Silica reinforced triblock copolymer gels

The effect of silica and polymer coated silica particles as reinforcing agents on the structural and mechanical properties of polystyrene-poly(ethylene/butylene)-polystyrene (PS-PEB-PS) triblock gel has been investigated. Different types of chemically modified silica have been compared in order to evaluate the influence of the compatibility between gel and filler.Time-resolved SANS and small-angle X-ray scattering (SAXS) shows that the presence of silica particles affects the ordering of the polystyrene domains during gelsetting. The scattering pattern of silica-reinforced gels reveals strong scattering at very low q, but no structure and formfactor information. However, on heating above the viscoelastic to plastic transition, the ‘typical’ scattering pattern of the copolymer gel builds-up. All reinforced gels are strengthened by the addition of the reinforcing agent. The transitions from a viscoelastic rubber to a plastic fluid and from a plastic fluid to a viscoelastic liquid are shifted to more elevated temperatures when silica is added to the triblock copolymer gel.     

Synthesis and properties of clay‐dispersed ABA triblock copolymer nanocomposite via ATRP

A novel clay‐dispersed ABA (PSe‐PMMA‐PSt) triblock copolymer nanocomposite was synthesized by atom transfer radical polymerization (ATRP). The resulting material showed an expansion of interlayer distance and higher thermal stability. The molecular weight (MW) and the molecular weight distribution (MWD) can be controlled. Exfoliated nanocomposite was achieved as revealed by X‐ray diffraction (XRD) and transmission electron microscopy (TEM). It was found that the addition of only a small amount of organo‐clay was enough to improve the thermal stabilities and properties of nanocomposite. POLYM. COMPOS. 26:465–469, 2005. © 2005 Society of Plastics Engineers.     

天然鳞片石墨制备可膨胀石墨的工艺研究

以攀枝花天然鳞片石墨为原料,高锰酸钾和双氧水为氧化剂,硝酸、硫酸和高氯酸作为插层剂,制备膨胀石墨。实验发现较佳的膨化温度为950 ℃,并以此温度制备膨胀石墨。结果显示,以双氧水和硫酸制备的膨胀石墨其膨胀容积为130.97~221.80 mL/g;以高锰酸钾和硝酸制备的可膨胀石墨其膨胀容积为150.65~247.19 mL/g;以高锰酸钾和高氯酸制备的膨胀石墨,在干燥温度和时间分别为50 ℃和4~5 h时膨胀容积可达300 mL/g以上。实验还采用XRD和SEM对制备的膨胀石墨结构和形貌进行分析,测试结果发现膨胀石墨的结构完整,可用于进一步制备复合相变材料。     

A study on electrical and thermal conductivities of ethylene–octene copolymer/expandable graphite composites

A series of ethylene–octene copolymer (EOC) composites have been prepared by melt‐mixing with different weight ratios of expandable graphite filler (0–50% by weight). Electrical conductivity [both alternating current (AC) and direct current (DC)] and thermal conductivity studies were carried out. Effect of filler loading and frequency on electrical conductivity was studied. DC conductivity has increased from 1.51 × 10^?13 S cm^?1 to 1.17 × 10^?1 S cm^?1. Percolation threshold by DC and also AC methods was observed at about 16 vol% of the filler. Real part of permittivity was found to be decreasing with increase in frequency while conductivity was increasing. Thermal conductivity was also found to be increasing gradually from 0.196 to 0.676 Wm^?1 K^?1 which is about 245% increase. Graphite not only increases the electrical and thermal conductivities but at and above 40 wt%, also acts as a halogen‐free, environmental friendly flame retardant. Shore‐A hardness of EOC/graphite composites shows that even with high graphite loading, the hardness is increased from about 50–68 only so that the rubbery nature of the composite is not affected very much. POLYM. ENG. SCI., 2012. © 2012 Society of Plastics Engineers     

聚乙醇酸/聚乙二醇/聚乙醇酸三嵌段聚合物的合成

采用溶液聚合法合成了三嵌段聚合物聚乙醇酸/聚乙二醇/聚乙醇酸,采用红外光谱、核磁共振、X射线衍射、DSC方法对聚合物进行了表征。聚合物的结晶度为57.95%,Tg和Tm分别为44.55℃和71.30℃。     

Properties and microstructure of expandable graphite particles pulverized with an ultra-high-speed mixer

The expandable graphite (EG) particles were pulverized to achieve different and smaller sizes using an ultra-high-speed mixer. The microstructure of particles was observed by a scanning electron microscope (SEM). The as-received EG particles showed an irregular flake shape. With the increase of the mixing time, the EG particles tended to be circular and the collapses and cracks in the EG surfaces appeared, and their average diameter and average area rapidly reduced. At the same time, their expansion volume after thermal treatment greatly decreased, resulting from the reduction of particle sizes and the direct release of the oxidant inside the EG particles instead of exfoliating the particles. The expanded EG particles revealed the typical wormlike structure.     

Synergism between hydrotalcite and silicate‐modified expandable graphite on ethylene vinyl acetate copolymer combustion behavior

Influence of independent Mg–Al‐layered double hydroxide (LDH), silicate modified expandable graphite (EG), mixture of LDH and EG at various ratios on ethylene vinyl acetate copolymer (EVA) combustion behavior and thermal stability was detected in sequence through the limiting oxygen index (LOI), vertical combustion (UL‐94) level, microscale combustion calorimeter (MCC) tests and thermal gravimetric/differential thermal gravimetric (TG/DTG) analysis. Results show that the 30 wt % LDH can improve the LOI of 70EVA/30LDH to 27.0%, but the combustion accompanies with serious melt‐dropping. While, the same amount of the EG can increase the LOI, UL‐94 level to 28.5%, V‐0 respectively. However, the combination of LDH and EG can further enhance the 70EVA/20LDH/10EG flame retardancy, it presents the LOI of 29.7%, UL‐94 level of V‐0, and total heat release of 29.5 kJ g^?1. The excellent flame retardancy is attributed to its compact residue. Compared with residue mass, the residue compactness plays a more important role in improving flame retardancy. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134 , 44634.     

Synthesis and evaluation of new amphiphilic polyethylene glycol-based triblock copolymer surfactants

We report in this investigation the synthesis of a new series of amphiphilic ABA-triblock copolymers consisting of double-chain hydrophobic moieties (A) of different chain lengths attached to each end of polyethylene glycols of different molecular weights (B). The identities of the prepared compounds were confirmed by elemental and Fourier transform infrared analyses. The prepared compounds showed good water solubility. Some of their surface properties, such as the critical micelle concentration, effectiveness of water surface tension reduction, surface excess concentration, standard free energies of adsorption and micellization, and surface area per molecule, were determined.     

Preparation of liquid‐filled micelles based on an amphiphilic triblock copolymer

A series of novel amphiphilic triblock poly(ethylene glycol)‐b‐poly(2‐aminoethyl methacrylate hydrochloride)‐b‐poly(heptadeca‐fluorodecyl acrylate) (PEG‐b‐PAEMA‐b‐PHFDA) comprised of two hydrophilic PEG and PAEMA segments and one hydrophobic PHFDA segment was designed and synthesized. The structure of the triblock copolymer was characterized by ¹H‐NMR and GPC analysis. The amphiphilic triblock copolymer was capable of self‐assembling into liquid‐filled micelles that consisted of PHFDA and liquid perfluorocarbons (PFCs) as the core and PEG as outer shell. PAEMA can be used as cross‐linking sites to increase the stability of the liquid‐filled micelles. The shape, size, and Acoustic properties of the obtained liquid‐filled micelles were investigated. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Preferential plasticization of SBS triblock copolymer

Thermoplastic rubbers made of triblock copolymers of styrene-butadiene-styrene in commercial formulations are commonly used in conjunction with petroleum extender oils, in order to reduce the melt viscosity of the rubber during its processing. These mineral oils contain known quantities of paraffinic-naphthenic and aromatic molecules, which in turn are preferably absorbed by the rubbery and glassy phases respectively, affecting selectively the copolymer domain structure and thus the rheological and mechanical properties. Using a plasticizer, the melt viscosity of the system is reduced due to the plasticization of the phases, as expected. The melt rheological transition temperature shown by the unplasticized block copolymer is still present in the oil extended formulations. The flow activation energy is affected by the temperature, type and content of plasticizer. For temperatures lower than the rheological transition temperature the aromatic oil gradually weakens and destroys the polystyrene aggregates and the paraffinic oil induces a greater segregation of the polystyrene aggregates. At temperatures above the rheological transition temperature the behaviour of the two is similar because the flow is homogeneous.     

不同氧化剂制备可膨胀石墨的研究

通过混酸法制备了两种不同氧化剂体系的可膨胀石墨(EG),并采用膨胀容积和X射线(XRD)对EG进行了表征。实验结果表明:K2Cr2O7为氧化剂制备的可膨胀石墨,氧化充分,插层效果好,膨胀容积(EC)大,K2Cr2O7同石墨的最佳比例是0.8∶10。     

Melt rheological behavior of a triblock copolymer based on aramide end‐segments

Melt rheological behavior of a ABA triblock polymer made of poly(tetramethylene oxide) (PTMO) (M_n = 2,900 g mol^?1) soft segment and aramide hard segment was studied. The aramide end‐segments ( A ) were short and mono‐disperse in length. The mid‐segment ( B ) consisted of PTMO₂₉₀₀ extended with terephthalate units to a molecular weight of 9000 g mol^?1. The molecular weight of the triblock was 9700 g mol^?1. Rheological behavior of this material was studied by parallel‐plate and capillary method. The ABA triblock copolymer was compared with a B polymer (PTMO‐terephthalate) of a similar molecular weight. The low molecular weight B polymer had a Newtonian behavior. The low molecular weight triblock copolymer had at high frequencies a low complex viscosity. However, at low frequencies the triblock copolymer had a very high complex viscosity. Also the G″/G′ ratio decreased with decreasing frequency to values less then one and the G′ seemed to have at low frequencies a plateau value. The activation energy of the process increased in value with decreasing shear rate. All these results indicate that the triblock copolymer at low frequencies had a gel‐like behavior and this probably due to the clustering of the aramide segments. The aramide clusters are thought to be the (weak) network points of the gel. This network was also found to have a time dependant rheological response and thus a thixotropic behavior. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Effects of expandable graphite on char morphology and pyrolysis of epoxy based intumescent fire-retardant coating

The current study was designed to investigate the effects of expandable graphite (EG) on fire protection properties of intumescent fire-retardant coating for steel structures. Several formulations of intumescent coating were prepared and tested according to ISO 834 for char expansion. The chars were found without cracks and bonded with the steel substrate. The results showed that the coating slowly degraded during the test and char remained in contact with vertically tested coated substrate. The coated substrates were also tested for weather resistance using humid and ultraviolet environment. The char was characterized by using FESEM, XRD, FTIR, TGA, and XPS analysis. FESEM examined char morphology of the coatings after furnace fire test. XRD and FTIR showed the presence of graphite, borophosphate; boron oxide and sassolite in the char. TGA and DTGA results disclosed that EG improved the residual mass of coating. XPS analysis showed the percentages of carbon and oxygen are 48.50 and 43.45 in char of formulation with 12.8% EG. The results of weathering test coatings showed decreased in char expansion because of a humidity and UV light. The formulation with 9.8% EG showed the maximum char expansion and high residual mass among the formulations investigated in this study. The weathering tested coated samples showed their capability of fire protection.     

Characterization of new formulations for the rotational molding based on ethylene–propylene copolymer/graphite nanocomposites

In this article, ethylene–propylene copolymer/lamellar graphite nanocomposites were processed to be used in rotational molding. The addition of graphite aims at increasing the thermal conductivity of polyolefin and reducing processing cycle time. This article describes the different ways to get a well‐controlled dispersion of fillers in the matrix. For that, the control of the filler/matrix interactions is necessary. Graphite was treated with a concentrated nitric acid and sulfuric acid solution to lead to a graphite intercalation compound (GIC). By heating at high temperature, expanded lamellar graphite is so obtained. As the graphite surface energy is higher than polyolefin matrix one, the initial graphite and expanded graphite were treated with stearic acid, commonly used in the case of calcium carbonate, in order to match the surface energy of the hydrophobic matrix. In addition, as for clay‐polyolefin compounding, an interfacial modifier, i.e. a maleated ethylene–propylene copolymer (EP‐g‐MA) was added to improve the interactions between fillers and hydrophobic polyolefin matrix. POLYM. ENG. SCI., 2008. © 2008 Society of Plastics Engineers     

超细鳞片石墨制备可膨胀石墨工艺及影响因素

以325目超细鳞片石墨为原材料,K2Cr2O7为氧化剂,浓H2SO4为插层剂,用化学氧化法制备可膨胀石墨(EG),通过正交试验法筛选出最优配方及工艺条件,即m(石墨)誜V(98%H2SO4)誜m(K2Cr2O7)=1誜3誜0.3,反应温度30℃,反应时间15 min,膨胀容积45 mL/g。制取最大膨胀容积EG的最优工艺条件和石墨粒径有关,用小粒径石墨制备EG比用大粒径石墨制备EG需要的氧化剂的量多,完成插层反应所需的时间短。     

以三嵌段共聚物为模板介孔氧化铝的形貌控制合成

以三嵌段共聚物作为结构导向剂,采用水热法合成了片状和棒状介孔氧化铝,采用X射线衍射仪、场发射透射电子显微镜、低温氮气吸脱附实验对合成的介孔氧化铝的晶相、形貌和介孔结构进行表征。研究结果表明,三嵌段共聚物的引入能够有效调控氧化铝的形貌、介孔结构以及孔参数。三嵌段共聚物在氧化铝前驱体表面的吸附诱导了晶体的取向生长,并最终形成了棒状氧化铝。     

The role of crystalline phase in triblock copolymer PS-PEG-PS based gas sensing materials

To reveal the role of crystalline phase in the matrix polymer of gas sensing conductive polymer composite materials, a series of triblock copolymer polystyrene-b-poly(ethylene glycol)-b-polystyrene (PS-PEG-PS) was synthesized by atom transfer radical polymerization (ATRP). The copolymers have similar molecular weights but different fractions of the crystalline PEG segments. As a result, the ratio of the crystalline phase to the amorphous one can be tuned regardless of the molecular weight of the entire copolymer. The composites consisting of the copolymer and carbon black exhibit gas sensing ability as characterized by the drastic increase in the electrical resistance when meeting organic solvent vapors. It is found that matrix swelling, which provides the composites with gas sensitivity, results from the contribution of the amorphous phase. The crystalline portions prove to be unchanged in the vapors with respect to their microstructure within the time of interests. The appearance of the crystalline phase in the matrix polymer helps to push the conductive fillers into the amorphous regions, which increases the effective filler content and leads to higher responsivity to solvent vapors at lower filler loading.     

Synthesis and properties of nanocomposite materials based on ultra-high-molecular-weight polyethylene and graphite nanoplates

A method for the synthesis of nanocomposite materials based on ultra-high-molecular-weight polyethylene and graphite nanoplates via polymerization filling is developed. Polyethylene formed during the synthesis evenly coats individual nanoplates; as a result, there is a uniform distribution of graphite nanoplates in the polymeric matrix. It is shown that the introduction of graphite nanoplates results in significant increases of the elastic modulus and deformation heat resistance and causes a sharp decrease in the gas permeability of the material.     

Fire performance and mechanical properties of acrylonitrile‐butadiene‐styrene copolymer/modified expandable graphite composites

The fire performance and mechanical properties of an acrylonitrile‐butadiene‐styrene (ABS) copolymer compounded with different expandable graphites (EG) and fire retardants were studied by using the limiting oxygen index test, the UL‐94 test, a mechanical test, and a thermogravimetric analysis. The ground EG treated with phosphoric acid and silane could have the great increase of the volume expansion ratio. The addition of the treated EG in ABS significantly enhances the fire performance but decreases the impact strength of ABS. ABS with the treated EG has a much higher impact strength than with the as‐received EG because of the smaller particle size of the treated EG and the better adhesion between the ABS and the treated EG. The addition of modified ammonium polyphosphate or decabromodiphenyl oxide/antimony trioxide can considerably improve the fire performance of ABS/treated EG composites because of a synergistic effect. The V‐0 grade (UL‐94) ABS composite with the limiting oxygen index of 32.5 can be obtained by adding small amounts of the treated EG and modified ammonium polyphosphate into ABS. Thermogravimetric analysis results indicate that the initial vapor release temperatures and the weight loss rates of ABS/EG composites are closely related to their fire performance and affected by the fire retardant used. Copyright © 2011 John Wiley & Sons, Ltd.