Graft Interpenetrating Polymer Networks Research Articles

Multifunctional graft-IPN hydrogels of cellulose nanofibers and poly(N-isopropyl acrylamide) via silver-promoted decarboxylative radical polymerization

Interpenetrating polymer networks (IPNs) have emerged as innovative materials for a wide range of applications. Owing to the crosslinked structure of their polymer components, IPNs exhibit superior properties relative to their single component counterparts. Here, we report a new class of multifunctional graft-interpenetrating polymer network (graft-IPN) hydrogel composites of poly(N-isopropylacrylamide) (PNIPAM) grafted onto cellulose nanofibers (CNFs) via silver(I)-promoted decarboxylative polymerization. This novel approach involves the Ag-promoted graft polymerization and the crosslinking of PNIPAM in the CNF network, forming a hybrid of semi-IPN and graft-copolymer hydrogel. Different from conventional PNIPAM-CNF IPNs, the CNFs in graft-IPN hydrogels form an interconnected network as a result of crosslinking between neighboring grafted PNIPAM. Silver nanoparticles (AgNPs) are also formed in situ in the graft-IPN hydrogel matrix, demonstrating the dual functionality of silver as both a catalyst in the polymerization and an eventual antibacterial agent in the hydrogel. The network structure of graft-IPN hydrogels can be controlled by crosslinker and Ag(I) concentration, therefore modulating their thermo-responsive, mechanical, and swelling properties. The grafting of PNIPAM from CNFs shifts the volume phase transition to 36 °C and significantly improves the mechanical strength and swelling capacity of the hydrogels. Ultimately, this work demonstrates the excellent potential of these multifunctional graft-IPN hydrogels with controllable thermosensitivity, mechanical strength and anti-microbial activity as engineered biomaterials for advanced applications in biomedicine, engineering, and industry.

Flexible acrylic-polyurethane based graft-interpenetrating polymer networks for high impact structural applications

Flexible graft-interpenetrating polymer networks (IPNs) were synthesized out of polyurethane (PU) and acrylic-based copolymers using two co-monomers, styrene and methyl methacrylate (MMA). Chemical bonds between the two polymers participating in the interpenetration network were utilized to decrease the system's phase separation. The effect of changing the composition of the two co-monomers on the properties of the IPN system was studied. Dynamic mechanical analysis (DMA), tensile, and shear tests were used to characterize the thermomechanical and mechanical properties of IPNs sheets/plates and IPNs as an adhesive. A scanning electron microscope (SEM) was utilized to characterize the failure mechanism of the tensile dog bone samples. Moreover, impact tests were performed on a sandwich structure with synthesized IPN as an inter-layer adhesive to characterize the toughness and stiffness of the IPN samples. Overall, excellent transparency and impact resistance in visible light range with a wide range of thermo-mechanical properties (from extreme elastomeric to more ductile) was observed in IPN samples, which shows their tremendous potential in various transparent, high-performance applications.

Quasi-static and dynamic mechanical behavior of transparent graft-interpenetrating polymer networks (graft-IPNs)

Mechanical characterization of transparent graft Interpenetrating Polymer Networks or graft-IPNs based on polyurethane and acrylic copolymer are reported under both quasi-static and dynamic loading conditions. This study builds on an earlier work detailing the synthesis of the graft-IPNs [1]. Optically transparent graft-IPNs were synthesized using elastomeric polyurethane (PU) phase and stiff acrylate-base copolymer (CoP) phase. The ratios of CoP:PU were varied from 90:10 up to 60:40 by weight. Two grades of graft-IPNs were synthesized by using 650 g mol−1 and 1400 g mol−1 poly (tetramethylene ether) glycol (PTMG) during synthesis to study the molecular weight effect. Quasi-static tensile and fracture tests as well as dynamic fracture tests were performed. The dynamic fracture tests were carried out at high strain rate using a modified-Hopkinson pressure bar in conjunction with an optical technique called Digital Gradient Sensing (DGS) and ultrahigh-speed photography. Quasi-static tests indicate significant enhancements in crack initiation toughness and change in failure mode (brittle to ductile) when the constituents were varied. Enhancements in crack inititation toughness were also observed under dynamic loading. These results were further compared with those for commercial poly (methyl methacrylate) (PMMA) and polycarbonate (PC) sheet stock. Further improvement in fracture properties were observed under quasi-static loading conditions with increase in molecular weight of PTMG. The relatively high values of fracture toughness obtained for graft-IPNs is attributed to the crosslinks generated between the CoP and PU networks.

Physical Properties of Micro Hollow Glass Bead Filled Castor Oil-Based Polyurethane/Epoxy Resin IPN Composites

ABSTRACTA series of micro hollow glass beads (HGB) filled castor oil-based polyurethane/epoxy resin graft interpenetrating polymer network (IPN) composites were prepared. The tensile and impact strengths, impact fractured surfaces, damping properties and thermal stability of the IPN composites were studied systematically in terms of composition. Results revealed that the addition of HGB into polyurethane/epoxy IPN can significantly improve not only the tensile strength but also the impact strength. The tensile strength was increased by 61% and at the same time the impact strength was increased by 25% when the HGB content was 1.5%. The damping properties were better than the composition of 0.5% or 2% HGB content when the HGB content was 1% or 1.5%. The thermal decomposition temperature was also slightly improved by the incorporation of HGB. It is suggested that the HGB reinforced polyurethane/epoxy resin IPN composites could be used as structural damping materials.

Effect of OMMT on the phase morphology controlling of PU/EP IPN

Organic montmorillonite (OMMT) modified polyurethane (PU) /epoxy resin (EP) (OMMT-PU/EP) graft interpenetrating polymer network nanocomposites with different content of OMMT were prepared. The effect of the OMMT content on the phase behavior of the PU/EP IPN system has been studied by Dynamic mechanical analysis (DMA). With the content of OMMT increased, the tan δ turned from single peak to two peaks and the damping temperature range became wider when the isocyanate index is low. Transmission electron microscope (TEM) and atomic force microscope (AFM) results showed that high content of OMMT favored phase separation to form a larger-size domain in nanocomposites, resulting in the broadening of damping temperature range. This work demonstrates that we can control phase behaviour of OMMT-PU/EP IPNs by changing the OMMT content. This result provides potential opportunity for this type of materials to be used as sound and vibration damping polymers over wide temperature ranges.

Sequential graft-interpenetrating polymer networks based on polyurethane and acrylic/ester copolymers

Highly transparent and tough graft-interpenetrating polymer networks (graft-IPNs) were synthesized using an elastomeric polyurethane phase (PU) and a highly stiff acrylate-base copolymer phase. The grafting points between the two networks were generated with the purpose of minimizing the phase separation process of the polymeric systems. In order to generate the grafting between the networks, an acrylic resin capable of undergoing both free radical and poly-addition poly- merization was employed. The thermo-mechanical properties, fracture toughness properties as well as network and surface phase morphology of the graft-IPNs synthesized were evaluated in this work. Data obtained suggested that the minimiza- tion of the phase separation was achieved by the generation of crosslinking points between both networks. High trans- parency was obtained in all samples as an indication of the high level of interpenetration achieved. The relative high values obtained for the fracture toughness tests suggest that generating chemical crosslinks between networks is a good approach for increasing the fracture toughness of polymeric materials.

Creep and recovery behaviors of magnetorheological elastomer based on polyurethane/epoxy resin IPNs matrix

This paper mainly investigated the creep and recovery behaviors of magnetorheological elastomers (MRE) based on polyurethane/epoxy resin (EP) graft interpenetrating polymer networks (IPNs). The influences of constant stress level, content of EP, particle distribution, magnetic field and temperature on the creep and recovery behaviors were systematically investigated. As expected, results suggested that the presence of IPNs leads to a significant improvement of creep resistance of MRE, and creep and recovery behaviors of MRE were highly dependent on magnetic field and temperature. To further understand its deformation mechanism, several models (i.e., Findley’s power law model, Burgers model, and Weibull distribution equation) were used to fit the measured creep and recovery data. Results showed that the modeling of creep and recovery of samples was satisfactorily conducted by using these models. The influences of content of EP and magnetic field on fitting parameters were discussed, and relevant physical mechanism was proposed to explain it qualitatively.

Preparation and characterization of a novel magnetorheological elastomer based on polyurethane/epoxy resin IPNs matrix

This paper proposes the preparation of a novel magnetorheological elastomer (MRE) with improved damping and mechanical properties. This MRE is based on polyurethane (PU)/epoxy resin (EP) graft interpenetrating polymer networks (IPNs). The tensile strengths, thermal stability, magnetorhelogical behavior, and damping properties of the MRE are studied systematically in terms of composition. The Fourier transform infrared (FTIR) spectra verifies the formation of IPN structures, and thermogravimetric analysis (TGA) revealed that the thermal decomposition temperature was raised by the addition of IPN structures. The test results from the materials test machine and the rheometer show that the presence of IPN can significantly improve the tensile strength and damping properties of the MRE. In addition, the mechanism for enhancing tensile strength and damping properties is proposed. The experiment results suggest that the damping performance of the MRE has a significant correlation with the magnetic strength, content of EP, and temperature. As the thermal endurance properties, tensile strength, and loss factor are improved by incorporating EP/PU IPN structure, it is expected that the PU/EP IPN MRE can be used as an intelligent structural damping material.

Tribological Properties of Hydroxyl-Terminated Liquid Nitrile Rubber-Modified Polyurethane/Epoxy Interpenetrating Polymer Network Composites

A series of castor oil-based polyurethane (PU)/epoxy resin (EP) graft interpenetrating polymer network (IPN) composites modified by two kinds of hydroxy-terminated liquid nitrile rubber (HTLN) was prepared. A systematic investigation of the tribological properties of the two kinds of HTLN-modified PU/EP IPN composites was carried out through a pin-on-disk arrangement under dry sliding conditions. Experimental results revealed that the incorporation of HTLN can improve the friction and wear properties of PU/EP IPN significantly. Both the friction coefficient and wear loss decreased with increasing content of HTLN. The worn surfaces of the samples were analyzed using scanning electron microscope and a three-dimensional (3D) noncontact surface-mapping profiler; the results showed that the worn surfaces of the PU/EP IPN composites became smooth when the HTLN was added. The mechanisms for the improvement of tribological properties are discussed.

Physical properties of aramid fiber reinforced castor oil-based polyurethane/epoxy resin IPN composites

A series of organic aramid fiber filled castor oil-based polyurethane/epoxy resin graft interpenetrating polymer network (IPN) composites were prepared. The tensile and impact strengths, impact fractured surfaces, damping properties and thermal stability of the IPN composites were studied systematically in terms of composition. Results revealed that the addition of aramid fiber can significantly improve not only the tensile strength but also the impact strength. The damping properties were better when the aramid fiber content were 5% and 7%. The thermal decomposition temperature was also slightly improved by the incorporation of aramid fiber. It is expected that the aramid fiber modified polyurethane/epoxy resin IPN composites may be used as structural damping materials.

Role of graded length side chains up to 18 carbons in length on the damping behavior of polyurethane/epoxy interpenetrating polymer networks

A series of novel polyurethane (PU)/epoxy resin (EP) graft interpenetrating polymer network (IPN) composites with graded length side chains were prepared from toluene diisocyanate (TDI), polytetrahydrofuran glycol (PTMG), EP, trimethylolpropane (TMP), and diol chain extenders. The effects of the side chain lengths, content, and groups on the damping properties and mechanical properties were investigated. Two damping peaks were observed in the PU/EP IPN system, indicating that the peak damping factor (tanδ) increased with increased side chain length at low temperatures. The introduction of an apolar side chain slightly narrowed the damping range. However, the side chain carrying polar groups broadened the damping temperature range. The strong H-bond interaction between the ester group of side chain and the NH of hard segments in PU was believed to favor microphase separation to form a larger-sized domain and induce the appearance of the relaxation peak at high temperatures. Consequently, the effective damping temperature range was broadened. The side chain content tethered in the hard segment remarkably influenced the damping properties of PU/EP IPNs both at low and high temperatures. The width and intensity of the tanδ peaks of PU/EP IPNs increased with increased side chain content. The mechanical properties (tensile strength and elongation at break) were significantly affected by the side chain content. Thus, an important method of improving the mechanical damping of elastomers by controlling the side chain molecular structure was established.

Preparation and characterization of tetrapod-shaped ZnO whisker filled polyurethane cross-linked epoxy/polyurethane damping composites

A novel kind of damping composite was prepared, which consisted of the tetrapod-shaped ZnO whisker and polyurethane cross-linked epoxy/polyurethane. The dynamic mechanical properties of these materials were investigated by dynamic thermal analysis. Results indicated that the effective damping temperature range (tan δ > 0.3) was obviously broadened from 33.7°C to 178.8°C due to the formation of graft interpenetrating polymer network. With addition of tetrapod-shaped ZnO whisker, the maximal value of damping peak was improved to 1.44 for the increase of the internal friction. The morphological studies proved the existence of partial phase separation, and it was also observed that uniformly dispersed tetrapod-shaped ZnO whiskers were tightly implanted into the polymer matrix. The thermal stability and the tensile strength of composite were improved by the incorporation of tetrapod-shaped ZnO whisker. The results revealed that morphology of graft interpenetrating polymer network and addition of tetrapod-shaped ZnO whisker could provide excellent damping properties for the polymer matrix composite.

Preparation, Characterization and Study of the Morphological, Mechanical and Thermal Properties of Epoxy/Urethane Interpenetrating Polymer Networks Nanocomposites

In this study epoxy/urethane (EP/PU) graft interpenetrating polymer networks (g-IPNs) nanocomposites were prepared by a simultaneous polymerization method and the effects of organophilic montmorillonite (Cloisite 30B) content on the mechanical, morphological and thermal properties of the nanocomposites were investigated. Cloisite 30B was dispersed in epoxy resin via a sonication method, after which g-IPN nanocomposites were prepared by thorough mixing of a synthesized isocyanate-terminated urethane pre-polymer with this epoxy resin (EP/PU weight ratio=75/25) followed by simultaneous curing of the resins. Polytetramethylene ether glycol (PTMEG) with molecular weight (Mw) of 3000 g/mol was used to prepare urethane prepolymers. Curing reactions were followed by Fourier Transform Infrared spectroscopy (FT–IR). Wide Angle X-ray diffraction (WAXD) was used to investigate the dispersion of Cloisite 30B in g-IPN nanocomposite specimens. Based on these results, an exfoliated morphology has been suggested for nano IPN specimens containing 1 and 3 wt.% of Cloisite 30B and an intercalated morphology for that with 5 wt.% of Cloisite 30B. Dynamic Mechanical Thermal Analysis (DMTA) was used to determine the glass transition temperature (Tg) of the IPNs. The maximum Tgwas observed for the nanocomposite with 3 wt.% of Cloisite 30B. The storage modulus (E′) of nanocomposites increased with increasing clay content. Thermogravimetric Analysis (TGA), tensile measurements and Scanning Electron Microscopy (SEM) were used to study the thermal, mechanical and morphological properties of the prepared specimens. The maximum tensile properties were obtained at 3 wt.% of Cloisite 30B. Furthermore, with increasing clay content, the onset of the thermal degradation temperature was delayed.

Damping, thermal, and mechanical properties of carbon nanotubes modified castor oil-based polyurethane/epoxy interpenetrating polymer network composites

A series of castor oil-based polyurethane (PU)/epoxy resin (EP)-graft interpenetrating polymer network (IPN) composites loaded with multi-walled carbon nanotubes (CNTs) were prepared. The damping properties, thermal stability, tensile and impact strengths, as well as fractured surfaces of the CNTs modified IPN composites were studied systematically. Results revealed that the incorporation of CNTs can improve the damping capacity especially when the CNTs content was 0.1%, though the thermal decomposition temperature decreased slightly. The storage modulus was also increased with the addition of CNTs. The mechanical properties of the modified polymer composites were improve. The tensile strength of the polymer composites increase by more than 30% compared to the matrix, when the CNTs contents were 0.1% and 0.7%. When the CNTs content was 0.3%, the impact strength of the modified composites increased by ca. 54% compared to the polymer matrix. It is expected that the modified composites may be used as structural damping materials.

Damping, thermal, and mechanical properties of montmorillonite modified castor oil-based polyurethane/epoxy graft IPN composites

A series of nature clay montmorillonite (MMT) filled castor oil-based polyurethane (PU)/epoxy resin (EP) graft interpenetrating polymer network (IPN) composites were prepared. The damping properties, thermal stability as well as mechanical strength of the IPN composites were studied systematically in terms of the composition. Results reveal that the addition of MMT can improve the damping properties of PU/EP IPN and can heighten the thermal decomposition temperature. Mechanical tests show that the tensile strength and impact strength of the IPN composites are significantly improved by the incorporating of MMT, especially when the MMT contents are 1% and 3%. It is expected that the MMT modified IPN composites may be used as structural damping materials in future.

Damping, Thermal, and Mechanical Properties of Polycaprolactone-Based PU/EP Graft IPNs: Effects of Composition and Isocyanate Index

A series of polycaprolactone (PCL)-based polyurethane (PU)/epoxy resin (EP) graft interpenetrating polymer networks (IPNs) were prepared and their damping propertiesand thermal stability, as well as mechanical properties, were systematically studied in terms of composition and the values of the PU isocyanate index (R). The morphologies of the PU/EP IPNs were observed by scanning electron microscope (SEM) and atomic force microscope (AFM) characterization and the relationship between the morphologies and the properties is also discussed. The damping properties and thermal stability measurements revealed that the formation of PU/EP IPNs could significantly improve not only the damping properties but also the thermal stability. Meanwhile, the mechanical tests showed that the tensile strengths of the IPNs decreased, while their impact strengths increased with increasing PU content. The value of the PU isocyanate index also had significant impacts on the properties of the IPNs when the PU to EP ratio was fixed, which could be an effective means for manipulating the fabrication of PU/EP IPNs. From the results obtained, the PCL-based PU/EP IPNs hold promise for use in structural damping materials.

Hydroxy-terminated liquid nitrile rubber modified castor oil based polyurethane/epoxy IPN composites: Damping, thermal and mechanical properties

A series of castor oil based polyurethane (PU)/epoxy resin (EP) graft interpenetrating polymer network (IPN) composites modified by hydroxy-terminated liquid nitrile rubber (HTLN) were prepared. The effects of HTLN content on the phase structure and damping properties of the HTLN modified PU/EP IPN composites were studied by scanning electron microscopy (SEM) and dynamic mechanical analysis (DMA). Thermogravimetric analysis (TGA) showed that the thermal decomposition temperature of the composites increased with increase of HTLN content. The tensile strength and impact strength of the IPN composites were also significantly improved, especially when the HTLN content was 5%. The modified IPN composites were intended for future use as structural damping materials.

Property evaluation and structure analysis of polyurethane/epoxy graft interpenetrating polymer networks

AbstractPolyurethanes obtained from 4,4′‐diphenylmethane diisocyanate (MDI) and polydiols with different molecular weights (polyethylene glycol and polyoxypropylene diols) were used as modifiers for diglycidyl ether of bisphenol A. Impact strength (IS), critical stress intensity factor (KC), flexural strength and flexural strain at break were measured as a function of polyurethane (PUR) type and content. Scanning electron microscopy (SEM), differential scanning calorimetry (DSC), and infrared spectroscopy (FTIR) were employed for the structure and morphology analysis. It was found that the addition of polyurethane with an excess of isocyanate groups to epoxy resin resulted in the formation of a grafted interpenetrating polymer network structure. The mechanical properties of epoxy resin were improved with 5 and 10% PUR. Moreover, it was observed that composites containing PUR based on higher molecular weight (PUR 1002 and PUR 2002) with long flexible segments exhibited higher impact strength while PUR prepared from polyethylene glycol had a higher flexural energy to break and a higher flexural modulus. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011

Dynamic mechanical properties of polysiloxane-modified, castor oil-based polyurethane/epoxy interpenetrating polymer network composites

A series of hydroxyl-terminated poly dimethyl siloxane (HTPDMS)-modified polyurethane (PU)/epoxy resin (EP) graft interpenetrating polymer network (IPN) composites were prepared. The morphologies of impact fracture surfaces, tensile and impact strengths, damping properties as well as thermal stability properties of the HTPDMS modified IPN composites were studied systematically. The results revealed that the impact strength of the IPN composites could be significantly improved after the incorporation of HTPDMS, whereas the tensile strength of the composites was impaired when the HTPDMS content were more than 5%. The studies also showed that the addition of HTPDMS can improve the damping properties of pure PU/EP IPN and can improve the thermal decomposition temperature. It is expected that the modified IPN composites may be used as structural damping materials.

Damping Properties of Polyurethane/Epoxy Graft Interpenetrating Polymer Network Composites Filled with Short Carbon Fiber and Nano-SiO2

A series of short carbon fiber (CF) and nano-SiO2 filled polyurethane (PU)/epoxy resin (EP) graft interpenetrating polymer network (IPN) composites were prepared. The damping properties as well as tensile and impact strength of the IPN composites were studied systematically in terms of composition. Results revealed that the addition of short CF and nano-SiO2 can significantly improve the damping properties of pure PU/EP IPN, particularly at higher frequencies. Mechanical tests showed that the tensile strength of the IPN composites was improved after the incorporation of short CF and nano-SiO2, while the impact resistance of the composites was impaired after the addition of CF and higher content (beyond 1 wt%) of nano-SiO2. It is proposed that the CF and nano-SiO2 filled IPN composites would be useful as structural damping materials.