Fracture of composites based on polyethylene and elastic particles

The composites based on low-density polyethylene with elastomer filling particles are studied. A fracture mechanism induced by the fracture of filler particles or their separation from the matrix polymer is revealed. The fracture of the composites is caused by the growth of formed rhombic pores. The natural relative elongation in a neck is shown to be an important characteristic of a polymer. If the relative elongation in a neck is lower than the strain of appearance of rhombic pores, they form at the stage of uniform tension after necking, and the composite remains plastic. If the relative elongation in a neck is higher than the strain of formation of rhombic pores, they nucleate during necking, and the material undergoes quasi-brittle fracture. Good adhesion between the matrix polymer and elastic particles hinders the appearance of rhombic pores in a neck and, thus, retains high deformation properties of the composites.     

Thermophysical characterization of the deformation behavior of polyethylene/kaolin composites

The deformation behavior at room temperature of injection-molded and blow-molded samples of high-density polyethylene (HDPE) differing in orientation (with respect to the melt flow direction) and in filler content (untreated and surface-treated kaolin, respectively) were characterized by the stretching calorimetry technique. Samples with longitudinal and transversal orientations were examined. Strain-softening and strain-hardening phenomena were observed, respectively, in the range of inelastic strains above the yield point. The depression of yield stresses for the filled composites compared to those for the corresponding neat polymers is associated with the onset of debonding of the matrix polymer from the filler surface. The analysis of the energy balance of the debonding process suggests that the fraction of a debonded interface is smaller in samples containing a coupling agent and larger filler particles.     

Influence of solid electrolyte particles size on ionic transport in model composite system (PVdF-HFP–Li1.3Al0.3Ti1.7(PO4)3)

The influence of filler particles size on lithium ion conductivity of composite polymer electrolytes was issued on model system vinylidenefluoride with hexafluoropropylene (PVdF-HFP)–Li_1.3Al_0.3Ti_1.7(PO₄)₃. Model electrolyte objects with filler grains of different sizes were prepared using a modified solvent casting method from a mixture of PVdF-HFP solution in dimethylformamide and Li_1.3Al_0.3Ti_1.7(PO₄)₃ solid electrolyte particles. The percolation threshold was defined and the transport properties of composite polymer electrolytes at different volume concentrations of the solid electrolyte investigated. A significant decrease in conductivity compared to that of ceramic solid electrolytes was observed. The size of the filler particles was found to affect the structure and transport properties of the prepared composite polymer electrolytes. The conductivity of the composite polymer electrolyte at 100 °C was found to increase by two orders of magnitude with the tenfold increase of the size of the filler particles.     

Morphology and percolation conductivity of polymer blends containing carbon black

The structure of the polymers polypropylene (PP), polyethylene (PE), and poly-(oxymethylene) (POM) and the blends PE-PP and PE-POM containing carbon black (CB) were studied. It was found that spatial distribution of CB depends on the interface interactions between the components of composites. It is possible to obtain three cases of filler spatial distribution: Filler can be distributed randomly within the polymer matrix, can be contained in one of the polymer components, or can be localized on the polymer-polymer boundary. The conditions of various filler distribution in the heterogeneous polymer matrix are given. The correlation between morphology of the composites and their percolation conductivity was found.     

Quantitative characterization of the orientation of macromolecules in intercalated nanocomposites of polyolefins/layered silicates by Raman spectroscopy

Raman spectroscopy is used to study variations in the orientational order of macromolecules in the uniaxially drawn intercalated nanocomposites based on two polymer matrices (polyethylene (PE) and isotactic polypropylene (PP)) and a filler (modified clay (MC)). The orientation parameters of macromolecules measured using Raman spectroscopy are compared with the X-ray data. It is demonstrated that, for the uniaxially drawn PE-MC and PP-MC intercalated nanocomposites, the filler impedes the orientation along the draw direction for the macromolecules localized in the noncrystalline phase of the polymer matrix. The orientational ability of the PE and PP crystallites in nanocomposites is not affected by the filler.     

Effect of irradiation on interfacial interaction and structure formation in filled PTFE composites

The supramolecular structure and tribological properties of filled polytetrafluoroethylene composites irradiated above the melting point of the crystalline phase of the polymer component and the phase transitions in them are investigated. In unirradiated composites, phase separation is observed, that is, the separation of the filler from the polymer matrix. The supramolecular structure of the polymer component does not depend on the nature and concentration of the filler, and it is characterized by the formation of lamellae during sintering and subsequent crystallization. Radiation exposure leads to the disappearance of the phase separation and the formation of axiolites with the radial orientation of fibrils, in the center of which the filler particles are located. Changes in the structure are explained by an increase in interfacial interactions through the radiation grafting of macromolecules (and low-molecular-weight products) to the surface of the filler particles. The linear wear rate of irradiated composites is 50 times lower relative to the unirradiated samples because of the transition from the delamination to abrasive wear mechanism.     

Chemical modification of the surface of Fe<Subscript>75</Subscript>Si<Subscript>25</Subscript> alloy particles with stearic acid under high-energy ball-milling conditions

The morphology, phase composition and surface structure of Fe₇₅Si₂₅-alloy particles are studied by electron microscopy, X-ray diffraction analysis, and Mössbauer, Auger, IR (infrared) and X-ray photoelectron spectroscopy. The alloy particles used as fillers for the polyethylene matrix are produced by high-energy ball milling in an organic medium with the addition of stearic acid. The addition of stearic acid is shown to promote plasticization of the brittle Fe₇₅Si₂₅ alloy and the formation of a surface layer of no more than 1.5 nm thick, consisting of oxides based on iron and silicon, responsible for the chemisorption of stearic acid on the surface. Chemical modification of the surface of filler particles with an amphiphilic surfactant is carried out to enhance their adhesion in the polymer matrix.     

Rheological and NMR studies of polyethylene/calcium carbonate composites

Rheometry, 13C CP/MAS NMR spectra and 1H spin-lattice relaxation times T1 and T1rho have been employed to study the structure and molecular dynamics in composites of polyethylene (LDPE) with calcium carbonate filler. It has been found that the addition of the filler into the polymer leads to an increase in composite rigidity and a decrease in mobility in its crystalline regions. The presence of the filler affects the crystallization process making the crystal structure less perfect and reduces the size of the crystallites.     

Studies of water penetration into LDPE--calcium lactate composite

Penetration of water into low-density polyethylene-calcium lactate composite is studied with NMR techniques. The presence of filler speeds up the water uptake by the polymer matrix and facilitates polyethylene degradation. Spatial distribution of absorbed water molecules within the composite visualised with MRI corroborates differences in dynamical behaviour of the absorbed water molecules revealed by T2 measurements.     

Synthesis and characterization of polymer encapsulated Cu–Ni magnetic nanoparticles for hyperthermia applications

Copper nickel alloy nanoparticles were synthesized by polyol reduction method and by physical melting process. The particles were further coated with a biodegradable polymer, polyethylene glycol. The particles have a curie temperature in the range of 43–46 °C and are designed to be used for hyperthermia applications. Morphology of these encapsulated particles was determined by electron microscopy. The curie temperature for alloy particles and encapsulated particles was also measured.     

Fractal and structural aspects of adhesion in particulate-filled polymer composites

Two types of composites based on poly(hydroxy ether) and graphite with various amounts of a filler have been investigated by various methods. The methods have been used to estimate the characteristics of adhesion and interfacial layer, including its thickness and tensile strength and interdependence between these values and adhesion. The results are treated on the basis of the theory of irreversible aggregation, cluster theory of the polymer structure and fractal analysis. It is established that all important characteristics of adhesion, interfacial layer and mechanical properties are interconnected with the difference between fractal dimensions of the surface of the aggregates of filler particles and of a polymer matrix, whose structure is distorted under the influence of the filler surface.     

Effect on ion dissociation in MWCNT-based polymer nanocomposite

Polymer nanocomposite has been proven to improve the property of polymer salt complex. Organo-modified clay and inorganic oxides are the most commonly used filler for polymer nanocomposite (PNC). However, single wall carbon nanotube (SWCNT)/multiwall carbon nanotube (MWCNT) are becoming popular filler for PNC for their high surface area and high mechanical stability. In this work, a series of PNC sample has been prepared by using polyethylene oxide (PEO)-polydimethylsiloxane (PDMS) blend as polymer matrix, an optimized salt stoichiometry of Ö/Li ~15, and surface-modified MWCNT as filler. The effect of ion-polymer and ion-MWCNT interaction in the polymer nanocomposite has been investigated by using XRD, SEM, FTIR, and electrical study. X-ray diffraction pattern confirms the dispersion of MWCNT inside the polymer chain and modifies the structural parameter of the polymer matrix. FTIR spectra indicate inclusion of MWCNT inside the polymer salt complex which changes the ion dissociation/association in the polymer host matrix. Further, the changes in structural, thermal, and electrical property of the polymer salt complex system have been studied by using SEM, DSC, and impedance analysis. Dc conductivity study shows that optimized PNC sample has conductivity of 8.04 × 10⁻⁵ S cm⁻¹. This is almost two order enhancement from pure polymer salt system (10⁻⁶ S cm⁻¹).

     

Effect of nanofillers on thermal and transport properties of potassium iodide–polyethylene oxide solid polymer electrolyte

In order to enhance the ionic conductivity of polyethylene oxide (PEO)–KI(80:20) based alkaline polymer electrolytes, nanosized inorganic filler ZnS has been incorporated into PEO–KI matrix and the corresponding nanocomposite polymer electrolytes are synthesized by the usual solution casting procedure. Atomic force microscope image of composite polymer electrolyte exhibits that the introduction of ZnS nanoparticles changes the surface morphology and aggregates them to form an arborization pattern. The prepared nanocomposite polymer electrolyte reveals an ionic conductivity of about 10^?4 S cm^?1 for 5 wt% ZnS at room temperature.     

Polarization model of strengthening of thermoplastic materials containing ultradisperse inorganic fillers

The polarization mechanism of strengthening was studied in thermoplastic polymers filled with ultradisperse powders of refractory SiMeON compounds obtained by plasmachemical synthesis. Thermostimulated depolarization current measurements showed the presence of spontaneous polarization charge in the filler and in filled thermoplastic compositions. Effects of the electric polarization field of the filler particles on the strength and structure of a boundary surface layer in a thermoplastic polymer binder contacting with the filler were studied on model samples. Material in the boundary layer exhibited an increase in the strength and a change in the degree of crystallinity and in the melting temperature.     

Amorphous solidification in polymer-platelet nanocomposites

Computer simulations are used to understand the molecular basis of the rheology changes in polymer melts when loaded with platelet filler particles, specifically when the polymer and nanofiller interact attractively. With decreasing temperature, there is increasing aggregation between chains and filler and an increase in the polymer matrix structural relaxation time. These lifetimes are predicted to diverge at an extrapolated temperature, which we identify with the emergence of an amorphous solid state. Our findings suggest that filled polymers are phenomenologically similar to solutions of associating polymers and to supercooled liquids near their glass transition.     

Effect of carbon nanotube amount on polyethylene welding process induced by laser source

This paper reports a study of the laser welding of polymeric joints composed by two polyethylene sheets, one pristine and the other filled by carbon nanotubes. In order to know the material modifications occurring during the laser exposure and the phenomena that seal the polymeric sheets, the physical, chemical and mechanical features of the welded area were analysed. The mechanical resistance of the welded joint and the structural changes of the polymer were checked by mechanical shear tests, absorption coefficient measurements, calorimetric analyses, mass quadrupole spectrometry and electron microscopy. The welding effectiveness was investigated as a function of the filler concentration.     

The influence of particle distribution and interphase on the thermal expansion coefficient of particulate composites by the use of a new model

In this work, the thermal expansion coefficient (CTE) of a composite containing spherical particles surrounded by an inhomogeneous interphase embedded in an isotropic matrix is evaluated by means of a new model. The thermomechanical properties of the interphase are formulated as continuous radial functions. It is assumed that this third phase developed between the polymeric matrix and the filler particles contains both areas of absorption interaction in polymer surface layers onto filler particles as well as areas of mechanical imperfections. It can be said that the concept of boundary interphase is a useful tool to describe quantitatively the adhesion efficiency between matrix and particles and that there is an effect of this phase on the thermomechanical properties of the composite. The thickness and volume fraction of this phase were determined from heat capacity measurements for various filler contents. On the other hand, it is assumed that the particle arrangement (distribution) which can be considered as an influence of neighboring inclusions and their interaction should affect the thermomechanical constants of the composite. The theoretical predictions were compared with experimental results as well as with theoretical values from expressions obtained from other workers and they were found to be in satisfactory agreement.     

Tribological and mechanical properties of composites based on ethylene-tetrafluoroethylene and quasicrystalline Al−Cu−Fe filler

Samples of composites, in which ethylene-tetrafluoroethylene copolymer is used as a matrix and quasicrystalline Al?Cu?Fe powder as a filler with 0, 1, 2, 4 and 8 vol % concentrations, are prepared. Electron microscopy studies of the sample structure are carried out. The influence of the filler on the crystallinity and temperatures of sample melting and destruction is investigated. The mechanical and tribological properties of the samples are tested. It is found that an increase in the filler content changes neither the mechanical nor thermodynamic characteristics of the material but significantly improves the tribological characteristics. The friction coefficient decreases twice at 1 vol % of the filler and the wear resistance increases by 40 times at 8 vol %. Experimental data indicate the probability of good adhesion of the filler particles to the fluoropolymer matrix. The composites under investigation may be of interest as promising materials for polymer friction bearings.     

Effect of surface treatment on sand erosion behavior of glass beads-filled epoxy resin

Effects of the adhesion between filler particle and matrix on the erosion rate were studied in cured epoxy resin filled with glass beads having mean diameter 17 um. In order to observe the effect of adhesion on erosion rate. the filler particles were treated with silane coupling agent, silicone oil and washed by acetone as well. The filler content of the specimen was varied and also the specimens were attacked by different size angular particles. The comparison of each type of specimen shows that by using acetone and silicone oil for surface treatment, the erosion rate is relatively high. Whereas the specimen in which the filler was treated by silane have low erosion rate. The difference of erosion behavior is influenced by impacting particle size and filler content. Using small impacting particles and also low filler content, the erosion behavior between silane and acetone treated was quite different. On the other hand, using large impacting particles and high filler content, the erosion behavior between them was similar.     

Nonisothermal Crystallization Kinetics and Microhardness of PP/CNT Composites

The nonisothermal crystallization kinetics and microhardness of nanocomposites consisting of a polypropylene matrix (PP) and carbon nanotube filler (CNT) have been investigated. Three types of PP matrixes have been used: two of them are nonfunctionalized PP that differ slightly in their melt flow index, whereas the third is grafted with maleic anhydride (MA). Ozawa formalism has been used to study the nonisothermal crystallization kinetics. The results show that the CNT filler has a nucleation role in the nonisothermal crystallization of PP. For all nanocomposites, the nonisothermal crystallization rate increases up to 4% CNT and then decreases slightly or remains almost constant at the higher filler content. This fact has been interpreted in terms of an aggregation of the particles at high filler concentration, which leads to a decrease of the nucleation ability of the filler because the number of heterogeneous nuclei decreases. The crystallization mechanism of the PP matrixes almost does not change in the presence of the CNT filler. The microhardness of the two nonfunctionalized PP increases when the filler content increases and then remains constant above a certain filler content. The experimental microhardness values of the composites based on the functionalized PP are lower than those of the corresponding calculated additive values. The decrease of the creep constant with the filler addition is not significant, as should be expected when inorganic filler is added to a polymer matrix. This is due to the very fine dispersion of the fillers into the polymer matrix at the nanoscale level.