Polyethylene compounds containing mineral fillers modified by acid coatings. 1: Characterization and processing

Research has been carried out to determine the effect of filler coatings on the processing properties of medium density polyethylene (MDPE) modified by an ultrafine grade of flame‐retardant magnesium hydroxide (Mg(OH)₂) filler. Selected filler coatings were acid‐group terminated and were of varying aliphatic chain length. The filler dry‐coating process has been optimized by characterizing the reaction between Mg(OH)₂ filler surface and the acid group, using spectroscopic techniques including Fourier transform infrared (FTIR) and X‐ray photoelectron spectroscopy (XPS). Using immersion calorimetry, the interactions between the fillers and the polyolefin matrix were shown to decrease on the addition of a fatty‐acid coating. Compounding torque and specific energy data relate to filler dispersion; qualitative analysis has demonstrated how the coatings provide a reduction in both size and number of particle agglomerates. MDPE compound processability was assessed by capillary rheometry; wall slip was evident in compounds containing uncoated Mg(OH)₂ filler. Consequently, the development of molecular orientation of the polymer during injection mold filling, quantified by a reversion analysis, is modified by the effects of filler coating chain length and addition level, an effect that has important implications to link the mechanical properties of MDPE‐Mg(OH)₂ composites to processing history.     

Effect of functionalization on dispersion of POSS‐silicone rubber nanocomposites

The nanocomposite of PDMS using functionalized fumed silica and nonreactive POSS as fillers were prepared by blend method in a planetary mixer. Fumed silica was functionalized by aliphatic and aromatic groups to study the filler–filler interactions with the aliphatic and aromatic POSS fillers and consequently their influence on the properties in the PDMS matrix. Transmission electron microscope (TEM) showed a good dispersion in the systems having the silica and POSS fillers with similar modifications. However, aliphatic and aromatic filler combinations showed more aggregated structures. Moreover, aliphatic POSS despite of good dispersion at higher loadings, act as lubricant, which is attributed to the disturbance in the PDMS‐ silica filler interaction and also the filler–filler interaction within fumed silica. There is a decrease in complex viscosity with the functionalization of fumed silica and with the aromatic/aliphatic POSS fillers. The thermal stability of aromatic functionalized fillers improves owing to the thermally stable phenyl groups. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Comparison of the morphology and mechanical properties of unmodified and surface‐modified nanosized calcium carbonate in a polypropylene matrix

Polypropylene‐(PP)‐based nanocomposites with unmodified and surface‐modified nanosized calcium carbonate (CaCO₃) were melt‐compounded to 3, 6, and 9 wt% filler contents. The nanofillers comprised two commercial grades from Mineral Technologies and one noncommercial pilot grade, and they differed in their particle size and/or surface modification. The fillers' dispersion and particle size and their adhesion to the matrix were examined by scanning electron microscopy. In addition, nanocomposite mechanical properties were determined and then compared with the properties of neat matrix material. Thermogravimetric analysis and differential scanning calorimetry were performed to determine the stearic acid content in the surface‐modified fillers and their thermal stability. Microscopic examination revealed that the commercial grades dispersed better in and adhered more strongly to the matrix than the pilot grade. Thermal analysis showed that the commercial grade contained less stearic acid and was thermally more stable. Better dispersion, smaller particle size distribution, and less stearic acid seemed to result in balanced mechanical performance. POLYM. COMPOS., 2011. © 2011 Society of Plastics Engineers     

Wall effects on flow of polymer/particulate/(carboxylic acid) in dies and rheometers

The addition of carboxylic acids to polyolefins results in an apparent slippage flow along rheometer and die walls. In this article, we seek to extend this investigation to polymer/particulate compounds. An experimental study on the influence of carboxylic acid additive in polyethylene/filler and polystyrene/filler compounds in rheometers is described. Capillary and cone‐plate experiments are reported. A series of particle fillers of varying character, including carbon black, calcium carbonate, zinc oxide, and talc are compared. The aliphatic fatty acid, octadecanoic acid, was used as an additive. Significant viscosity reductions were observed. The greatest effects were found in polyethylene/(carbon black) and polystyrene/(calcium carbonate) compounds. All of the polyethylene compounds exhibited slip flow, but the polystyrene compounds did not. Apparently much of the octadecanoic acid was interacting with the polar particle fillers and not with the die wall. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 651–658, 2004     

Mechanical,thermal and electrical properties of multi‐walled carbon nanotube/aluminium nitride/polyetherimide nanocomposites

A series of polyimide‐based nanocomposites containing polyimide‐grafted multi‐walled carbon nanotubes (PI‐g MWCNTs) and silane‐modified ceramic (aluminium nitride (AlN)) were prepared. The mechanical, thermal and electrical properties of hybrid PI‐g MWCNT/AlN/polyetherimide nanocomposites were investigated. After polyimide grafting modification, the PI‐g MWCNTs showed good dispersion and wettability in the polyetherimide matrix and imparted excellent mechanical, electrical and thermal properties. The utilization of the hybrid filler was found to be effective in increasing the thermal conductivity of the composites due to the enhanced connectivity due to the high‐aspect‐ratio MWCNT filler. The use of spherical AlN filler and PI‐g MWCNT filler resulted in composite materials with enhanced thermal conductivity and low coefficient of thermal expansion. Results indicated that the hybrid PI‐g MWCNT and AlN fillers incorporated into the polyetherimide matrix enhanced significantly the thermal stability, thermal conductivity and mechanical properties of the matrix. Copyright © 2012 Society of Chemical Industry     

AC and DC dielectric properties of some polypropylene/calcium carbonate composites

AC dielectric properties and thermally stimulated polarization (TSP) and depolarization (TSD) currents were studied in a series of CaCO₃-filled polypropylene composites. The filler content (0 to 50 weight percent) and the average particle size (3.0 to 16.1 μm) at constant filler content (30 weight percent) were varied in separate groups of samples. In a third group of samples the filler (20 to 40 weight percent) was surface treated with stearates. The AC dielectric behavior of composites containing untreated fillers is largely determined by a small amount of adsorbed water. Upon heating, the dielectric properties show maxima (increasing with decreasing frequency) which disappear on cooling. In the case of stearate-treated fillers the dielectric loss level is higher, the dispersion and loss curves on heating reflect a combination of dipolar and protonic processes with water desorption. In the dry state the onset of an audio frequency relaxation process is observed in the pre-melting zone. The thermally stimulated currents of the composites containing treated and untreated fillers are also different. In the case of the untreated fillers the TSP curves show maxima indicating water desorption which are increasingly intense and roughly exponential with filler content. The high temperature conductivity and the intensity of the pre-melting depolarization peak pass through a minimum as a function of filler content. Above 20 weight percent filler content the activation energy of high temperature conductivity decreases. In the case of the surface treated samples, the thermally stimulated response is different for “wet” and dried samples. The dry samples exhibit a relaxation between the amorphous and crystalline transitions of the matrix polymer which is probably due to interfacial relaxation caused by the enhanced surface conductivity of the stearate-treated fillers.     

Rheological investigation of polyamide 6 TiO2‐ and BaSO4‐nanocomposites

Commercially available TiO₂ and BaSO₄ nanoparticles were incorporated in polyamide 6 (PA 6) via twin screw extrusion. The primary particle size of nanoparticles was 15 nm and 20 nm. The compounds were manufactured via multiple extrusion and dilution processing steps. The dispersion of the nanoparticles in the matrix was investigated by scanning electron microscopy and image analysis, micro‐tomography, and transmission electron microscopy. The rheological properties were determined via plate–plate‐rheometer. It was found that for TiO₂ fillers a threefold extrusion process is sufficient to realize a dispersion index of 94.4%. BaSO₄ fillers were hardly dispersible, ending up with a maximum dispersion index of 71%. Deagglomeration does not lead to a change in rheological properties but the number of extrusion steps decreases the rheological properties. A good particle‐matrix interaction leads to higher moduli and viscosity. The remaining agglomerates seem to act as defects decreasing the energy absorption of the respective compounds. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Synthetic Ni‐talc as filler for producing polyurethane nanocomposites

New synthetic Ni‐talc was used as filler in the synthesis of polyurethane (PU) nanocomposites by in situ polymerization and to emphasize the contribution of the new material compared with natural talc. Good dispersion of Ni‐talc was supported by homogeneous green coloration observed in the polymer matrix. X‐ray diffraction (XRD) analyses indicate the intercalation of polymeric matrix into the filler layers by the increase in d₀₀₁‐spacing value of the Ni‐talc for the nanocomposites when compared to the pristine filler. The nanocomposites obtained with synthetic talc showed an improvement in the crystallization temperature and in thermal stability when compared to pure PU and the composite obtained with natural talc. The young modulus of PU/talc materials containing both Ni‐talc and natural talc were slight higher than pure PU. As shown by scanning electron microscope (SEM), Ni‐talc fillers were well dispersed into the polymeric matrix probably due to the good compatibility of both phases filler/polymer mainly achieved by the filler OH interaction with the urethane group of the polymeric chain. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41854.     

In Situ synthesis of inorganic filler‐filled polyethylene using polyethersulfone‐supported TiCl4 catalyst system

In situ ethylene polymerizations with inorganic fillers were performed using catalyst based on titanium tetrachloride supported on polyethersulfone. The inorganic fillers used were MgO, TiO₂, and CaCO₃, which were pretreated with cocatalyst (methylaluminoxine) for better dispersion onto the polymer matrix. The formation of polyethylene (PE) within the whole matrix was confirmed by Fourier transform infrared studies. The wide‐angle X‐ray diffraction profile of the synthesized PEs indicated the presence of crystalline region. It was found that the nature of inorganic filler did not have any remarkable effect on the melting characteristics of the polymer, but the degree of crystallinity of PE was found to be higher for TiO₂‐filled PE. The amount of filler incorporated into the matrix was also evaluated through thermogravimetric analysis, where TiO₂‐filled PE showed ～ 49% of filler material, which was also reflected in the higher productivity obtained by this system. The morphology of the filler‐filled PEs was different, whereas the elemental dispersion was found to be uniform on the surface as elucidated through energy‐dispersive X‐ray spectroscopy. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Rubber toughening in polypropylene: A review

The recent advances in the studies of the toughening methods and theories of polypropylene (PP)–elastomer blends are reviewed in the present article. Inclusions are key to toughening PP; they can play the role of agent‐induced crazing, cause shear yielding of the matrix around them, and end the propagation of cracks. The major theories interpreting the toughening mechanisms of the blends are: multiple crazing, damage competition theory, shear‐yielding theory, microvoids, and cavitation theories. The factors affecting the toughening effect are relatively complicated. Therefore, these theories have been verified only in some cases when they have been applied in relevant conditions. To achieve the objective of better toughening, it is important to improve the uniform distribution of dispersed‐phase particle size and suitable filler size, as well as improving the dispersion of the inclusions formed in the matrix; in addition the matrix materials or fillers must be functional with suitable modifier in order to enhance the interfacial adhesion or to improve the interfacial morphological structure between the filler and matrix. However, the exact toughening mechanisms for PP–rubber blends have to be studied further because of complications resulting from the crystallinity of the matrix. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 409–417, 2000     

Yielding behaviour of thermoplastic/elastomer blends cured by gamma irradiation

Mechanical blends of thermoplastic medium density polyethylene (MDPE) and elastomeric ethylene propylene diene monomer (EPDM) have been prepared with a fixed composition of 60/40 wt%. They have been used either in their gum form or loaded with two different reinforcing fillers, high abrasion furnace (HAF) carbon black or precipitated SiO₂ (Hi Sil) of concentration 25–100 phr (parts per hundred parts of resin) with respect to the blend. Curing was achieved by gamma irradiation. Yielding properties (yield stress, yield strain and cold drawing) have been followed as a function of irradiation dose for different blend compositions. Yield stress values increased with irradiation dose and with the content of the reinforcing filler, but yield strain and cold drawing values decreased with irradiation dose and also with the filler content. The data obtained reveal that Hi Sil is more effective as a reinforcing filler, and the prepared blends are suitable for load‐bearing applications. © 2001 Society of Chemical Industry     

Microstructural design of lead oxide–epoxy composites for radiation shielding purposes

Composite epoxy samples filled with PbO and Pb3O4 were fabricated to investigate the mass attenuation characteristics of the composites to X‐rays in the diagnostic imaging energy range. The effect of density on the attenuation ability of the composites for radiation shielding purposes was studied using a calibrated X‐ray machine. Characterization of the microstructure properties of the synthesized composites was performed using synchrotron radiation diffraction, optical microscopy, and scanning electron microscopy. The results indicate that the attenuation ability of the composites increased with an increase in density. The particle size of WO₃ fillers has a negligible effect on the value of mass attenuation coefficient. Microstructural analyses have confirmed the existence of fairly uniform dispersion of fillers within the matrix of epoxy matrix with the average particle size of 1–5 μm for composites with filler loading of ≤ 30 wt % and 5–15 μm for composites with filler loading of ≥ 50 wt %. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Reinforcement of polyolefins‐based nanocomposites: combination of compatibilizer with high shear extrusion process

The structure and properties of polypropylene (PP) and ethylene propylene copolymer (EPR) blends filled with nanosilica have been investigated. The nanocomposites were prepared via direct melt mixing using high shear corotating twin screw extruder. The effects of the process as well as adding amaleated‐Polyethylene MAPE compatibilizer were assessed by morphology studies, thermal analysis and mechanical testing. From SEM and TEM investigations, a separate dispersion of filler and rubber in the PP matrix prevails in the PP/EPR/SiO₂ systems. Encapsulation of the filler particles into the elastomer takes place when MAPE is used, promoting filler/polymer interactions and resulting in a simultaneous improvement in stiffness and toughness. Interestingly, the results indicated that high‐shear processing is an effective method to improve the dispersion of the EPR phase and fillers through the matrix. The dispersed phase droplet size was reduced with the increase of the shear rate by varying the screw rotation speed from 300 to 800 rpm, which induces a high shear stress exerted onthe materials. To sum up, what is expected from an efficient compatibilization‐process association is the reduction of the dispersed elastomer domains characteristic size, their stabilization by creation of an interphase and thus, enhanced mechanical properties. POLYM. ENG. SCI., 55:2328–2338, 2015. © 2015 Society of Plastics Engineers     

Melt fracture and rheology of linear low density polyethylene ‐ calcium carbonate composites

Rheological behavior and melt fracture of linear low‐density polyethylene (LLDPE) calcium carbonate (CaCO₃) composites were investigated. Two types of commercial inorganic fillers were used, unmodified and modified with stearic acid. Rheological capillary studies were conducted to assess the influence of inorganic filler incorporation as well as chemical treatment on the rheological properties and instability sequence of polyethylene‐based composites. Strong suppression of melt flow instabilities was observed for both types of composites. Mooney analysis was applied to examine the influence of mineral filler addition and stearic acid modification on the wall slip. Moreover, chemical treatment of calcium carbonate allows to obtain better dispersion of the inorganic filler in a polymeric matrix. POLYM. ENG. SCI., 57:998–1004, 2017. © 2016 Society of Plastics Engineers     

Effect of nanofillers on the properties of flexible protective polymer coatings

Nanofillers with different size, shape, chemical structure, aspect ratio, and purity, including pristine montmorillonite (MMT‐Na) and hydrotalcite (HT) lamellar clays, and nonpurified single‐walled carbon nanotubes (SWNT) and fullerenes (FUL) were dispersed in a waterborne flexible acrylic coating. SEM and WAXD analysis of drawn‐down composite films containing 5 and 10 wt% fillers confirmed the random orientation of the MMT‐Na and HT platelets having intercalated or partially exfoliated structures. SEM analysis of composites containing SWNTs revealed the presence of clusters rather than single fibers and irregularly shaped carbonaceous impurities. Low aspect ratio, but well‐dispersed particles were observed in the FUL composites. Only the SWNT filler improved the thermal stability of the unfilled polymer; the presence of SWNT and MMT‐Na had a negligible effect on the glass transition temperature (T_g) of the coating. The presence of all nanofillers increased the tensile secant modulus of the polymer and decreased somewhat tensile strength and elongation at break to different degrees depending on type of filler and concentration. Some nanofillers significantly reduced the water vapor transmission rate of the unfilled matrix. Experimental data are discussed in terms of parameters known to affect mechanical and barrier properties including volume fraction, orientation, aspect ratio, dispersion, interfacial adhesion, and filler hydrophilicity. The results of this work indicate that it is possible to improve certain properties of acrylic protective coatings through the addition of low cost, unmodified nanoclays or by using nonpurified carbon allotropes, without a significant compromise of the strength and ductility of the polymeric matrix. POLYM COMPOS., 27:368–380, 2006. © 2006 Society of Plastics Engineers     

Nylon 11/silica nanocomposite coatings applied by the HVOF process. I. Microstructure and morphology

Nylon 11 coatings filled with nanosized silica and carbon black have been produced using the high velocity oxy‐fuel (HVOF) combustion spray process. The physical properties and microstructure of coatings produced from nylon 11 powders with starting particle sizes of 30 and 60 μm have been evaluated as a function of the filler content, filler chemistry, and processing conditions. The nominal filler content was varied from 5 to 20 vol %. Co‐milling of the nano‐sized fillers with the polymer powders produced an embedded 4–8 μm thick filler layer on the surfaces of the polymer particles. Optimization of the HVOF processing parameters based on an assessment of the degree of splatting of polymer particles was accomplished by varying the jet temperature (via hydrogen/oxygen ratio). Gas mixtures with low hydrogen contents minimized polymer particle degradation. The filler was found to be agglomerated at the splat boundaries in the final coating microstructures. Aggregates of silanated silica and carbon black were of the order of 50 nm in size, whereas the aggregates of untreated silica and hydrophilic silica were of the order of 100 nm. The morphology of the polymer and the microstructure of the coatings depended on the filler surface chemistry and the volume fraction of the filler, as well as the initial nylon 11 particle size. Although all filled coatings had higher crystallinities than pure nylon 11 coatings, coatings produced from a smaller starting polymer particle size exhibited improved spatial distribution of the silica in the matrix and lower crystallinity. In addition, coatings prepared from smaller polymer particles had a higher density and lower porosity. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 1684–1699, 2000     

Influence of iron carbide filler in carbon matrix on the adhesive properties of acrylic pressure-sensitive adhesives

Inorganic fillers can improve coating properties, such as scratch resistance and UV stability and can significantly enhance the fillers usability in coatings and realize new market opportunities. In the pressure-sensitive adhesive (PSA) technology the inorganic fillers are used to change the very important properties of pressure-sensitive adhesives, such as tack, peel adhesion and shear strength. In the current study, the above mentioned properties of synthesized acrylic PSA using iron carbide filler in carbon matrix were investigated. The acrylic PSA containing iron carbide filler (Fe₃C,C) was examined with SEM/EDX technique and the PSA adhesive and cohesive properties were examined by using a special strength machine according to AFERA tests. The conclusion is that the application of this kind of fillers allows the manufacturing of self-adhesive materials with moderate adhesiveness and very good removability.     

Study of the effect of the concentration,size and surface chemistry of zirconia and silica nanoparticle fillers within an epoxy resin on the bulk properties of the resulting nanocomposites

Epoxy resin nanocomposites were prepared by curing bisphenol‐F with an aliphatic amine in the presence of SiO₂ and ZrO₂ nanoparticles as inorganic fillers. Both types of particles were prepared with diameters of around 10 nm and 70 nm to study size effects in the nanocomposites. The nanoparticles showed a different constitution: while silica was amorphous and spherical in nature, zirconia was crystalline and non‐spherical. Both nanoparticles were surface‐functionalized with novel diethylene‐glycol‐based capping agents to increase the compatibility with the epoxy matrix. The organic functionalities were attached to the nanoparticle surface via phosphonic acid (zirconia) and trialkoxysilane (silica) anchor groups. The homogeneity of the distribution of surface‐modified inorganic nano‐sized fillers in the matrix up to 5.8 vol% in case of silica and 2.34 vol% in case of zirconia was determined by small‐angle X‐ray scattering and transmission electron microscopy. Mechanical properties such as hardness and storage modulus were increased with increasing filler content while thermal stability of the obtained materials was nearly unaffected after incorporation of nanoparticles. Copyright © 2011 Society of Chemical Industry     

The influence of the dispersed phase on the morphology,mechanical and thermal properties of PLA/PE‐LD and PLA/PE‐HD polymer blends and their nanocomposites with TiO2 and CaCO3

This research investigated the impact of different processing temperature (extrusion at 160°C and 180°C) and the influence of the TiO₂ and CaCO₃ fillers on morphology, mechanical, and thermal properties of polylactide (PLA) blended with low‐density polyethylene (PE‐LD) and high‐density polyethylene (PE‐HD) in 90/10 weight ratio. The impact of the particle size of the filler was also examined with the three types of TiO₂ filler. It has been shown that the different processing temperature has no significant impact on the morphology, mechanical, and thermal properties of PLA/PE‐LD 90/10 and PLA/PE‐HD 90/10 polymer blends. It has also been shown that better phase interaction is not the crucial factor for the improvement of the mechanical properties but the domain size distribution of the dispersed phase within the matrix and the dispersion of the filler are. Samples with a narrow size distribution of the dispersed phase domain (5 to 10 μm) with the higher portion of larger domains that are uniformly distributed within the polymer matrix showed best mechanical properties. POLYM. ENG. SCI., 59:1395–1408 2019. © 2019 Society of Plastics Engineers     

Influence of stearic acid treatment of filler particles on the structure and properties of ternary‐phase polypropylene composites

In this study, ternary‐phase polypropylene (PP) composites containing an ethylene–octene copolymer (EOR) and calcium carbonate (CaCO₃) were investigated. Particular consideration was given to the influence of stearic acid treatment of the filler on the phase morphology and mechanical properties of the composites. In composites containing an uncoated filler, a separate dispersion of the elastomer and filler particles in the PP matrix was observed. The use of filler treated with stearic acid had no effect either on the dispersion or the interaction of the filler and the polymer components. However, the surface‐treated filler was found to promote the β‐hexagonal crystallization of PP and gave a composite with lower T_{c onset} and T_c values. As a consequence, differences in mechanical properties, in particular, impact strength, were exhibited in which calcium carbonate with stearic acid treatment was apparently more effective in increasing the impact strength of the composites in comparison with the composites containing the uncoated filler. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 3445–3454, 1999