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A series of four water-blown flexible polyurethane foams was produced in which the water content was varied from 2 to 5 pph at a constant isocyanate index of 110. A portion of each foam was thermally compression molded into a plaque. The morphology of the foams and plaques was investigated using DMS, DSC, FTIR, TEM, SEM, swelling, WAXS, and SAXS. A high degree of phase separation occurs in these foams and the degree of phase separation is independent of water (hard segment) content. In the foam with the lowest water content the morphology is similar to that of typical segmented urethane elastomers. Small hard segment domains are present with a correlation distance of roughly 7.0 nanometers. When the water content is increased a binodal distribution of hard segments appears. There are the small hard segment domains typical of segmented urethane elastomers as well as large hard segment aggregates greater than 100 nanometers in diameter. The large domains are thought to be aggregates of polyurea that precipitated during the manufacture of the foam. The foam making process successfully incorporated the trifunctional polyols into a network indicating a high degree of polymerization for the hydroxyl-isocyanate reaction. Unreacted isocyanate is present in the foams a month after curing. It is believed to be trapped in the large urea aggregates. WAXS patterns of the foams suggest hard segment ordering that may be of a paracrystalline nature but certainly lacking in true crystallinity. / Master of Science

A set of flexible water-blown slab stock polyurethane foams and their respective compression molded plaques as well as a chemically similar polyurea-urethane elastomer, PUUE, were studied to better understand the relaxation behavior and the molecular orientation upon deformation in these systems. The two main experimental techniques used in this investigation were stress relaxation in tension and deformation-IR dichroism. The stress relaxation in the foams and their respective plaques increased with hard segment content. The stress relaxation in the foams also appeared to depend very little on its anisotropic cell geometry and hence, mainly on the material comprising, the cell-wall struts and windows. Segmental orientation was measured as a function of elongation and relaxation, as well as hysteresis behavior for several of the plaques and the PUUE elastomer. The orientation changes upon deformation in the soft segments of both materials were small. Small changes in orientation with time and upon cyclic straining were also observed for the soft segments. The orientation at the interface of the hard and soft segments was influenced more by the soft segments in comparison to the hard segments in the plaques and in the PUUE elastomer. Significant transverse orientation upon deformation was observed in the hard segments of the plaques and up to elongations of 100 percent for the PUUE elastomer. Based on this transverse orientation behavior, the polyurea aggregates in the plaques were thought to possess a lamellar-like structure with the long axis of the aggregates aligning in the stretch direction. Relaxation and hysteresis behavior were observed upon following the orientation of the hard segments of the PUUE elastomer, but were negligible in that of the hard segments of the plaques. / Master of Science

This research has investigated the effects of a dilute urea solution, an acid-simulated perspiration solution, and distilled water on a polyurethane-coated fabric. Investigations were made into the feasibility of using the Glass Plate Method, where treated samples were heated between glass plates and the LaunderOmeter® Method where samples were treated with solutions in an enclosed system in a constant temperature bath. The degradative effects of the solutions, when used with the Glass Plate Method, were measured by flex and surface abrasion and the degradative effects of the solutions, when used with the LaunderOmeter® Method, were measured by surface abrasion. The pH was observed before and after treatments in the LaunderOmeter® . It was found that the urethane film of the test fabric could be completely decomposed with all three solutions when treated at 95°C for six hours in the LaunderOmeter®. However, those samples treated with urea had higher abrasion resistance and appeared less decomposed visually. This was in conflict with reports that the addition of urea to distilled water would increase the rate of hydrolysis, and could be used to simulate perspiration. This is assuming that the effects of the solutions were indeed causing hydrolysis. The LaunderOmeter® Method was found to be more controllable than the Glass Plate Method. Replications of treatments at 72°C for two hours were carried out on the polyurethane synthetic leathers using the LaunderOmeter® Method. Again, the urea-treated samples demonstrated a higher abrasion resistance. Distilled water and the acid-simulated perspiration solution gave comparable results. / Master of Science

Lignin based polyurethane films were synthesized by solution casting from hydroxypropyl lignins and diisocyanates. Kraft and steam explosion lignin, hexamethylene diisocyanate (HDI) and tolylene diisocyanate (TDI), were used for the study. It was found necessary to use stoichiometric excess amounts of diisocyanates in the synthesis of the thermosetting polyurethanes. The investigation primarily addresses the effect of synthesis variables and soft segment incorporation on the thermal and mechanical properties. The first part of the study examined the effect of lignin type, of diisocyanate type and of composition (NCO/OH ratio). Stoichiometric excess was found to cause a significant increase in the glass transition temperature. Use of HDI resulted in films with lower moduli as compared to TDI. NCO/OH stoichiometry variation had no noticeable effect on modulus or tensile strength. In the second part of the study involving incorporation of soft segments, four polyethylene glycols were used. No soft segment phase in the network was detectable by differential scanning calorimetry or dynamic mechanical analysis. The glass transition temperature of lignin phase dropped by as much as 70°C for HDI and 115°C for TDI based polyurethanes with inclusion of glycols up to 25% of the polyol weight. The swelling tendencies showed an expected increase with glycol content. Effect on mechanical properties were more pronounced in HOI than in TDI based polyurethanes. The modulus and tensile strength decreased, and the ultimate strain values increased with polyethylene glycol content. Last part of the study involved synthesis and characterization of kraft polyurethanes with polybutadiene glycol with functionality in excess of 2.0. The miscibility of this phase with hydroxypropyl lignin phase was found to be poor as observed by scanning electron microscopy. Glass transition temperature for the lignin phase increased with polybutadiene glycol content of the polyurethane in contrast to observations on polyethylene glycol modified polyurethanes. There were no significant improvements in tensile properties. The incompatibility of soft segments was seen to result in a more condensed lignin phase, and was thus found to be the major limitation in its applicability in modification of the network properties. The study demonstrates the utility of concept of network modification in the synthesis of lignin based thermosetting polyurethanes. By proper choice of synthesis variables, and with the use of glycols of sufficient compatibility, significant improvements in properties can be realised in these polyurethanes. / M.S.

This thesis was a study of the effect of the variation of cross-linkage on the mechanical properties of a polyurethane elastomer prepared from 33’ Bitolyene 44’ diisocyanate and the polyester of adipic acid and ethylene glycol. The investigation consisted of the preparation of polyurethane elastomer, solvent absorption and swelling tests, tensile properties test and hardness test. Three groups of polymer material were prepared. In the first group the R value was varied from 1.0 to 4.5, (the ratio of 33’ Bitolyene 44’ diisocyanate to polyester) and fixed amounts of excess diisocyanate were used. Ethylene glycol was used as the cross-linking agent. In the second and third groups the R value was fixed at 1.65 and 2.5, and the amount of excess diisocyanate after chain extension was varied. The preparation of the elastomer was accomplished by a method based on the literature and preliminary experiments carried out for the purpose of determining optimum conditions for the specific polymer under investigation. All mechanical tests were accomplished by conventional and standard methods. All tests were conducted at 75° F. In addition to these tests the hardness test was carried out at 300° F. The preparation of polyurethane elastomer by bulk polymerization was conducted at atmospheric pressure and 130° C with the reaction requiring a period of 30 minutes for completion. For the molding process, casting, cold molding, hot molding and curing were used. The various degrees of cross-linkage could be obtained by using different ratios of 33’ Bitolylene 44’diisocyanate to polyester and by varying the amount of cross-linked agent, ethylene glycol. The properties associated with cross-linking varied in such a way as to indicate an increase in cross-linking as the R value increased. The solvent absorption and swelling properties decreased with an increase of the R value. The mechanical properties improved with an increased R value. Also the hardness increased with an increase of the R value. / Master of Science

It is known that the classical inverse square root singularity used in Linear Elastic Fracture Mechanics (LEFM) is lost as a crack intersects a stress free surface. As a result, the stress and displacement equations are given as eigenvalue series expansions, with the lowest order eigenvalue dominating the series. The thickness averaged stress and surface displacement singularity exponents were determined for a commercially available polyurethane. Multiple specimen geometries were used to “benchmark” the optical methods. Tests have been run to determine the surface effect on a straight front crack. Results of these tests were compared with analytical results and related to LEFM concepts. / Master of Science

The polyhydroxy character of lignocellulosics and their natural abundance make them good candidates for the manufacture of polyurethanes. The cure characteristics of hydroxypropyl-cellulose and hydroxypropyl lignin (HPC and HPL, respectively) with polymeric methylene diphenyl diisocyanate (MDI) was studied via dynamic mechanical thermal analysis (DMTA). HPC/MDI and HPL/MDI resins flow at 30°C and proceed to cure at 50°C. The latter has excellent thermal stability over the former. Crosslinking of HPL and HPC with MDI follow an nth order kinetics, with an order of reaction of 2 and an apparent activation energy in the range of 12.9 kcal/mol - 14.7 kcal/mol. The rate of cure with time is higher in HPL-based polymers than HPC-based ones at the initial stage of cure; the difference vanishes at later stages. This demonstrates that the hydroxyl groups in HPC are less accessible to the NCO groups, and that cure rate might be dependent on diffusion limitations at later stages. Degree of cure, under all cure schedules, follows a parallel trend, and has to do with the fact that the hydroxyl groups of HPC are less accessible to isocyanate. Both HPL and HPC react with MDI at a reduced rate in comparison to a synthetic polyol: caprolactone triol. Time-glass transition temperature superposition was used to calculate times to vitrification of the HPL-based polymers, and is presented in a TTT cure diagram. This bio-based polymer displays the s-shaped vitrification pattern characteristics of thermosets. A similar approach did not work with HPC-based polymers. HPC- and HPL-based polymers did not display damping transitions, in isothermal cure, typical of gelation and vitrification. As the isocyanate to hydroxyl ratio (NCO:OH) increased, the glass transition temperature of the polymers increased, and the transition amplitude and width decreased and increased, respectively. In practical terms, this study illustrates that it is advantageous to use a) to use high isocyanate to hydroxyl ratios in order to produce polyurethanes which retain desirable damping behavior over a wider range of temperature. b) to use HPC/MDI resins in those situations where retention of stiffness at temperatures below 230° is required. c) to use HPL where rapid cure is desired. The study also reveals that the relative reactivity of water, HPL and HPC with isocyanate takes the form water > HPL > HPC. / Master of Science

In this thesis, the effect of interphase bonding on the cohesiveness of domain structure was addressed. The interchain attractive forces between rigid segments and the phase separation between hard and soft segments have been improved by introducing either urea groups or ionic units. The urea linkages have the possibility of extensive hydrogen bonding while ionic units interact with each other by coulombic interactions, which provide even stronger interchain associations than the hydrogen bonding effects. This thesis addressed the preparation and characterization of polytetrahydrofuran based segmented polyurethane-urea and ionene elastomers. The urea linkages were effectively introduced to the polyurethane elastomers through an unconventional route which was based on carbamate-isocyanate interactions. The carbamates were generated principally from isocyanate functional prepolymers and tertiary alcohols. The carbamates were rearranged thermally and/or catalytically to produce amines which were rapidly converted to ureas. The effects of varying the size of the rigid and flexible segments in polyurethane elastomers on physical behavior were investigated. The importance of hydrogen bonding interactions in promoting phase separation of hard and soft segments and the cohesiveness of hard segment domain structure was demonstrated. Living, difunctional polytetrahydrofuran dioxonium ions were prepared via triflic anhydride initiation. The direct coupling of these "living" polytetrahydrofuran dioxonium ions with a ditertiary amine was used to produce a novel segmented ionene elastomer. The ionenes thus synthesized displayed interesting solution behavior and could be molded, or cast to produce good physical properties. Photochromic as well as thermochromic phenomena were also noticed in these systems. / Ph. D.

Thesis (M.S.)--University of Michigan, 1988.