Ternary Blends to Improve Heat Distortion Temperature and Rheological Properties of PVC

Summary: Binary and ternary blends of PVC mixed with α‐methylstyrene/acrylonitrile‐butadiene‐styrene copolymer (AMS‐ABS) and ethylene/vinyl acetate/carbon monoxide terpolymer (EVA‐CO) are investigated, with the aim to obtain a new PVC based material with an improved heat distortion temperature and good processability. Dynamic Mechanical Thermal Analysis (DMTA) reveals that ternary PVC/AMS‐ABS/EVA‐CO blends exhibit two glass transition temperatures: the lower T_g corresponds to a PVC/EVA‐CO phase and the higher one to a PVC/AMS‐ABS phase. An analysis of PVC respective interactions with AMS‐ABS and EVA‐CO leads to assert that the distribution of PVC in the ternary PVC/AMS‐ABS/EVA‐CO system is basically controlled by the binary immiscible blend composition, taken as Φ AMS‐ABS/Φ EVA‐CO ratio. The inclusion of AMS‐ABS and EVA‐CO to form ternary blends based on PVC, allows to improve heat distortion temperature (owed to the presence of AMS‐ABS), maintaining a low viscosity in the molten state, due to the plasticizing effect of EVA‐CO.

Viscosity function obtained at T = 170 °C from extrusion capillary measurements.     

Ternary Gels of a Polymer Blend and a Recycled Oil: Their Use as Bitumen Modifiers

A blend of random ethylene‐vinyl acetate copolymer (EVA) and triblock styrene‐butadiene‐styrene copolymer (SBS) was dissolved in a recycled engine oil to obtain ternary thermoreversible gels. As the temperature was increased, first a network associated with EVA disappeared, and a second one associated with SBS dominated, maintaining the elastic response of the system. The principal advantage of these ternary systems is that their mechanical properties and thermal stability are better than that of binary gels. These gels, made from waste, can be used as bitumen modifiers to obtain binders of improved properties and good stability, which are useful for road surfacing.

Temperature sweeps of elastic modulus performed at a frequency of 1 Hz.     

Layered Silicate‐Induced Enhancement of Fracture Toughness of Epoxy Molding Compounds over a Wide Temperature Range

Summary: The fracture toughness of EMC was dramatically increased over a wide temperature range by the addition of a very low volume fraction of layered silicates to EMC filled with micro‐silica particles. Layered silicate‐EMC nanocomposites containing intercalated and the exfoliated silicates were fabricated by using o‐cresol and biphenyl type epoxy resins, respectively. It was found that exfoliated silicates were more effective than intercalated silicates at toughening EMC at temperatures above T_g of the epoxy resin. Enhanced fracture toughness of EMC over a wide temperature range, from ambient to 230 °C has been attributed to the presence of layered silicates, which induces macroscopic crack deflection and severe plastic deformation in front of the crack tip.

     

Heat Induced Structure Modifications in Polymer‐Layered Silicate Nanocomposites

Summary: The success of the use of layered silicates in polymer nanocomposites, to improve physical and chemical properties is strictly related to a deeper knowledge of the mechanistic aspects on which the final features are grounded. This work shows the temperature induced structural rearrangements of nanocomposites based on poly[ethylene‐co‐(vinyl acetate)] (EVA) intercalated‐organomodified clay (at 3–30 wt.‐% silicate addition) which occur in the range between 75 and 350 °C. In situ high temperature X‐ray diffraction (HT‐XRD) studies have been performed under both nitrogen and air to monitor the modifications of the nanocomposite structure at increasing temperatures under inert/oxidative atmosphere. Heating between 75 and 225 °C, under nitrogen or air, causes the layered silicate to migrate towards the nanocomposite surface and to increase its interlayer distance. The degradation of both the clay organomodifier and the VA units of the EVA polymer seems to play a key role in driving the evolution of the silicate phase in the low temperature range. The structural modifications of the nanocomposites in the high temperature range (250–350 °C), depended on the atmosphere, either inert or oxidizing, in which the samples were heated. Heating under nitrogen led to deintercalation and thus a decrease of the silicate interlayer space, whereas exfoliation was the main process under air leading to an increase of the silicate interlayer space.

Heat induced structural modification of EVA‐clay nanocomposite under nitrogen and air.     

Modification of Rheological Properties Under Elongational Flow by Addition of Polymeric Fine Fibers

A new technique to provide melt elasticity using flexible fine fibers prepared from a polymer with high melting point is demonstrated. A polymer composite of poly(propylene) with a small amount of fine fibers of poly(butylene terephthalate) shows marked strain‐hardening behavior in elongational viscosity, i.e., a rapid increase in the transient elongational viscosity with time or strain. The blend also shows prominent normal stress difference at steady shear. These elastic properties have not been observed for polymer composites with rigid fibers and can be applicable to the modification of rheological properties and thus the improvement of processability.

     

Study of the Fire Performance of Magnesium Hydroxide Sulfate Hydrate Whisker Flame Retardant Polyethylene

Summary: Halogen‐free, flame retardant low density polyethylene (LDPE) composites, using magnesium hydroxide sulfate hydrate (MHSH) whiskers as a flame retardant, combined with microencapsulated red phosphorous (MRP) as a synergist, have been prepared using a two‐roll mill. Their fire properties were determined by using the limiting oxygen index (LOI), the UL‐94 test and cone calorimetry. The results showed that MRP was a good synergist in improving the flame retardance of the LDPE/MHSH whisker system. Poly[ethylene‐co‐(vinyl acetate)] (EVA), used as a compatibilizer, increased the fire performance of LDPE/MHSH whisker composites.

HRR curves for LDPE/MHSH whisker composites.     

New Polylactide/Layered Silicate Nanocomposites, 6

The measurement of rheological properties of any polymeric material under molten state is crucial to gain fundamental understanding of the processability of that material. In the case of polymer/layered silicate nanocomposites, the measurements of rheological properties are not only important to understand the knowledge of the processability of these materials, but is also helpful to find out the strength of polymer‐layered silicate interactions and the structure‐property relationship in nanocomposites. This is because rheological behaviors are strongly influenced by their nanoscale structure and interfacial characteristics. In order to get this knowledge in the case of polylactide/montmorillonite nanocomposites, we have studied melt rheological properties of these materials in detail. On the basis of rheological data, we have conducted foam processing of pure polylactide and one representative nanocomposite by a newly developed pressure cell technique using carbon dioxide as a physical‐blowing agent.

The time variation of the elongational viscosity of one of the intercalated polylactide/montmorillonite nanocomposites.     

Exertion of Inhibiting Effect by Aluminosilicate Layers on Swelling of Solution Blended EVA/Clay Nanocomposite

Summary: Ethylene vinyl acetate (EVA) copolymer/dodecyl ammonium ion intercalated montmorillonite (12Me‐MMT) nanocomposites were swelled in xylene under atmospheric condition. Swelling index of these nanocomposites decreased with filler loading indicating that the solvent uptake of these nanocomposites was inversely related to the filler contents. The volume fractions of nanocomposites showed an increasing trend with filler concentration because of unswelling effect exerted by aluminosilicate layers. The cross‐link density was determined using the Flory‐Rehner equation and it was observed that the cross‐link density of these nanocomposites also showed an increasing trend with increasing filler loading. Free energy change (ΔG_mix) and the change in entropy (ΔS_mix) on swelling of EVA/12Me‐MMT nanocomposites in xylene were calculated and these values reaffirmed that the interaction between polymer chains and silicate layers was very strong which induced remarkable inhibiting ability on EVA matrix when swelled in xylene.

TEM photograph of EVA/12Me‐MMT nanocomposite containing 8 wt.‐% 12Me‐MMT.     

Environmental Stress‐Cracking Resistance of LDPE/EVA Blends

Blends of low‐density polyethylene with random copolymers of ethylene and vinyl acetate (PE/EVA) are studied with respect to their environmental stress‐cracking resistance (ESCR) using the Bell‐telephone test. This system shows the shortest time to failure in the ESCR test after annealing at 50 °C in a stress‐cracking agent (Igepal solution) compared with that in the tests conducted at 30 and 70 °C. The increase of the time to failure at 70 °C as compared with that at 50 °C is probably the result of the semicrystalline proportion of EVA melting. Transmission electron microscopy images (see Figure) reveal that EVA particles are molten and deformed in bending direction of the sample at 70 °C in contrast to samples annealed at 50 and 30 °C. TEM pictures of a failed sample during the test conducted at 50 °C indicate that EVA particles can stop crack propagation.

TEM image of PE/EVA‐5.4 after 1 000 h in ESCR test conditions at 70 °C.     

Thermal‐ and Sun‐Promoted Generation of Silver Nanoparticles Embedded into Poly(vinyl alcohol) Films

Nanocomposites based on poly(vinyl alcohol) and silver nanoparticles were efficiently prepared by sun‐ and thermal‐promoted reduction processes. Uniaxial drawing of the Ag/PVA nanocomposites favoured the anisotropic distribution of silver particles, providing oriented films with polarisation‐dependent tunable optical properties. These dichroic properties were more pronounced for nanocomposites produced by sun exposition, which provided more compact and interacting metal clusters. The results obtained suggest the nanocomposite films could find potential applications as colour polarising filters, radiation responsive polymeric objects and smart flexible films in packaging applications.

     

Thermo‐Physical and Impact Properties of Epoxy Containing Epoxidized Linseed Oil, 2

Summary: Biobased neat epoxy materials containing epoxidized linseed oil (ELO) were processed with an amine curing agent. A defined amount of diglycidyl ether of bisphenol F (DGEBF) was replaced by ELO. The thermophysical properties of the amine‐cured biobased neat epoxy were measured by dynamic mechanical analysis (DMA). The Izod impact strength increased with an increase in the amount of ELO added. The change in the Izod impact strength was correlated with the thermophysical properties measured by DMA.

Relation between the Izod impact strength and loss factor for amine‐ and anhydride‐cured ELO‐containing epoxy resins.     

Enhanced Properties of Dissimilar Rubber Blends Using Microencapsulated Sulfur Through Acetylene Plasma Polymerization

Surface modification of sulfur by vacuum plasma polymerization with acetylene was applied in order to modify its surface properties without losing reactivity for vulcanization. A nm‐thin layer of crosslinked polyacetylene was deposited on the surface of the sulfur powder. Its surface energy was decreased as monitored by wetting in liquids of various polarities. A delay in the onset of weight loss by sublimation in thermal gravimetric analysis was shown by the plasma‐modified sulfur. Scanning electron microscopy showed a core/shell structure of the coated sulfur. In 50:50 blends of styrene‐butadiene rubber and ethylene‐propylene‐diene rubber, the encapsulated sulfur samples resulted in pronounced improvements in the mechanical properties relative to the use of unmodified sulfur.

     

Binary and Ternary mLLDPE Blends: Tailoring Their Properties Using Complex Viscosity Measurements

Summary: Metallocene‐catalysed linear low density polyethylenes (mLLDPEs) of different molecular weights are mixed with a base mLLDPE to obtain a pre‐determined grade and a suitable extrusion processability. Complex viscosity results are revealed as a very suitable tool to tailor the properties of the prepared binary and ternary blends. The investigated blends show symptoms of miscibility like time‐temperature superposition and observance of Cox‐Merz rule. This allows to evaluate the molecular weight distribution, supplying also practical data related to the polyethylene grade and ‘sharkskin’ instability. The complex viscosity curve of a model sample that would have both, a suitable grade and processability, is created; blends are prepared to match the model curve. The blend with a low molecular weight mLLDPE shows a parallel shift of the complex viscosity to lower values (molecular weight distribution is not broadened), postponing sharkskin, but changing the polymer grade. Satisfactory results are neither obtained with blends of a high molecular weight mLLDPE. Best results are obtained with ternary blends, which combine the modifications provided by low and high molecular weight mLLDPEs, approaching the complex viscosity and molecular weight distribution of the model.

Complex viscosity results of PR‐207 (– —), PR‐209 (···) and PR‐210 (– –) ternary blends, as compared with those of base samples PR‐201 (symbols) and the model (line).     

Nanocomposites Based on Polyethylene and Polyhedral Oligomeric Silsesquioxanes, 1 – Microstructure,Thermal and Thermomechanical Properties

Nanocomposites of linear low‐density polyethylene (LLDPE), with three different amounts of polyhedral oligomeric silsesquioxanes (POSS), were prepared through melt‐mixing in a batch‐mixer at 150 °C. The structure of the prepared nanocomposites was studied by X‐ray scattering and optical microscopy. The surface morphology of the nanocomposites was investigated through field‐emission SEM. The thermal properties of the pure LLDPE and nanocomposites were studied by differential scanning calorimeter (DSC). Thermomechanical properties were assessed on a Paar‐Physics MCR501 rheometer using a solid‐state rectangular fixture. Results exhibited a significant improvement in both the storage and loss moduli of the neat LLDPE upon the incorporation of the POSS particles. A substantial improvement in thermal stability was also observed in the high‐temperature region.

     

Synthesis and Characterisation of Anhydride‐Cured Epoxy Nanocomposites Containing Layered Silicates Modified with Phenolic Alkylimidazolineamide Cations

Summary: Phenolic alkylimidazolineamides were prepared and applied as modifiers in order to render layered silicates organophilic and to prepare polymeric nanocomposites. The imidazolineamine, 2‐{2‐[heptadec‐8‐enyl]‐4,5‐dihydro‐1‐imidazol‐1‐yl}‐1‐ethaneamine (IA), was reacted in bulk with one of the two phenolic compounds, ethyl 4‐hydroxybenzoate (P) or methyl 3‐[3,5‐di(tert‐butyl)‐4‐hydroxyphenyl]propionate (HP), which is an intermediate for antioxidants, to prepare the two phenolic imidazolineamides, PIA and HPIA. During protonation in water, both phenolic imadazolineamides were used successfully to exchange interlayer sodium cations of sodium bentonite and fluorohectorite, thus producing organophilic layered silicates with an increased interlayer distance of around 3.3 nm. The new phenolic organophilic layered silicates represent a novel class of phenolic organic/inorganic hybrid materials. They were applied as fillers in hexahydrophthalic anhydride‐cured bisphenol‐A diglycidyl ether (BADGE). Thermal analysis (DSC), transmission electron microscopy (TEM), wide angle X‐ray scattering (WAXS), and mechanical tests were used to evaluate the thermal, mechanical, and morphological properties. Although fracture toughness, measured as the stress intensity factor, K_Ic, and the energy release rate, G_Ic, increased by around 50% with increasing silicate content without sacrificing glass temperature, both tensile strength and Young's modulus increased only marginally. Low matrix reinforcement was attributed to inadequate compatibility matching, as evidenced by the slightly lower interlayer distances of the layered silicates encapsulated in the epoxy matrix.

Representative TEM micrographs of the sample ER‐bent‐PIA/10.     

Oxygen Barrier Properties of Poly(ethylene terephthalate) Nanocomposite Films

Nanocomposites of poly(ethylene terephthalate) and two different montmorillonite‐based organoclays were prepared by a co‐rotating twin screw extruder. Dispersion of nanoclays in the polymer matrix was examined by TEM and XRD. Nanocomposites with lower content of organoclay showed exfoliated morphology while by increasing the amount of organoclay the intercalated morphology was more prevalent. Both organoclays had a good intercalation with PET and were uniformly dispersed within the polymer. Oxygen permeability of thin films of nanocomposites showed that the nanocomposites had better oxygen barrier properties than the neat PET. Tensile and impact properties of the nanocomposites also were measured.

     

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.     

Compressible Magnetorheological Fluids Based on Composite Polyurethane Microspheres

A novel CMRF is synthesized from modified silicone oil, containing composite polyurethane microsphere additives, and surface‐coated iron particles. The CMRF is designed to act as a liquid spring with controllable damping properties in a damper system. The fluid compressibility is characterized by force/displacement measurements. The addition of composite polyurethane‐microspheres increases the strength and compressibility of the fluid. It also decreases the concentration of iron particles needed in order to achieve the same yield stress as commercially available MRF. Surface coating surface of the iron particles with poly(2,3,4,5,6‐pentafluorostyrene) via RAFT provides dispersion stability.

     

Segmented Block Copolymers with Monodisperse Hard Segments: The Influence of H‐Bonding on Various Properties

The properties of segmented‐copolymer‐based H‐bonding and non‐H‐bonding crystallisable segments and poly(tetramethylene oxide) segments were studied. The crystallisable segments were monodisperse in length and the non‐hydrogen‐bonding segments were made of tetraamidepiperazineterephthalamide (TPTPT). The polymers were characterised by DSC, FT‐IR, SAXS and DMTA. The mechanical properties were studied by tensile, compression set and tensile set measurements. The TPTPT segmented copolymers displayed low glass transition temperatures (T_g, ?70 °C), good low‐temperature properties, moderate moduli (G′ ≈ 10–33 MPa) and high melting temperatures (185–220 °C). However, as compared to H‐bonded segments, both the modulus and the yield stress were relatively low.

     

Processability and Properties of Re‐Graded,Photo‐Oxidized Post‐Consumer Greenhouse Films

Summary: The recycling of post‐consumer plastics leads, in general, to secondary materials having properties worse than those of the reclaimed material and certainly worse than those of the same virgin polymer. This is because of the degradation undergone by the objects during their use and because of the thermo‐mechanical degradation undergone during the reprocessing operations. The change of the molecular architecture is responsible for this worsening of properties. The use of stabilizing systems can slow the degradation during the melt processing but cannot give any improvement of the final properties of the material. In order to enhance the properties of the recycled plastics, some rebuilding of the molecular structure is necessary. The use of suitable additives can enlarge the molecular weight distribution or can create branching and cross‐linking during the melt processing of the photo‐oxidized PE. The processability in film blowing and the mechanical properties of these secondary materials are reported in this work. The rheological behavior, the filmability and most of the mechanical properties of the secondary PE with the rebuilt molecular structure are better than those of the post‐consumer material and similar to those of the virgin polymer.

TS in the machine and in the transverse direction for all the samples extruded at 50 rpm.