Interfacial mechanical behavior of 3D printed ABS

We describe an experimental approach for characterizing the local mechanical behavior of acrylonitrile butadiene styrene (ABS) structures processed through fused deposition modeling. ABS test specimens processed in various build orientations were subject to multiscale mechanical tests as well as local morphology and chemical analyses. Instrumented indentation, local dynamic mechanical analysis, and atomic force microscopy tests were used to explore the mechanical behavior and morphology of build surfaces and weld interfaces. An interfacial stiffening effect was found for the majority of the specimens tested, with up to a 40% increase in the indentation elastic modulus measured with respect to the build surfaces. Raman spectroscopy mapping of the interfacial areas revealed ～30% less butadiene/styrene and butadiene/acrylonitrile ratios with respect to analysis of the build surfaces. The results provide insight into the multiscale behavior of additive manufactured structures and offer the potential to guide processing–structure–property understanding of these materials. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43671.     

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.     

Influence of temperature on the microstructure and mechanical properties of stretched polypropylene

Microstructure and mechanical properties of isotactic polypropylene (iPP) stretched at different temperatures were studied. Strain‐induced fibrils were observed after stretching. Crystallinity (X_c), crystallite thickness (L_c), long period (L_pf), and diameter (D_f) of fibrils were characterized by Differential Scanning Calorimetry and Small angle X‐ray scattering. L_pf of stretched iPP below 60°C was found to be lower than undrawn iPP. X_c, L_c, and D_f increased with increasing draw temperature. Tensile test showed that Young's moduli of stretched iPPs were negatively dependent on X_c and L_c. The fraction of taut tie molecules was estimated from the mechanical model. Results showed that more tie molecules were formed in the samples stretched at lower temperatures. Dynamical mechanical analysis showed that glass transition temperature was strongly dependent on the draw temperature. The glass transition peak disappeared in stretched iPPs obtained below 80°C. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42622.     

Preparation and ionic conductive properties of all‐solid polymer electrolytes based on multiarm star block polymers

A series of star block polymers with a hyperbranched core and 26 arms are successfully synthesized by atom transfer radical polymerization of styrene (St), and poly(ethylene glycol) methyl ether methacrylate from a hyperbranched polystyrene (HBPS) multifunctional initiator. All‐solid polymer electrolytes composed of these multiarm star polymers and lithium salts are prepared. The influences of polyoxyethylene (PEO) side‐chain length, PEO content, lithium salt concentration and type, and the structure of polymer on ionic conductivity are systematically investigated. The resulting polymer electrolyte with the longest PEO side chains exhibits the best ionic conductive properties. The maximum conductivity is 0.8 × 10^?4 S cm^?1 at 25°C with EO/Li = 30. All the prepared multiarm star block polymers possess good thermal stability. The mechanical property is greatly improved owing to the existence of polystyrene blocks in the multiarm star polymer molecules, and flexible films can be obtained by solution‐casting technique. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Pre‐dispersing of montmorillonite nanofiller: Impact on morphology and performance of melt compounded ethyl vinyl acetate nanocomposites

Ethyl vinyl acetate (EVA) copolymers are potential materials for biomedical applications due to their exceptional mechanical properties and biocompatibility. As new medical device designs continue to reduce in size, new materials are required that exhibit improved strength and toughness. In this research, EVA nanocomposites containing synthetic montmorillonite (MMT) are being investigated as new biomedical materials with similar flexibility, biocompatibility, and biostability to neat EVA, but with far superior tensile strength and toughness. We show that the pre‐dispersing of the organo‐MMT prior to melt compounding with the EVA matrix can facilitate nanofiller exfoliation and dispersion in the EVA, thereby enabling significant improvement of EVA nanocomposite performance when high organo‐MMT loading (5 wt %) was added. It was observed that the polarity of pre‐dispersing medium influenced the nanofiller's surfactant organization and distribution, organo‐MMT exfoliation, and dispersion in the EVA, and also interphases of the host copolymer. Consequently, changes in morphology have brought noticeable effects on the mechanical and thermal properties of the EVA. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43204.     

Anisotropic mechanical behavior of semi‐crystalline polymers: Characterization and modeling of non‐monotonic loading including damage

In this work, the mechanical response of high density polyethylene (HDPE) to complex uniaxial tensile loadings is firstly characterized experimentally, taking into account the damage occurring in large deformation and the initial anisotropy induced by the forming process. Anisotropic effects are characterized through tensile tests using several complex loading paths involving large deformation, and for different orientation with respect to the extrusion direction. A mechanical model is then developed, based on a non‐equilibrium thermodynamic approach of irreversible processes, resulting in a new thermodynamic potential describing both the elasto‐viscoelastic–viscoplastic behavior and the volume variation due to damage. Results show that transverse strains and volume strain of HDPE highly depend on specimen orientation, whereas the apparent Young's modulus is not affected by this orientation. The developed model is validated for HDPE, and satisfyingly predicts the complex response of HDPE to complex loadings paths. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44468.     

Shape‐memory behavior of high‐strength amorphous thermoplastic poly(para‐phenylene)

The purpose of this study was to investigate the shape‐memory behavior of poly(para‐phenylene) (PPP) under varying programming temperatures, relaxation times, and recovery conditions. PPP is an inherently stiff and strong aromatic thermoplastic, not previously investigated for use as a shape‐memory material. Initial characterization of PPP focused on the storage and relaxation moduli for PPP at various frequencies and temperatures, which were used to develop continuous master curves for PPP using time–temperature superposition (TTS). Shape‐memory testing involved programming PPP samples to 50% tensile strain at temperatures ranging from 155°C to 205°C, with varying relaxation holds times before cooling and storage. Shape‐recovery behavior ranged from nearly complete deformation recovery to poor recovery, depending heavily on the thermal and temporal conditions during programming. Straining for extended relaxation times and elevated temperatures significantly decreased the recoverable deformation in PPP during shape‐memory recovery. However, PPP was shown to have nearly identical full recovery profiles when programmed with decreased and equivalent relaxation times, illustrating the application of TTS in programming of the shape‐memory effect in PPP. The decreased shape recovery at extended relaxation times was attributed to time‐dependent visco‐plastic effects in the polymer becoming significant at longer time‐scales associated with the melt/flow regime of the master curve. Under constrained‐recovery, recoverable deformation in PPP was observed to have an exponentially decreasing relationship to the bias stress. This study demonstrated the effective use of PPP as a shape‐memory polymer (SMP) both in mechanical behavior as well as in application. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 42903.     

Thermal,mechanical, and rheological properties of poly(ε‐caprolactone)/halloysite nanotube nanocomposites

Naturally available halloysite nanotubes (HNTs) with hollow nanotubular structures were used as reinforcement in poly(ε‐caprolactone) (PCL). The PCL/HNT nanocomposites were prepared by melt mixing the polymer with as‐received HNTs up to 10 wt % in an internal batch mixer. Transmission electron microscopy analysis indicated that the HNTs were dispersed uniformly on the nanoscale throughout the PCL matrix. Differential scanning calorimeter studies revealed that the PCL crystallinity was decreased in the nanocomposites, and the HNTs dispersed in the PCL matrix led to an increase in the non‐isothermal crystallization temperature of the PCL. Tensile and dynamic mechanical tests showed great enhancement in strength and stiffness at low HNT content, while still maintaining the ductility of the PCL. The glass transition temperature (T_g) of the pristine PCL was substantially increased with increase in filler loading, which indicates good reinforcing effect imparted by the addition of HNT. Melt rheological studies revealed that the nanocomposites exhibited strong shear thinning behavior, and a percolated network of HNT particles was formed. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Enhancing the mechanical and thermal properties of polyacrylonitrile through blending with tea polyphenol

Several polyacrylonitrile (PAN)/tea polyphenol (TP) blends were prepared with various mixing weight ratios (percentage). With a commercial acrylonitrile–butadiene–styrene (ABS) as reference, the results show that the PAN/TP blends with 12.5 wt % TP had a better antiwear ability and similar hardness to those of ABS. All of the prepared PAN/TP blends showed a lower impact strength than the referenced ABS. However, some values were indeed higher than those reported for engineering materials in the literature, for example, polystyrenes and some ABS blends. Differential scanning calorimetry, differential thermogravimetry, and dynamic mechanical analysis indicated that the PAN/TP blends had enhanced the thermal stability compared to the pure PAN. Fourier transform infrared spectral analysis suggested that the H bonds increased in the PAN/TP blends. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40411.     

Effect of coupling agent on structure and properties of micro–nano composite fibers based on PET

Poly(ethylene terephthalate) (PET)/carbon black (CB) micro–nano composite fibers were manufactured by melt spinning method. To achieve good dispersion, nano‐CB particles were modified by coupling agent (CA). The effect of CA on structure and properties of the fibers were investigated via scanning electron microscopy (SEM), tensile testing, differential scanning calorimetry (DSC), wide‐angle X‐ray diffraction (WAXD), sonic orientation, and birefringence, respectively. At 2 wt % CA dosage, CB particles present the optimal dispersion in the fibers, shown in SEM images. Besides, the fibers possess the maximum breaking strength, the lowest crystallization temperature, and the highest crystallinity. After CA modification, the superior interfacial structure between PET and CB is beneficial to improve mechanical properties of the fibers. The well dispersed CB particles provide more heterogeneous nucleation points, resulting in the highest crystallinity. Furthermore, the fibers with 2 wt % CA dosage possess the maximum orientation and shrinkage ratio. According to Viogt–Kelvin model, the thermal shrinkage curves of the fibers can be well fitted using single exponential function. The three‐phase structure model of crystal phase–amorphous phase–CB phase was established to interpret the relationship among shrinkage, orientation, and dispersion of CB particles. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43846.     

Influence of molecular structure and reinforcement on fatigue behavior of tough polypropylene materials

Molecular structure and reinforcement heavily influence the crack growth resistance of polypropylene materials. Aim of this study is to investigate the fatigue behavior of different unreinforced and reinforced tough polypropylene materials used for piping applications. Due to high resistance against crack growth, these materials cannot be tested in the application relevant quasi‐brittle failure mode within feasible amounts of time. In this work, the new cyclic cracked round bar test, developed for tough polyethylene materials, has been examined as a possible method to characterize this important type of failure mode in homo‐, random‐, and reinforced polypropylene. Even though molecular mass distribution, which is often used to explain differences in crack growth resistance of polymers, was similar for unreinforced materials, fatigue lifetimes differed greatly. The mismatch of molecular mass and fatigue lifetime was mainly attributed to the different buildup and morphology of the base polymer. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43948.     

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.     

Synthesis and aqueous solution properties of novel thermosensitive polyacrylamide derivatives

A series of novel thermosensitive polymers were synthesized with acrylamide and thermosensitive macromonomers by radical polymerization in water solution. The structures of the copolymers were characterized by ¹H‐NMR. The effects of the polymer concentration, NaCl concentration, shear rate, and chemical structure on the thermothickening behavior of the polymer solution were investigated by advanced rheometry. The luminous transmittance of the solution with various polymer concentrations was tested by visible spectrometry. The results show that the thermothickening behavior was due to the phase separation of the polymer solution or intramolecular repulsions between the hydrophobic side chains and hydrophilic backbone at high temperatures. Finally, the thermothickening properties of the novel copolymer were studied under conditions simulating an underground oil reservoir. This novel copolymer is expected to be used as an oil‐displacing agent to enhance oil recovery in the future. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 766‐775, 2013     

Characterization of the viscoelastic behavior of the pure bitumen grades 10/20 and 35/50 with macroindentation and finite element computation

In this article, we present an identification procedure that allows the determination of the viscoelasticity behavior of different grades of pure bitumen (bitumen 35/50 and bitumen 10/20). The procedure required in the first stage a mechanical response based on macroindentation experiments with a cylindrical indenter. A finite element simulation was performed in the second stage to compute the mechanical response corresponding to a viscoelasticity model described by three mechanical parameters. The comparison between the experimental and numerical responses showed a perfect matching. In addition, the identification procedure helped to discriminate between different bitumens characterized by different asphaltene and maltene contents. Finally, the developed procedure could be used as an efficient tool to characterize the mechanical behavior of the viscoelastic materials, thanks to the quantified relationship between the viscoleastic parameters and the force–penetration response. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 3440–3450, 2013     

Effect of the graphite nanoplatelet size on the mechanical,thermal, and electrical properties of polypropylene/exfoliated graphite nanocomposites

Polypropylene (PP)/exfoliated graphite nanoplatelet (xGnP) nanocomposites with various intrinsic aspect ratios of graphite nanoplatelets (GnPs; large and small in diameter) were prepared by a melt‐mixing procedure. Transmission electron microscopy showed that all types of xGnP were well‐dispersed in the polymer matrix. The effects of the dimensions and loading of the xGnPs on the morphology, mechanical reinforcement, and electrical properties of PP/xGnP were studied. A differential scanning calorimetry study of the PP/xGnP morphology indicated that all types of xGnP additives were heterogeneous nucleation sites for PP crystallization. Tensile testing, DMA, and thermogravimetric analysis of PP/xGnPs with different types of GnP additives showed enhancements in their mechanical properties, heat resistance, and thermal stability compared to plain PP. We also found a significant increase in the conductivity of PP/xGnP. The PP/xGnP with a large diameter of GnPs demonstrated the lowest percolation threshold, equal to 4 vol % of the xGnP loading. The mechanical properties were estimated by means of micromechanical modeling. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Morphologies and mechanical properties of polylactide/thermoplastic polyurethane elastomer blends

To explore a potential method for improving the toughness of a polylactide (PLA), we used a thermoplastic polyurethane (TPU) elastomer with a high strength and toughness and biocompatibility to prepare PLA/TPU blends suitable for a wide range of applications of PLA as general‐purpose plastics. The structure and properties of the PLA/TPU blends were studied in terms of the mechanical and morphological properties. The results indicate that an obvious yield and neck formation was observed for the PLA/TPU blends; this indicated the transition of PLA from brittle fracture to ductile fracture. The elongation at break and notched impact strength for the PLA/20 wt %TPU blend reached 350% and 25 KJ/m², respectively, without an obvious drop in the tensile strength. The blends were partially miscible systems because of the hydrogen bonding between the molecules of PLA and TPU. Spherical particles of TPU dispersed homogeneously in the PLA matrix, and the fracture surface presented much roughness. With increasing TPU content, the blends exhibited increasing tough failure. The J‐integral value of the PLA/TPU blend was much higher than that of the neat PLA; this indicated that the toughened blends had increasing crack initiation resistance and crack propagation resistance. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Identification of relationship between the synthesis/process parameters and properties of a sol–gel‐derived polymer nanocomposite system

A Ti‐containing silicate‐based epoxy‐functional polymer nanocomposite system was synthesized by a sol–gel route with or without the introduction of a reflux process, which was followed by UV‐induced epoxy polymerization. Influences of synthesis and process parameters, including Ti content, sol ageing, reflux process, and UV‐irradiation on various properties of the system were detailed. It was demonstrated that the introduction of a reflux process during the sol–gel synthesis could significantly modify the chemical and physical properties of the resultant material system along with other parameters such as Ti content. Overall results showed that the synthesis and process parameters examined could be employed to modify the microstructure, and to tune the final properties of this polymer nanocomposite system. The technique described herein, therefore, could be used to develop a new process regime to obtain materials of this type with desired properties, which might potentially be employed in certain applications such as dental restoration. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Understanding the surface properties of polybenzoxazines: Interaction of polybenzoxazine model compounds with metal ions and water

The structure of polybenzoxazines (and their properties) is mainly defined by the existence of intra‐ and intermolecular hydrogen bonds. The effect of different substituents present in the phenolic ring of polybenzoxazines can modulate these intermolecular forces and the interaction with other materials, such as metals. To extend this knowledge, a series of structure‐controlled polybenzoxazines and polybenzoxazine model compounds have been synthesized. The interactions with different metal ions have been investigated using UV–vis and NMR analysis. Association constants have been estimated by UV–vis titration method and the effect of the presence of different substituents in the aromatic ring has been established. Water contact angles have also been measured. The different techniques give us information about the inner hydrogen bonding structure. Cyano group, present as substituent in polybenzoxazine compounds, acts as an additional coordination point towards metal ions and water. Our findings should allow modulating the adhesion and other surface properties of the benzoxazine‐derived polymers by playing with the properties of the substituents and their structure (phenoxy/phenolic). © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 44099.     

Soybean‐ and castor‐oil‐based thermosetting polymers: Mechanical properties

Maleic anhydride modified soybean‐ and castor‐oil‐based monomers, prepared via the malination of the alcoholysis products of the oils with various polyols, such as pentaerythritol, glycerol, and bisphenol A propoxylate, were copolymerized with styrene to give hard rigid plastics. These triglyceride‐based polymers exhibited a wide range of properties depending on their chemical structure. They exhibited flexural moduli in the 0.8–2.5 GPa range, flexural strength in the 32–112 MPa range, glass transition temperatures (T_g) ranging from 72 to 152°C, and surface hardness values in the 77–90 D range. The polymers prepared from castor oil exhibited significantly improved modulus, strength, and T_g values when compared with soybean‐oil‐based polymers. These novel castor and soybean‐oil‐based polymers show comparable properties to those of the high‐performance unsaturated polyester (UP) resins and show promise as an alternative to replace these petroleum‐based materials. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 1497–1504, 2006     

Tailoring the crystalline morphologies and mechanical properties of high‐density polyethylene parts by a change in the fluid flow pattern under gas‐assisted injection molding

In this study, an increase in the cooling rate of high‐density polyethylene parts was carried out via a change in the fluid flow pattern to introduce gas cooling under a gas‐assisted injection‐molding process; this was conducive to the retention of orientation chains shaped during the injection stage and further developed into much more oriented crystals. Morphological observation showed that the parts without gas cooling (WOGC) were composed of oriented crystals except the gas channel zone, whereas the parts with gas cooling (WGC) were full of oriented crystals, especially much more interlocking shish‐kebab structures in the subskin zone. The WGC parts had a higher degree of orientation than the corresponding zone of the WOGC parts. Although the lower crystallinity, the wider orientation regions, and much more interlocking shish‐kebab structures led to considerable increases from 32 and 990 MPa in the WOGC parts to 36 and 1150 MPa in the WGC parts for the yield strength and elastic modulus, respectively. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40349.