Rotary injection reaction injection molding (RI-RIM). Part II: Interfacial segregation of release systems

This paper describes the shear imposed interfacial segregation of release systems for the facilitated attenuation of polyurethane (PU) adhesion to metal coun-terfaces using a RI-RIM system. It is shown that the migration rate of the dispersed release additives due to a shear imposed stress in the resin fluid is much greater than that arising from Fickian diffusion, thereby removing a vital constraint from conventional practice. The novel rotary injection RIM system is presented to simulate the on-line injection and shear induced interfacial segregation in model PU/abherent systems. A wide range of recipes comprising single (liquids or solids) and multicomponent (liquid-liquid and solid-liquid) release materials were injected into the polymerizing resin mixture to provide cohesively weak and friable “particle” boundary layer assemblies at the PU/metal interface. An instrumented Blister Test was employed to evaluate the quality of the molded interfaces in terms of adhesion and the concentration distribution of the injected species in the final cured moldings was determined through high pressure liquid chromatography (HPLC). A comparison of the results on the shear modified and the compounded interfaces confirm an accentuated lateral migration of the additives to the interface resulting in an appreciable diminution in the adhesion of the system. Finally, transport models are suggested to account for the observed augmented transport.     

Rotary injection reaction injection molding (RI-RIM). Part I: Basic design features

This paper describes the basic design features of a new reaction injection molding (RIM) processing device, Rotary Injection RIM (RI-RIM). The new design includes a novel mixing concept which furnishes high intermaterial contact area upon shear imposed rotary injection of the RIM components for effective in situ polymerization. This system operates in low pressure and laminar flow conditions, as opposed to the high pressure and turbulent flow, found in conventional RIM systems. The mixing process is described and quantified in terms of the various forces which govern the injection process. A progressive diminution in the average size of the dispersions generated is found with increasing rate of shear, continuous-phase viscosity, and injection rate. These results are compared with those expected from traditional shear mixing (bulk convective shearing) under comparable conditions and the current system found to be more efficacious. Reaction molding experiments with RI-RIM using a model polyurethane system are described and the influence of operating conditions on the mechanical properties of the finished moldings are elucidated. A detectable change in the morphology of the system is observed following increase in the total shear strain imparted to the initial mix of the multiphase reactants. It is suggested that the observed change is affected by a segregation between the components of the segmented polymer.     

聚氨酯乳液的改性及其应用研究

用丙酮法合成了固含量为35%的聚氨酯成膜乳液。主要考查了复合型软段对聚氨酯成膜乳液及其胶膜性能的影响,并考查了乳液在水性印刷油墨中的应用。结果表明,亲水基团-COOH质量分数达到1.5%,能保证乳液的力学稳定性;随着不同聚多元醇复配比例的变化,乳液的稳定性和黏度、聚氨酯胶膜的力学性能以及吸水性均呈规律性变化,所制备的水性聚氨酯油墨对PET薄膜的附着力好。     

Improved adhesion of silicone rubber to polyurethane by surface grafting

Polyurethane (PU) has widespread applications in implantable devices because of its excellent mechanical and biocompatible properties, whereas weak biostability limits its long‐term implantation. The introduction of silicone rubber (SR) onto the PU surface is an effective method for improving the biostability of PU, but the adhesion of these two polymers is unsatisfactory. In this study, the surface modification of PU via grafting through the introduction of vinyl and Si H groups onto the PU surface was attempted to improve the adhesion of PU to SR. Fourier transform infrared, energy‐dispersive X‐ray spectroscopy, and X‐ray photoelectron spectroscopy were employed to investigate the graft reaction on the PU surface. The interfacial and surface morphology was characterized with scanning electron microscopy. Different PU/SR interfaces after oscillation and shear were compared as well. The results indicated that the PU surface was activated by diisocyanate, which generated free isocyanate groups for the further grafting of vinyl and Si H groups. When addition‐type, room‐temperature‐vulcanized SR was poured onto the PU surface, the vinyl and Si H groups on the PU surface underwent an addition reaction, which improved the adhesion of PU and SR by connecting them with chemical bonds. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Mechanical properties and linear infrared dichroism of thin films of polyurethane nanocomposites

Morphological, mechanical, and Fourier transform infrared dichroic investigations were performed on neat polyurethane (PU) polymer matrix and PU+CaCO₃ nanocomposite thin films to determine how the nanofiller influenced the mechanical properties. The measurements were performed on strips that were cut from the prepared films in parallel and perpendicular directions with respect to the direction of film preparation. Optical microscopy of PU and the PU+CaCO₃ nanocomposite revealed the strain‐induced transition from a continuous spherulitic morphology to a fiberlike structure. The stress–strain behavior of the neat PU and PU+CaCO₃ nanocomposite films showed significant differences at large strain regimes. The experimental results suggest that the mechanical properties were strongly related to the orientational behavior of the separated phases. The orientation of the hard and soft segments was analyzed by the orientation function calculated from the IR absorbances. A correlation between the orientations of segments, tensile properties, and hardness of the investigated polymer films was established. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

"纳米内交联"耐高速聚氨酯新胶轮的研发

针对分散相尺寸和两相界面粘结这两个影响纳米复合材料性能的关键因素,运用“纳米内交联”技术,合成了聚氨酯纳米复合材料,生产出耐高速聚氨酯胶轮,与普通有机蒙脱土填充聚氨酯材料性能和其胶轮内生热的对比测试表明:“纳米内交联”耐高速聚氨酯纳米复合材料综合性能优异,阻尼性大幅度降低,从而大幅度降低了聚氨酯胶轮高速转动时的内生热,为解决长期困扰聚氨酯界的“聚氨酯高速转动内生热极大”的难题开辟了新路。     

Property–composition dependence of polyurethane–poly(vinyl chloride) polyblends

The dynamic mechanical properties of polyblends of a polyurethane (PU) elastomer and poly(vinylchloride) (PVC) at five compositions were studied at 110 Hz, between ?120 and 120°C. The study also included tensile testing at 25°C, and examination of polyblend morphology and fire-retardant properties. The results were analyzed using suitable two-phase mechanics models valid for such systems. This analysis, together with the morphological evidence and the thermomechanical spectra, indicate that these polymer alloys are essentially heterogeneous and their useful mechanical properties are due to good adhesion between the two phases. This conclusion is also corroborated by the tensile properties study. Fire retardancy is significant only above ～60% by weight of PVC.     

Field-Induced Phase Fractionation in Multiphase Polymer Flow Systems: A Review

The paper reviews the kinetics and morphology of the various phase-segregation processes that may be encountered in multiphase polymer flow systems. A primary aim of this review has been to investigate how certain processing variables influence the polymer structure and the degree of phase segregation in various geometries of interest. A pronounced distinction is made between the terms “diffusion” and “field-induced segregation.” The former is conventionally regarded as the mass transfer resulting from Brownian motion and, in any case, is a randomizing process. The latter, on the other hand, implies “flow” of matter subject to a “driving potential.” As opposed to diffusion in the classical sense, field-driven transport may be affected against the concentration gradient. It is seen that the application of an appropriate lateral field generates transversal migration of suspended material or additive and, in certain cases, the segment domains in the “matrix” polymer. In particular, the potential of shear fields to generate locally segregated flow structures, which might be preserved during the fabrication procedure, has been assessed. It has been shown that with an expression for the lateral “drift” velocity, the time and space evolution of the cross-flow concentration profile may be obtained from the continuity relation. Even though one finds a surprisingly large variety of driving forces available for segregation transport, the efficacy of highly specific processes lies in the novel application of boundary conditions. Convection promoted shear transport has been cited as a relevant example with an initial condition which specifies a cross-flow velocity component in an existing shear field. Other promising configurations include the sequential flow in two-phase flow and rheological segregation. The investigation reveals that migratory transport in polymer processing channels has the potential to generate localized changes in the polymer morphology and structure, apart from affecting phase redistribution of additive species (both solid and liquid systems) on a more global scale. Experimental evidence obtained on the phase fractionation in polydispersed low-density polyethylene (LDPE) and thermosetting polyurethane (PU) clearly demonstrates the phenomenon.     

Investigations on the adhesion and interfacial properties of polyurethane foam/thermoplastic materials

The adhesion and interfacial properties of polyurethane (PU) foams with thermoplastic (TP) materials were investigated using different techniques. The adhesion performance of PU foam with TP materials was evaluated using the peel test method, and the adhesion durability was checked after different climate treatments. X‐ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), and contact angle measurements were used to study the surface and interface morphology of PU foam and TP material system. Three types of PU foam samples which differ in their composition and also five commercially available TP blends systems, based on poly(carbonate), poly(styrene‐co‐maleic anhydride), poly(acrylonitrile‐butadiene‐styrene), and silicone acrylate rubber have been used. The slow reacting foam shows the best adhesion properties with all the TP materials. The climate treatments strongly effected the PU foam adhesion durability with poly(carbonate) containing TP materials (70–80% loss in adhesion), but nearly no effect with poly(styrene‐co‐maleic anhydride). The samples with lowered adhesion could be separated by peeling without visible foam residues on the TP surface. AFM, XPS, and surface tension studies have shown that the surface properties of the TP material are still governed by the PU foam. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 479–488, 2007     

Shear induced finite orientational order in urethane/urea elastomers

New experimental results on urethane/urea free standing thin films (60 μm) prepared from a polypropylene oxide isocyanate terminated triol prepolymer (PU) and polybutadiene diol (PBDO) in the amount of 60% (PU/60PBDO) by weight of polybutadiene, which exhibit periodic patterns upon the application of a mechanical field are used to critically analyse these systems. We focus in this work on the analysis of the casting conditions and on the solid film characterization before and after UV irradiation. The casting of the different solutions was observed by polarizing optical microscopy (POM) coupled to a shearing system. The stress-strain and swelling data collected for the film before UV irradiation allowed the detection of an orientational order induced by the solution casting conditions, involving shear and evaporation of the solvent, which manifests itself in the anisotropy of the stress-strain and swelling film's properties in toluene. After UV irradiation of the elastomeric film, the interlinking of PBDO chains and amines linkages enhances the orientational order enabling instabilities to appear and the mesophase to become evident in the system as shown by POM, stress-strain and small angle light scattering data. Segregated soft and hard parts of the copolymer are thought to constitute the material unit, which is anisotropically distributed. The results here presented reinforce the earlier made claim that these systems do have an anisotropic structure akin to liquid crystallinity.     

Effect of Adhesive Thickness on Joint Strength: A Molecular Dynamics Perspective

Recent studies suggest that adhesion in thin joints depends on several factors including temperature, interface toughness, strain rate, surface roughness of adherends, bondline thickness of adhesives, and many others. Influence of thickness on joint properties is surprising but experimentally well documented without reasonable explanations. In this study, we attempt to address the mechanical behavior of polymer adhesives by molecular dynamics (MD) simulation. We show that interfacial strength of the joints in tensile, shear, or combined loading significantly depends on the coupling strength between adhesives and adherends. Failure of joints is always at the interface when coupling strength is weaker. With stronger interfaces, cohesive failure occurs by cavitation or by bulk shear depending on the loading condition. When joints are loaded in tension, it requires an exceedingly stronger interface to realize pure shear failure, otherwise failure is through interface slip. Under a mixed mode condition, interface slip is difficult to avoid. As long as failure is not at the interface alone, the yield strength of joints improves significantly with the reduction of thickness. Increase in bulk density and change in polymer configurations with the reduction of adhesive thickness are believed to be the two key factors in improving mechanical behavior of adhesives.     

Toughening of polylactide via in situ formation of polyurethane crosslinked elastomer during reactive blending

Polylactide (PLA)/polyurethane (PU) composites were prepared by reactive blending method with in situ formation of PU particles via the reaction between polyester polyol (PPG) and toluene‐2,4‐diisocyanate (TDI). The interfacial compatibility and adhesion between the PLA and PU phases were greatly improved by the reaction of the terminal hydroxyl groups of PLA and N?C?O groups of TDI forming graft copolymer, as confirmed by FTIR spectroscopy. The elongation at break and notch impact strength of PLA/PU composites increased considerably with increasing PU content, and the tensile strength of PLA/PU composites decreased slightly compared with that of pure PLA. Upon addition of 12 wt % PU, the elongation at break and notch impact strength increased to 175.17% and 10.96 kJ/m², respectively, about 27 times and 5.4 times greater than the corresponding values for the pure PLA. The tensile strength decreased only slightly to 48.65 MPa. The excellent interfacial adhesion, the dispersed PU elastomeric particles acting as stress concentration areas, and the triggering of large matrix shear yield as well as many fibrils by internal cavitation were the main mechanical toughening mechanisms. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134 , 44383.     

聚氨酯改性环氧树脂胶粘剂的制备及性能研究

由端-NCO基聚氨酯(PU)预聚物与环氧树脂反应,制备了PU接枝改性环氧树脂。着重探讨了PU预聚物的含量、活性稀释剂的含量和异氰酸酯结构等因素,对改性环氧树脂的粘度和粘接性能的影响。实验结果表明,该改性环氧树脂的粘度随着PU预聚物含量的增加而逐渐增大,随着活性稀释剂含量的增加而逐渐降低,而且在相同的条件下,用不同的二异氰酸酯改性环氧树脂的粘度大小次序为:IPDI型>MDI型>TDI型;该改性环氧树脂在PU预聚物含量为20%时,对铝片/铝片的剪切强度最大(7.82 MPa);在PU预聚物含量为10%时,对铁片/铁片的剪切强度最大(11.70 MPa),而且TDI型和IPDI型改性环氧树脂的粘接性能明显好于MDI型改性环氧树脂。     

Structural,mechanical, and biocompatibility analyses of a novel dental restorative nanocomposite

Structure and biocompatibility are key parameters that determine the usefulness of dental materials for clinical use. Novel polyurethane (PU) nanocomposite material was prepared by chemically binding nanohydroxyapatite (nHA) to the diisocyanate component of the PU backbone by solvent‐polymerization. nHA was incorporated into PU by the stepwise addition of monomeric units of the PU. The PU/nHA composite was analyzed by ¹³C Nuclear magnetic resonance (structural) and X‐ray diffraction (phase analysis). The tensile strength and elastic modulus was evaluated for mechanical properties. These analyses revealed linkage between the hard‐ and soft‐segments are urethane linkage and showed high mechanical properties with increase in content of nHA. To assess biocompatibility osteoblast cells were seeded on to the material and allowed to adhere and proliferate. Osteoblast‐like cell growth and proliferation was assessed by MTS assay. It was found that cells adhered and proliferated on these novel substrates. To test bacterial adhesion discs of composite with and without nHA were incubated with standardized suspensions of oral bacterium Streptococcus sanguinis strain NCTC 7863. PU composites with nHA exhibited biocompatibility with respect to mammalian cell growth and showed significantly reduced bacterial adhesion as compared to PU alone. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Quantitative measurement of adhesion between polypropylene blends and paints by tensile mechanical testing

A tensile mechanical test suiable to measure the adhesion between brittle coatings and ductile substrates was applied to measure the adhesion of painted layers on polypropylene blends. The test involves the tensile deformation of the painted assembly, resulting in the periodic cracking of the brittle coating on the ductile substrate. The interfacial shear strength was determined by measuring the strength of the coating, the thickness of the coating, and the average width of paint fragment after the crack density reaches saturation. Apparent interfacial shear strength was obtained for different paints on the same kind of blend, which gave consistent results over the experimental strain rate range from 10^?4 to 10^?3 sec^?1. Interfacial delamination was studied by optical microscopy (OM) and transmission electron microscopy (TEM). The delamination was observed to mainly occur near the adhesion promoter and substrate interface.     

聚氨酯/镀银纳米石墨导电胶的制备与性能研究

以聚氨酯(PU)预聚体为基体,以镀银纳米石墨为导电填料,采用共混法制备PU/镀银纳米石墨导电胶,并与PU/纳米石墨导电胶进行电学性能、力学性能和热稳定性能对比。结果表明:PU/镀银纳米石墨导电胶和PU/纳米石墨导电胶的导电渗流阈值分别为3%和9%,此时对应的电导率分别为0.044 S/cm和0.012 S/cm;前者的力学性能(最大剪切强度为5.76 MPa)高于后者(最大剪切强度为3.65 MPa),并且前者的起始分解温度比后者提高了近10℃,说明前者的应用前景比后者更广阔。     

Shear strain and microscopic characterization of a bamboo bonding interface with poly(vinyl alcohol) modified phenol–formaldehyde resin

The study of the shear strain distribution at the bonding interface helped us to understand the bamboo bonding interface response mechanisms to solve problems of ply bamboo deformation or bonding failure. The shear strain distribution across a two‐ply bamboo sheet bonded with a ductile phenol–formaldehyde resin (PF) modified by poly(vinyl alcohol) (PVA) was measured by means of electronic speckle pattern interferometry, along with tensile strength measurements to prove the shear stain distribution on a macroscopic scale. This research effectively combined macroscopic mechanical properties with microcosmic interfacial mechanical properties. The shear strength and shear strain results showed that PF modified with 20% PVA performed better than common PF and PF modified with 5 and 10% PVA. Microscopic fluorescent characterization of the bonding interface also provided evidence that a new bonding mechanism was adequate for bamboo bonding under the ductile PF modified with 20% PVA. Moreover, we suppose that the results of this study will help in the choice of bamboo‐specific adhesives under different strain conditions. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 1345‐1350, 2013     

Study on high‐solid content Si/PU polyurethane dispersion with PES/PPG composite soft segment

A polyol consists of silicone chains and epoxy acrylate structures, referred to as silicon polyether (PES), was used to prepare crosslinked Si/PU dispersions. Both PES and propylene oxide glycol (PPG) were mixed as soft segments. The effects weight ratios of PES to PPG on properties of the resultant polyurethane dispersions were studied. Morphology and properties of the Si/PU dispersions were characterized by particle size, transmission electron microscopy (TEM), and viscometer. It is shown that the Si/PU dispersions possessed wider particle size distribution and higher average particles diameter because of the use of PES, which contains crosslinked silicone side chains. The Si/PU dispersions have higher solid content as compared to the conventional water‐based polyurethane, because of the volume fraction ratio of bigger particle to small particle from the Si/PU dispersions. As increasing weight ratio of PES to PPG, the solid content of the Si/PU dispersions increased firstly, and then decreased. When the ratio ranges from 4 : 10 to 5 : 10, solid content of the Si/PU dispersions is up to 55%. It was also noticed that apparent viscosity of the Si/PU dispersions decreased with increasing PES to PPG ratio. In the Si/PU dispersions, solid content was increased and viscosity was decreased by the use of PES. Therefore, PES is a potential compound for the application of PU dispersions. In addition, stability of the crosslinked Si/PU dispersions decreases slightly at high‐ and low‐temperature; however, which can meet the basical requirements. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Methods for improving the performance of silane coupling agents

The use of silane coupling agents in mineral- and glass-reinforced composites is well known. They impart improved initial mechanical properties, but, more importantly, they cause mechanical properties to be retained during the use of the composite. The main cause of loss of mechanical properties is attack of water at the interface. Recent research has focused on imparting more durable bonding of the silane coupling agent to both the polymer and the reinforcement. Improved silane coupling agent systems have been developed by utilizing several techniques: blends of hydrophobic silanes with hydrophilic silanes to give greater hydrophobic character; use of 1,2-bis-(trimethoxysilyl)ethane as an additive to give increased siloxane crosslinking; use of more thermally stable silanes such as phenyltrimethoxysilane and N-[2-(vinylbenzylamino)-ethyl]-3-aminopropyltrimethoxysilane to give increased thermal stability; and the use of a carboxy-functional silane with a carboxy-functional polymer and zinc salt to give ionomer bonds at the interface. The effectiveness of these new coupling agent systems was tested by measuring the flexural strength of composites and the adhesion strength of coatings on inorganic substrates. The results show that composites have increased flexural strength and better strength retention during thermal aging; coatings have greater adhesion strength; there is greater resistance of interfacial bonding to degradation by moisture; and thermoplastic composites have better properties after high shear processing.     

The Mechanical and Tribological Properties of Anodic Oxidation Treatment Carbon Fiber-Filled PU Composite

The interfacial adhesion of the carbon fiber (CF) reinforced polyurethane (PU) composite was improved by the means of anodic oxidation treatment. The mechanical and reciprocating sliding wear properties were studied and results showed that the anodic oxidation treatment have definitely improved the mechanical strength. And the wear and the friction coefficient of PU decreased with the addition of CF. The friction coefficients of anodic oxidation treated CF/PU composites are lower than those of PU and CF/PU composite. The interfacial adhesion between the CF and PU dominated the main wear mechanisms.