Polyurethane Nanocomposites Containing Laminated Anisotropic Nanoparticles Derived from Organophilic Layered Silicates

Abstract

Polyurethanes represent extraordinarily versatile polymeric materials which can be tailored to meet the highly diversified demands of modern technologies such as coatings, adhesives, reaction injection molding, fibers, foams, rubbers, thermoplastic elastomers, and composites. [1±3] It is an important objective in polyurethane development to improve resistance against mechanical deformation without sacrificing high elongation at break. Since the early pioneering advances by Otto Bayer, [4] polyurethane properties are modified either by varying polyurethane microstructure, resulting from step-growth polymerization of isocyanate resins with polyols, or by dispersing inorganic and organic fillers within the polyurethane continuous matrix. A wide variety of fillers, including clay and wollastonites, are being applied in polyurethane formulations to reduce costs and to reinforce the polyurethane matrix. [5] Properties of filled polyurethanes are dependent upon filler shape, average diameter and interfacial coupling. Anisotropic particles with a large length/diameter ratio (aspect ratio), e.g., whiskers and fibers, were found to be especially effective in matrix reinforcement. Frequently, filler addition is accompanied by increased strength and stiffness at the expense of substantially reduced elongation at break.Although nanoscale anisotropic particles are expected to offer attractive potential for polyurethane reinforcement, application of anisotropic nanofillers is restricted by the limited availability of nanowhiskers, poor dispersion, and handling problems associated with potential health hazards resulting from inhalation of such particles. Therefore, several attempts have been made to produce nanowhisker dispersions in polyols which are much easier to handle. For example, N-(4-aminobenzoyl)-caprolactam was polymerized at 200 C in dihydroxy-terminated poly(tetrahydrofuran) to produce dispersions of rigid polybenzamide nanowhisker of approximately 2000 nm length and 200 nm diameter. Interfacial coupling and steric stabilization were achieved by reacting hydroxy end groups of the polyol with N-acyl-lactam end groups located at the polybenzamide whisker surface. Upon curing with diisocyanate, the resulting polyurethane nanocomposites exhibited the unusual combination of increased tensile strength and Young's modulus without sacrificing high elongation at break. [6,7] Particle formation via sol/gel technology leads to dispersions of mainly isotropic nanoparticles in polyurethane. [8] Recently, intercalation of organophilic layered silicates with polymers has been introduced as an attractive route leading to versatile polymer nanocomposites which contain nanoscale layered silicates with high aspect ratio. Layered silicates, e.g., clay, consist of anionically charged layers of aluminum/magnesium or magnesium/lithium silicates where cations such as sodium, potassium, magnesium or calcium are located in the interlayer galleries. They are rendered organophilic when gallery cations are exchanged by quaternary alkyl ammonium...

Synthetic, layered nanoparticles for polymeric nanocomposites (PNCs)

“…The presence of these very long fibers may explain the statement: ''During dispersion, the fairly large isotropic mica particles of average diameter around 5000 nm are broken down into much smaller anisotropic nanoparticles resembling short fiber reinforcement of 500 nm length and 20 AE 50 nm diameter''. 37 Breaking FM plates of ca. 5000 nm diameter into 20-50 nm thick ''fibers'' seems rather improbable for the employed dispersing method.…”

“…SEM of the fractured surfaces revealed extensive matrix shear yielding for the neat resin, whereas the predominant fracture mode of the PNC were prepared by pre-intercalating ME-100 with MDD2EG, dispersing 2.5, 5, 7.5, and 10 wt% of the organoclay in tri-hydroxy-terminated-PPG (poly-or oligopropylene glycol), adding curing agent (N,N-dimethylbenzylamine), and then curing the system with di-isocyanatodi-phenyl-methane. 37 At 80 o C the presence of organoclay slightly reduced the reaction rate. At 10 wt% of clay loading the interlayer spacing of FM (d 001 ¼ 0.9 nm) increased to 8.8 nm.…”

“…The elongation at break and tensile strength versus clay content for PU with neat FM and FM preintercalated with MDD2EG. 37 reinforce, but rather to change the rheological behavior of the polyol solution during preparation of rigid PU foams. 141 Higher viscosity of the thixotropic system stabilized a dispersion of flame retardants [Sb 2 O 3 , Al(OH) 3 , CB, or melamine], while on shearing dramatically reduced viscosity facilitated foaming.…”

“…The elongation at break and tensile strength versus clay content for PU with neat FM and FM preintercalated with MDD2EG. 37 Copyright SPN). The melt compounded specimens were intercalated.…”

Synthesis and properties of poly(4-vinylpyridine)/ montmorillonite nanocomposites

“…Among them, in situ polymerization was the first method used to synthesize polymer-clay nanocomposites based on polyamide 6 [1] that showed enhanced mechanical properties such as increased moduli, strength, heat resistance and decreased gas permeability [2][3]. Polymer-clay nanocomposites based on epoxy [4], polyurethanes [5][6] and poly-(ethylene terephthalate) [7] obtained via the in situ method have been found to increase tensile strength and modulus. Additionally, increased thermal stability and flame resistance have been reported for several nanocomposite systems [8][9][10].…”