Enhanced fracture energy during deformation through the construction of an alternating multilayered structure for polyolefin blends

The effects of polymer blend components on the phase morphology, crystallization behavior and mechanical performance of materials processed by high speed thin‐wall injection molding (HSTWIM) and compression molding (CM) processes were investigated. High density polyethylene (HDPE) and polypropylene (PP) containing different ratios of rubber phase (0%, 18% and 21%) were selected to construct different blends. HSTWIM is shown to trigger the formation of a multilayered structure for these blends with oriented polymer crystals and epitaxial growth of HDPE crystals on PP. Such a layered structure is thought to provide a good template for morphological control of various functional polymer composites. Moreover, the addition of rubber in the multilayered structure with the rubber phase partially distributed between layers is observed. These issues are thought to be responsible for the much enhanced fracture energy compared with specimens from CM. The structural details and formation mechanism of these layered structures consisting of different compositions were investigated. Such a study could provide some guidelines for the preparation of high performance bio‐mimic materials or various functional polymer composites with alternating multilayered structure. © 2018 Society of Chemical Industry     

Processing and properties of polymeric nano‐composites

Polymeric nano‐composites are prepared by melt intercalation in this study. Nano‐clay is mixed with either a polymer or a polymer blend by twin‐screw extrusion. The clay‐spacing in the composites is measured by X‐ray diffraction (XRD). The morphology of the composites and its development during the extrusion process are observed by scanning electron microscopy (SEM). Melt viscosity and mechanical properties of the composites and the blends are also measured. It is found that the clay spacing in the composites is influenced greatly by the type of polymer used. The addition of the nano‐clay can greatly increase the viscosity of the polymer when there is a strong interaction between the polymer and the nano‐clay. It can also change the morphology and morphology development of nylon 6/PP blends. The mechanical test shows that the presence of 5–10 wt.% nano‐clay largely increases the elastic modulus of the composites and blends, while significantly decreases the impact strength. The water absorption of nylon 6 is decreased with the presence of nano‐clay. The effect of nano‐clay on polymers and polymer blends is also compared with Kaolin clay under the same experimental conditions.     

Effect of blend ratio on the dynamic mechanical and thermal degradation behavior of polymer–polymer composites from low density polyethylene and polyethylene terephthalate

Microfibrillar polymer–polymer composites (MFCs) based on low-density polyethylene (LDPE) and polyethylene terephthalate (PET) were prepared by cold drawing-isotropization technique. The weight percentage of PET was varied from 5 to 45 %. Microfibrils with uniform diameter distribution were obtained at 15 to 25 wt% of PET as evident from the scanning electron microscopy (SEM) results. Dynamic mechanical properties such as storage modulus (E′), loss modulus (E″) damping behavior (tan δ) were examined as a function of blend composition. The E′ values were found to be increasing up to 25 wt% of PET. An effort was made to model the storage modulus and damping characteristics of the MFCs using the classical equations used for short-fiber reinforced composites. The presence of PET microfibrils influenced the damping characteristics of the composite. The peak height at the β-transitions of loss modulus was lower for MFCs with 25 % PET, showing that they had superior damping characteristics. This phenomenon could be correlated with the PET microfibrils morphology. The thermal degradation characteristics of LDPE, neat blends and microfibrillar blends (MFBs) were compared. The determination of activation energy for thermal degradation was carried out using the Horowitz and Metzger method. The activation energy for thermal degradation of microfibrillar blends was found to be higher than that for the corresponding neat blends and MFCs. The long PET microfibrils present in MFBs could prevent the degradation and enhance the activation energy.     

The Effect of Antibacterial Particle Incorporation on the Mechanical Properties,Biodegradability, and Biocompatibility of PLA and PHBV Composites

The composites based on polylactide (PLA) and poly (3‐hydroxybutyrate‐co‐3‐hydroxyvalerate) (PHBV) with the addition of antibacterial particles: silver (Ag) and copper oxide (CuO) are characterized. Basic mechanical properties and biodegradation processes, as well as biocompatibility of materials with human cells are determined. The addition of Ag or CuO to the polymers do not significantly affect their mechanical properties, flammability, or biodegradation rate. However, several differences between the base materials are observed. PLA‐based composites have higher tensile and impact strength values, while PHBV‐based ones have a higher modulus of elasticity, as well as better mechanical properties at elevated temperatures. Concerning biocompatibility, each of the tested materials support the growth of fibroblasts over time, although large differences are observed in the initial cell attachment. The analysis of hydrolytic degradation effects on the structure of materials shows that PHBV degrades much faster than PLA. The results of this study confirm the good potential of the investigated biodegradable polymer composites with antibacterial particles for future biomedical applications.     

Curing behavior,mechanical properties,intermolecular interaction,and morphology of silicone/polypyrrole/polymer electrolyte composites

The curing behavior, mechanical properties, intermolecular interaction, and morphology of silicone, polypyrrole, and polymer electrolyte composites were studied. A rigid‐body pendulum rheometer was used to determine the curing behavior of silicone/PEL blends. The polymer structure was evaluated using FTIR and Differential Scanning Calorimetery. The mechanical properties, including stress, strain, and hardness, were measured using a material testing system. The morphology of the composites was measured using scanning electron micrographs. The intermolecular interaction of the composites was measurement using dynamic mechanical analysis. The results show that the curing reaction rate is fast upon addition of 10 wt % of polymer electrolyte for silicone. The linear molecular structure of the polymer electrolyte was wound around the silicone polymer network structure forming a semi‐interpenetrating network. The intermolecular interaction was influenced by the composites, and the Ppy film effect on the surface of SP10 blends is more uniform than that of silicone. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 2754–2764, 2006     

Preparation,structural development,and mechanical properties of microfibrillar composite materials based on polyethylene/polyamide 6 oriented blends

The preparation of microfibrillar composites (MFCs) based on oriented blends of polyamide 6 (PA6) and high‐density polyethylene (HDPE) is described. By means of conventional processing techniques, the PA6 phase was transformed in situ into fibrils with diameters in the upper nanometer range embedded in an isotropic HDPE matrix. Three different composite materials were prepared through the variation of the HDPE/PA6 ratio with and without a compatibilizer: MFCs reinforced by long PA6 fibrils arranged as a unidirectional ply; MFCs containing middle‐length, randomly distributed reinforcing PA6 bristles; and a nonoriented PA6‐reinforced material in which the PA6 phase was globular. The evolution of the morphology in the reinforcing phase (e.g., its visible diameter, length, and aspect ratio) was followed during the various processing stages as a function of the blend composition by means of scanning electron microscopy. Synchrotron X‐ray scattering was used to characterize selected unidirectional ply composites. The presence of transcrystalline HDPE was demonstrated in the shell of the reinforcing PA6 fibrils of the final MFCs. The impact of the compatibilizer content on the average diameter and length of the fibrils was assessed. The influence of the reinforcing phase on the tensile strength and Young's modulus of the various composites was also evaluated. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

γ‐Radiation‐treated starch/poly(vinyl alcohol) composites for cotton fabric sizing

Films of different composites based essentially on maize starch (MS)/poly(vinyl alcohol) (PVA) blends were prepared by the solution‐casting technique and subjected to various doses (20–100 kGy) of γ‐radiation. The MS/PVA blends were modified by the addition of glycerol (GY) and a graft copolymer (GP) of MS with acrylamide separately or together with the polymer blend solutions before casting. The γ‐treated composites were evaluated in terms of the apparent viscosity and their suitability as sizing materials for cotton fabrics. The sizeability of these composites for cotton fabrics was assessed in terms of the size removal percentage at different temperatures and the effect on the tensile properties and water absorption. The change in the apparent viscosity with the shear rate showed that γ‐irradiation improved the behavior of MS/PVA blends and their composites with GY or GP as a sizing material for cotton fabrics. Moreover, the improvement in the tensile mechanical properties of the sized cotton fabrics with these composites gave further support to this finding. The results for the size removal percentage and water adsorption indicated that these composites could be removed by washing at 70°C for 10 min. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 91: 3818–3826, 2004     

Structure and properties of phase change materials based on HDPE,soft Fischer‐Tropsch paraffin wax,and wood flour

Phase‐change materials based on high density polyethylene (HDPE), soft Fischer‐Tropsch paraffin wax (M3), and alkali‐treated wood flour (WF) were investigated. The blend and composite samples were prepared by melt mixing using a Brabender Plastograph, followed by melt pressing. They were characterized in terms of their morphology, as well as thermal, mechanical, thermo‐mechanical, and water absorption properties. Although SEM micrographs showed some evidence of intimate contact between the WF particles and the HDPE matrix as a result of alkali treatment, poor filler dispersion, and interfacial adhesion were also observed. Partial immiscibility of the HDPE and the M3 wax was noticed, with the WF particles covered by wax. There was plasticization of the HDPE matrix by the wax, as well as partial cocrystallization, inhomogeneity and uneven wax dispersion in the polymer matrix. The HDPE/WF/M3 wax composites were more homogeneous than the blends. The presence of wax reduced the thermal stability of the blends and composites. Both the presence of M3 wax and WF influenced the viscoelastic behavior of HDPE. The HDPE/M3 wax blends showed an increase in the interfacial amorphous content as the wax content increases, which resulted in the appearance of a β‐relaxation peak. The presence of M3 wax in HDPE reduced the mechanical properties of the blends. For the composites these properties varied with WF content. An increase in wax content resulted to a decrease in water uptake by the composites, probably because the wax covered the WF particles and penetrated the pores in these particles. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Some aspects of preparation methods and properties of polyaniline blends and composites with organic polymers

Interest in applications for polyaniline (PANI) has motivated investigators to study its mechanical properties, the thermostability of its conductivity, its processibility, etc. and its use in polymer composites or blends with common polymers. As a result, several methods to produce composites/blends containing PANI have been developed, allowing the preparation of a wide spectrum of such materials. Here, generalized approaches for the preparation of such materials are reviewed. Specifically, we consider two distinct groups of synthetic methods based on aniline polymerization either (1) in the presence of or inside a matrix polymer or (2) the blending of a previously prepared PANI with a matrix polymer. Some aspects of these methods are analyzed, emphasizing features that determine properties of the final composites/blends.     

Chitin/polyurethane blends: a thermal and morphological study

Chitin is an abundant natural polymer having important properties such as biocompatibility and biodegradability combined with healing capability. Its use in biomedical applications has been hindered by its poor processing properties such as low solubility and stiffness in the solid state. In an attempt to obtain flexible and more processable chitin‐based materials, we prepared blends of the polymer with a polyurethane containing a soft segment based on biodegradable polycaprolactone. A certain degree of miscibility was found between chitin and the polyurethane, as demonstrated by a shift in the glass transition of the polyurethane observed in dynamical mechanical analyses, with a simultaneous decrease in crystallinity of chitin observed in X‐ray diffraction analyses. A phase inversion of the blends took place for a 50/50 (w/w) composition ratio as demonstrated from thermal, dynamic mechanical, tensile and X‐ray diffraction measurements. Blends of chitin with the polycaprolactone‐based polyurethane can be effectively used to produce tough materials useful in biomedical applications. The mechanical strength of the blends demonstrated that they are able to support tensions above those required for bone replacement, making them good candidates for that purpose. Copyright © 2010 Society of Chemical Industry     

Next generation high‐performance carbon fiber thermoplastic composites based on polyaryletherketones

Interest in carbon fiber reinforced composites based on polyaryl ether ketones (PAEKs) continues to grow, and is driven by their increasing use as metal replacement materials in high temperature, high‐performance applications. Though these materials have seen widespread use in oil, gas, aerospace, medical and transportation industries, applications are currently limited by the thermal and mechanical properties of available PAEK polymer chemistries and their carbon fiber composites as well as interfacial bonding with carbon fiber surfaces. This article reviews the state of the art of PAEK polymer chemistries, mechanical properties of their carbon fiber reinforced composites, and interfacial engineering techniques used to improve the fiber‐matrix interfacial bond strength. We also propose a roadmap to develop the next generation of high‐performance long fiber thermoplastic composites based on PAEKs. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44441.     

Formulation of new synthetic binders: Thermomechanical properties of resin/recycled polymer blends

Synthetic binders are special paving materials manufactured by mixing polymers, resins, and oils. These materials may have improved mechanical properties as compared with the traditional modified bitumen. This work is part of a comprehensive study on the design of synthetic binders with selected mechanical properties. In this sense, upgraded mechanical properties of the final synthetic binder can be attained by understanding and correlating the mechanical properties of its individual constituents as a function of composition and temperature. With this aim, this work deals with the thermomechanical properties of recycled polymer/resin blends, over a wide range of temperature and composition. Recycled polymer/resin blends are thermorheologically complex materials, due to the development of multiphase domains depending on polymer concentration. Thus, these blends show a predominantly gel‐like behavior at high polymer concentrations and a predominantly viscous behavior, with high thermal susceptibility, for low polymer concentrations. The dynamic viscosities of the blends, as a function of polymer concentration and temperature, can be predicted using a logarithmic mixing rule. POLYM. ENG. SCI., 2012. © 2011 Society of Plastics Engineers     

Structure and properties of phase‐change materials based on high‐density polyethylene,hard Fischer–Tropsch paraffin wax,and wood flour

Phase‐change materials based on high‐density polyethylene (HDPE), a hard Fischer–Tropsch paraffin wax (H1 wax), and alkali‐treated wood flour (WF) were investigated. The blends and composites were prepared by melt‐mixing. They were characterized in terms of their morphology as well as thermal, mechanical, thermomechanical, and water absorption properties. Although the scanning electron microscopy micrographs showed some evidence of intimate contact between WF and the HDPE matrix, there were poor filler dispersion and interfacial adhesion. The percentage miscibility of H1 wax in HDPE seems to have decreased with increasing wax content in the blends. A fairly strong affinity between the WF and H1 wax was noticed. There was plasticization of the HDPE matrix by the wax as well as inhomogeneity and uneven wax dispersion within the polymer matrix. The presence of H1 wax and WF influenced the crystallization behavior of the HDPE matrix. The incorporation of wax reduced the thermal stability of the blends and composites, but stabilized the WF. The H1 wax and WF differently influenced the viscoelastic properties of the HDPE matrix. In contrast to the blends where the tensile properties improved in the presence of wax, the composites showed poorer properties. An increase in wax content resulted in a decrease in water uptake by the composites. POLYM. COMPOS., © 2011 Society of Plastics Engineers.     

Recycled milk pouch and virgin LDPE‐LLDPE‐based jute fiber composites

The present investigation deals with the thermo‐mechanical recycling of post consumer milk pouches (LDPE‐LLDPE blend) and its use as jute fiber composite materials for engineering applications. The mechanical, thermal, morphological, and dynamic‐mechanical properties of recycled milk pouch‐based jute fiber composites with different fiber contents were evaluated and compared with those of the virgin LDPE‐LLDPE/jute fiber composites. Effect of artificial weathering on mechanical properties of different formulated composites was determined. The recycled polymer‐based jute fiber composites showed inferior mechanical properties as well as poor thermal stability compared to those observed for virgin polymer/jute fiber composites. However, the jute‐composites made with (50:50) recycled milk pouch‐virgin LDPE‐LLDPE blend as polymer matrix indicated significantly superior properties in comparison to the recycled milk pouch/jute composites. Overall mechanical performances of the recycled and virgin polymeric composites were correlated by scanning electron microscopy (SEM). The dynamic mechanical analysis showed that storage modulus values were lower for recycled LDPE‐LLDPE/jute composites compared to virgin LDPE‐LLDPE/jute composites throughout the entire temperature range, but an increase in the storage modulus was observed for recycled‐virgin LDPE‐LLDPE/jute composites. POLYM. COMPOS. 28:78–88, 2007. © 2007 Society of Plastics Engineers     

A review of the research and advances in electromagnetic joining of fiber‐reinforced thermoplastic composites

The demand for polymer composites in structural and nonstructural applications has expanded rapidly due to their lightweight, high strength, and stiffness characteristics. Joining of polymer composite is not an easy task as inadequate joint strength leads to failure of a structure due to stress concentration. The following are the three basic methods available for joining of thermoplastic composites: adhesive joining, mechanical fastening, and fusion bonding. Electromagnetic joining is a class of fusion bonding where electromagnetic force is used for generation of heat. Electromagnetic joining has gained new interest among the research fraternity with the development of thermoplastic composites. This type of joining or welding technique offers many advantages over other joining techniques. This joining technique can be used for assembly as well as repairing of thermoplastic polymer‐based composites parts. The main aim of this article is to review the different electromagnetic joining methods for thermoplastic composites and present the recent developments in this area. The electromagnetic joining methods such as induction welding, microwave welding, and resistance welding have been comprehensively discussed in the context of their applicability for joining of thermoplastic polymer‐based composites. POLYM. ENG. SCI., 59:1965–1985, 2019. © 2019 Society of Plastics Engineers     

Examining chemical structure at the interface between a polymer binder and a pharmaceutical crystal with neutron reflectometry

The mechanical properties of many composites are determined in part by the chemical structure and bonding at the interface between constituents in the microstructure. The study of these interfaces in molecular crystal - polymer composites is difficult using traditional techniques such as electron microscopy or X-ray scattering because of weak or detrimental interactions between the probe and materials. Here, the interface between acetaminophen and a poly(ester urethane) copolymer is analyzed using ellipsometry, infrared spectroscopy, and neutron reflectometry. These materials were chosen for their relevance to pharmaceutical tablets and plastic-bonded explosives. The acetaminophen was shown to dissolve into the polymer coating and creates an interphase region between the two materials; this mixing is almost certainly produced by typical formulation conditions, and likely affects mechanical response of the composite. Additionally, reflectometry shows that plasticizing the polymer alters this interphase region. These techniques can be applied to similar composites to reveal the relation between formulation conditions, constituent interface microstructure characteristics, and bulk mechanical response.     

The effect of γ‐Irradiation and reactive extrusion on the structure and properties of polycarbonate and starch blends: A work oriented to the recycling of thermoplastic wastes

Polymer materials with improved properties can be obtained through polymer blends. As a polymer mixture is generally immiscible and incompatible, it is necessary to develop new methods to improve the interfacial adhesion. In this study, polycarbonate‐based extruded thermoplastic were developed by blending polycarbonate with thermoplastic starch using extensive process engineering based on structure–property correlations. Starch was destructurized and plasticized followed by melt‐blending with polycarbonate. The optimal conditions for processing of the thermoplastics blends were found to be 230°C, 2 min of processing time, and 3–6 wt % of glycerol. The effect of γ‐irradiation on the fabrication of the blend was studied. Changes in structure, morphology, and properties resulting from γ‐exposure in the range 0–150 kGy were investigated. Electron spin resonance results revealed that numerous radicals remained trapped in the materials after irradiation even after a long time enabling reactions between starch and polycarbonate. Results obtained from tensile test, differential scanning calorimetry, and dynamic mechanical analysis revealed the relatively good affinity between the two components after blending in a micro‐extruder. Irradiated blends are thermally more stable than those non‐irradiated. Mechanical tests also showed that the efficiency of the irradiation depended greatly on the dose applied to the initial materials. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Molecular dynamics simulation of mechanical properties and interaction energy of polythiophene/polyethylene/poly(p‐phenylenevinylene) and CNTs composites

Carbon nanotubes (CNTs) have very important applications in ultrastrong lightweight materials. CNTs can improve mechanical properties of polymer matrix such as breaking stress and Young's modulus. In this article, we studied the interaction between polythiophene (PT)/polyethylene (PE)/poly(p‐phenylenevinylene) (PPV) and CNTs by molecular dynamics (MD) simulation based on a reactive force field (ReaxFF). We studied the influence of CNT diameter, polymer type, and temperature on interaction energy. We found that a large radius CNT at low temperature shows the strongest interaction energy with PT. In addition, we computed the mechanical properties of CNTs‐polymer composites such as the breaking stress, breaking strain, and Young's modulus. Our results show that there is a direct relation between mechanical properties and interaction energy. We found that the mechanical properties of CNTs‐PT composite are better than CNTs‐PPV and CNTs‐PE and it is a good candidate for ultrastrong lightweight materials. We studied the influence of temperature on the mechanical properties. Our results show that CNTs‐polymer composites show stronger mechanical properties at low temperature. We found that ReaxFF can reproduce the other force fields results and it is a very powerful force field to study the various properties of CNTs‐polymer composites. POLYM. COMPOS., 35:2261–2268, 2014. © 2014 Society of Plastics Engineers     

Wear and mechanical properties of reactive thermotropic liquid crystalline polymer/unsaturated polyester/glass fiber hybrid composites

To improve the performance of unsaturated polyester (UP) under cold‐heat alternate temperature, self‐synthesized reactive thermotropic liquid crystalline polymer (TLCP)‐methacryloyl copolymer (LCMC), UP, and glass fiber (GF) hybrid composites was prepared by molding technology. The apparent activation energy and crystal behavior analysis of LCMC/UP blends were investigated by Differential scanning calorimetry and X‐ray diffraction (XRD), respectively, the results showed that the addition of LCMC can reduce apparent activation energy and accelerate the curing reaction of UP, the XRD analysis indicated that the crystal phase of LCMC still exist in the blends after blending with UP. The effect of LCMC content on the properties of LCMC/UP/GF hybrid composites such as impact strength, bending strength, and ring‐on‐block wear were also investigated through static mechanical tests and wear tests. The mechanical properties of hybrid composites increased significantly because of the addition of LCMC. The wear tests showed that LCMC can improve the wear resistance of the UP/GF/LCMC hybrid composites even though the content of LCMC was at a relatively low level (5–7.5 wt %). This makes it possible to develop novel kind of UP‐based materials with good wear resistance for various applications. The Worn surface was observed by scanning electron microscopy (SEM) and the mechanism for the improvement is discussed in this paper. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 3899–3906, 2007     

Interfacial contributions in lignocellulosic fiber‐reinforced polyurethane composites

Whereas lignocellulosic fibers have received considerable attention as a reinforcing agent in thermoplastic composites, their applicability to reactive polymer systems remains of considerable interest. The hydroxyl‐rich nature of natural lignocellulosic fibers suggests that they are particularly useful in thermosetting systems such as polyurethanes. To further this concept, urethane composites were prepared using both unused thermomechanical pulp and recycled newsprint fibers. In formulating the materials, the fibers were considered as a pseudo‐reactant, contributing to the network formation. A di‐functional and tri‐functional poly(propylene oxide)‐based polyol were investigated as the synthetic components with a polyol‐miscible isocyanate resin serving as a crosslinking agent. The mechanical properties of the composites were found to depend most strongly on the type of fiber, and specifically the accessibility of hydroxy functionality on the fiber. Dynamic mechanical analysis, swelling behavior, and scanning electron micrographs of failure surfaces all provided evidence of a substantial interphase in the composites that directly impacted performance properties. The functionality of the synthetic polyol further distinguished the behavior of the composite materials. Tri‐functional polyols generally increased strength and stiffness, regardless of fiber type. The data suggest that synthetic polyol functionality and relative accessibility of the internal polymer structure of the fiber wall are dominant factors in determining the extent of interphase development. Considerable opportunity exists to engineer the properties of this material system given the wide range of natural fibers and synthetic polyols available for formulation. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 546–555, 2001