Thermoplastic Polyurethane Nanocomposites Produced via Impregnation of Long Carbon Nanotube Forests

TPU was infiltrated into vertically aligned, 3.5 mm‐long MWNT forests to produce continuously reinforced anisotropic nanocomposites, and thermomechanical and electrical testing has revealed multifunctionality which shows promise for numerous applications. A 1000% increase in the storage modulus at 70 °C was observed as compared to the neat TPU, and these continuously aligned composites showed electrical conductivity two orders‐of‐magnitude greater (≈1.5 S · cm^?1) than randomly aligned composites prepared using CNTs from these forests. The heightened improvement for the continuously reinforced composite appears to be owed to the extremely high aspect ratio of these CNTs and the interconnected network which remains after infiltration.

     

Influence of Screw Speed on Electrical and Rheological Percolation of Melt‐Mixed High‐Impact Polystyrene/MWCNT Nanocomposites

The influence of screw speed on the electrical and rheological percolation of HIPS/MWCNT composites prepared via melt mixing was investigated. Microscopic examination of these composites using POM, FESEM and HRTEM revealed optimum MWCNT dispersion was achieved at intermediate screw speeds. On addition of MWCNTs to HIPS, the electrical conductivity of HIPS increased by up to 12 orders of magnitude. At screw speeds up to 100 rpm an electrical percolation of 1–3 wt.‐% was achieved. This increased to 3–5 wt.‐% when the screw speed was increased to 150 rpm. The onset of a rheological percolation was detected for an MWCNT loading of 5 wt.‐%, irrespective of screw speed employed. An up‐shift in the Raman G‐band of 24 cm^?1 was observed, implying strong interfacial interaction between HIPS and MWCNTs.

     

A Model for the Elastoplastic Behavior of Isotactic Poly(propylene) Below the Yield Point

Observations are reported on isotactic poly(propylene) (iPP) in a series of tensile loading‐unloading tests with a constant strain rate at room temperature. A constitutive model is developed for the elastoplastic behavior of a semicrystalline polymer at isothermal uniaxial deformations with small strains. The stress‐strain relations are determined by 5 adjustable parameters which are found by fitting the experimental data.

The stress σ (MPa) versus strain ε in a tensile loading‐unloading test with the maximum strain ε_max = 0.09. Circles: experimental data. Solid line: results of numerical simulation.     

Polymeric Toughening of Particle Filled Cyanate Ester Composites

Summary: The present study examines the effect of polymeric tougheners on the performance of silica filled cyanate ester composites. The polymeric tougheners used have been shown to enhance cyanate ester tougheners in binary toughener/matrix systems. Tougheners that were able to form a favourable phase‐separated morphology resulted in the greatest increase in crack resistance. The addition of these tougheners resulted in minimal loss of strength, and a slight decrease in modulus. Importantly the viscosity of the compounded systems was low enough for them to be readily processable. Whilst conserving most secondary properties, toughener addition did result in a slight increase in composite hydrolytic degradation. This issue was linked to the additive/ additive compounding processes. Removal of this extra moisture should eliminate this concern, permitting the used of these composites in electronic applications.

Effect of ETBN content on the crack resistance of particle filled cyanate ester composites and SEM image of 15 matrix wt.‐% ETBN.     

Porous Superabsorbent Hydrogel Composites: Synthesis,Morphology and Swelling Rate

Summary: Novel porous hydrogel composites with very high swelling capacity and enhanced rate of water absorption were synthesized in aqueous media at room temperature under normal atmospheric conditions. The porosity was induced through either foaming conducted in the course of polymerization or non‐solvent dewatering of the as‐synthesized gels. Kaolin was incorporated as an inorganic component in the polymerization process. The foaming technique was used to form porosity using three systems of different porogens (porosity generators), i.e. sodium bicarbonate, acetone and their combination. The as‐synthesized gels were dried through oven drying and non‐solvent dewatering. Morphology and swelling rate of the superabsorbent hydrogel composites (SHCs) were studied versus either the porogen system or the drying method. It was found that the simultaneous polymerization‐foaming technique had great influence on the improvement of porosity, morphology of the porous structure and the rate of water absorption. It was also shown that the drying procedure had remarkable influence on preserving the preformed porosity. Methanol as a dewatering solvent produced SHCs with higher porosity and swelling rate in comparison with the porosity of the hydrogels dewatered in acetone. Our invented methodology including simultaneous polymerization and foam formation using dual‐porogen system and the subsequent methanol‐dewatering approach was found to be the most efficient, highly practical, and cost‐effective route for preparing improved superabsorbing hydrogel materials.

     

Colloidal Crystalline Arrays of β‐Polymorphic Poly(vinylidene fluoride)

Stable layers of nearly monodisperse spheres of β‐polymorphic poly(vinylidene fluoride) with iridescent properties are prepared. The colloidal crystalline arrays (CCAs) were characterized by optical microscopy, differential scanning calorimetry (DSC), and FT‐IR spectroscopy. FT‐IR spectroscopic and wide‐angle X‐ray scattering (WAXS) studies revealed a β‐polymorphic PVF₂ structure, the DSC study showed that the level of crystallinity in the CCA was much higher than that in the melt‐crystallized sample, and UV‐visible spectroscopy showed extinction peaks at 323 and 510 nm in the CCAs. The β‐polymorphic PVF₂ structure, along with the optical extinction properties of these CCAs, raises the prospect of their application in optical filters and/or piezoelectric sensors.

Optical micrograph of PVF₂ CCA films cast on glass substrates.     

Formation of in situ CB/PET Microfibers in CB/PET/PE Composites by Slit Die Extrusion and Hot Stretching

Summary: In this present study, the in situ fabrication of a microfibrillar composite based on poly(ethylene terephthalate) (PET), polyethylene (PE), and carbon black (CB) is attempted. PET and CB were first melt mixed. The CB/PET compound and PE were subsequently melt extruded through a slit die and then hot stretched. The morphological observation of the as‐stretched extrudate indicated that well‐defined microfibers of CB/PET compound could be generated at appropriate CB contents and a fixed hot stretch ratio. In addition, CB was always selectively located in PET. The microfibrillar CB/PET/PE composite has the potential to be a new electrically conductive polymer composite.

Morphology of the carbon black/poly(ethylene terephthalate)/polyethylene (PE) composite after additional mixing in the mixer at the processing temperature of PE.     

The Effect of Particle Matrix Adhesion on the Mechanical Properties of Silica Filled Cyanate Ester Composites

Summary: The effect of silica and its surface treatment on the mechanical properties of composites was studied as part of the evaluation of cyanate ester matrices as potential electronic encapsulants. Three filler surface treatments were used, as a qualitative interfacial adhesion scale, in an attempt to gauge the magnitude of interfacial adhesion between untreated filler and the cyanate ester matrix. There was strong interfacial adhesion between matrix and untreated filler. The level of silica content most affected composite modulus and fracture toughness. Filler surface treatment most affected composite strength and fracture toughness/energy. Composite fracture was found to occur via crack pinning and/or crack blunting depending on the strength of adhesion. The composites evaluated were found to possess suitable mechanical properties for potential use as electronic encapsulants.

     

Mechanical Properties of Electron Beam Cured Monomer and Monomer/Liquid Crystal Films

This article reports on mechanical properties of electron beam cured tripropylene glycol diacrylate (TPGDA) and propoxylated glycerol triacrylate (GPTA) films. This study has been motivated by the need to have direct access to those properties for analyzing the thermo‐mechanical behavior and electro‐optical properties of polymer dispersed liquid crystal systems in general, and systems made either of TPGDA or GPTA and low molecular weight liquid crystals in particular. Representative examples of these systems are considered in this work. The effects of the degree of crosslinking on the mechanical strength of the polymer network are analyzed by considering different doses of the electron beam irradiation. As the radiation dose increases, the mechanical strength of the film is enhanced. Addition of a small amount of liquid crystals leads to remarkable plasticizing effects.

Young modulus and rubbery state modulus as a function of EB dose for cured TPGDA films. The filled symbols represent the Young modulus and the open symbols represent the rubbery state modulus. Circles are for pure TPGDA and squares are for TPGDA/E7 mixture with 15 wt.‐% E7.     

Tensile Fracture and Failure Behavior of Thermoplastic Starch with Unidirectional and Cross‐Ply Flax Fiber Reinforcements

Thermoplastic starch (MaterBi®) based composites containing flax fibers in unidirectional and crossed‐ply arrangements were produced by hot pressing using the film stacking method. The flax content was varied in three steps, viz. 20, 40 and 60 wt.‐%. Static tensile mechanical properties (stiffness and strength) of the composites were determined on dumbbell specimens. During their loading the acoustic emission (AE) was recorded. Burst type AE signal characteristics (amplitude, width) were traced to the failure mechanisms and supported by fractographic inspection. The mechanical response and failure mode of the composites strongly depended on the flax content and the flax fiber lay‐up. It was established that the tensile strength increases until 40 wt.‐% flax fiber content but stays almost constant above this value. In the case of 40 wt.‐% unidirectional fiber reinforcement, the tensile strength of the composite was 3 times greater than that of the pure starch matrix. The flax fiber reinforcement increased the tensile modulus of the pure starch by several orders of amplitude.

SEM picture of the fracture surface of a composite with UD flax reinforcement.     

Design of a Microfluidic System to Investigate the Mechanical Properties of Layer‐by‐Layer Fabricated Capsules

A microfluidic system was designed, fabricated and implemented to study the behavior of polyelectrolyte capsules flowing in microscale channels. The device contains microchannels that lead into constrictions intended to capture polyelectrolyte microcapsules which were fabricated with the well‐known layer‐by‐layer (LbL) assembly technique. The behavior of hollow capsules at the constrictions was visualized and the properties of the capsules were investigated before and after introduction into the device.

Time series of video frames showing capsules being compressed into a constriction.     

The Solid State Postcondensation of PET, 2

Summary: A process for the solid state polycondensation of PET is proposed. It is shown that by correctly choosing the prepolymerisation conditions it is possible to crystallise the product and to directly polymerise it in a dispersed phase. This process is significantly faster than the “standard” PET processes, and allows one to obtain high molecular weights directly from a prepolymer without the need to use an intermediate solution polymerisation step.

Reactor set‐up for precursor preparation and dispersed phase prepolymerisation.     

Preparation and Properties of Vinylester Resin/Clay Nanocomposites

Summary: Vinylester resin matrix composites were fabricated with 1, 3, 5 and 10 wt.‐% loadings of organoclay. The composite samples were subjected to various characterization techniques like X‐ray diffraction, flexural testing, dynamic mechanical analysis, thermogravimetric analysis, and scanning electron microscopy. The clay samples as well as the clay–resin composites were investigated by X‐ray diffraction. From the shift in the peak positions and the change in d‐spacing values, it was evident that there was intercalation in the 10 wt.‐% composites, whereas exfoliation occurred in the 1, 3, and 5 wt.‐% composites. The flexural strength and the breaking energy of all the composites were decreased compared with the unfilled resin, but there was an increase in flexural modulus value by 13%. From the dynamic mechanical analysis of the 3 and the 5 wt.‐% composites, it was observed that the loss modulus value was higher in the 3 wt.‐% composites, but the glass transition temperature was slightly higher in the 5 wt.‐% composites. Thermal degradation behavior was also improved in the 5 wt.‐% composites compared with the 3 wt.‐% composites.

Fracture surface of 3 wt.‐% clay filled vinylester resin matrix composite in different magnifications.     

Rheology and Physical Characteristics of Synthetic Biodegradable Aliphatic Polymer Blends Dispersed with MWNTs

PLA/PBAT blends and PLA/PBAT/MWNT nanocomposite systems were prepared via a melt mixing process to examine their thermal and rheological properties. To compare the polymer blend/MWNT nanocomposite with a pure polymer/MWNT nanocomposite, PLA/MWNT, PBAT/MWNT, and PLA/PBAT/MWNT nanocomposite systems were prepared. TEM and SEM were used to observe that one phase has better affinity with the MWNT, while the MWNT was found to increase both the thermal properties of the PLA/PBAT blends and rheological properties of the PLA/PBAT/MWNT nanocomposite with distinct shear‐thinning behavior due to the addition of the MWNT. An increase in the storage (G′) and loss (G″) moduli for the PLA/PBT/MWNT nanocomposite was also observed.

     

The Reinforcement of Elastomeric Networks by Fillers

Summary: The mechanisms involved in rubber reinforcement are discussed. A better molecular understanding of these mechanisms can be obtained by combining characterization of the mechanical behavior with an analysis of the chain segmental orientation accompanying deformation. While the strain dependence of the stress is the most common quantity used to assess the effect of filler addition, experimental determination of segmental orientation can be used to quantify the interfacial interactions between the elastomeric matrix and the mineral inclusions.

SEM micrograph of natural rubber containing 10 wt.‐% of organomodified clay.     

Coaxial Electrospinning with Triton X‐100 Solutions as Sheath Fluids for Preparing PAN Nanofibers

Coaxial electrospinning using surfactants as sheath fluid for preparing high‐quality polymer nanofibers is studied. PAN nanofibers are fabricated using this process with Triton X‐100 solutions in DMF. FESEM demonstrates that the Triton X‐100 solution has a significant influence on the quality of the nanofibers. The nanofiber diameters can be controlled by adjusting the concentration of Triton X‐100 in the sheath fluids with a scaling law D = 640 C^?0.32. The mechanism of the influence of Triton X‐100 solutions on the formation of PAN fibers is discussed and it is demonstrated that coaxial electrospinning with surfactant solution is a facile method for achieving high‐quality polymer nanofibers.

     

Gas‐Phase Assisted Surface Polymerization Behavior of β‐Propiolactone on Inorganic and Organic Substrates and Consequent Composite Production

Summary: Gas‐phase assisted surface polymerization (GASP) of β‐propiolactone (βPL) was investigated using substrate‐supported anionic initiators to produce a strongly bonded poly(β‐propiolactone) (PPL)/CaO composite and a novel PPL crystalline deposit with a high melting point value on Al plates. The polymerization of βPL smoothly proceeded in the gas phase to give high‐molecular‐weight PPLs having high PDI values. An almost linear relationship between value and incremental increase in the deposit suggested the living nature of the GASP of βPL. The obtained polymer‐coated substrates, especially PPL/CaO composite, showed strong interaction at the organic/inorganic interface. Moreover, the thermal and structural analyses of deposits revealed that some specific conformations were formed on CaO powder and Al plate surfaces to give highly crystallized deposits. These results demonstrate that the GASP is an effective method for coating any substrate that has a complex shape and a surface morphology.

Accumulation process of poly(β‐propiolactone) on CaO as substrate‐supported initiator during GASP.     

Thermal Degradation Behavior of Poly(propylene) with a Novel Silicon‐Containing Intumescent Flame Retardant

Summary: A novel intumescent flame retardant (PSiNII), containing silicon, phosphorus and nitrogen, has been synthesized and incorporated into poly(propylene) (PP). The flame retardancy of PP/PSiNII, evaluated by the limiting oxygen index (LOI) value, can be enhanced up to 29.5 vol.‐% from 17.4 vol.‐% with 20% total loading amount of PSiNII. The thermal degradation behavior of PP/PSiNII are investigated by thermogravimetric analysis (TGA) under nitrogen and air, and pressure differential scanning calorimetry (PDSC) under 1.5 MPa of oxygen. The PP/PSiNII‐3 degrades at 400 °C for different time, and the process is investigated by FTIR which indicates there is P? O in the char. The morphologies of char formed at 400 °C for 10 min and after LOI test are investigated by scanning electron microscopy (SEM). The morphological structure of the char exhibits the swollen cells in the inner and a smooth outer surface, which do good to the thermal properties and fire performance of PP. The thermal stability of PP is improved by incorporating PSiNII.

Inner surface of PP/PSiNII‐3 after LOI test.     

Static and Dynamic Mechanical Properties of Vinylester Resin Matrix Composites Filled with Fly Ash

Summary: Vinylester resin matrix composites were prepared with a fly ash loading of 30, 40, 50 and 60 wt.‐%. Flexural properties of the composites were investigated. It was found that the flexural strength was lowered in all the filled composites, but the flexural modulus showed a significant increase of 10, 57, 112% in case of 30, 40 and 50 wt.‐% fly‐ash‐loaded composites respectively, compared to the neat resin. However, there was a decrease in the mechanical properties in case of 60 wt.‐% fly‐ash‐filled composites. The dynamic mechanical analysis was carried out to obtain information about the matrix‐filler interaction at the interface. The storage modulus value at room temperature was highest for the 50 wt.‐% fly‐ash‐filled composites, corroborating with the observed flexural modulus value. The fractured surfaces were examined under SEM and were correlated with the mechanical properties.

Large voids evident in the 60 wt.‐% fly‐ash‐filled composites.     

Preparation and Characterization of Conducting Systems based on EPDM/PE/PS‐co‐DVB/HSb

Summary: Blends of different compositions were prepared from: a thermoplastic elastomer (EPDM), a low density polyethylene (PE), a polystyrene crosslinked with a small amount of divinylbenzene (PS‐co‐DVB) and an inorganic proton conductor: antimonic acid (HSb). The blends obtained were sulfonated heterogeneously with chlorosulfonic acid and were then structurally and electrically characterized by means of the following techniques: differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), crystallization kinetics under non‐isothermal conditions and complex impedance spectroscopy.

Dynamic mechanical analysis for EPDM and EP‐3 blends series.