Taking advantage of their inherent abrasion resistant, weather resistant, and outstanding mechanical strength, film-grade thermoplastic polyurethanes (TPU) are currently being used as paint protective films but are also being considered for paint replacement within the automotive industry. Special grades of TPU with shape memory behaviour offer an additional feature of self-healing to decorative coatings but there are concerns of shape fixity at service temperatures which are above their glass transition temperature (Tg). In this study, the shape memory behaviour of a developmental TPU film with Tg around room temperature was investigated. In order to understand the shape memory behaviour, the TPU film was laminated to a rigid polymer substrate of either polypropylene (PP) or acrylonitrile butadiene styrene (ABS). Three different acrylic based pressure sensitive adhesives were tested to bond the film to the substrate, namely a commercial high shear strength transfer tape and two solvent based adhesives of high and low shear strength that were manually cast. The influence of the adhesive was given significant attention as a variable of study in this thesis. The characterization of all the polymeric films and substrates was based on a series of thermo-mechanical tests (tensile test, stress relaxation test, DSC and DMA). The adhesives were characterized by lap-shear test, peel test, and parallel plate rheometry. The results of material characterization were used to support the analysis and interpretation of shape memory behaviour. The TPU based laminate was deformed by a matched mold thermoforming process with a pair of arched matched molds. The recovery behaviour of formed samples was quantified with a newly designed measurement method and the results were reported as recovery ratio and recovery rate. During recovery, the surrounding temperature was considered to be an important variable. The recovery behaviour of specimens was investigated in a controlled environment at setpoint temperatures of 15oC, 45oC or 65oC. No shape memory effect was found at 15oC (below TPU’s Tg), and yet both recovery ratio and recovery rate increased with temperature, from 45oC to 65oC (both above the TPU’s Tg). Since the recovery process was related to the elastic response of the hard segment phase within the TPU, the recovery stress was strongly related to strain conditions. By varying the draw depth into the mold from 6 mm, to 10 mm or 12 mm (8.86%, 15.90% or 19.88% strain, respectively), the recovery measurement results showed that the shape memory effect was weaker with lower strain as less recovery stresses were generated in the TPU film. With the draw depth of 10 mm, the highest recovery ratio and recovery rate were observed, and yet an inexplicable decrease in the recovery ratio and recovery rate occurred as the draw depth increased further from 10mm to 12mm. In regards to the influence by a substrate, TPU/PP laminate showed a more significant recovery behaviour than TPU/ABS laminates at both 45oC and 65oC. The elastic modulus of the substrate was found to have a key role on the recovery process; the recovery nature of formed laminate decreased with stiffer substrate. Three adhesives with differing rheological and adhesion properties were tested to bond the TPU film to a substrate. The formed laminates with “strongest” adhesive (transfer tape) in terms of stiffness and adhesion strength showed the highest recovery ratio/rate over laminates made with “weaker” solvent cast adhesives, at both 45oC and 65oC. A finite element analysis (FEA) was employed to simulate the stress transfer within a multilayer structure bonded by a viscoelastic adhesive layer of varying stiffness; the simulated result showed that the relatively low stiffness adhesive could reduce the stress transfer efficiency within layers of a laminate. It suggested that more recovery stresses were transferred from TPU to substrate with a stiffer adhesive layer (transfer tape) and hence increased the recovery ratio and recovery rate. Therefore, adhesive with relatively low stiffness and adhesion strength could be a better choice to reduce the recovery effect of TPU laminate after forming. However, TPU was found to slide at the unsealed edge of formed laminate when the solvent based adhesives were used; the sliding behavior reduced the recovery by releasing stored recovery stress. In the case of HS and LS adhesives at high temperature (65oC), cohesive failure was observed when the edge of specimen was sealed led to a higher bending moment thus increased the recovery ratio over 24 hours investigations. Therefore, adhesives of weaker shear strength do not necessarily overcome the nature of shape recovery by the TPU when formed part shape needs to be preserved. / Thesis / Master of Applied Science (MASc) / Nowadays, smart materials in particular shape-memory polymers have been widely used in the industrial and medical applications. Thermoplastic polyurethane (TPU) is one of the significant shape memory polymer groups. The two-phase morphology of a typical TPU gives a unique shape memory behaviour over a defined temperature range. However, this shape memory effect affects the shape fixity of formed TPU. In this study, a special-grade TPU film was laminated to a rigid polymer substrate using selected pressure sensitive adhesives (PSAs). In order to investigate the effect of adhesive layer on the shape memory behaviour of this TPU based laminate, three PSAs with varying properties were applied. The laminate was thermoformed, quenched and processed in a temperature-controlled chamber with a designed recovery measurement method. The shape memory effect was observed at temperatures above the transition temperature of TPU, and this recovery effect was enhanced at higher temperature. Furthermore, the mechanical property of the substrate material was considered as a key factor on the recovery behaviour of the laminate; the recovery of the formed laminate was restricted with a stiffer substrate. The most significant discovery from the recovery results indicated that the shape memory effect was reduced with the adhesive with relatively low adhesion strength, however, the delamination of the laminate occurs with weaker adhesives.

No description available.

Phosphorus containing monomers, bis(3-aminophenyl)methyl phosphine oxide (m-DAMPO) and bis(3-aminophenyl)phenyl phosphine oxide (m-DAPPO), were synthesized and incorporated into a thermoplastic poly(arylene ether imide) based upon 2,2'-bis[4-(3,4-dicarboxyphenoxy)phenyl]propane dianhydride and 1,3-phenylene diamine, in order to study their influence on flame resistance and other properties. DAMPO or DAPPO were quantitatively incorporated in concentrations of 25, 50, 75 and 100 mole percent, using the "one pot" ester-acid method. The number average molecular weights of the prepared materials were controlled to 20,000g/mol by off-setting the stoichiomety and endcapping with phthalic anhydride. This strategy enabled one to distinguish the effects of the phosphine oxide incoporation from the influence of molecular weight. The resulting copolymers demonstrated a significant increase in char yield as a function of the phosphine oxide content, thus suggesting improved fire resistance. Glass transition temperatures similar to the control were determined by DSC analysis. Analysis of the mechanical behavior of the DAMPO system at room temperature showed that tensile strength and elongation at failure values were comparable to the control system, while the DAPPO containing copolymers were surprisingly brittle. The influence of the reactive endgroup on the synthesis, cure behavior and network properties of thermosetting polyetherimides was investigated. Reactive phenylacetylene, acetylene and maleimide terminated poly(ether imide) oligomers were prepared and characterized. Optimal reaction conditions were established to produce fully endcapped oligomers with imidized structures and controlled molecular weight. The phenylacetylene endcapped system was synthesized by a conventional ester-acid method. The acetylene endcapped system was prepared via modified ester-acid method and the maleimide endcapped system was fabricated utilizing an amic-acid route. It was determined that phenylethynyl endcapped polymers could be thermally cured at high temperatures (350-380°C) providing good processibility. The networks exhibited thermal stability, chemical resistance and good adhesion strength, ideal as "primary" bonding adhesives. Acetylene and maleimide endcapped systems were prepared for application as "secondary" bonding materials, meaning that they are cured at a lower temperature than that of the Tg of the primary structure. Lap shear test results indicated good adhesion to titanium when cured at 250°C -280°C. The cured materials showed high glass transition temperatures and good thermal and thermo-oxidative stability as determined by DSC, TGA and DMA. Good chemical resistance was demonstrated via solvent extraction measurements. The influence of molecular weight between crosslinks (Mc) on thermal and mechanical behavior was also investigated. Lower molecular weight oligomers exhibited lower Tg and cure temperatures, whereas the cured networks resulting from lower molecular weight oligomers afforded higher Tg and higher gel fractions, but reduced toughness. / Ph. D.

The effect of surface pretreatment on the adhesive bonding and bond durability of carbon fiber/epoxy and carbon fiber/bismaleimide matrix composites was studied. Methyl ethyl ketone (MEK) wipe, peel ply, grit blast and gas plasma treatments were the pretreatments of interest. Chemical and physical changes which occurred in the cured composite surfaces following pretreatment were characterized with x-ray photoelectron spectroscopy (XPS), ion scattering spectroscopy (ISS), contact angle analysis, diffuse reflection infrared spectroscopy (DRIFT), profilometry and scanning electron microscopy (SEM). Double lap shear and Boeing wedge configurations were used to evaluate the strength as well as the durability of the composites bonded with an epoxy film adhesive. Fluoropolymer residues which were found on the composite surfaces were fully removed by grit blasting and oxygen plasma treatments, but not by an MEK wipe. The use of a peel ply prevented fabrication contamination from depositing on the bonding surfaces. In addition to its cleaning effect, oxygen plasma was also capable of incorporating additional polar functionality into the composite surface. The presence of the fluoropolymer contamination on the MEK-wiped surface resulted in low surface energy and wettability, whereas peel ply, grit blast and oxygen plasma improved both the surface energy and the wettability of the composite surfaces. The grit blasted and peel ply surfaces were observed to have a significant degree of roughness, as measured by profilometry and seen by SEM. A rubber-toughened epoxy film adhesive was used for the bonding studies. Lap shear strengths were evaluated under ambient conditions as well as at 82°C, both dry and following a 30 day/71°C water exposure. Wedge durability testing was carried out in a dry 75°C oven, 75°C water, 100°C water and aircraft de-icing fluid. Relative to the MEK-wiped controls, lap shear strength as well as hot/wet durability was improved by the peel ply and oxygen plasma treatments for both epoxy and bismaleimide composites. Grit blasting was seen to have some utility for the epoxy composites at room temperature, but was generally observed to be detrimental to strength and durability, particularly in the case of the bismaleimide composites. In order to separate the effect of surface chemistry from the effect of surface roughness on composite bond strength, a study was carried out in which surface functionality was varied while the topography remained constant. For this purpose, peel ply surfaces, which have a consistent and reproducible degree of roughness, were treated with fluoropolymer compounds and gas plasmas, as well as left untreated. It was found that the removal of fluoropolymer contamination was the main contributor to the observed bond strength improvement following plasma treatment; however, highly functionalized oxygen plasma-treated surfaces showed evidence of improved durability in a hot aqueous environment. The effect of elapsed time following oxygen plasma treatment of epoxy composites was also studied. XPS atomic concentration, wettability by water and a liquid epoxy resin, and lap shear strengths were plotted as a function of time following removal from the plasma reactor. Changes which occurred in the chemistry and wettability of an oxygen plasma-treated surface had a subsequent negative effect on the lap shear strengths of the bonded specimens. A study was carried out using model epoxy and bismaleimide compounds in thin film form, for the purpose of studying surface chemistry and interfacial reactions following an oxygen plasma treatment. XFS and infrared reflection-absorption spectroscopy (IR-RAS) were used to probe the reactions which occurred. Close correspondence was found between the XPS and IR-RAS analysis of functional groups incorporated into the surface of the films by the plasma treatment. IR-RAS analysis of the model surfaces following exposure to a neat, liquid epoxy resin revealed that, while adsorption of the liquid epoxy occurred on both plasma-treated and nonplasma-treated surfaces, the oxygen plasma treated surface alone was capable of initiating ring-opening reactions in the epoxy. However, this effect was not observed unless immediate contact was made between the plasma-treated surface and the liquid epoxy resin. / Ph. D.

A novel concept, the fracture efficiency, is proposed in this dissertation as a performance index of fracture specimen designs for adhesive bonds. Evaluated based on a simple quantity, the fracture efficiency parameter, the fracture efficiency represents how much crack driving force a certain specimen design can produce along the bondline for a given maximum non-singular stress in the adherends. In this dissertation, a study of membrane peeling specimens shows that various existing test geometries have little difference in the fracture efficiency. Furthermore, the study shows that it is unlikely to develop new n1embrane peeling tests with high fracture efficiency. Therefore, gross inelastic energy dissipation in the film specimen may occur when using the membrane peeling tests, and may result in large errors in the film adhesion measurement when only elastic material response is considered in the analysis. As a result, the use of a backing material for film adhesion measurement is suggested because of the significant increase in the fracture efficiency when a proper backing material is used. Besides the use as one of the guidelines for fracture specimen designs, it is also demonstrated in this dissertation that the fracture efficiency parameter can also be used to help one determine the validity of a measured bond fracture strength. The study of fracture efficiency leads to new analyses of several existing fracture test geometries, and contributes to a better understanding of the standard blister, island blister, peninsula blister, peel, and cracked lap shear tests. It is found that the island blister and peninsula blister tests can produce very high energy release rates at low pressures by using a small island radius or a small peninsula width. However, these so called "high energy release rate" tests also induce localized high stress concentrations near the debond front and therefore, yielding or rupturing may still unavoidable in such specimens. The significant localized inelastic effect on the measurement of the bond fracture strength is also demonstrated in the peninsula blister experiment for an adhesive tape specimen subjected to a relatively low pressure load. Another important conclusion drawn from the analyses of various membrane peeling tests is that the existing membrane blister tests are special cases of the peel test if compared very near the debond front. Besides analyses for membrane peeling specimens, this dissertation also reports a new closed form solution for the cracked lap shear specimen using a geometrically nonlinear beam-column approach. Excellent agreement for energy release rates has been shown between the closed form solution and geometrically nonlinear finite element analyses. The study also discusses how to design a cracked lap shear specimen of constant energy release rate and high fracture efficiency. / Ph. D.

The strength of materials solution for a new bonded cantilever beam test specimen to determine adhesive shear properties is reviewed and discussed. A parametric analysis for the adhesive shear stress and for the end deflection reveals the specimen dimensions required for reliable bonded adhesive shear properties determination. Recommendations are provided for conducting reproducible tests. A pure and quasi-uniform shear test for stiff adhesives is proposed. Analytical solutions are compared with Finite Element solutions from VISTA and NOVA for the stresses in the adhesive. It appears that the assumption of pure shear is nearly valid even for very stiff and/or very thick adhesives. In order to increase the end point deformations for stiff adhesives, a modified specimen is proposed. Three-dimensional effects through the thickness of the adhesive layer are studied with the program ABAQUS. Experiments were performed using the two methods derived from theory and good correlation between theory and experiment were obtained with some restrictions. For both methods, experimental results underlined the need for defining proper specimen geometry prior to testing. Simple numerical codes are proposed to facilitate this purpose. / Master of Science

This study developed and analyzed a modification of the blister test permitting nearly constant strain energy release rate testing of adhesive bonds. The work consisted of three parts; (1) development of the testing technique to evaluate strain energy release rate and to record the time dependent nature of the fracture process, (2) numerical analysis of the constrained blister test to determine the applicability of an approximate solution for several materials, and (3) development of an. analytical technique to evaluate the strain energy release rate for relatively stiff specimens. / Master of Science

Polymeric diphenylmethane diisocyanate, pMDI, is a wood adhesive that provides excellent composite board properties. Much is unknown about the specific mechanism of pMDI/wood adhesion under conditions that are typical of wood gluing operations. The present research describes the use of ¹⁵N cross-polarization, magic-angle spinning (CP/MAS) NMR as a technique for probing the cure chemistry and bondline morphology of pMDI-bonded wood composites. A 99% ¹⁵N-enriched pMDI resin with desirable adhesive properties was synthesized. A series of model cellulose/¹⁵N-pMDI composites, cured as a function of cellulose precure moisture content, were tested prior to solid wood composites in order to test the feasibility of this technique. Solid wood/¹⁵N-pMDI composites were then cured as a function of wood precure moisture content, cure temperature, and cure time. The ¹⁵N CP/MAS NMR spectra clearly show the dominance of the isocyanate/water reaction on the cure chemistry of all composites tested, both cellulose and solid wood. Four prominent resonances are observed in each spectrum: residual isocyanate, polyurea, and the amide and imide nitrogens of biuret type structures. Different trends in the relative intensities of these resonances are observed as a function of the press variables. Significant amounts of urethane formation are not detected; however, low amounts could be obscured by signal overlap. Relaxation studies using variable contact time experiments were complicated by excessively long cross-polarization rates for nonprotonated nitrogens. However, experiments using variable spin lock times prior to fixed contact periods indicate that the cured resin in these composites is probably a homogeneous continuum. The utility of ¹⁵N CP/MAS NMR for elucidating fine structural and morphological information from complex isocyanate-cured wood composites is clearly demonstrated. / Master of Science

Hydroxyakyl lignin derivatives were reacted with polymeric methylene diphenyl diisocyanate (PMDI) and hexamethoxy-methyl-melamine (HMMM) to form polyurethane and polyether wood adhesives respectively. Adhesive performance in shear block tests indicated: (a) that the combination of lignin and PHDI reduced the adhesive strength shown by neat PMDI. The HMMM failed to produce an acceptable wood adhesive in the absence of lignin, requiring 50-60% lignin derivative co-substrate for peak performance; (b) adhesive performance was related to molecular weight, if an organic solvent was the carrier, or solubility if the formulation was emulsified; (c) adhesive performance for the lignin based adhesives was better than a urea formaldehyde reference. Structure property relationships were determined by correlating data obtained by the analysis of (in vivo) cured adhesive films and (in vitro) adhesive strength data resulting from shear block testing. The results indicated that: (a) glass transition temperatures of the in vivo cured adhesives were inversely related to the strength of the adhesives cured in vitro; (b) variations in infrared analysis of the in vivo cured adhesives were used to determine the levels of products from the cross linking reaction. In vitro adhesive strength was directly related to the level of reaction products determined to be present in the in vivo wood adhesives; (c) the relationships between the analysis of in vivo and in vitro cured adhesives indicated that the lignin component may act as a soft segment blocks or domains in a more rigid polymer matrix. Particle board was produced with the lignin adhesives with: (a) properties equal to those produced with commercial OF resins; (b) spray application greatly reducing the effects of carrier compatibility; (c) none of the lignin based adhesives were water resistant. / Master of Science

Structural adhesives are materials that are capable of bearing significant loads in shear, and sometimes tension, over a range of strains and strain rates. Adhesively bonded structures can dissipate large amounts of mechanical energy and can be lighter and more efficient than many bolted or vibration welded parts. The largest barrier to using structural adhesives in more applications is the many challenges engineers are presented with when designing and analyzing adhesively bonded structures. This study develops, characterizes and compares several material models for use in finite element analysis of adhesively bonded structures, in general, and a bonded tongue and groove (TNG) joint in particular. The results indicate that it is possible to develop a general material model for ductile adhesives used in structural applications under quasi-static conditions. Furthermore, the results also show that it is also possible to take bulk material data and apply it to an adhesively bonded specimen provided that the mode of failure of the bulk test specimen closely approximates the mode of failure of the bonded joint. / Master of Science