Showing papers in "Express Polymer Letters in 2014"
TL;DR: A review of different classes of polyhydroxyalkanoates, their main properties, processing aspects, commercially available ones, as well as limitations and related improvements being researched, with specific focus on potential applications of PHAs in packag- ing is presented in this paper.
Abstract: Polyhydroxyalkanoates (PHAs) are gaining increasing attention in the biodegradable polymer market due to their promising properties such as high biodegradability in different environments, not just in composting plants, and pro- cessing versatility. Indeed among biopolymers, these biogenic polyesters represent a potential sustainable replacement for fossil fuel-based thermoplastics. Most commercially available PHAs are obtained with pure microbial cultures grown on renewable feedstocks (i.e. glucose) under sterile conditions but recent research studies focus on the use of wastes as growth media. PHA can be extracted from the bacteria cell and then formulated and processed by extrusion for production of rigid and flexible plastic suitable not just for the most assessed medical applications but also considered for applications includ- ing packaging, moulded goods, paper coatings, non-woven fabrics, adhesives, films and performance additives. The present paper reviews the different classes of PHAs, their main properties, processing aspects, commercially available ones, as well as limitations and related improvements being researched, with specific focus on potential applications of PHAs in packag- ing.
651 citations
TL;DR: In this article, composites were fabricated using TLCP-g-GO as reinforcing filler and the mechanical properties and thermal properties of com- posites were systematically investigated, and it was found that the thermal and mechanical properties of the composites are enhanced effectively by the addition of fillers.
Abstract: Graphene oxide (GO) sheets were chemically grafted with thermotropic liquid crystalline epoxy (TLCP). Then we fabricated composites using TLCP-g-GO as reinforcing filler. The mechanical properties and thermal properties of com- posites were systematically investigated. It is found that the thermal and mechanical properties of the composites are enhanced effectively by the addition of fillers. For instance, the composites containing 1.0 wt% of TLCP-g-GO present impact strength of 51.43 kJ/m 2 , the tensile strength of composites increase from 55.43 to 80.85 MPa, the flexural modulus of the composites increase by more than 48%. Furthermore, the incorporation of fillers is effective to improve the glass transition temperature and thermal stability of the composites. Therefore, the presence of the TLCP-g-GO in the epoxy matrix could make epoxy not only stronger but also tougher.
101 citations
TL;DR: In this paper, three blends were prepared from poly(lactic acid) (PLA) and three thermoplastics, polystyrene (PS), polycarbonate (PC) and poly(methyl methacrylate) (PMMA), and the results showed that the structure and properties of the blends cover a rela- tively wide range.
Abstract: Blends were prepared from poly(lactic acid) (PLA) and three thermoplastics, polystyrene (PS), polycarbonate (PC) and poly(methyl methacrylate) (PMMA). Rheological and mechanical properties, structure and component interac- tions were determined by various methods. The results showed that the structure and properties of the blends cover a rela- tively wide range. All three blends have heterogeneous structure, but the size of the dispersed particles differs by an order of magnitude indicating dissimilar interactions for the corresponding pairs. Properties change accordingly, the blend con- taining the smallest dispersed particles has the largest tensile strength, while PLA/PS blends with the coarsest structure have the smallest. The latter blends are also very brittle. Component interactions were estimated by four different methods, the determination of the size of the dispersed particles, the calculation of the Flory-Huggins interaction parameter from sol- vent absorption, from solubility parameters, and by the quantitative evaluation of the composition dependence of tensile strength. All approaches led to the same result indicating strong interaction for the PLA/PMMA pair and weak for PLA and PS. A general correlation was established between interactions and the mechanical properties of the blends.
95 citations
TL;DR: In this paper, the authors present a review of the latest progress in the field of in-line composites monitoring with a focus on Fiber Reinforced Polymeric-based (FRP) composite structures.
Abstract: Composites manufacturing is characterized by many degrees of freedom. Different materials, geometries and thermo-dynamical conditions contribute to a behavior that is difficult to predict. Monitoring the running process (in-line monitoring) eliminates the need for prediction; real time data provided by appropriate sensing systems can be used in the direction of process optimization, quality upgrade or material characterization. The aim of the review at hand is to record and discuss the latest progress in the field of in-line composites monitoring with a focus on Fiber Reinforced Polymeric- based (FRP) composite structures. Summaries of each sensor's principles of operation, appropriate association with poly- mer/composite properties detection, brief descriptions of representative studies, a critical overview of implementation aspects and discussion on the upcoming trends, contribute in constructing a complete picture.
88 citations
TL;DR: In this paper, electroactive polyimide (EPI)/graphene nanocomposite (EPGN) coatings were prepared by thermal imidization and then characterized by Fourier transformation infrared (FTIR) and transmission electron microscope (TEM).
Abstract: In this study, electroactive polyimide (EPI)/graphene nanocomposite (EPGN) coatings were prepared by thermal imidization and then characterized by Fourier transformation infrared (FTIR) and transmission electron microscope (TEM). The redox behavior of the as-prepared EPGN materials was identified by in situ monitoring for cyclic voltammetry (CV) studies. Demonstrating that EPGN coatings provided advanced corrosion protection of cold-rolled steel (CRS) electrodes as compared to that of neat EPI coating. The superior corrosion protection of EPGN coatings over EPI coatings on CRS electrodes could be explained by the following two reasons. First, the redox catalytic capabilities of amino-capped aniline trimer (ACAT) units existing in the EPGN may induce the formation of passive metal oxide layers on the CRS electrode, as indicated by scanning electron microscope (SEM) and electron spectroscopy for chemical analysis (ESCA) studies. More- over, the well-dispersed carboxyl-graphene nanosheets embedded in the EPGN matrix hinder gas migration exponentially. This would explain enhanced oxygen barrier properties of EPGN, as indicated by gas permeability analysis (GPA) studies.
80 citations
TL;DR: In this paper, a green route to prepare insoluble polyvinyl alcohol (PVOH) cast films with potential application as antimicrobial packaging was proposed, where PVOH was cast from different aqueous solutions and analyzed by Dif- ferential Scanning Calorimetry (DSC) and Dynamic Mechanical Analysis (DMA) to determine their physical properties under two storage conditions.
Abstract: In this paper, we propose a green route to prepare insoluble poly(vinyl alcohol) (PVOH) cast films with potential application as antimicrobial packaging. First PVOH films were cast from different aqueous solutions and analyzed by Dif- ferential Scanning Calorimetry (DSC) and Dynamic Mechanical Analysis (DMA) to determine their physical properties under two storage conditions. In order to obtain insoluble films, PVOH was then crosslinked by citric acid (CTR) as con- firmed by Nuclear Magnetic Resonance (NMR) analyses. The crosslinking reaction parameters (curing time, crosslinker content) were studied by comparing the characteristics of PVOH/CTR films, such as free COOH content and glass transi- tion temperature (Tg) value, as well as the impact of the crosslinking reaction on mechanical properties. It was found that for 40 and 10 wt% CTR contents, 120 and 40 min of crosslinking times were necessary to bind all CTR respectively. Brittle films were obtained for 40 wt% CTR whereas 10 wt% CTR content led to ductile films. Finally, films containing hydrox- ypropyl-!-cyclodextrin (HP!CD), chosen as a potential vector of antimicrobial agent, were prepared. The obtained results show that the incorporation of HP!CD in the PVOH matrix does not mainly influence the physical and mechanical proper- ties of the films.
77 citations
TL;DR: Viability testing showed that the nanofibers can provide long term stability for huge amounts of living bacteria if they are kept at (or below) 7°C, and all kinds of nanowebs prepared in this work dissolved instantly when they got in contact with water, thus the developed biohybrids can provide new potential ways for curing bacterial vagi- nosis.
Abstract: The aim of this work was to investigate the suitability of electrospinning for biodrug delivery and to develop an electrospinning-based method to produce vaginal drug delivery systems. Lactobacillus acidophilus bacteria were encapsu- lated into nanofibers of three different polymers (polyvinyl alcohol and polyvinylpyrrolidone with two different molar masses). Shelf life of the bacteria could be enhanced by the exclusion of water and by preparing a solid dosage form, which is an advantageous and patient-friendly way of administration. The formulations were stored at -20, 7 and 25°C, respec- tively. Viability testing showed that the nanofibers can provide long term stability for huge amounts of living bacteria if they are kept at (or below) 7°C. Furthermore, all kinds of nanowebs prepared in this work dissolved instantly when they got in contact with water, thus the developed biohybrid nanowebs can provide new potential ways for curing bacterial vagi- nosis.
65 citations
TL;DR: In this article, reduced graphene oxide or graphene was dispersed in ultra high molecular weight polyethylene (UHMWPE) using two methods to prepare nanocomposite films.
Abstract: Reduced graphene oxide or graphene was dispersed in ultra high molecular weight polyethylene (UHMWPE) using two methods to prepare nanocomposite films. In pre-reduction method, graphite oxide (GO) was exfoliated and dis- persed in organic solvents and reduced to graphene before polymer was added, while reduction of graphene oxide was car- ried out after polymer addition for in situ reduction method. Raman spectroscopic study reveals that the second method results in better exfoliation of graphene but it has more amorphous content as evident from selected area electron diffraction (SAED) pattern, wide angle X-ray and differential scanning calorimetry (DSC). The nanocomposite film produced by pre- reduction method possesses higher crystallinity (almost the same as that of the pure film) as compared to the in situ method. It shows better modulus (increased from 864 to 1236 MPa), better strength (increased from 12.6 to 22.2 MPa), network hardening and creep resistance (creep strain reduced to 9% from 50% when 40% of maximum load was applied for 72 h) than the pure film. These findings show that graphene can be used for reinforcement of UHMWPE to improve its tensile and creep resistance properties.
63 citations
TL;DR: In this paper, the effect of dynamic vulcanization and influence of various types of peroxides as cross-linking agents were studied in detail, and three structurally different peroxideides, namely dicumyl peroxide (DCP), 3,3,5,7,7-pentamethyl 1,2,4-triox- epane (PMTO) and cumyl hydroperoxide (CHP) were taken for investigation.
Abstract: Novel thermoplastic vulcanizates (TPVs) based on silicone rubber (PDMS) and polyamide (PA12) have been prepared by dynamic vulcanization process. The effect of dynamic vulcanization and influence of various types of perox- ides as cross-linking agents were studied in detail. All the TPVs were prepared at a ratio of 50/50 wt% of silicone rubber and polyamide. Three structurally different peroxides, namely dicumyl peroxide (DCP), 3,3,5,7,7-pentamethyl 1,2,4-triox- epane (PMTO) and cumyl hydroperoxide (CHP) were taken for investigation. Though DCP was the best option for curing the silicone rubber, at high temperature it suffers from scorch safety. An inhibitor 2,2,6,6-tetramethylpiperidinyloxyl (TEMPO) was added with DCP to stabilize the radicals in order to increase the scorch time. Though CHP (hydroperoxide) had higher half life time than DCP at higher temperature, it has no significant effect on cross-linking of silicone rubber. PMTO showed prolonged scorch safety and better cross-linking efficiency rather than the other two. TPVs of DCP and PMTO were made up to 11 minutes of mixing. Increased values of tensile strength and elongation at break of PMTO cross-linked TPV indi- cate the superiority of PMTO. Scanning electron micrographs correlate with mechanical properties of the TPVs. High stor- age modulus (E!) and lower loss tangent value of the PMTO cross-linked TPV indicate the higher degree of cross-linking which is also well supported by the overall cross-link density value. Thus PMTO was found to be the superior peroxide for cross-linking of silicone rubber at high temperature.
63 citations
TL;DR: In this paper, the effect of polyacrylonitrile nanofibrous interlaminar layers on the impact properties of unidirectional and woven carbon fabric-reinforced epoxy (EP) matrix composites was investigated.
Abstract: The effect of polyacrylonitrile nanofibrous interlaminar layers on the impact properties of unidirectional and woven carbon fabric (CF)-reinforced epoxy (EP) matrix composites was investigated. The nanofibers were produced directly on the surface of carbon fabrics by a needleless electrospinning method, and composites were then prepared by vacuum-assisted impregnation. Interlaminar shear stress tests, three-point bending, Charpy-impact and instrumented falling weight tests were carried out. The fracture surfaces were analyzed by scanning electron microscopy. Due to the nano-sized reinforcements, the interlaminar shear strength of the woven and unidirectional fiber-reinforced composites was enhanced by 7 and 11%, respectively. In the case of the falling weight impact tests carried out on woven reinforced composites, the nanofibers increased the absorbed energy to maximum force by 64% compared to that measured for the neat composite. The Charpy impact tests indicated that the nanofiber interleaves also led to a significant increase in the initiation and total break energies. Based on the results, it can be concluded that the presence of nanofibers can effectively increase the impact properties of composites without compromising their in-plane properties because the thickness of the composites was not altered by the presence of interleaves. The improvement of the impact properties can be explained by the good load distri- bution behavior of the nanofibers.
60 citations
TL;DR: In this paper, the effect of crosslinking of carboxylated nitrile butadiene rubber (XNBR) by magnesium aluminum layered double hydroxide (MgAl-LDH), known also as hydrotalcite (HT), on rheometric, mechano-dynamical and barrier properties was investigated.
Abstract: The presence of carboxyl groups in carboxylated nitrile butadiene rubber (XNBR) allows it to be cured with dif- ferent agents. This study considers the effect of crosslinking of XNBR by magnesium aluminum layered double hydroxide (MgAl-LDH), known also as hydrotalcite (HT), on rheometric, mechano-dynamical and barrier properties. Results of XNBR/HT composites containing various HT loadings without conventional curatives are compared with XNBR com- pound crosslinked with commonly used zinc oxide. Hydrotalcite acts as an effective crosslinking agent for XNBR, as is particularly evident from rheometric and Fourier transform infrared spectroscopy (FTIR) studies. The existence of ionic crosslinks was also detected by dynamic mechanical analysis (DMA) of the resulting composites. DMA studies revealed that the XNBR/HT composites exhibited two transitions - one occurring at low temperature is associated to the Tg of elas- tomer and the second at high temperature corresponds to the ionic transition temperature Ti. Simultaneous application of HT as a curing agent and a filler may deliver not only environmentally friendly, zinc oxide-free rubber product but also ionic elastomer composite with excellent mechanical, barrier and transparent properties.
TL;DR: In this article, four kinds of nanosilica particles with different surface modification were employed to fabricate low-density polyethylene (LDPE) composites using melt mixing and hot molding methods.
Abstract: Four kinds of nanosilica particles with different surface modification were employed to fabricate low-density polyethylene (LDPE) composites using melt mixing and hot molding methods. The surface chemistry of modified nanosil- ica was analyzed by X-ray photoelectron spectroscopy. All silica nanoparticles were found to suppress the space charge injection and accumulation, increase the volume resistivity, decrease the permittivity and dielectric loss factor at low fre- quencies, and decrease the dielectric breakdown strength of the LDPE polymers. The modified nanoparticles, in general, showed better dielectric properties than the unmodified ones. It was found that the carrier mobility, calculated from J-V curves using the Mott-Gurney equation, was much lower for the nanocomposites than for the neat LDPE.
TL;DR: In this article, the shape memory polymers (SMPs) are used to memorize one or more temporary shapes and recover to the permanent shape upon an external stimulus that is usually heat.
Abstract: Shape memory polymers (SMPs) are capable of memorizing one or more temporary shapes and recovering to the permanent shape upon an external stimulus that is usually heat. Biodegradable polymers are an emerging family within the SMPs. This minireview delivers an overlook on actual concepts of molecular and supramolecular architectures which are followed to tailor the shape memory (SM) properties of biodegradable polyesters. Because the underlying switching mech- anisms of SM actions is either related to the glass transition (Tg) or melting temperatures (Tm), the related SMPs are classi- fied as Tg- or Tm-activated ones. For fixing of the permanent shape various physical and chemical networks serve, which were also introduced and discussed. Beside of the structure developments in one-way, also those in two-way SM polyesters were considered. Adjustment of the switching temperature to that of the human body, acceleration of the shape recovery, enhancement of the recovery stress, controlled degradation, and recycling aspects were concluded as main targets for the future development of SM systems with biodegradable polyesters.
TL;DR: In this article, the effect of plasticization of PLA on the mechanical and physical properties of the derived TPE was investigated, and four plasticizers were selected: tributyl acetyl citrate (TBAC), TBC, glycerol triacetate (GTA), and triethyl-2-acetylcitrate (TEAC).
Abstract: Bio-based thermoplastic elastomers (TPE) containing natural rubber and poly(lactic acid) were prepared by melt blending in an internal mixer. The blend ratio was 60% of natural rubber and 40% of poly(lactic acid). Dynamic vulcaniza- tion of natural rubber was performed with the sulfur system. The 2 mm - thick sheet samples were prepared by compres- sion molding. The objective of this study was to investigate the effect of plasticization of PLA on the mechanical and physical properties of the derived TPE. Four plasticizers were selected: tributyl acetyl citrate (TBAC), tributyl citrate (TBC), glycerol triacetate (GTA), and triethyl-2-acetyl citrate (TEAC). The investigated properties were the tensile proper- ties, tear strength, thermal ageing and ozone resistance, hardness, resilience, tension set and compression set. All plasticiz- ers increased the strain at break. TBAC and TBC increased the stress at break. All plasticizers decreased the tear strength, hardness and resilience, and slightly changed the tension and compression set. TBAC seemed to be the best plasticizer for the TPE. The presence of 4 pph (parts per hundred resin) of plasticizer provided the highest strength and tensile toughness and the strain at break increased with the increasing plasticizer content. The plasticizers decreased the Tg and Tcc of the PLA and did not affect the degree of crystallinity of PLA in the TPE.
TL;DR: In this paper, an influence of IL-f/epoxy weight ratio (3, 6 and 9/100, phr), carbon nanofiller type and content on viscosity of epoxy compositions during storage at ambient tem- perature was evaluated.
Abstract: Epoxy nanocomposites with commercial carbon nanotubes (CNT) or graphene (GN) have been prepared using phosphonium ionic liquid (trihexyltetradecylphosphonium bis(2,4,4-trimethylpentyl) phosphinate, IL-f). IL-f served simul- taneously as nanofiller dispersing medium and epoxy resin catalytic curing agent. An influence of IL-f/epoxy weight ratio (3, 6 and 9/100, phr), carbon nanofiller type and content on viscosity of epoxy compositions during storage at ambient tem- perature was evaluated. Curing process was controlled for neat and CNT or GN modified epoxy compositions (0.25- 1.0 wt% load) using differential scanning calorimetry and rheometry. Epoxy nanocomposites exhibited slightly increased glass transition temperature values (146 to 149°C) whereas tan ! and storage modulus decreased (0.30 to 0.27 and 2087 to 1070 MPa, respectively) as compared to reference material. Crosslink density regularly decreased for composites with increasing CNT content (11 094 to 7020 mol/m 3 ). Electrical volume resistivity of the nanocomposites was improved in case of CNT to 4"10 1 #"m and GN to 2"10 5 #"m (nanofiller content 1 wt%). Flame retardancy was found for modified epoxy materials with as low GN and phosphorus content as 0.25 and 0.7 wt%, respectively (increase of limiting oxygen index to 26.5%).
TL;DR: In this article, a series of nanocrystalline cellulose (NCC) reinforced natural rubber/butadiene rubber/structure-butane rubber/styrene butadiene (SBR) blends were prepared via mastication of NR/NCC, BR/SBR and other ingredients.
Abstract: A series of nanocrystalline cellulose (NCC) reinforced natural rubber/butadiene rubber/styrene-butadiene rubber (NR/BR/SBR) blends were prepared via mastication of NR/NCC, BR/SBR and other ingredients. Resorcinol and hexamethylene tetramine (RH) was adopted to modify the interface between NCC and rubber matrix. The morphology, dynamic viscoelastic behavior, apparent crosslink density, mechanical performance and dynamic mechanical property of NR/BR/SBR/NCC blends were discussed in detail. The results showed that NCC was uniformly dispersed in composites and RH could enhance the adhesion of NCC and matrix. According to the dynamic mechanical analysis, NCC performed comparable reinforcing effect with carbon black (CB), and the modulus was improved with modification of RH. Mechanical tests showed that the replacement of CB by NCC in the blends did not deteriorate mechanical properties of composites. Besides, the blends exhibited best mechanical properties, when 10 phr NCC substituted CB.
TL;DR: In this paper, a simple green route as well as synthetic routes has been used for the preparation of pure phase Bismuth ferrite (BiFeO3) particles, which are in the range of 50-60 nm and exhibit mixed morphology.
Abstract: Bismuth ferrite (BiFeO3) is considered as one of the most promising materials in the field of multiferroics. In this work, a simple green route as well as synthetic routes has been used for the preparation of pure phase BiFeO3. An extract of Calotropis Gigantea flower was used as a reaction medium in green route. In each case so formed BiFeO3 particles are of comparable quality. These particles are in the range of 50-60 nm and exhibit mixed morphology (viz., spherical and cubic) as confirmed by TEM analysis. These pure phase BiFeO3 nanoparticles were first time surface modified effectively by mean of two silylating agent's viz., tetraethyl orthosilicate (TEOS) and (3-Aminopropyl)triethoxysilane (APTES). Modi- fied and unmodified BiFeO3 nanoparticles were efficiently introduced into polyvinylacetate (PVAc) matrix. It has been shown that nanocomposite prepared by modified BiFeO3 comprise superior dispersion characteristics, improved ferroelec- tric properties and favorable magneto-dielectric properties along with excellent wettability in compare to nanocomposite prepared by unmodified BiFeO3. These preliminary results demonstrate possible applications of this type of nanocompos- ites particularly in the field of multiferroic coating and adhesives.
TL;DR: In this paper, the authors present the results of a project OP VaVpI Centre for Nanomaterials, Advanced Technologies and Innovation (CZ.1.05/2.1/1.00/01.0005).
Abstract: Ministry of Interior of the Czech Republic [VG20102014049]; Project OP VaVpI Centre for Nanomaterials, Advanced Technologies and Innovation [CZ.1.05/2.1.00/01.0005]; GACR [P208/12/0105]
TL;DR: In this paper, a structure-property relationship of natural rubber (NR)/silica (SiO2) composites modified by a novel multi-functional rubber agent, N-phenyl- N!- ("-triethoxysilane)-propyl thiourea (STU), is investi- gated in detail.
Abstract: Vulcanization property and structure-properties relationship of natural rubber (NR)/silica (SiO2) composites modified by a novel multi-functional rubber agent, N-phenyl- N!-("-triethoxysilane)-propyl thiourea (STU), are investi- gated in detail. Results from the infrared spectroscopy (IR) and X-ray photoelectron spectroscopy (XPS) show that STU can graft to the surface of SiO2 under heating, resulting in a fine-dispersed structure in the rubber matrix without the con- nectivity of SiO2 particles as revealed by transmission electron microscopy (TEM). This modification effect reduces the block vulcanization effect of SiO2 for NR/SiO2/STU compounds under vulcanization process evidently. The 400% modulus and tensile strength of NR/SiO2/STU composites are much higher than that of NR/SiO2/TU composites, although the crys- tal index at the stretching ratio of 4 and crosslinking densities of NR/SiO2 composites are almost the same at the same dosage of SiO2. Consequently, a structure-property relationship of NR/SiO2/STU composites is proposed that the silane chain of STU can entangle with NR molecular chains to form an interfacial region, which is in accordance with the experimental observations quite well.
TL;DR: In this article, the authors compared the effect of varying the carboxylic-group content of thermally reduced graphene oxides (TRGs) on the anticorrosive properties of as-prepared poly(methyl methacrylate) (PMMA)/TRG compos-ite (PTC) coatings.
Abstract: We present comparative studies on the effect of varying the carboxylic-group content of thermally reduced graphene oxides (TRGs) on the anticorrosive properties of as-prepared poly(methyl methacrylate) (PMMA)/TRG compos- ite (PTC) coatings. TRGs were formed from graphene oxide (GO) by thermal exfoliation. The as-prepared TRGs were then characterized using Fourier transform infrared (FTIR) spectroscopy and X-ray photoelectron spectroscopy (XPS). Subse- quently, the PTC materials were prepared via a UV-curing process and then characterized using FTIR spectroscopy and transmission electron microscopy (TEM). PTC coatings containing TRGs with a higher carboxylic-group content exhibited better corrosion protection of a cold-rolled steel electrode that those with a lower carboxylic-group content. This is because the well-dispersed TRG with a higher carboxylic-group content embedded in the PMMA matrix effectively enhances the oxygen barrier properties of the PTC. This conclusion was supported by gas permeability analysis.
TL;DR: In this paper, the chemical recycling of the poly(ethylene terephthalate), (PET), has been successfully carried out by glycoly-sis in the presence of bis (2-hydroxyethyl) tereylate (BHET) resulting in the formation of hydroxytelechelic oligomers.
Abstract: The chemical recycling of the poly(ethylene terephthalate), (PET), has been successfully carried out by glycoly- sis in the presence of bis (2-hydroxyethyl) terephthalate (BHET) resulting in the formation of hydroxytelechelic oligomers. These oligomers were then treated with carboxytelechelic poly(!-caprolactone) oligomers of —n = 2300 and —n = 730 g·mol -1 molecular weight, in the absence or presence of the titanium tetrabutyloxide (Ti(OBu)4) as a catalyst to get multiblock copolyesters. The chemical structure of the synthesized copolyesters was investigated by size exclusion chro- matography (SEC) and proton Nuclear Magnetic Resonance ( 1 H NMR) spectroscopy. Moreover the differential scanning calorimetry (DSC) was used to explore their thermal properties. The ester-ester interchange reaction was observed between the two oligopolyesters, was studied and discussed in detail.
TL;DR: In this article, the authors employed the lamina of montmorillonite (MMT) as a plane template to anchor cationic lignin (CL) on its two sides, resulting in the formation of CL-MMT hybrid materials (CLM).
Abstract: Lignin was viewed as a spherical microgel in aqueous alkali. While spread out in a monolayer or adsorbed on a surface, lignin was made up of flexible, disk-like molecules with approximately the same thickness of 2 nm. According to this principle, we employed the lamina of montmorillonite (MMT) as a plane template to anchor cationic lignin (CL) on its two sides, resulting in the formation of CL-MMT hybrid materials (CLM). The isotherm adsorption behavior and structure characteristics of CLM were studied. The results showed that CLM was individually dispersed nanosheets with a thickness of about 5 nm when the mass ratio of CL to MMT is more than 2:1 and prepared at acidic or neutral pH. Compared to the co- coagulation of lignin and styrene-butadiene rubber (SBR), CLM obviously accelerated the coagulation rate, due to the reduc- tion of surface activity of CL restricted by MMT. The nanoscale dispersion of CLM in SBR matrix significantly improved the tensile strength of CLM/SBR nanocomposites to 14.1 MPa by adding only 10 phr CLM and cardanol glycidyl ether (CGE) as compatibilizer. Dynamic mechanical analysis (DMA) showed that the glass transition temperature of SBR/CLM nanocomposites decreased with increasing CLM loading. Correspondingly, a special interfacial structure was proposed.
TL;DR: Gum ghatti-cl-poly(acrylamide-aniline) interpenetrating network (IPN) was synthesized by a two-step aqueous polymerization method, in which aniline monomer was absorbed into the network of gum ghattis-cl poly(acarlamide) and followed by a polymerization reaction between anILine monomers.
Abstract: Gum ghatti-cl-poly(acrylamide-aniline) interpenetrating network (IPN) was synthesized by a two-step aqueous polymerization method, in which aniline monomer was absorbed into the network of gum ghatti-cl-poly(acrylamide) and followed by a polymerization reaction between aniline monomers. Initially, semi-IPN based on acrylamide and gum ghatti was prepared by free-radical copolymerization in aqueous media with optimized process parameters, using N,N!-methylene- bis-acrylamide, as cross-linker and ammonium persulfate, as an initiator system. Optimum reaction conditions affording maximum percentage swelling were: solvent (mL) =12, Acrylamide (AAm) (mol·L -1 ) = 1.971, Ammonium peroxydisulfate (APS) (mol·L -1 ) = 0.131·10 -1 , N,N!-methylene-bis-acrylamide (MBA) (mol·L -1 ) = 0.162·10 -1 , reaction time (min) = 210, temperature (°C) = 100 and pH = 7.0. The resulting IPN was doped with different protonic acids. The effect of the doping has been investigated on the conductivity and surface morphology of the IPN hydrogel. The maximum conductivity was observed with 1.5N HClO4 concentration. The morphological, structural and electrical properties of the candidate polymers were studied using scanning electron micrscopy (SEM), Fourier transform infrared spectroscopy FTIR and two-probe method, respectively.
TL;DR: In this paper, the curing kinetics and mechanism of modified epoxy novolac resin (MDEN) with methanol etherified amino resin were studied by means of differential scanning calorimetry (DSC), Fourier transform- infrared (FT-IR) spectroscopy and chemorheological analysis.
Abstract: The curing kinetics and mechanism of epoxy novolac resin (DEN) and modified epoxy novolac resin (MDEN) with methanol etherified amino resin were studied by means of differential scanning calorimetry (DSC), Fourier transform- infrared (FT-IR) spectroscopy and chemorheological analysis. Their kinetics parameters and models of the curing were examined utilizing isoconversional methods, Flynn-Wall-Ozawa and Friedman methods. For the DEN mixture, its average activation energy (Ea) was 71.05 kJ/mol and the autocatalytic model was established to describe the curing reaction. The MDEN mixture exhibited three dominant curing processes, termed as reaction 1, reaction 2 and reaction 3; and their Ea were 70.05, 106.55 and 101.91 kJ/mol, respectively. Besides, Ea of reaction 1 was similar to that of DEN mixture, while Ea of reactions 2 and 3 corresponded to that of the etherification reaction between hydroxyl and epoxide group. Moreover, these three dominant reactions were n th order in nature. Furthermore, their curing mechanisms were proposed from the results of DSC and FTIR. The chemorheological behavior was also investigated to obtain better plastics products via opti- mizing the processing schedules.
TL;DR: In this article, a molecularly imprinted nanocomposites MIPRhB-PPy/TiO2 were successfully prepared by sur- face molecular imprinting technique with rhodamine B (RhB) as template molecule.
Abstract: Highly selective molecularly imprinted nanocomposites MIPRhB-PPy/TiO2 were successfully prepared by sur- face molecular imprinting technique with rhodamine B (RhB) as template molecule. The prepared MIPRhB-PPy/TiO2 coated with a thin imprinted layer could respond to visible light. The static and dynamic binding experiments revealed that MIPRhB-PPy/TiO2 possessed strong affinity, high adsorption capacity and fast adsorption rate for RhB. The selectivity experiments indicated that MIPRhB-PPy/TiO2 had excellent recognition selectivity for RhB. Selective photocatalytic degra- dation experiments indicated that the apparent rate constant (k) for the photodegradation of RhB over MIPRhB-PPy/TiO2 is 0.0158 min -1 , being 3.6 times of that over non-imprinted nanocomposites NIP-PPy/TiO2 (0.0044 min -1 ). Compared with the NIP-PPy/TiO2, MIPRhB-PPy/TiO2 showed higher photocatalytic selectivity toward RhB under visible light, which was attributed the introduction of the imprinted cavities on the surface of MIPRhB-PPy/TiO2. Moreover, MIPRhB-PPy/TiO2 exhibited high reusability and stability. The results indicate that molecularly imprinted nanocomposites MIPRhB-PPy/TiO2 have a promising perspective in industrial wastewater treatment.
TL;DR: In this paper, the authors used reduced graphene oxide decorated with halloysite nanotubes (HNTs-d-rGO) hybrid composite as the additive in polyamide 6 (PA6) matrix.
Abstract: The improvement of flame-retardant properties of polyamide 6 (PA6) was achieved by using reduced graphene oxide decorated with halloysite nanotubes (HNTs-d-rGO) hybrid composite as the additive in PA6 matrix. The intimate integration of reduced graphene oxide (rGO) and halloysite nanotubes (HNTs) through a three-step chemical functionaliza- tion, enabled the combination of their unique physical and chemical characteristics together. The nanostructure of HNTs-d- rGO was determined by Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM). A morphological study revealed that HNTs-d-rGO was dispersed uniformly in PA6 matrix. From the results of cone calorimetry measurements, the fire retardant properties of PA6 were further improved with the addition of HNTs-d-rGO when compared with that of either HNTs, or GO, or a mixture of HNTs and GO (HNTs- m-GO) used in PA6 matrix. The results indicate clearly that higher flame-retardant activity of the integrated HNTs-d-rGO nanostructures than that of the simple mixture verifies the importance of the intimate integration between HNTs and rGO, which ascribe to the combination of the stable silica layer created by HNT and the barrier effect of rGO.
TL;DR: In this paper, a template-based approach for the dispersion of hydrophilic nanoparticles within hydrophobic polymer matrices is investigated, where a mixture of high density polyethylene (HDPE) and PEO at 50/50 wt% is prepared by melt mixing and the addition of small amounts of organo-clay promotes the necessary refinement of the blend morphology.
Abstract: The efficiency of a novel template-based approach for the dispersion of hydrophilic nanoparticles within hydrophobic polymer matrices is investigated. The procedure envisages the permeation of a well dispersed nanoparticle suspension inside a micro-porous matrix, obtained through selective extraction of a sacrificial phase from a finely interpen- etrated co-continuous polymer blend. Specifically, a blend of high density polyethylene (HDPE) and polyethylene oxide (PEO) at 50/50 wt% is prepared by melt mixing. The addition of small amounts of organo-clay promotes the necessary refinement of the blend morphology. Once removed the PEO, the micro-porous HDPE matrix is dipped in a colloidal sus- pension of zinc oxide nanoparticles which exhibits low interfacial tension with HDPE. A system prepared by traditional melt mixing is used as reference. Melt- and solid-state viscoelastic measurements reveal a good quality of the filler disper- sion despite the uneven distribution on micro-scale. The latter can be capitalized to minimize the filler content to attain a certain improvement of the material properties or to design nano-structured polymer composites.
TL;DR: In this paper, the morphology and the mechanical properties of polylactide/poly(hydroxybutyrate-co-hydroxyvalerate) blends of various compositions were studied.
Abstract: The morphology and the mechanical properties of polylactide/poly(hydroxybutyrate-co-hydroxyvalerate) blends of various compositions were studied. The statistical analysis of the scanning electron microscopy images allowed finding two statistical ensembles of the minor-phase particles. The first ensemble involves the dispersed particles, whereas the sec- ond one contains the coalesced particles. The mean diameters of both dispersed and coalesced minor-phase particles were calculated and plotted against the blend composition. Young's modulus, tensile strength, elongation at break, and Charpy impact strength of the blends were determined and examined as a function of the blend composition. The Young's modulus values were shown to be in accordance with theoretical predictions.
TL;DR: In this article, a copolymer, Poly(MMA-co-MA), was synthesized by radical polymerization of maleic anhydride (MA) and methyl methacrylate (MMA), characterized and transformed into multifunctional nanochelating resin beads (80-150 nm) via hydrolysis, graft ing and crosslink reactions.
Abstract: Chelating resins are suitable materials for the removal of heavy metals in water treatments. A copolymer, Poly(MMA-co-MA), was synthesized by radical polymerization of maleic anhydride (MA) and methyl methacrylate (MMA), characterized and transformed into multifunctional nanochelating resin beads (80-150 nm) via hydrolysis, graft- ing and crosslink reactions. The resin beads were characterized by swelling studies, field emission scanning electron microscopy (FESEM) and Fourier transform infrared spectroscopy (FTIR). The main purpose of this work was to deter- mine the adsorption capacity of the prepared resins (swelling ratio ~55%) towards metal ions such as Hg 2+ , Cd 2+ , Cu 2+ from water at three different pH values (3, 6 and 9). Variations in pH and types of metal ions have not significantly affected the chelation capacity of these resins. The maximum chelation capacity of one of the prepared resin beads (Co-g-AP3) for Hg 2+ was 63, 85.8 and 71.14 mg/g at pH 3, 6 and 9, respectively. Approximately 96% of the metal ions could be desorbed from the resin. Adsorption capacity of these resins towards three commercial synthetic azo dyes was also investigated. The max- imum adsorption of dye AY42 was 91% for the resin Co-g-AP3 at room temperature. This insures the applicability of the synthesized resins for industrial applications.
TL;DR: In this article, the state of carbon nanotube (CNT) dispersion in epoxy is characterized at different stages of nanocomposite preparation: in the original masterbatch with high CNT concentration, after masterbatch dilution, in the process of curing and in the final nano-composite.
Abstract: The state of carbon nanotube (CNT) dispersion in epoxy is likely to change in the process of composite produc- tion. In the present work CNT dispersion is characterized at different stages of nanocomposite preparation: in the original masterbatch with high CNT concentration, after masterbatch dilution, in the process of curing and in the final nanocompos- ite. The evaluation techniques included dynamic rheological analysis of the liquid phases, optical, environmental and charge contrast scanning electron microscopy, electrochemical impedance spectroscopy and dynamic mechanical analysis. The evolution of the CNT dispersion was assessed for two CNT/epoxy systems with distinctly different dispersion states induced by different storage time. Strong interactions between CNT clusters were revealed in the masterbatch with a longer storage time. Upon curing CNT clusters in this material formed a network-like structure. This network enhanced the elastic behaviour and specific conductivity of the resulting nanocomposite, leading to a partial electrical percolation after curing.