Experimental and modeling investigation of shape memory behavior of polyurethane/carbon nanotube nanocomposite

In the current study, mechanical, thermal, thermo‐mechanical, and shape memory behavior of polyurethane/carbon nanotube nanocomposites were investigated, and also a modified Halpin‐Tsai equation was used for the first time to model shape recovery stress of these smart composites. Results showed that strength enhanced with the addition of MWCNTs and improved to a maximum value of 130% for PU‐1wt%CNTs. SEM micrographs were also used to prove the presence of agglomerates at higher CNT contents. By investigating thermogravimetry curves, it was concluded that the incorporation of carbon nanotubes transferred thermal degradation to a higher temperature. Storage modulus improved for nanocomposite samples which showed the reinforcing effect of CNTs on polyurethane. Memory behavior showed that recovery stress was increased for PU‐CNTs samples to a maximum value of 100% and not any harmful effect on shape recoveries observed. Finally, modified Halpin‐Tsai equation was obtained with the correction factor of K = exp(−1.79‐152V_f).     

聚氨酯/环氧树脂互穿网络聚合物的性能研究

互穿聚合物网络（Interpenetrating polymer net-work,简称IPN）广泛应用的为聚氨酯基的互穿网络聚合物。其合成多集中在弹性体方面。本文用同步法合成的聚氨酯／环氧树脂互穿网络硬质泡沫塑料材料（简称PU／ERIPNF）,机械性能较好,并研究了其动态力学性能及形态变化。     

Polylactic acid-based polyurethane/polyamide 6,12 and graphene nanocomposite: Structure and physical property study for packaging application

This effort reports on novel polylactic acid-derived polyurethane (PU) and polyamide 6,12 (PA6,12)-based blends and graphene-reinforced nanocomposite. PU/PA6,12 (50:50) blend was opted as matrix based on molecular weight and shear stress performance. PU/PA6,12 with 5?wt% graphene (PU/PA6,12/graphene 3) showed improved T₀ and T_max of 515 and 541°C relative to neat blend. PU/PA6,12/graphene 3 also revealed significantly high tensile (53?MPa) and flexural strength (1,711?MPa). For Eschericia coli, Staphylococcus, and Pseudomonas bacterial strains, nanocomposite with higher graphene loading produced significant inhibitory effects. Novel nanocomposites displayed fine antimicrobial and barrier properties against O₂ and H₂O to be used as a packaging material.     

Synthesis and design of polyurethane and its nanocomposites derived from canola-castor oil: Mechanical,thermal and shape memory properties

The recent global pandemic and its tremendous effect on the price fluctuations of crude oil illustrates the side effects of petroleum dependency more evident than ever. Over the past decades, both academic and industrial communities spared endless efforts in order to replace petroleum-based materials with bio-derived resources. In the current study, a series of shape memory polymer composites (SMPC's) was synthesized from epoxidized vegetable oils, namely canola oil and castor oil fatty acids (COFA's) as a 100% bio-based polyol and isophorone diisocyanate (IPDI) as an isocyanate using a solvent/catalyst-free method in order to eventuate polyurethanes (PU's). Thereafter, graphene oxide (GO) nanoplatelets were synthesized and embedded in the neat PU in order to overcome the thermomechanical drawbacks of the neat matrix. The chemical structure of the synthesized components, as well as the dispersion and distribution levels of the nanoparticles, was characterized. In the following, thermal and mechanical properties as well as shape memory behavior of the specimens were comprehensively investigated. Likewise, the thermal conductivity was determined. This study proves that synthesized PU's based on vegetable oil polyols, including graphene nanoparticles, exhibit proper thermal and mechanical properties, which make them stand as a potential candidate to compete with traditional petroleum-based SMPC's.     

Synthesis and characterization of novel segmented polyurethane/clay nanocomposite via poly(ε-caprolactone)/clay

A novel segmented polyurethane/clay (PU/clay) nanocomposite based on poly(caprolactone), diphenylmethane diisocyanate, butanediol, and poly(caprolactone)/clay prepolymer was synthesized as evidenced by FTIR and X-ray diffraction studies. Poly(caprolactone)/clay (PCL/clay) prepolymer was first synthesized in a nanocomposite form as confirmed by X-ray diffraction. X-ray diffraction study showed that PU/clay contained crystalline structure due to the presence of PCL/clay. In mechanical properties, about 1.4% PCL/clay in PU/clay resulted in a large increase in the elongation of PU/clay. However, when the amount of PCL/clay was 4.2%, the elongation of PU/clay was reduced drastically. This behavior indicated that PU/clay can be transformed from an elastomer to a thermoplastic material as the amount of PCL/clay in PU/clay increased. Additionally, the lap shear stress of PU/clay was at least three times that of neat PU as a result of the PCL/clay component. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 2225–2233, 1999     

Bio‐based hyperbranched polyurethane/Fe3O4 nanocomposites as shape memory materials

The bio‐based shape memory polymers have generated immense interest as advanced smart materials. Mesua ferrea L. seed oil‐based hyperbranched polyurethane (HBPU)/Fe₃O₄ nanocomposites were prepared by the in‐situ polymerization technique. The transmission electron microscopy confirmed the homogeneous distribution of the Fe₃O₄ nanoparticles in polymer matrix, whereas Fourier transform infrared spectroscopic study revealed the presence of strong interfacial interactions between them. The incorporation of Fe₃O₄ (0 to 10 wt%) into the HBPU resulted in an increase in tensile strength (5.5–15 MPa) and scratch resistance (3–6 kg). The thermo‐gravimetric analysis indicated the improvement of thermal stability (240–270°C) of the nanocomposites. The nanocomposites exhibited full shape fixity, as well as almost full shape recovery under the microwave stimulus. The shape recovery speed increased with the increase of Fe₃O₄ nanoparticles content in the nanocomposites. Thus, the studied nanocomposites might be used as advanced shape memory materials in different potential fields. Copyright © 2013 John Wiley & Sons, Ltd.     

Effects of graphene quantum dot (GQD) on photoluminescence,mechanical, thermal and shape memory properties of thermoplastic polyurethane nanocomposites

A group of shape memory polyurethane‐based nanocomposites containing graphene quantum dot nanoparticles (GQDs) were prepared via in‐situ polymerization method. GQD nanoparticles were synthesized by a facile and rapid microwave‐assisted method and characterized by Fourier‐transform infrared spectroscopy (FTIR), X‐ray diffraction pattern, field emission scanning microscopy, transmission electron microscopy, and fluorescence analysis. Chemical structure and hydrogen bonding index (HBI_[C=O]) of the nanocomposites were analyzed via FTIR spectra. The results show that the incorporation of GQDs in PU matrix reduces HBI_(C=O) of nanocomposites. Crystalline structure and thermal properties of the nanocomposites were investigated by differential scanning calorimetry. As results indicate, nucleation effect of GQDs raises crystallinity content of the samples. Mechanical examinations indicate that incorporation of GQDs improves Young's modulus of the nanocomposites, while their elongation at break values are reduced. In addition, shape memory analyses reveal that the presence of GQDs in PU matrix increases the shape fixity ratios in nanocomposites.     

Ultra low density and highly crosslinked biocompatible shape memory polyurethane foams

We report the development of highly chemically crosslinked, ultra low density (～0.015 g/cc) polyurethane shape memory foams synthesized from symmetrical, low molecular weight, and branched hydroxyl monomers. Sharp single glass transitions (T_g) customizable in the functional range of 45–70 °C were achieved. Thermomechanical testing confirmed shape memory behavior with 97–98% shape recovery over repeated cycles, a glassy storage modulus of 200–300 kPa, and recovery stresses of 5–15 kPa. Shape holding tests under constrained storage above the T_g showed stable shape memory. A high volume expansion of up to 70 times was seen on actuation of these foams from a fully compressed state. Low in vitro cell activation induced by the foam compared with controls demonstrates low acute bio‐reactivity. We believe these porous polymeric scaffolds constitute an important class of novel smart biomaterials with multiple potential applications. © 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2012     

Synthesis and thermal properties of antimony doped tin oxide/waterborne polyurethane nanocomposite films as heat insulating materials

The waterborne polyurethane (WPU) was synthesized from the polycondensation between isophorone diisocyanate (IPDI) and polyoxypropylene glycol (N‐210) and then dispersed into water. Subsequently, the WPU emulsion was modified with antimony doped tin oxide (ATO) nanoparticle by ultrasonic dispersion. The ATO/WPU emulsion was cast onto Teflon molds. After being dried, ATO/WPU films were prepared. TEM indicated that the ATO nanoparticles were homogeneously dispersed in the polymer matrix at the nanometer scale. DSC showed that the ATO/WPU nanocomposites displayed increased glass transition temperatures compared to the control WPU. The mechanical properties of the films were characterized by dynamic‐mechanical analysis (DMA). The higher glass transition temperature and storage modulus indicates the superior mechanical properties of WPU modified by ATO nanoparticles over the conventional unmodified WPU. The thermal behaviors of the films were evaluated by thermogravimetric analysis (TGA). It could be found that the incorporation of ATO into WPU can improve the thermal stability dramatically. The results from UV–visible–near infrared spectra indicated that the ATO/WPU films could decrease the infrared transmission effectively. The heat‐insulation measurements showed that glass coated with ATO/WPU films possessed better heat‐insulating effect than empty glass. Copyright © 2010 John Wiley & Sons, Ltd.     

Semi‐interpenetrating polymer networks based on polyurethane and polymethacrylate functional prepolymers: Morphology and mechanical properties in dependence of the concentration of functional groups

Grafted semi‐interpenetrating polymer networks (IPNs) were prepared from polyurethane (PU) prepolymers with polyester soft segments and hard segments containing carboxylic functional groups as well as polymethacrylate (PM) prepolymers with tertiary amine functional groups. The dependence of morphological and mechanical properties on the concentration of functional groups was studied. The enhanced miscibility of PU and PM prepolymers was observed at concentrations of functional groups of 0.25 mmol/g of polymer and above. Despite the improved miscibility, the PM prepolymers showed a tendency toward phase separation. Because the observed glass‐transition temperature shifts of PU prepolymers indicated substantial miscibility, we ascribed this phenomenon to the presence of methyl methacrylate rich sequences in the PM prepolymer. The observed changes in mechanical properties by increasing the content of functional groups were typical for ionomers. Young's modulus increased as a result of physical interactions between functional groups. A significant drop in tensile strength was observed in IPN samples with phase‐separated PU and PM prepolymers. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 40: 115–123, 2002     

Novel silver/polyurethane nanocomposite by in situ reduction: Effects of the silver nanoparticles on phase and viscoelastic behavior

A novel silver/poly(carbonate urethane) nanocomposite was prepared through in situ reduction of a silver salt (AgNO₃) added to a solution consisting of a commercial poly(carbonate urethane) dissolved in N,N‐dimethylformamide (DMF). In this system, the presence of the poly(carbonate urethane) was proved to protect the silver nanoparticles, whose formation was confirmed by means of UV–vis spectroscopy, from aggregation phenomena. The silver morphology developed in the solid state after DMF casting was imaged by FESEM. Homogeneous dispersion of silver nanoprisms in the poly(carbonate urethane) matrix was clearly observed. The effects of dispersion of silver nanoparticles within the poly(carbonate urethane) matrix were investigated by means of ATR‐FTIR and multifrequency dynamic mechanical thermal analyses. The obtained results revealed that the presence of silver nanoparticles modifies both the phase and the viscoelastic behaviors of poly(carbonate urethane). As a matter of fact, the hydrogen bond formation in the hard and soft segments was found to be hindered and the molecular motions of the soft segments were restricted, because a comparatively higher activation energy was required for the related α‐relaxation process. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 344–350, 2008     

Thermal,mechanical, and morphological properties of soybean oil-based polyurethane/epoxy resin interpenetrating polymer networks (IPNs)

A series of interpenetrating polymer networks (IPNs) based on epoxy (EP) resin and polyurethane (PU) prepolymer derived from soybean oil-based polyols with different mass ratios were synthesized. The structure, thermal properties, damping properties, tensile properties, and morphology of soybean oil-based PU/EP IPNs were characterized by Fourier-transform infrared spectroscopy, differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), universal test machine, and scanning electron microscopy (SEM). DSC and DMA results show that the glass transition temperature of the soybean oil-based PU/EP IPN decreases with the increase of PU prepolymer contents. Soybean oil-based PU/EP IPNs have better damping properties than that of the pure epoxy resin. The tensile strength and modulus of PU/EP IPNs decrease, while elongation at break increases with the increase of PU prepolymer contents. SEM observations reveal that phase separation appears in PU/EP IPNs with higher PU prepolymer contents.     

Comparative study between core-shell and interpenetrating network structure polyurethane/polyacrylate composite emulsions

Anionic aqueous polyurethane dispersion was prepared by using carboxyl acid group to make the polyurethane dispersible, and then nanograde core-shell and crosslinked IPN structure polyurethane/polyacrylate composite latex (PUA) were synthesized by soap-free emulsion polymerization method with polyurethane dispersion as seed. FTIR, DSC, dynamic light scattering, TEM, ESCA, TGA, electronic tensile machine were employed to investigate the structures and properties of the composite latex and their polymers. Meanwhile the core-shell composite PUA emulsion and the crosslinked IPN composite PUA emulsion were compared. The results showed that the particle morphology of PUA composite emulsion is inverted core-shell structure with polyacrylate as the core and with polyurethane as the shell. The morphology of the crosslinked PUA emulsion was multi-core structure. The surface in core-shell PUA contains rich PU phase. The phase structure of the crosslinked PUA is more uniform. Three transition temperatures are observed for the core-shell composite PUA, two transitions are observed for the film from the crosslinked PUA. The TGA curves of core-shell PUA and crosslinked PUA exhibit two stages, the first stage corresponds to the thermal decomposition of hard segments in seed polyurethane; the second stage corresponds to the decomposition of soft segments in PUA and decomposition of polyacrylate. With the increase of glycidyl methacrylate (GMA) amounts in PUA composite emulsions, the tensile strength of the PUA films as well as the average diameter of the PUA composite emulsion particles increase, the elongation at break of the PUA films decreases.     

Structure and properties of polyurethane/polyacrylate latex interpenetrating networks hybrid emulsions

Some new kinds of novel polyurethane (PU)/polyacrylate (PA) latex interpenetrating networks (LIPNs) were synthesized. Firstly PU dispersions were synthesized by self-emulsification polymerization. Then PU/PA LIPNs using PU dispersion as the seed were prepared by soap free emulsion polymerization. The effects of different PU/PA ratios, the blending method and the NCO/OH molar ratio of PU components on PU/PA LIPNs performance were also investigated. The structure and properties of PU/PA LIPNs such as mechanical properties, particle size, morphology of the surface were characterized by dynamic mechanical analysis, scanning electron microscopy, and dynamic light scattering. It was found that PU/PA LIPNs can markedly improve the water resistance and the mechanical properties of PU latex much more than those of PU/PA physical blends due to a great deal of interpenetrating and entangling between PU and PA latex. Moreover, the particle size of PU/PA LIPNs is related to the PA content and NCO/OH molar ratio of PU components: the higher the NCO/OH molar ratio in PU dispersions, the larger is the particle size of PU/PA LIPNs, and the average particle size of PU/PA LIPNs becomes larger with an increase in PA content.     

Preparation and physicochemical properties of hydroxyapatite/polyurethane nanocomposites

In this study, nanohydroxyapatite/polyurethane （nHA/PU） composites with various contents of methoxy- poly（ethylene glycol） modified nHA （0 wt%, 10 wt%, 20 wt% and 30 wt%） were prepared by solution blending process. The physicochemical properties of the composite membranes were investigated by Fourier transform infrared spectroscopy （FTIR）, X-ray diffraction （XRD）, Transmission electronic microscopy （TEM）, Differential scanning calorimetry （DSC）, Thermo gravimetric analysis （TGA） and tensile tests. TEM photos of the nanocomposites showed that the nHA was uniformly dispersed in the polymer matrix. The membrane with 10 wt% nHA showed the highest tensile strength which was about 75% higher than that of the pure PU membrane. However, the tensile strength decreased when high content （above 20 wt%） fillers were added, which was still higher than that of pure PU. TGA measurements suggested that the thermal stability of the membranes was improved owing to nHA fillers. XRD and DSC results illustrated that the crystallinity of PU soft segments decreased with the increasing content of nanoparticles in the composites.     

Morphology and properties of waterborne polyurethane/clay nanocomposites

Aqueous emulsion of polyurethane ionomers, based on poly(tetramethylene glycol) or poly(butylene adipate) as soft segment, isophorone diisocyanate as diisocyanate, 1,4-butandiol as chain extender, dimethyl propionic acid as potential ionic center, triethylene tetramine as crosslinker, and triethyl amine as neutralizer, were reinforced with organoclay to give nanocomposites. The particle size of emulsion was measured and the morphology of these nanocomposites was observed by transmission electron microscope, where the effectively intercalated or exfoliated organoclay was observed. The reinforcing effects of organoclay in mechanical properties of these nanocomposites were examined by dynamic mechanical and tensile tests, and the Shore A hardness was measured. Enhanced thermal and water resistance and marginal reduction in transparency of these nanocomposites were observed compared with pristine polymer.     

Effect of thermal expansion on shape memory behavior of polyurethane and its nanocomposites

The effects of thermal expansion on shape memory performance of shape memory polyurethanes and their nanocomposites with organoclay, carbon nanofiber (CNF), silicon carbide (SiC), and carbon black (CB) were evaluated. The shape memory test cycle involved tensile deformation at above the trigger temperature to initiate shape memory function, cooling to room temperature to fix the shape, and shape recovery induced by heating to above the trigger temperature. Phenomenological models were used to interpret the experimental data on coefficient of thermal expansion (CTE). It was found that Kerner model showed good fit for composites of SiC and CB, and Halpin model gave better fit for composites of organoclay and CNF. It was observed that thermal expansion exerts negative effect on recovered strain, the extent of which depends on the magnitude of temperature gradient, CTE, and the level of tensile strain. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 1437–1449, 2008     

Investigation on Structures and Properties of Shape Memory Polyurethane/Silica Nanocomposites

In this study, high performance shape memory polyurethane (SMPU)/silica nanocomposites with different silica weight fraction including SMPU bulk, 3%, 4.5%, 6%, 7.5%, 10%, were prepared by sol‐gel process initiated by the solid acid catalyst of p‐toluenesulfonic acid (PTSA). Field emission scanning electron microscopy (FE‐SEM) and transmission electron microscopy (TEM) observation show that the silica nanoparticles are dispersed evenly in SMPU/silica nanocomposites. Tensile test and dynamic mechanical analysis (DMA) suggest that the mechanical properties and the glass transition temperature (T_g) of the nanocomposites were significantly influenced by silica weight fraction. Thermogravimetric analysis (TGA) was utilized to evaluate the thermal stability and determine the actual silica weight fraction. The TGA results indicate that the thermal stability can be enhanced with the hybridization of silica nanoparticles. Differential scanning calorimetry (DSC) was conducted to test the melting enthalpy (ΔH) and the results suggest that the ΔH was markedly improved for the SMPU/silica nanocomposites. Thermomechanical test was conducted to investigate the shape memory behavior and the results show that the shape fixity is improved by hybridization of silica and good shape recovery can be obtained with the increasing of cycle number for all the samples.     

Effect of blowing agent content on the structure and flame-retardant properties of rigid polyurethane foam/expanded graphite composites

Driven by global environmental issues, the development of green building materials has become an immediate focus. In this work, n-pentane was used as an environmentally friendly blowing agent to prepare flame-retardant rigid polyurethane foam (RPUF) with the addition of expandable graphite (EG) successfully, and the effect of n-pentane content on flame retardancy and compressive properties of RPUF/EG composites was investigated through limit oxygen index (LOI), vertical burning test (UL-94), scanning electron microscope (SEM), thermogravimetric analysis (TGA), and compressive properties test. SEM results show that the content of EG and n-pentane causes a change in the cell structure of RPUF. The change of the n-pentane content has also an obvious effect on the thermal stability, flame retardancy, and specific compressive strength of RPUF/EG composites. In addition, the cell structure of RPUF matrix has an obvious influence on the distribution of EG in the composites, which indirectly affects the flame-retardant efficiency of EG. This research explores the conditions for the application of environmentally friendly RPUF and expands its application prospects.