (4) delignified sisal fibers (mercerized or not). Fluorescence emission was quite independent of the carboxylic acid content and average molecular weight (determined by viscosimetry) of the cellulose polymers. Microcrystalline cellulose (Avicel), cotton linters, and mercerized delignified sisal cellulose were acetylated in homogeneous medium (DMAc/LiCl as solvent system) to obtain soluble polymers in dichloromethane for comparison of spectra recorded in the solid and liquid states. Fluorescence of cellulose acetates in solution (CH2Cl2) and in the solid state was compared under similar experimental conditions to non-esterified celluloses in the solid state. The importance of the solid state for fluorescence emission could be demonstrated. Fluorophores are present in minute amounts in the polymer and their favorable energy transfer for excitation in the solid state likely enhances fluorescence emission. Among numerous fluorophores, dityrosine appeared to be a good candidate for fluorescence because it displayed emission in the fluorescence range of cellulose. Dityrosine is an amino acid involved in the lignification of non-woody plants. Mercerized sisal impregnated with tyrosine in the presence of peroxidase and hydrogen peroxide did not show enhanced emission, in contrast to para-hydroxycinnamic acid (coumaric acid), which is also involved in the lignification process at least for non-woody plants. The origin of cellulose fluorescence remains uncertain and appears to have several origins. This study clearly underlines the importance of the solid state for enhancing fluorophore emission.

Fracture Behavior of Organic Silicon Rubber at Different Extension Rate

2011 ◽  
Vol 687 ◽  
pp. 571-575
Author(s):  
Xiao Liu ◽  
Wei Fang Zhang ◽  
Sheng Wang Liu ◽  
Wei Guo Hou ◽  
Mei Li Ding
Keyword(s):  
Tensile Strength ◽  
Fracture Behavior ◽  
Tensile Fracture ◽  
Extension Rate ◽  
Silicon Rubber ◽  
Organic Silicon ◽  
Flat Region ◽  
Secondary Cracks ◽  
Rough Region ◽  
Relationship Of

Fracture behavior of organic silicon rubber at the extension rate of 100, 300, 500 and 700 mm/min at room temperature was studied in this paper. The fracture surface morphology was observed by scanning electron microscopy (SEM). Effects of different extension rate on the tensile strength tensile fracture behavior and mechanism were investigated. The results showed that fracture of the organic silicon rubber was composed by flat region and rough region, while the rough region was relatively small. With the increasing extension rate, the area of flat region enlarged while rough region decreased, and the secondary cracks appeared when the extension rate reached critical value. The relationship of the tensile strength and elongation with the extension rate were similar, both of which rised and then droped as the extension rate increased, and further studies were needed for the fracture mechanism.

scholarly journals Modification of epoxy resins with thermoplastic segmented polycarbonate-based polyurethanes

2014 ◽  
Vol 68 (6) ◽  
pp. 755-765 ◽  
Author(s):  
Jelena Pavlicevic ◽  
Mirjana Jovicic ◽  
Vesna Simendic ◽  
Oskar Bera ◽  
Radmila Radicevic ◽  
...  
Keyword(s):  
Tensile Strength ◽  
Epoxy Resin ◽  
Hard Segment ◽  
Crosslinking Agent ◽  
Polyurethane Elastomers ◽  
Hard Segment Content ◽  
Weight Content ◽  
Epoxy Curing ◽  
Hard Segments ◽  
Modified Epoxy

In this work, epoxy hybrid materials were synthesized by addition of thermoplastic segmented aliphatic polyurethanes with good elastic properties. The modified epoxy samples were obtained by curing of previously homogenized mixture of prepared polyurethane melts, epoxy resin and crosslinking agent Jeffamine D-2000. The influence of different weight content of polyurethanes (5, 10 and 15 wt. % compared to pure epoxy resin) as well the influence of different hard segments of elastomers (20, 25 and 30 wt. %) on the curing of modified epoxy systems was studied. The curing was followed by differential scanning calorimetry (DSC), in dynamic regime from 30 to 300?C, at three heating rates (5, 10 and 20?C/min). With the increase of hard segments content of polyurethanes added in higher concentration (10 and 15 wt. %) into epoxy matrix, the temperature of maximum ratio of curing was shifted to lower values (from 205 to 179?C). Obtained DSC data were analyzed using two integral methods (Ozawa-Flynn-Wall and Kissinger-Akahira-Sunose) and one differential kinetic model (Friedman). The significant differences were observed in the second part of the epoxy curing (for the reaction degrees higher than 60 %), where the values of activation energies remarkably increase. The addition of polyurethane elastomers retarded the curing process due to decreased mobility of reactant molecules caused by higher viscosity of reaction mixture. By detailed analysis of determined kinetic parameters, it is concluded that the influence of slow diffusion is more pronounced in the presence of thermoplastic polycarbonate-based polyurethanes, which confirmed their effect on the mechanism of epoxy curing. The highest tensile strength and hardness showed the DGEBA modified with the polyurethane with highest hard segment content. Increasing the hard segment content of polyurethane and its concentration in matrix, the tensile strength of modified epoxy was increased. The elongation at break of modified epoxy samples was significantly improved by addition of polycarbonate-based polyurethanes with low hard segment content, due to higher content of flexible soft segment chains.

scholarly journals Achievement of Both Mechanical Properties and Intrinsic Self-Healing under Body Temperature in Polyurethane Elastomers: A Synthesis Strategy from Waterborne Polymers

Polymers ◽  
2020 ◽  
Vol 12 (4) ◽  
pp. 989 ◽  
Author(s):  
Liangdong Zhang ◽  
Teng Qiu ◽  
Xiting Sun ◽  
Longhai Guo ◽  
Lifan He ◽  
...  
Keyword(s):  
Tensile Strength ◽  
Body Temperature ◽  
Healing Process ◽  
Waterborne Polyurethane ◽  
Polymer Materials ◽  
Self Healing ◽  
Polyurethane Elastomers ◽  
Elongation At Break ◽  
Synthesis Strategy ◽  
A Chain

Inspired by the growing demand for smart and environmentally friendly polymer materials, we employed 2,2′-disulfanediyldianiline (22DTDA) as a chain extender to synthesize a waterborne polyurethane (WPUR). Due to the ortho-substituted structure of the aromatic disulfide, the urea moieties formed a unique microphase structure in the WPUR, its mechanical strength was enhanced more 180 times relative to that of the material prepared without 22DTDA, and excellent self-healing abilities at body temperature in air or under ultrasound in water were obtained. If the self-healing process was carried out at 37 °C, 50 °C or under ultrasound, the ultimate tensile strength and elongation at break of the healed film could reach 13.8 MPa and 1150%, 15.4 MPa and 1215%, or 16 MPa and 1056%, respectively. Moreover, the WPUR films could be re-healed at the same fracture location over three cutting–healing cycles, and the recovery rates of the tensile strength and elongation at break remained almost constant throughout these cycles.

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