Effect of molecular weight of curing agents on properties of nanocomposites based on epoxy resin and organoclay with reactive modifier

Nanocomposites of epoxy resin and clay modified with half neutralized salt of Jeffamine D400 were prepared by curing separately with three polyetheramines curing agents of different molecular weights and reactivity. The molecular weight of curing agents and their structural similarity with modifier played an important role in deciding the curing behavior, thermomechanical, and morphological properties of epoxy/clay nanocomposites. Morphological analysis carried out by X‐ray diffraction (XRD) and transmission electron microscope (TEM) clearly show that the dispersion of clay layers in epoxy matrix decreases with decreasing molecular weight of the curing agents. Curing study done by using temperature modulated differential scanning calorimetry (MDSC) demonstrates that extragallery reaction rate increases with decreasing molecular weight of curing agents. Dynamic mechanical analysis (DMA) of epoxy/3 wt % modified clay composite prepared by curing with curing agent of higher molecular weight shows around 270% improvement in storage modulus (glassy) as compared with its neat epoxy network. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44595.     

Reaction‐induced phase separation and resulting thermomechanical and surface properties of epoxy resin/poly(ethylene oxide)–poly(propylene oxide)–poly(ethylene oxide) blends cured with 4,4′‐diaminodiphenylsulfone

We investigated the phase separation, cure kinetics and thermomechanical properties of diglycidyl ether of bisphenol‐A/4,4′‐diaminodiphenylsulfone/poly(ethylene oxide)–poly(propylene oxide)–poly(ethylene oxide) (PEO–PPO–PEO) triblock copolymer (TBCP) blends. Fourier transform infrared spectroscopy, differential scanning calorimetry, and atomic force microscopy revealed that the blends exhibited heterogeneous phase morphology in which the TBCP formed dispersed domains in epoxy matrix, due to reaction induced phase separation. A fraction of phase‐separated PEO phase underwent partial crystallization whereas another fraction formed interphases between the dispersed domains and epoxy matrix. Moreover, the dispersed PEO chains improved the compatibility and interfacial adhesion between the matrix and domains and, consequently, significantly improved the mechanical properties of epoxy resin. Furthermore, the thermal degradation studies and contact angle measurements disclosed that the dispersed domains were well protected by the epoxy matrix. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44406.     

Enhanced oil resistance and mechanical properties of nitrile butadiene rubber/lignin composites modified by epoxy resin

This is probably the first report on developing nitrile butadiene rubber (NBR) composites with enhanced performance s via lignin bridged epoxy resin in the rubber matrix. NBR/lignin masterbatch has been prepared through latex‐compounding method, and then epoxy resin (F51) was added in the NBR/lignin compounds by the melt compounding method. Lignin‐epoxy resin networks were synthesized in situ during the curing process of rubber compounds through epoxide?hydroxyl reactions. Compared with lignin filler, lignin‐F51 networks showed an improved oil resistance ability and led to increased mechanical properties, crosslinking density, and thermal stability of the rubber composites. This method provides a new insight into the fabrication of novel interpenetrating polymer networks in rubber composites and enlarges the potential applications of lignin in high performance rubber composites. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 42922.     

Effect of nanocrystalline cellulose addition on needleless alternating current electrospinning and properties of nanofibrous polyacrylonitrile meshes

Needleless alternating current (AC)‐electrospinning is capable of achieving high nanofiber generation rates while adding more flexibility to the process development when compared to common direct current (DC)‐electrospinning. However, AC‐electrospinning process may produce very different results than DC‐electrospinning when using the same precursors. This study demonstrated that stable AC‐electrospinning of uniform and mechanically strong polyacrylonitrile (PAN) nanofibrous meshes can be achieved at 30 ± 5 kV rms voltage when 0.75–6.0 wt % of nanocrystalline cellulose‐II with respect to PAN is added to a typical PAN precursor solution. Efficient generation (up to 2 g/h rate or 0.7 g h^?1 cm^?2 mass flux) of nanofibers with 250–500 nm fiber diameters has been observed when using flat fiber‐generating electrodes with diameters up to 25 mm. Depending on the amount of nanocellulose, nanofibrous nanocellulose/PAN meshes revealed large variations in tensile modulus (90–273 MPa) and yield strength (1.0–2.5 MPa), whereas the fiber diameter, air permeability, air resistance, mesh porosity, and water absorption were less affected. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 45772.     

Preparation and characterizations of RTV epoxy blends using amide maleic anhydride‐g‐liquid polybutadience as both reactive toughening and curing components

Amide maleic anhydride‐g‐liquid polybutadience (AMALPB) was synthesized using maleic anhydride‐g‐liquid polybutadience (MALPB) with ethylenediamine (EDA), and its structure was confirmed by FTIR and ¹H‐nuclear magnetic resonance spectra, respectively. It was then used as a reactive toughening agent to make blends with diglycidyl end‐capped poly(bisphenol‐A‐co‐epichlorohydrin epoxy cured at room temperature. Their thermal decomposing behaviors did not show much difference because both EDA and AMALPB possessed similar aliphatic groups. All their glass transition temperatures (T_g) increased more than 10 °C than that of the neat epoxy, and with the addition of AMALPB, the blends were greatly strengthened upon heating as show from their storage moduli. When AMALPB was added at 10 wt %, its elongation at break increases to a maximum of 8.8% which was about two times higher than that of the neat epoxy, and its tensile strength also increased. However, the excessive addition of AMALPB resulted in an apparent decline in their tensile strength at content above 20%. The simultaneous improvements in both tensile strength and strain were attributed to the existence of well‐dispersed rubber particles in the continuous matrices performing plastic deformation that resulted from the chemical bonds of interfaces among the rubber particles and matrix, and meanwhile, inducing the deflection of the cracks. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 45985.     

Dynamic mechanical analysis of ethylene/1‐hexene copolymers: The effect of the catalyst type on the short‐chain branching distribution and properties of the amorphous and crystalline phases

Dynamic mechanical analysis was used to study ethylene/1‐hexene copolymers with different compositions, molecular weight distributions, and profiles of short‐chain branching (SCB) versus molecular weight. These copolymers were produced over a highly active supported titanium–magnesium catalyst (TMC), a highly active supported vanadium–magnesium catalysts (VMC), and a supported zirconocene catalyst. A higher fraction of the crystalline phase in the copolymers prepared with VMC was shown to result in higher elastic modulus values. β relaxation was found to be sensitive to the SCB distribution versus the molecular weight. The copolymers prepared with the zirconocene catalyst and VMC were characterized by more uniform SCB distributions and higher temperatures of β relaxation compared to the copolymers prepared with TMC. The mobility of the polymer chains at room temperature in the amorphous phase obtained by the spin‐probe method rose with increasing branch content in the copolymers and was not sensitive to different SCB distribution profiles. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44638.     

Effects of 4,4′‐diaminodiphenyl ether on the structures and properties of isocyanate‐based polyimide foams

A series of thermal insulation, acoustic absorption isocyanate‐based lightweight polyimide (PI) foams with 4,4′‐diaminodiphenyl ether (ODA) units were prepared from polyaryl polymethylene isocyanate (PAPI) and the esterification solution derived from pyromellitic dianhydride (PMDA) and ODA. The structures and properties of the PI foams prepared with different molar ratio of ODA/PMDA were investigated in detail. The results show that the ODA units have great influence on the foam properties. With the increase of the ODA units, the density decreases firstly and then increases. When the molar ratio of ODA/PMDA is 3/10, the foam reaches the minimum density (13.7 kg/m³). Moreover, with increasing the ODA units, the acoustic absorption properties increase firstly and then decrease owing to the variation of the average cell diameter of the PI foams. All PI foams show excellent thermal stability, and the 5% and 10% weight loss temperature are in the range of 250–270 °C and 295–310 °C, respectively. In addition, the PI foams present low thermal conductivity and thermal diffusivity. Furthermore, the mechanical property was also evaluated and the compressive strength of the PI foams is in the range of 33.0–45.7 kPa. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46029.     

Tough,stable spiroacetal thiol‐ene resin for 3D printing

Though over 30 years old, 3D printing has seen an explosion of interest in recent years as technology has become sufficiently advanced and affordable, enabling widespread usage, and investigation of the technique as a method of manufacture. However, the materials commonly used for printing applications frequently suffer from poor mechanical properties and are only suitable for prototyping and non‐load‐bearing objects. We report a stable, tough resin formulation which incorporates spiroacetal molecules into the polymer backbone and displays widely varying and tunable mechanical properties. We characterize the system via (photo‐)DSC, rheology, and tensile testing; further, we detail a comprehensive heat treatment investigation to optimize material performance and elucidate the structure–property relationships present in the printed and non‐printed semi‐crystalline photopolymer. Annealing the material at 40 °C for 120 hours produced a tough thiol‐ene with a homogenous crystal structure. Printed samples exhibited comparable morphology their cast analogues, but suffered from reduced tensile properties as a result of interlayer adhesion. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46259.     

Effect of vinyl and phenyl group content on the physical and dynamic mechanical properties of HVBR and SSBR

High‐vinyl polybutadiene rubber (HVBR) and solution‐polymerized styrene–butadiene rubber (SSBR) can meet the requirements of high‐performance tires due to their excellent wet skid resistance and lower rolling resistance. In this paper, the effects of the vinyl and phenyl groups and their contents on the vulcanization behavior, mechanical strength, fatigue resistance, heat resistance, and wear resistance of HVBR and SSBR were investigated, and the dynamic viscoelasticities of HVBR and SSBR vulcanizates with or without carbon black were explored by dynamic mechanical analysis (DMA). The experimental results showed that the vinyl groups contributed more to the wear resistance and fatigue resistance of vulcanizates than the phenyl groups, but the phenyl groups contributed more to the mechanical strength of the vulcanizates than the vinyl groups. The DMA results showed that the vinyl and phenyl groups could significantly improve the road‐gripping capability and wet skid resistance of HVBR and SSBR vulcanizates, but carbon black could slightly weaken the effect of vinyl and phenyl groups on the wet skid resistance of vulcanizates, and the effect of carbon black on vinyl groups was more significant. Despite the presence of carbon black, the phenyl groups contributed more heat buildup to the vulcanizates than the vinyl groups. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 45975.     

Effect of the sodium dodecyl sulfate/monomer ratio on the network structure of hydrophobic association hydrogels with adjustable mechanical properties

The study of gel‐network structure is not as extensive as the study of the application of hydrogels. However, the distribution of the inner structure is crucial for designing hydrogels with tunable mechanical properties to meet certain kinds of demands. In this study, a series of hydrophobic association hydrogels (HA‐gels) were synthesized by free‐radical micellar copolymerization in a sodium dodecyl sulfate (SDS) surfactant solution. The hydrophobic monomer was palmityl alcohol poly(oxyethylene acrylate) (AEO–AC), which is an ecofriendly alternative to the traditional octyl phenol poly(oxyethylene acrylate). Interestingly, we found that the molar ratio [or ratio point (R)] of SDS to AEO–AC played a key role in tuning the mechanical properties. All series HA‐gels denominated a similar down–up–down tendency with increasing R, and the best R is 3. This result was consistent with the microscopic network structure number of the hydrophobic monomer (N_H = 21–24), and this indicated that each hydrophobic monomer associated three SDS monomers in its internal networks. The resulting AEO–AC–acrylamide gels exhibited the best mechanical strength (yield maximum broken stress = 218 kPa) and the maximum effective crosslink density. Moreover, the relationship between the network structure and the mechanical properties of the HA‐gels was investigated with various Rs. Two different interaction effects of distribution between SDS and AEO–AC are discussed in detail. The HA‐gels exhibited self‐healing properties and maintained their shape in water over 160 days. The results indicate that changing R is an effective method for tuning the mechanical properties of HA‐gels as a type of prospective biomedical material. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45196.     

Dielectric,mechanical and transport properties of bisphenol A polycarbonate/graphene nanocomposites prepared by melt blending

Nanocomposites based on polycarbonate (PC) and different amounts of untreated graphene nanoplatelets (GnP) (from 1 to 7 wt %) were prepared by melt blending. The nanocomposites were thoroughly characterized employing the following techniques: broad band dielectric spectroscopy, thermally stimulated depolarization currents, differential scanning calorimetry, tensile testing, dynamic mechanical thermal analysis, and water vapor, carbon dioxide and oxygen permeability measurements. The presence of a MWS relaxation mode indicated the accumulation of electrical charges trapped at the interfaces of the polycarbonate with graphene 2D platelets. The addition of GnP produced nanocomposite materials with enhanced mechanical and barrier properties. The melt mixed PC/graphene nanocomposites prepared here exhibit well‐balanced properties, even though unmodified graphene nanoplatelets were used. In addition, the nanocomposites were obtained by a single extrusion process, which is easily scalable for industrial applications. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44654.     

Effect of nanoparticles on the mechanical properties of acrylonitrile–butadiene–styrene specimens fabricated by fused deposition modeling

Acrylonitrile–butadiene–styrene (ABS) nanocomposite filaments with different inorganic nanofillers for fused deposition modeling (FDM) were prepared by melting extrusion and printed via a commercial FDM three‐dimensional printer. The effects of the nanoparticles on the mechanical strength, anisotropy, and thermal properties of the ABS specimens were evaluated. The performances of the virgin ABS samples manufactured by FDM and injection molding were also studied. The results show that the tensile strength (TS) of the pure ABS made by FDM was just up to 70% of the value obtained from the injection‐molded specimens. The mechanical anisotropy of the pure ABS samples was very evident when the building orientation was changed. However, we found that the addition of nanofillers significantly reduced the mechanical anisotropy and improved the mechanical strength and thermostability of the ABS samples fabricated by FDM technology. The TS and flexural strength of the ABS samples increased by 25.7 and 17.1%, respectively, with the introduction of nanomontmorillonite. The addition of nano calcium carbonate lowered the mechanical anisotropy of ABS from 42.1 to 23.9%. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44470.     

Laser confocal microscopical characterization of toughened epoxy resins: Correlations between structural features and mechanical properties

Laser confocal microscopy is used to analyze the morphology of an epoxy resin (DGEBA) modified with different amounts of toughening agent carboxyl terminated butadiene acrylonitrile (CTBN). The size and phase volume of the distributed spherical toughening particles is ranging from 0.7 to 1.6 µm and 5 to 40 vol %, respectively. These morphological parameters and particles/µm² reveal a nonlinear relationship with the amount of toughening agent. With increasing particle size and number the glass transition temperature and the tensile modulus are decreasing, whereas the fracture toughness increases. Particles larger than 1.3 µm and a value of particles/µm² higher than 0.15 exhibit a more significant impact on the resin properties. Linear correlations between the rubber phase volume and the glass transition temperatures as well as the mechanical properties, i.e., tensile modulus and fracture toughness are ascertained. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46094.     

The influence of filler surface modification on mechanical and material properties of layered double hydroxide‐containing polypropylene composites

The processing and properties of layered double hydroxides (LDHs)‐containing polypropylene (PP) composites have been studied extensively. However, no detailed studies have reported on how stearic acid (SA)‐intercalated and SA‐coated LDHs influence the properties of melt‐processed PP/LDH composites. Here, four different types of LDHs: synthesized (cLDH1) and commercial (cLDH2) SA‐coated LDH, SA‐intercalated LDH (iLDH), and unmodified LDH (nLDH), were used to fabricate composites using a master‐batch‐dilution technique in a twin‐screw extruder. The characterization results showed that microcomposites were formed when cLDH2 and nLDH were used, whereas nanocomposites were formed when iLDH and cLDH1 were used. Strong nucleating behavior was observed for the nLDH‐, cLDH1‐, and cLDH2‐containing composites, whereas iLDH delayed the crystallization process of the PP matrix. A significant improvement in modulus, with a balance of tensile and impact strengths, was observed in the case of the cLDH1‐containing composite, whereas the nLDH‐containing composite showed good improvement in temperature‐dependent load‐bearing capacity. On the other hand, the PP/iLDH composite showed a remarkable improvement in thermal stability and a reduction in the peak‐heat‐release rate. Therefore, this study gives us an opportunity to design PP composites with desired properties by the judicious choice of LDH, which further widens the application of PP matrices. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45024.     

Effect of the matrix resin structure on the mechanical properties and braking performance of organic brake pads

Two chemically modified phenolic resins (PFs) designed and developed for the matrix resins of organic friction materials were characterized. The braking performance of organic brake pads based on the two modified resins and reinforced with hybrid fibers was investigated on a full‐scale test bench. The results indicate that the modified PF with more internal friction units possessed much higher impact and compression strengths, greater toughness, and better braking stability. We concluded that the matrix resin with more adjustable structural units allowed for an adjustable Young's modulus and dynamic mechanical properties and, hence, could indirectly allow an adjustable friction coefficient for organic brake pads during braking process and, furthermore, enable the optimization of braking stability of the friction couples. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2012     

Effects of plasticizer on structures,non‐isothermal crystallization,and rheological properties of polyarylates

We herein report the effects of plasticizer content (1–5 wt %) on the structure, non‐isothermal crystallization kinetics, thermal stability, and rheological property of a new type of multicomponent polyarylate (PAR). Fourier transform infrared spectra reveal the presence of a specific interaction between plasticizer and PAR chains, indicating the good dispersion of the plasticizer at the molecular level. The plasticizer influences on the non‐isothermal crystallization behavior of the PAR in two different ways: a mobility enhancer of PAR chains and an impurity to the crystallization of PAR. The melt‐crystallization temperature (T_mc) and enthalpy (ΔH_mc) of the plasticized PARs at cooling runs are higher than those of the neat PAR, which is owing to the enhanced mobility of PAR chains by the plasticizer. On the other hand, the non‐isothermal crystallization rates at different cooling rates of 5–40 °C/min are slower for the PARs with higher plasticizer contents, which is due to the impurity effect of the plasticizer on the melt‐crystallization of PARs. Although the PARs with 1–5 wt % plasticizer have lowered thermal decomposition temperatures, compared to the neat PAR, they are thermally stable up to ～400 °C. The complex melt viscosity of PAR with only 1 wt % plasticizer is far lower than that of the neat PAR. Overall, it is found that only 1 wt % plasticizer is quite effective to facilitate the melt‐processibility and to increase the crystallinity of PAR. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 45704.     

Preparation of ferric phosphonate/phosphinate and their special action on flame retardancy of epoxy resin

Fe‐ and P‐based compounds have demonstrated promising performance in enhancing flame retardancy of epoxy resins. In this context, this work focuses on the preparation of new Fe/P hybridized nanomaterials and their effect on flame retardancy of epoxy resins. The Fe/P hybrids were facilely prepared via forming ferric phosphinates and phosphonates using hydrothermal reaction. Attractively, ferric phosphinates and phosphonates exhibit the morphology of 1D nanorod and 2D nanosheet, respectively. When incorporating these two fillers in epoxy resin, the limiting oxygen index values of composites were enhanced to above 28 and the composites exhibited self‐extinguishing behavior, thus indicating greatly improved fire resistance. Further investigation revealed that the flame retarding behavior, in particular for ferric phosphonate nanosheets, took place mainly in gas phases via delaying the release of flammable gas. Attractively, it was found that the Fe/P hybrids took part into the pyrolysis reaction of epoxy resins through forming Fe? O and P? O bonds. This finding may provide a new insight to design a series of high performance flame retardants for epoxy resins. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46206.     

Influence of different concentrations of glycidylisobutyl‐POSS on the glass transition of cured epoxy resin

In this study, polyhedral oligomeric silsesquioxane glycidylisobutyl‐POSS was dispersed in epoxy resin by ultrasound, and the parameters of a phantom model, the Williams–Landel–Ferry (WLF) and Vogel–Fulcher–Tammann (VFT) equations were modeled using dynamic mechanical analysis (DMA) to evaluate their influence on the glass transition state. The relaxation and retardation time distributions were estimated using a nonlinear regularization method, and the estimated physical parameters were discussed based on the results obtained from transmission electron microscopy (TEM). The TEM analysis indicated higher POSS dispersion with a spherical shape. The POSS dispersion was associated with the formation of micelles due to their hybrid character. The micelles favored the interconnections of the nodular microstructure of the epoxy thermosetting, which led to an increase in their T_g values. These interconnections increased the structure's percolation, promoted a reduction in the thermal expansion coefficient and resulted in a more homogeneous glass transition, in terms of a cooperative distribution in the relaxation times at the time scale measured. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41453.     

Properties and microstructure of polyurethane resins from liquefied wood

In this article, polyurethane resins were synthesized from liquefied benzylated wood and toluene diisocyanate (TDI)–trihydromethylene propane (TMP) prepolymer (as curing agent). The relations of their segmented structure and properties of were investigated. Results indicated that polyurethane resins made from benzylated wood solution have good mechanical and thermal properties. With the increase of curing agent amount from 23.8 to 53.5%, the degree of phase segregation increased, and under experimental conditions in this article, phase transition was detected with a curing agent amount of 69.9%. After this transition, the mechanical properties of polyurethane resins were improved. Thermal history treatment can also influence microstructure and thermal stabilities of polyurethane samples. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 95: 1175–1180, 2005     

Strain rate dependent mechanical properties of a high‐strength poly(methyl methacrylate)

Strain rate dependency is an important issue for the mechanical response of materials in impact events. Dynamic mechanical properties of a high‐strength poly(methyl methacrylate) (PMMA) were studied by using split Hopkinson pressure bar technology. The maximum stress is enhanced with the increase of strain rate, and then keeps a constant with the further increase of strain rate, which is accompanied with a linear increase of fracture energy density. The critical data of strain rate and maximum stress were determined. Eyring's equation was applied for analyzing the influence factors, which relate to the hardening induced by strain rate and softening caused by adiabatic temperature rise. Inherent physical mechanisms were clarified and the strategies for designing advanced impact‐resistant polymers were proposed. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46189.