The effect of shear on mechanical properties and orientation of HDPE/mica composites obtained via dynamic packing injection molding (DPIM)

The interfacial interaction and orientation of filler play important roles in the enhancement of mechanical performances for polymer/inorganic filler composites. Shear has been found to be a very effective way for the enhancement of interfacial interaction and orientation. In this work, we will report our recent efforts on exploring the development of microstructure of high density polyethylene (HDPE)/mica composites in the injection‐molded bars obtained by so‐called dynamic packing injection molding (DPIM), which imposed oscillatory shear on the melt during the solidification stage. The mechanical properties were evaluated by tensile testing and dynamic mechanical analysis (DMA), and the crystal morphology, orientation, and the dispersion of mica were characterized by scanning electron microscopy and two‐dimensional wide‐angle X‐ray scattering. Compared with conventional injection molding, DPIM caused an obvious increase in orientation for both HDPE and mica. More importantly, better dispersion and epitaxial crystallization of HDPE was observed on the edge of the mica in the injection‐molded bar. As a result, increased tensile strength and modulus were obtained, accompanied with a decrease of elongation at break. The obtained data were treated by Halpin–Tsai model, and it turned out that this model could be also used to predict the stiffness of oriented polymer/filler composites. Copyright © 2009 John Wiley & Sons, Ltd.     

Biomimetic chitosan‐treated clay–elastomer composites with water‐responsive mechanically dynamic properties

Biomimetic hydrophobic polymer composites with water‐responsive mechanically adaptive behaviors were successfully prepared using hydrophilic chitosan‐treated clay (chi‐clay) as the water‐activated, pH‐sensitive and reinforcing phase and elastomeric thermoplastic polyurethane (TPU) as the matrix. Structural characterization, swelling tests in three representative solutions with different pH values, and dynamic mechanical analysis under wet and dry conditions were performed on the resultant chi‐clay‐TPU composites with varying chi‐clay contents. The results showed that the equilibrium swelling degree of TPU increased significantly with increasing chi‐clay content and that water transportation in all the composites followed Fickian diffusion mechanism. The presence of chi‐clay provided remarkable enhancement of the storage modulus of TPU and offered water‐responsive changes of the modulus. Such changes increased with chi‐clay content and were pH‐sensitive, with the acidic condition rendering the largest modulus difference. These water‐responsive polymer composites may find potential applications in biomedical fields and beyond. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2014 , 52, 55–62     

Comparison of the effect of mica and talc and chemical coupling on the rheology,morphology, and mechanical properties of polypropylene composites

The effect of filler types of mica and talc on the oscillatory shear rheological properties, mechanical performance, and morphology of the chemically coupled polypropylene composites is studied in this work. The Maleic Anhydride grafted Polypropylene (MAPP) was used as an adhesion promoter for coupling mineral particles with the polypropylene matrix. The samples were prepared by a co‐rotating, L/D = 40, 25 mm twin screw extruder. The tensile tests carried out on the injection molded samples showed a reinforcing effect of talc up to 20 wt% on the Polypropylene (PP). The tensile strength of PP‐mica composites showed a slight decrease at all percentages of mica. The effect of chemical coupling by using MAPP on the tensile strength was more pronounced in increasing the tensile strength for PP‐mica than PP‐talc composites. The complex viscosity curve of pure PP and the composites, showed a Newtonian plateau (η₀) up to 30 wt% at low frequency terminal zone. By increasing the filler content to 40 and 50 wt%, the complex viscosity at very low shear rates sharply increased and showed yield behavior that can be due to the formation of filler particles networks in the melt. At the optimum amount of coupling agent, a minimum in cross over frequency curve against MAPP content is observed. The optimum amount of coupling agent for PP‐talc composites is about 1.5%, and about 3% for PP‐mica formulations. The analysis of viscosity behavior at power‐law high region, revealed the more shear thinning effect of mica than talc on the PP matrix resin. Copyright © 2009 John Wiley & Sons, Ltd.     

Polymerization of anilinium–DBSA in the presence of clay particles: kinetics and formation of core‐shell structures

This paper is an extension of previous work on polymerization of anilinium–DBSA (dodecylbenzenesulfonic acid) in an aqueous dispersion in the presence of mica or talc silicate particles. The presence of mica or talc particles greatly accelerates the polymerization process of anilinium‐DBSA and an encapsulated structure is formed as well. The catalytic effect of various metallic cations which exist in the chemical compositions of mica or talc on the polymerization kinetics of anilinium‐DBSA was investigated. The conductivity results along with microscopy observations prove a well formed encapsulated structure for the polyaniline/mica composites, but less for the polyaniline/talc composites. The anilinium‐DBSA complex and mica aqueous dispersions pretreated at different temperatures prior to polymerization have shown a significant effect on the polymerization rate of anilinium‐DBSA. The higher the dispersion temperature, the higher is the polymerization rate found. Copyright © 2001 John Wiley & Sons, Ltd.     

Thermal stability and flammability of silicone polymer composites

Silicone polymer composites filled with mica, glass frit, ferric oxide and/or a combination of these were developed as part of a ceramifiable polymer range for electrical power cables and other high temperature applications. This paper reports on the thermal stability of polymer composites as determined by thermogravimetric techniques, thermal conductivity and heat release rate as measured by cone calorimetry. The effects of fillers on thermal stability and flammability of silicone polymer are investigated. Of the fillers studied, mica and ferric oxide were found to have a stabilising effect on the thermal stability of silicone polymer. Additionally, mica and ferric oxide were found to lower heat release rates during combustion, but only mica was found to increase time to ignition.     

Synthesis and properties of poly(acrylamide‐co‐acrylic acid)/polyacrylamide superporous IPN hydrogels

Poly(acrylamide‐co‐acrylic acid)/polyacrylamide [P(AM‐co‐AA)/PAM] hydrogel with superporous and interpenetrating network (IPN) structure was prepared by a prepolymerization reaction and a synchronous polymerization reaction and frothing process. Scanning electron microscope (SEM) images show that the resultant hydrogel possesses abundant interconnected pores. DSC indicates that the porous structure enhances the swelling ratio and reduces the interaction between water and the hydrogel. In contrast, the IPN by PAM decreases water absorbency and enhances water retentivity. It is found that a superporous stucture in the hydrogel increases the equilibrium swelling ratio and decreases the compressive strength of the hydrogel. On the other hand, the increase in AM oligomer (oligo‐AM) amount decreases the equilibrium swelling ratio and improves the compressive strength of the hydrogel. Therefore, the two‐steps synthesis method can be used to construct a hydrogel with superporous and IPN structure. The swelling and mechanical properties of the hydrogel can be improved effectively. Copyright © 2008 John Wiley & Sons, Ltd.     

Protein‐ and homo poly(amino acid)‐based hydrogels with super‐swelling properties

The use of super‐swelling polymers is steadily increasing and the applications in industry are continuing to grow. With the authorization of the superabsorbents in food packaging by the Food and Drug Administration recently, demand may soon take off in the market. However, the increase in prices of petroleum products in recent years may be a drawback for these acrylic‐based materials. Thus, there is now a need to develop natural‐based super‐swelling hydrogels which are more economical and environment friendly. In addition, the super‐swelling gels are promising novel functions in the biomedical and pharmaceutical applications. This review is aimed to highlight research and trends in protein‐ and homo poly(amino acid)‐based super‐swelling hydrogels. Thus, the proteinaceous hydrogels, including chemically modified soy‐, fish‐ and collagen‐based proteins, are discussed. The protein‐polysaccharide, protein‐synthetics, and the inorganic composites are also investigated as hybrid materials. Finally, the super‐swelling hydrogels based on homo polypeptides, i.e. poly(aspartic acid), poly(glutamic acid), and poly(ε‐L‐lysine) are reviewed. Copyright © 2009 John Wiley & Sons, Ltd.     

Composites of poly (dimethylsiloxane) and spherically shaped poly (2‐hydroxyethylmethacrylate) particles for biomedical use

Silicone rubbers have shown considerable promise in the biomedical field, but their hydrophobicity leads to serious problems in long‐term implants. In our study, composites of poly (dimethylsiloxane) (PDMS) and spherically shaped poly (2‐hydroxyethylmethacrylate) (PHEMA) microparticles were prepared. Unlike previous silicone hydrogel composites, suspension polymerization was carried out in an aqueous medium to prepare PHEMA particles directly, which avoided the removal of organic phase and give hydrogel particles with high purity. Very fine PHEMA particles with uniform geometry and small size were obtained through various influencing factors during their formation. Through the introduction of PHEMA particles, PDMS matrix was endowed with hydrophilicity to a certain extent. With an increase in hydrogel content, higher swelling ability and surface wettability of the composites were observed. We have also demonstrated that smaller sized particles are more favorable for hydrophilicity improvement. The results of improved swelling ability, surface wettability, and low affinity to lipid show that this composite material is suitable for biomedical use. Copyright © 2009 John Wiley & Sons, Ltd.     

Effects of matrix molecular weight on structure and reinforcement of high density polyethylene/mica composites

Three types of high-density polyethylene(HDPE)with different molecular weights(high,medium and low)were adopted to evaluate the influence of matrix molecular weight on the structure-property relation of injection-molded HDPE/mica composites through a combination of SEM,2d-WAXS,DSC,DMA and tensile testing.Various structural factors including orientation,filler dispersion,interfacial interaction between HDPE and mica,etc.,which can impact the macroscopic mechanics,were compared in detail among the three HDPE/mica composites.The transcrystallization of HDPE on the mica surface was observed and it exhibited strong matrix molecular weight dependence.Obvious transcrystalline structure was found in the composite with low molecular weight HDPE,whereas it was hard to be detected in the composites with increased HDPE molecular weight.The best reinforcement effect in the composite with low molecular weight HDPE can be understood as mainly due to substantially improved interfacial adhesion between matrix and mica filler,which arises from the transcrystallization mechanism.     

The interfacial adhesion of wood fiber–reinforced UHMWPE composite filled with acid‐treated clay

Wood fiber–reinforced ultrahigh molecular weight polyethylene (wood fiber/UHMWPE) composites have been filled with acid‐treated clay to enhance the adhesion. According to the modification, the interlaminar shear strength of composites has been greatly improved. X‐ray photoelectron spectroscopy and scanning electron microscopy are used to examine the microscopic properties of resultant composites. The enhanced interlaminar shear strength is attributed to the clay interlock, which improves the wetting between wood fibers and resins.     

Covalent Functionalization of Graphene by Nucleophilic Addition Reaction: Synthesis and Optical‐Limiting Properties

Covalent functionalization of reduced graphene oxide (rGO) was performed by using conjugated polymers with different monomers through nucleophilic addition of nitrogen anions to rGO. Three conjugated polymers containing tetraphenylethylene, carbazole, and phenyl groups were used, and as a result of π–π interactions and the “polymer‐wrapping” effect, the dispersion stability of rGO was improved. Even if the reaction site in the polymers was the same, there were great differences in the reactivities of the polymers, the dispersion stabilities of the resultant composites, and also the optical limiting (OL) performances of the resultant composites. The differences may be attributed to the π‐conjugated structure and steric hindrance of the moiety in the polymer skeleton, which has scarcely been reported. Besides, the resultant rGO‐P1 and rGO‐P3 materials both showed excellent OL responses, even at 4 μJ. This behavior should enable their potential application in photonic and optoelectronic devices to protect human eyes or optical sensors from damage by intense laser irradiation.     

Effects of chain extender and uniaxial stretching on the properties of PLA/PPC/mica composites

Poly(lactic acid) (PLA)/poly(propylene carbonate) (PPC)/mica composites with different amount of chain extender (CE) were melt compounded and then processed via two routes (compression molding and uniaxial stretching) into sheets and films. The tensile, thermal, and oxygen barrier properties of all the samples were investigated. Tensile test showed that the tensile strength and elongation at break of all films were much higher than that of all sheets, especially for PLA/PPC/mica with 0.9‐wt% CE composite (CM₃(CE)_0.9) film. The crystallinity of all films increased significantly after uniaxial stretching of sheet samples. The Fourier transform infrared spectroscopy (FTIR) results proved the chemical reactions occurred between PLA/PPC and CE. Scanning electron microscope (SEM) analysis revealed that compatibility and interfacial adhesion of all samples were improved after adding mica and CE, and they were further enhanced after uniaxial stretching. The addition of CE was not favorable to improve the oxygen barrier performance of PLA/PPC/mica sheet samples. However, the oxygen barrier performance of film samples was significantly improved after uniaxial stretching. In particular, the CM₃(CE)_0.9 film had the lowest oxygen permeability coefficient (1.4 × 10^?15 cm³·cm/(cm²·s·Pa)), and this was the best oxygen barrier properties reported in the literature for PLA‐based composites, which was comparable with PA film. This study demonstrated the high efficiency of uniaxial stretching on improvement of properties of composites, which would promote the application of biodegradable polymers in oxygen sensitive food packaging.     

Preparation and characterization of poly(acrylic acid)‐iron rich smectite superabsorbent composites

A novel poly(acrylic acid)‐iron rich smectite (IRS) superabsorbent composite was synthesized by graft copolymerization reaction of acrylic acid (AA) in the presence of N,N‐methylenebisacrylamide (MBA) as a crosslinker. IRS was used to strengthen the hydrogel products in the polymerization process. Water absorbencies for these superabsorbent composites in water and saline solutions were investigated. IRS caused a reduced equilibrium swelling as low as 8–26%. However, grafted IRS particles resulted in improved gel strength as high as 66% compared to the IRS‐free sample. IRS modified superabsorbent hydrogel composites exhibited higher thermal stability compared to the IRS‐free sample. The pH dependent reversible swelling behavior of hydrogels was also investigated. It is found that the swelling process is pH dependent and reversible for synthesized superabsorbent. Superabsorbent hydrogel composites were characterized by thermogravimetric analysis (TGA) and scanning electron microscopy (SEM). FTIR spectroscopy was confirmed grafting of acrylic chains onto the surface of IRS particles. From the standpoint of these results, these strengthened and thermostabilized hydrogels may be considered as good candidates for a controlled release study and agricultural applications. Copyright © 2007 John Wiley & Sons, Ltd.     

Rheological Behavior for Mica-filled Polypropylene Composite Melts

The study on rheological properties of a series of mica-filled polypropylene (PP) composites was carried out. The influence of surface-treatment of mica particles on dynamic rheological behavior of the composites were dealt with. The viscosity (η) and dynamic modulus ( G‘ ) of the composite melts were higher than those of PP matrix, especially those for systems treated with silane, which was attributed to the interfacial adhesion enhancement. However, surface-treatment of mica by titanate resulted in lower η and G‘, as compared with the treatment by silane. The reason for this is believed to be the formation of the mono-molecular layer on the mica surface.     

Enzyme degradability of benzylated sisal and its self‐reinforced composites

To produce natural polymer based composite materials, sisal fibers were slightly benzylated and then molded into sheets. Because the modified skin portions of the fibers acquired certain thermoplasticity and the unmodified core parts remain constant, the resultant composites fall into the category of self‐reinforced ones. The present article is devoted to the evaluation of the materials biodegradability with the help of cellulase. It was found that the inherent biodegradability of plant fibers is still associated with the benzylated sisal and the molded composites, as characterized by structural variation, weight loss and deterioration of mechanical performance of the materials. Reaction temperature and time, pH value of the enzyme solution, and dosage of the enzyme had significant influences on the decomposition behavior of the materials. In principle, the enzymolysis of sisal and its self‐reinforced composites is a diffusion‐controlled process. Due to the insusceptibility of lignin to cellulase and the hindrance of it to the cellulase solution, the degradation rates of the materials are gradually slowed down with an increase in time. Copyright © 2003 John Wiley & Sons, Ltd.     

Preparation,swelling behaviors and application of polyacrylamide/attapulgite superabsorbent composites

A series of superabsorbent composites, polyacrylamide/attapulgite (PAMA), were prepared from acrylamide (AM) and attapulgite micropowder in aqueous solution, using N,N′‐methylenebisacrylamide (MBA) as a crosslinker and ammonium persulfate (APS) as an initiator and then saponified with sodium hydroxide solution. This paper focuses on swelling behaviors of the PAMA superabsorbent composites in various saline solutions. The results indicate that saline solutions can weaken the swelling abilities of the PAMA compsites greatly. Water absorbency of the PAMA composites with 20 and 40 wt% attapulgite in aqueous chloride salt solutions has the following order: Li⁺ = Na⁺ = K⁺, Mg²⁺ > Ca²⁺ = Ba²⁺ all through the range of concentration investigated. However, swelling properties of the composites are complicated in CuCl_2(aq), AlCl_3(aq) and FeCl_3(aq) solutions and are related to saline solutions concentration. The deswelling behavior of PAMA composites is more obvious in univalent chloride salt solutions than in divalent and trivalent ones. The influence of kind and valence of anions on swelling ability of the composites is limited and almost the same. Moreover, reswelling capability, practical water retention ability in sand soil of the composites and the effect of pH on water absorbency of the PAMA composites were investigated. The PAMA composite shows good water retention and reswelling ability in sand soil, and may be used as a recyclable water‐managing material for the renewal of arid and desert environment. Copyright © 2006 John Wiley & Sons, Ltd.     

An Electroconductive Filler for Shielding Plastics

A well characterised grade of mica was used to prepare nickel-coated mica fillers by an electroless coating technique. These fillers were incorporated into polypropylene (PP) and acrylonitrile-butadiene-styrene (ABS) using a Haake Internal mixer and a two-roll mill to produce conducting composites suitable for EMI shielding applications. Compounded polymers were fabricated into sheets of different thickness by compression moulding. The dependence of conductivity on sample thickness was studied and samples were tested for electrical resistivity, shielding efficiency, and thermal and mechanical properties. Reduced sample thickness during compression moulding decreased the electrical resistance of the polymer composites due to orientation and the formation of a good conducting network. Volume resistivity of PP composites was lower than for ABS composites with 50% Ni coating and equivalent filler weight fracions, showing that better conductivity could be achieved in a semi crystalline polymer than in an amorphous polymer. 0.6 weight fraction of 50 wt.% nickel coated mica in ABS showed a shielding efficiency of 16dB compared with 27.8dB in PP.     

Nanostructure and properties of polysiloxane‐layered silicate nanocomposites

The relationship between nanostructure and properties in polysiloxane layered silicate nanocomposites is presented. Solvent uptake (swelling) in dispersed nanocomposites was dramatically decreased as compared to conventional composites, though intercalated nanocomposites and immiscible hybrids exhibited more conventional behavior. The swelling behavior is correlated to the amount of bound polymer (bound rubber) in the nanocomposites. Thermal analysis of the bound polymer chains showed an increase and broadening of the glass‐transition temperature and loss of the crystallization transition. Both modulus and solvent uptake could be related to the amount of bound polymer formed in the system. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 1595–1604, 2000     

Ethanol‐Precipitable,Silica‐Passivated Perovskite Nanocrystals Incorporated into Polystyrene Microspheres for Long‐Term Storage and Reusage

Perovskite nanocrystals (PNCs) are emerging luminescent materials due to their fascinating physic‐optical properties. However, their sensitive surface chemistry with organic polar solvents, oxygen, and moisture greatly hinders their developments towards practical applications. Herein we promote silica‐passivated PNCs (SP‐PNCs) by in situ hydrolyzing the surface ligands of (3‐aminopropyl) triethoxysilane. The resultant SP‐PNCs possesses a high quantum yield (QY) of 80 % and are precipitable by polar solvents, such as ethanol and acetone, without destroying their surface chemistry or losing QY, which offers an eco‐friendly and efficient method for separation, purification, and phase transfer of PNCs. Moreover, we further promoted a swelling–deswelling encapsulation process to incorporate the as‐made SP‐PNCs into non‐crosslinked polystyrene microspheres (PMs), which can largely increase the stability of the SP‐PNCs against moisture for long‐term storage.     

Ethanol‐Precipitable,Silica‐Passivated Perovskite Nanocrystals Incorporated into Polystyrene Microspheres for Long‐Term Storage and Reusage

Perovskite nanocrystals (PNCs) are emerging luminescent materials due to their fascinating physic‐optical properties. However, their sensitive surface chemistry with organic polar solvents, oxygen, and moisture greatly hinders their developments towards practical applications. Herein we promote silica‐passivated PNCs (SP‐PNCs) by in situ hydrolyzing the surface ligands of (3‐aminopropyl) triethoxysilane. The resultant SP‐PNCs possesses a high quantum yield (QY) of 80 % and are precipitable by polar solvents, such as ethanol and acetone, without destroying their surface chemistry or losing QY, which offers an eco‐friendly and efficient method for separation, purification, and phase transfer of PNCs. Moreover, we further promoted a swelling–deswelling encapsulation process to incorporate the as‐made SP‐PNCs into non‐crosslinked polystyrene microspheres (PMs), which can largely increase the stability of the SP‐PNCs against moisture for long‐term storage.