Cast Polyurethane Research Articles

Evaluation of the Accuracy of Conventional and Digital Impression Techniques for Implant Restorations.

The increased use of CAD systems can generate doubt about the accuracy of digital impressions for angulated implants. The aim of this study was to evaluate the accuracy of different impression techniques, two conventional and one digital, for implants with and without angulation. We used a polyurethane cast that simulates the human maxilla according to ASTM F1839, and 6 tapered implants were installed with external hexagonal connections to simulate tooth positions 17, 15, 12, 23, 25, and 27. Implants 17 and 23 were placed with 15° of mesial angulation and distal angulation, respectively. Mini cone abutments were installed on these implants with a metal strap 1 mm in height. Conventional and digital impression procedures were performed on the maxillary master cast, and the implants were separated into 6 groups based on the technique used and measurement type: G1 - control, G2 - digital impression, G3 - conventional impression with an open tray, G4 - conventional impression with a closed tray, G5 - conventional impression with an open tray and a digital impression, and G6 - conventional impression with a closed tray and a digital impression. A statistical analysis was performed using two-way repeated measures ANOVA to compare the groups, and a Kruskal-Wallis test was conducted to analyze the accuracy of the techniques. No significant difference in the accuracy of the techniques was observed between the groups. Therefore, no differences were found among the conventional impression and the combination of conventional and digital impressions, and the angulation of the implants did not affect the accuracy of the techniques. All of the techniques exhibited trueness and had acceptable precision. The variation of the angle of the implants did not affect the accuracy of the techniques.

Effect of moisture exposure on scratch behavior of model polyurethane elastomers

Effect of moisture exposure on scratch behavior of four model cast polyurethane (CPU) elastomers with different soft segments is investigated. Two model CPU systems contain less polar ether groups and the other two contain more polar ester groups in the soft segment polyols. The ASTM D7027/ISO 19252 standard scratch test was chosen to determine the scratch behavior of the model CPU systems in dry and water-saturated conditions. It is found that the absorbed moisture alters the surface characteristics, mechanical properties and the corresponding scratch behaviors of PU elastomers in different fashions, depending on the PU chemical constituents. The homogeneously absorbed water molecules in the less polar polyether-based PU elastomers serve as plasticizer to degrade the mechanical properties and increase the coefficient of friction (COF), thus leading to deterioration in scratch resistance. However, for the more polar polyester-based PU elastomers, because of the interaction between water molecules and the polar bonding sites, clustering of water occurs on the surface and acts as lubricant to decrease the COF, which improves the scratch resistance. A 3-D finite element method (FEM) modeling was conducted to further understand the observed scratch-induced deformation in the model systems. The present study provides guidelines for preparing scratch-resistant PU elastomers that are exposed to humid environment during service.

Key parameters of biomimetic patterned surface for wet adhesion

Inspired by the polygonal arrays on the toe pads of tree frogs and newts, micro hexagonal pillars were fabricated on a cast polyurethane elastomer (CPUE) surface so that a network of interconnected channels was formed. To investigate the effect of channel sizes, adhesion experiments were carried out with a flat polymethyl methacrylate (PMMA) probe and the patterned surface of CPUE samples under wet conditions. It was found that single factors alone, such as channel width (W), length (L), and height (H) have a slight effect on wet adhesion force. Comparatively, the values of width-to-length (W/L), height-to-length (H/L), and height-to-width (H/W) determine the wet adhesion force significantly. Actually, the wet adhesion force is reduced with increasing W/L values. Furthermore, optimal ranges of H/L and H/W values clearly enhance the wet adhesion force, even considering the reduction with the increasing W/L values.

Impact of Natural Oil-Based Recycled Polyols on Properties of Cast Polyurethanes

Impact of Natural Oil-Based Recycled Polyols on Properties of Cast Polyurethanes

Modification of castable polyurethane with hydroxyethylated diphenylolpropane

Castable monolithic polyurethane based on oligo(ethylene glycol adipate) was modified using hydroxyethylated diphenylolpropane {2,2'-[propane-2,2-diylbis(p-phenyleneoxy)]diethanol] as a chain extender instead of 1,4-butanediol, which allowed preparation of a noncrystallizing elastomer with enhanced levels of strength and heat resistance.

Cast polyurethanes obtained from reactive recovered polyol intermediates via crude glycerine decomposition process

In this work, the possibility of applying intermediates from polyurethane waste recycling in polyurethane synthesis was presented. Polyurethanes were synthesised in a two-step method using a mixture of petrochemical polyol and glycerolysate, used as a reactive component, 4,4-diphenylmethane diisocyanate (MDI) and 1,4-buthanediol (BD). Glycerolysates were produced during decomposition of polyurethane elastomer by crude glycerine from biodiesel production. The glycerolysates were incorporated into polyurethane structure and co-created a soft segment with their functional groups. Chemical structure and properties of the cast polyurethanes were characterised by Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), dynamic mechanical analysis (DMA) and mechanical tests. Results showed that higher incorporation of glycerolysates shifts the glass transition to higher temperatures and the mechanical properties indicates that material exhibits more stiff structure. Prepared polyurethanes which contained glycerolysates have good and similar (in a small amount of glycerolysate) properties to the reference polyurethane which indicates the possibility of glycerolysate application as a polyol in the polyurethane synthesis.

Scratch behavior of model polyurethane elastomers containing different soft segment types

The scratch behavior of a series of model cast polyurethane elastomers (CPU) is investigated according to the ASTM D7027/ISO 19252 scratch test methodology. Four model CPU systems considered in this study were synthesized by the same hard segment, but with four different types of soft segment polyols to systematically alter their phase morphology, coefficient of friction (COF), yield stress, tensile strength and damping behavior. Attenuated total reflectance Fourier transform infrared spectroscopy, atomic force microscopy, COF measurement, uniaxial tensile and compressive true stress-strain curves generation, and dynamic mechanical analysis (DMA) were carried out to link intrinsic material properties to the observed scratch-induced deformation mechanisms of the model CPU systems. The observed scratch damage mechanisms of the model CPU systems are found to correlate well with COF, tensile strength, compressive yield stress and DMA damping behavior. The present study demonstrates that the scratch performance of polymers can be predicted by their intrinsic material properties. Implication of the present study for designing scratch resistant polyurethane elastomers is discussed.

Experimental study on compressive, flexural and fatigue behavior of warp-knitted spacer fabrics reinforced polyurethane cast elastomer composites

This paper reports an experimental study on compressive, flexural and fatigue behavior of polyurethane cast elastomers (PCE) reinforced with warp-knitted spacer fabrics (WKSF). It aims to investigate new applications for these fabrics as the reinforcements for elastomeric parts such as shoe soles, rubber floor coverings, vibration dampening and shock absorbing pads, etc. A series of polyester WKSF with different thickness, structure of outer layer fabric and spacer yarns density was prepared and converted to PCE reinforced WKSF using the hand molding method. All the samples, including the neat PCE, were subjected to static compression, flat and spherical compression, three-point bending and flexural fatigue tests. The results showed that reinforcing PCE with WKSF, considerably enhances its spherical compressive strength (concentrated loading), flexural strength and fatigue resistance. However, it deteriorates flat compressive strength (distributed loading) and recovery behavior after static compression loading. The effect of fiber weight fraction, thickness, structure of outer layer fabric and spacer yarns density on the mentioned properties of the composites was discussed in the paper.

Highly functional polyols from castor oil for rigid polyurethanes

Novel high hydroxyl number and high functionality polyols were developed using thiol-ene reaction of castor oil with mercaptoethanol or mercaptanized castor oil with allyl alcohol (by photochemical reaction) and 2-hydroxyethyl acrylate (by Michael thiol-ene reaction). The polyols had OH numbers of 220–295mgKOH/g and functionalities close to 6. Cast polyurethane resins were prepared with methylene diphenyl diisocyanate (MDI), dicyclohexylmethane-4,4′-diisocyanate (HMDI) and m-xylylene diisocyanate (XDI). XDI gave rubbery to leathery polyurethanes with all three polyols, while MDI and HMDI gave amorphous glasses with good mechanical properties. Rigid polyurethane foams of good properties were made with MDI and three castor oil-based polyols.

Deposition of Electrically Conductive Coatings on Castable Polyurethane Elastomers by the Flame Spraying Process

Deposition of metallic coatings on elastomeric polymers is a challenging task due to the heat sensitivity and soft nature of these materials and the high temperatures in thermal spraying processes. In this study, a flame spraying process was employed to deposit conductive coatings of aluminum-12silicon on polyurethane elastomers. The effect of process parameters, i.e., stand-off distance and air added to the flame spray torch, on temperature distribution and corresponding effects on coating characteristics, including electrical resistivity, were investigated. An analytical model based on a Green’s function approach was employed to determine the temperature distribution within the substrate. It was found that the coating porosity and electrical resistance decreased by increasing the pressure of the air injected into the flame spray torch during deposition. The latter also allowed for a reduction of the stand-off distance of the flame spray torch. Dynamic mechanical analysis was performed to investigate the effect of the increase in temperature within the substrate on its dynamic mechanical properties. It was found that the spraying process did not significantly change the storage modulus of the polyurethane substrate material.

SU‐E‐I‐02: Characterizing Low‐Contrast Resolution for Non‐Circular CBCT Trajectories

Purpose:The use of non‐circular scanning trajectories with optimization‐basedreconstruction algorithms can be used in conjunction with non‐planaracquisition geometries for axial field‐of‐view (FOV) extension incone‐beam CT (CBCT). To evaluate the utility of these trajectories,quantitative image quality metrics should be evaluated. Low‐contrastresolution (LCR) and CT number accuracy are significant challenges forCBCT. With unprecedented axial coverage provided by thesetrajectories, measuring such metrics throughout the axial range iscritical. There are currently no phantoms designed to measurelow‐contrast resolution over such an extended volume.Methods:The CATPHAN (The Phantom Laboratory, Salem NY) is the current standardfor image quality evaluation. While providing several useful modulesfor different evaluation metrics, each module was designed to beevaluated in a single slice and not for comparison across axialpositions. To characterize the LCR and HU accuracy over an extendedaxial length, we have designed and built a phantom with evaluationmodules at multiple and adjustable axial positions.Results:The modules were made from a cast polyurethane resin. Holes rangingfrom 1/8 to 5/8 inch were added at a constant radius from the modulecenter into which rods of two different plastic materials were pressedto provide two nominal levels of contrast (1.0% and 0.5%). Largerholes were bored to accept various RMI plugs with known electrondensities for HU accuracy evaluation. The modules can be inserted intoan acrylic tube long enough to cover the entire axial FOV and theirpositions adjusted to desired evaluation points.Conclusion:This phantom allows us to measure the LCR and HU accuracy across theaxial coverage within a single acquisition. These metrics can be usedto characterize the impact different trajectories and reconstructionparameters have on clinically relevant image quality performancemetrics.Funding was provided in part by Varian Medical Systems and NIH R01 Grants Nos. CA158446, CA182264, EB018102, and EB000225. The contents of this poster are solely the responsibility of the authors and do not necessarily represent the official view of any of the supporting organizations.

Altered polyurethane cast for a partial removable dental prosthesis

Altered polyurethane cast for a partial removable dental prosthesis

Use of implant-supported interim restorations to transfer periimplant soft tissue profiles to a milled polyurethane definitive cast

A customized impression coping is often used in conjunction with conventional implant impression techniques to transfer a well-defined periimplant soft tissue profile resulting from an implant-supported interim restoration to the definitive cast with a removable gingival replica and achieve the desired esthetic outcome of the definitive restorations. However, a direct line of sight between the intraoral scanner and the periimplant soft tissue is needed during the data acquisition of the digital impression techniques, and it is not possible to use customized scannable impression copings to support periimplant soft tissue. This study describes a clinical technique with implant-supported interim restorations to transfer desired periimplant soft tissue profiles to the milled definitive polyurethane cast with a removable periimplant soft tissue replica to maximize the esthetic outcome of the definitive restorations.

The use of a scannable impression coping and digital impression technique to fabricate a customized anatomic abutment and zirconia restoration in the esthetic zone

This report described the fabrication of a customized anatomic abutment and zirconia restoration in the esthetic zone with a digital pathway. The implant level impression was made with a scannable impression coping and intraoral digital scanner. The milled definitive polyurethane cast with corresponding implant analog, customized anatomic abutment, and definitive zirconia restoration were made with a computer-aided design and computer-aided manufacturing (CAD/CAM) process.

Fabrication of Interconnected Porous Elastomers by a Microsphere‐Templating Process

ABSTRACTIn this work, a solvent‐free microsphere‐templating process was developed to fabricate porous elastomers. The process starts with preparation of a porous wax template by thermal sintering at a temperature close to the wax melting temperature. Then, low‐viscosity monomers for elastomeric polyurethane were cast into the wax template. Finally, after casting and curing of the elastomer, the wax component was removed by mechanical forces (centrifuge or squeezing) to produce a porous elastomer. With this process, polyurethane scaffolds with a co‐continuous porous structure were successfully prepared. The optimal sintering temperature for the wax template was attained about 4°C below the wax peak melting temperature, leading to a stable process for joining wax microspheres into a three‐dimensional porous template. Mechanistic approaches were found to be effective for extracting wax in the cast polyurethane; more than 90% of wax can be simply removed by mechanical squeezing above the wax melting temperature. After wax removal, the polyurethane demonstrated a morphology with micropores interconnected by microchannels, indicating the interconnectivity of the porous structure. Tensile tests showed that the resulting porous material is highly deformable and elastic, exhibiting typical properties of polyurethane elastomers. © 2012 Wiley Periodicals, Inc. Adv Polym Techn 2013, 32, 21330; View this article online at wileyonlinelibrary.com. DOI 10.1002/adv.21330

Study of the Main Influence Factors on Compression Set of PTMG Based Polyurethane Elastomer

The present study described the effect of the different synthetic methods, hard segment types, chain extension coefficient and the starting NCO/OH molar ratio on the compression set and the other properties of castable polyurethanes based on polytetrahydrofuran glycol (PTMG).The result showed that the system of PTMG/TDI/MOCA prepared by a quasi-prepolymer method and with the starting molar ratio of TDI to PTMG of 6:1 exhibits lower compression set.

Influence of Diisocyanates on Dynamic Mechanical Properties of Castable Polyurethane Elastomers

A series of castable polyurethane elastomers, based on polytetramethylene glycol as soft segments and toluene diisocyanate, 4, 4’-diphenylmethane diisocyanate, P-phenylene diisocyanate as diisocyanates respectively, were synthesized. The dynamic mechanical analysis method was utilized to determine tan delta property (tanδ). Also the influence of diisocyanates on the dynamic mechanical properties of castable polyurethane elastomers was analyzed. It can be concluded that the P-phenylene diisocyanate system elastomers have the most excellent dynamic mechanical properties.

Effects of BaSO4, CaCO3, kaolin and quartz fillers on mechanical, chemical and morphological properties of cast polyurethane

For industrial applications of engineering polymers such as polyurethane, polyamides and polyesters, the addition of suitable reinforcing inorganic fillers is a practical and convenient method to achieve the desirable mechanical and chemical properties. In this study, the mechanical, chemical and morphological properties of cast polyurethane samples containing barium sulphate, calcium carbonate, kaolin and quartz fillers were investigated. In the formulation of these samples, the ranges of inorganic filler were 0–40 phr. The results of mechanical property tests, such as tear resistance, tensile strength, elongation at break, Young’s modulus, hardness and abrasion resistance, were evaluated. The chemical resistance of the samples was determined against xylene and methyl ethyl ketone. The chemical resistance of the filled cast polyurethane was determined by the solubility parameters of polymer/solvent. Finally, the experimental results and SEM images showed that samples containing 30 phr calcium carbonate produced the best results.

Kompozycje poliuretanowe do szybkiego prototypowania zawierajace bentonity modyfikowane silseskwioksanami

Cast polyurethane resins (PUR) filled with bentonites modified with silsesquioxanes (POSS) were prepared. The effect of amount and type of modified bentonites as well as the type of resin used on mechanical and processing properties of composites containing 1,5—4,5 wt. % nanofiller was studied. The addition of modified bentonites to the polyurethane resin resulted in the increase of tensile strength by 40 % and Charpy impact resistance by 70 %, however, the decrease in Rockwell hardness by 18 % was found. The structure of the composites resembled that of typical aluminosilicate clay/polymer nanocomposites with fine platelets morphology of brittle fractures observed by scanning electron microscopy (SEM) and the disappearance of the peak corresponding to the distance between bentonite platelets in WAXS diffractogram.

Influence of the Treatment with Sulfuric Acid on Adhesion of Natural Rubber and Cast Polyurethane Elastomers

In this study, natural rubber (NR) was treated with sulfuric acid to improve its adhesion properties to polar polymer. T-peel strength tests, scanning electron microscopy, contact-angle measurement (water), Energy Dispersive X-ray Detector were used to analyze the nature of the NR surface modifications which were carried out with sulfuric acid. A noticeable decrease in contact angle was observed on the rubber surface by contact-angle measurements which can be ascribed to the increase of oxidized moieties on the rubber surface. EDX revealed that oxidized moieties were created through treatment with sulfuric acid. The surface modification and mode of bond failure were studied by scanning electron microscopy (SEM). Immersion in sulfuric acid for 15min produced the maximum adhesion strength (10kN/m) and produced a mixed failure mode (interface & rubber failure in the rubber). Treatment with sulfuric acid produced improved wettability as well as chemical (surface oxidation) and morphological modifications (roughness) of the rubber surface.