Hydration of a low‐grade magnesium oxide. Lab‐scale study

BACKGROUND: Low grade magnesium oxide (LG‐MgO) is a by‐product from the calcination of natural magnesite that is currently hydrated to magnesium hydroxide by storing it in the open for up to 6 months. It is eight to ten times cheaper than pure magnesium oxide and therefore the revalorization of this by‐product is very attractive for those applications requiring great quantities of magnesium hydroxide for which high purity is not required. Here the hydration of LG‐MgO is studied as a function of two parameters: hydrating agent and temperature. RESULTS: Addition of acetic acid during the hydration of LG‐MgO improved the effectiveness of treatment. At 50 °C, the maximum percentage hydration was 40% in pure water and increased to 65% and 70% using aqueous solutions of 0.5 and 1.0 mol L^?1 acetic acid. Increase of temperature also had a positive effect on the final degree of hydration. When the treatment was carried out with 0.5 mol L^?1 acetic acid, the hydration increased from 50 to 65 and 80% at 25, 50 and 90 °C respectively. Accordingly under the optimum conditions of 90 °C and 0.5 mol L^?1 acetic acid 80% hydration was achieved within 8 h. CONCLUSIONS: The results showed that much shorter hydration times are possible and therefore an industrial alternative to the spontaneous process could satisfy an increasing demand for magnesium hydroxide. Moreover, agitation is not needed as the reaction is chemically controlled. Copyright © 2012 Society of Chemical Industry     

The influence of hydrating agents on the hydration of industrial magnesium oxide

BACKGROUND: The influence of different hydrating agents on the pH of the hydrating solutions, rate of hydration of MgO to Mg(OH)₂ and product surface area was studied as a function of temperature of hydration. Hydrating agents used were aqueous solutions of ammonium chloride, magnesium acetate, magnesium nitrate, nitric acid, acetic acid, magnesium chloride, sodium acetate and hydrochloric acid and distilled water as control. These were chosen to determine either the effect of addition of a common ion, the effect of changing the solution pH or due to the presence of an acetate ion, found earlier to have a beneficial effect on the hydration of MgO. RESULTS: There was no significant difference in the hydration behaviour of the hydrating agents up to 50 °C, where less than 10% of magnesium hydroxide was formed. The amount of hydroxide increased at temperatures above 60 °C. When compared with the hydration in water, all the hydrating agents, with the exception of sodium acetate, showed a significant increase in the degree of hydration. Sodium acetate formed the lowest amount of magnesium hydroxide, ranging between 1.2 and 12.2% magnesium hydroxide. The largest percentage (56.7%) of magnesium hydroxide was formed from hydration in magnesium acetate. CONCLUSION: It seems that MgO hydration is a dissolution‐precipitation process controlled by the dissolution of MgO. The increased degree of hydration in magnesium acetate is possibly due to the presence of acetate and Mg²⁺ ions. Copyright © 2010 Society of Chemical Industry     

表面改性对聚丙烯/微米氢氧化镁复合材料性能的影响

研究了表面处理剂（钛酸酯和硅烷偶联剂）和原位聚合方法对聚丙烯/微米氢氧化镁（MH）复合材料的力学性能及流变性能的影响。采用DSC、SEM和毛细管流变仪对PP/MH（80/20）复合材料的性能进行了研究。结果表明：原位聚合改性后的微米MH与PP基体间的界面黏结力得到了加强,复合材料的冲击强度较填充未改性MH的复合材料提高了26.4 ％。在PP基体中添加聚合物包覆改性微米MH粒子的复合材料熔体流动速率较纯PP上升了64 ％。在相同剪切速率下,填充聚合物包覆改性MH的复合材料熔体表观黏度明显低于填充未改性微米MH的复合材料,表明聚合物包覆改性后的MH降低了其对PP熔体流动的阻碍作用,改善了PP/MH复合材料的流动性能。     

Thermal behavior and morphological properties of novel magnesium salt–polyacrylamide composite polymers

Magnesium salt–polyacrylamide composite polymers have been prepared by blending magnesium chloride and magnesium hydroxide, respectively, with polyacrylamide aqueous solution. The thermal behavior of the dried magnesium salt–polyacrylamide composite polymers has been studied. Differential scanning calorimetric (DSC) analysis and thermal gravimetric analysis (TGA) were carried out to investigate the changes of the composite polymers' behavior with temperature. The kinetics of the thermal decomposition of magnesium salt–polyacrylamide composite polymers was investigated over temperature range of 35–800°C with three heating rates of 10, 20, and 40°C/min under nitrogen atmosphere. Flynn and Wall's model was usedto determine the activation energies of thermal decomposition for magnesium salt–polyacrylamide composite polymers. The activation energies needed to decompose 50 wt% of magnesium hydroxide‐polyacrylamide (MHPAM) composite polymer ranged from of 28.993–174.307 kJ/mol which are higher than the values for magnesium chloride–polyacrylamide (MCPAM) composite polymer (21.069–39.412 kJ/mol). Therefore, MHPAM composite polymer has a better thermal stability compared with MCPAM composite polymer. The morphological properties of magnesium salt–polyacrylamide composite polymers were studied using scanning electron microscopy (SEM). Energy‐dispersive X‐ray (EDX) spectroscopy was used to determine the composition of the chemical elements. POLYM. COMPOS., 2011. © 2011 Society of Plastics Engineers     

Rheological properties of poly(trimethylene terephthalate) in capillary flow

The shear viscosity, extensional viscosity, and die swell of the PTT melt were investigated using a capillary rheometer. The results showed that the PTT melt was a typical pseudoplastic fluid exhibiting shear thinning and extensional thinning phenomena in capillary flow. There existed no melt fracture phenomenon in the PTT melt through a capillary die even though the shear rate was 20,000 s^?1. Increasing the shear rate would decrease the flow activation energy and decline the sensitivity of the shear viscosity to the melt temperature. The molecular weight had a significant influence on the flow curve. The flow behavior of the PTT melt approached that of Newtonian fluid even though the weight‐molecular weight was below 43,000 s^?1 at 260°C. The extensional viscosity decreased with the increase of the extensional stress, which became more obvious with increasing the molecular weight. The sensitiveness of the extensional viscosity to the melt temperature decreased promptly along with increasing the extensional strain rate. The die swell ratio and end effect would increase along with increasing the shear rate and with decreasing the temperature, which represented that the increase of the shear rate and the decrease of temperature would increase the extruding elasticity of the PTT melt in the capillary die. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 705–709, 2005     

氢氧化镁改性技术及阻燃效果研究进展

在环保型的无机阻燃剂中,氢氧化镁有阻燃、抑烟、填充的三重功能和热稳定性好、分解温度高、无腐蚀性、无毒、无味等特点,因而成为有机高分子材料阻燃添加剂的首要选择。综述了氢氧化镁作为阻燃剂时,其表面有机化改性过程中改性剂种类和改性条件的研究进展。总结了不同改性剂改性后的氢氧化镁填充到不同的高分子聚合物中,其对复合材料的阻燃性能和机械力学性能的影响。     

Preparation of PTT/clay nanocomposites with solid‐state polymerized polytrimethylene terephthalate

To enhance the effectiveness of polytrimethylene terephthalate (PTT) for the preparation of clay‐based nanocomposites by melt intercalation and to upgrade the mechanical performance of these materials, solid‐state‐polymerization (SSP) experiments with neat PTT were carried out at 190, 200, and 210°C prior compounding to increase the average molecular weight and, based on this, the melt viscosity of this polymer. The progress of SSP was registered by time dependent sampling of intrinsic viscosity data. From this, activation energy of 180.6 kJ mol^?1 was calculated. A characteristic sublimate formed during these SSP‐reactions was identified by mass‐spectroscopy to be a mixture of cyclic oligomers containing 2, 3, 4, and 5 monomeric units. The melt viscosity of neat PTT(SSP) could be increased from ～ 460 to 15,000 Pa s^?1. Therefore, tensile strength and Young's modulus were improved by 3.5 and 9%, respectively. Manufacturing of PTT(SSP) and the modified nanoclay was carried out with a corotating twin‐screw‐extruder at 230°C. A concentration of 3% of the inorganic filler component in the composites was aimed at. Compared with the data of virgin PTT, tensile strength, and modulus of the PTT(SSP)‐based nanocomposites could be enhanced by ～ 9 and 40%, respectively. Additionally, a SSP‐reaction of the nanocomposite prepared with non‐pretreated PTT and nanoclay was performed at 210°C to test the robustness of the matrix polymer PTT against the influences of the nanofiller. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Nanocomposites based on aromatic polyesters and organically modified clay

Milled polybutylene terephthalate (PBT) and polytrimethylene terephthalate (PTT) were mixed with organically modified clay and extruded to prepare nanocomposites by melt intercalation. The modifier of the nanofiller belongs to the group of trialkylbenzylammonium cations. Manufacturing of the materials was carried out with a co‐rotating twin‐screw‐extruder at 230°C and 240°C for PTT and PBT, respectively. A concentration of 3% of the inorganic filler component in the composites was aimed at. The influence of mechanical stress during extrusion on the stability of the neat polymers was tested at different speeds of rotation between 100 rpm and 800 rpm. The composites were characterized with regard to the experimental filler content and the properties of the matrix polymers like melt and crystallization temperatures, degrees of crystallinity, intrinsic viscosities, and melt viscosities. Additionally, mechanical properties were analyzed by tensile tests and discussed in terms of processing and the filler presence. The dominance of PBT as polymer matrix was highlighted. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Preparation,structure, and properties of the PTT/SGF composites

Short glass fiber reinforced poly(trimethylene terephthalate) composites (PTT/SGF) were prepared by twin screw extruder. The structural feature and physical properties of these composites were studied by scanning electron microscope, differential scanning calorimetry, thermalgravimetric analyzer, capillary rheometer, universal tester, etc. The glass fiber was modified by the silane coupling agent before being blended with the polymer. The results suggest that there is strong interaction between SGF and PTT matrix, which leads to an increasing on the tensile strength, Young's modulus, impact strength and thermal stability of the composites with proper contents of SGF. Rheological behavior of the PTT/SGF composites melt is complicated, combining a dilate fluid at lower shear rate and a pseudo-plastic fluid at higher shear rate. The melt apparent viscosity of composites decreases with increasing SGF content because of the rigid fibers improving the flow of the melt. Moreover, the flow activation energy of the composites suggests that the melt with more SGF has lower sensitivity to the processing temperature. In conclusion, the composite with 10–20 wt% content of SGF has better properties. POLYM. COMPOS., 2009. © 2008 Society of Plastics Engineers     

PET/PTT并列复合纤维生产工艺探讨

探讨了150 dtex/48 f聚对苯二甲酸乙二醇酯(PET)/聚对苯二甲酸丙二醇酯(PTT)双组分并列预取向丝(POY)的生产工艺.结果表明:选择特殊设计的纺丝组件,喷丝板的长径比大于2,孔形为花生形,选用特性黏数为0.53 dL/g的PET和特性黏数为1.02 dL/g的PTT切片质量比为50/50,PET的纺丝温...     

Permanently electrostatic dissipative (ESD) property via polymer blending: Rheology and ESD property of blends of PETG/ESD polymer

Rheological and electrical properties were studied on blends of a PETG polyester (cyclohexanedimethanol-modified polyethylene terephthalate) and an inherently static dissipative high molecular weight polyether based copolymer, hereafter referred to as ESD polymer. Several important electrical properties and flow phenomena have been observed. First of all, the PETG blends could result in ESD protected material with excellent performance and a minimal effect on physical properties and melt processability. The rheological characterization reveals that the ESD polymer has a high melt viscosity even at a temperature more than 150 degrees above its melting temperature and that it exhibits pseudoplastic behavior. The PETG melt shows a near constant dynamic viscosity at a low frequency region. The viscosity of the ESD polymer and PETG melt exhibits a cross over at the temperature range from 200–220°C; the PETG melt is the lower viscosity component at low shear rate and the ESD polymer is the lower viscosity component at high shear rate. This appears to result in the existence of a small composition difference in the thickness direction of an injection-molded ESD polymer/PETG part, with a greater fraction of the ESD polymer component in the skin section. This, in turn, could enhance the surface conductivity of the skin region of an injection-molded part. © 1993 John Wiley & Sons, Inc.     

Melt rheology of ion-containing polymers. I. Effect of molecular weight and excess neutralizing agent in model elastomeric sulfonated polyisobutylene-based ionomers

Melt rheology of elastomeric triarm sulfonated polyisobutylene model ionomers has been studied. The molecular weights (M _n) of the polymers have been varied from 8300 to 34,000. The sulfonated materials were neutralized with potassium hydroxide either to the exact stoichiometric equivalence point or to twice this amount, i.e., 100% excess neutralizing agent was added. For comparison one nonsulfonated precursor of M _n = 8300 was also studied. It was observed that the introduction of one sulfonate group at each chain end of the triarm poly-isobutylene molecule changes the state of matter at room temperature. Specifically, the unsulfonated materials are viscous liquids while the sulfonated ionomers are solid elastomers at room temperature. The zero-shear melt viscosity of the unsulfonated precursor is 900 poise (90 Pa·s), at room temperature while for those materials neutralized with potassium hydroxide to the exact stoichiometric point it is above 9 × 10³ poise (900 Pa·s) at 180°C. As expected, the zero shear viscosity increases with an increase in the molecular weight. Significant ionic interactions still persist at 180°C as evident by the high viscosity of the ionomers. However, at higher frequencies (～600 rad/s), the melt viscosity decreases to about 5 × 10³ poise for the different molecular weight materials. The melt viscosity of ionomers containing 100% excess neutralizing agent shows a dramatic increase. The excess KOH is speculated to be incorporated into the ionic domains rather than uniformly distributed throughout the matrix. This results in an increased strength of the ionic aggregates, thereby increasing the melt viscosities. Thus, due to the very pronounced effect on rheological properties it is important to know not only the extent of neutralization (up to full neutralization) but also the amount of excess neutralizing agent, if any, which is present in the sample.     

Bismaleimide and bisazomethine high temperature polymers

Conjugated aromatic bisazomethine, resulting from the reaction of terephthaldicarboxaldehyde and aniline, has been found to react with bismaleimidodiphenylmethane to provide polymeric compositions with glass transition temperature higher than 300°C. These two materials form a low viscosity melt at ca. 150°C and the melt shows only a small viscosity increase when maintained at 120°C over a period of 8 h. Differential scanning calorimetry (DSC) of this composition shows that upon heating above 200°C, it cures rapidly to produce a thermally stable polymer. Thermal mechanical analysis (TMA) of the cured composition does not detect any softening up to 350°C. In the thermal gravimetric analysis (TGA), no weight loss is observed up to 400°C in air and the material leaves a rather large amount of residue (ca. 60%) even up to 600°C. Dynamic mechanical thermal analysis (DMTA) shows that the polymer maintains its high modulus with increasing temperature up to 250°C.     

Composites of ethylene‐vinyl acetate copolymers with modified magnesium hydroxide–thermo‐oxidative ageing

Flame retardant composites must perform their protective roles permanently, also under conditions of intermittent or long‐term exposure to sunlight, moisture or increased temperature. The aim of our work was characterization of the thermo‐oxidative ageing (90 °C) and the changes in flammability of ethylene‐vinyl acetate copolymer composites with 40 and 60 wt.% of magnesium hydroxide. The neat polymer and its composites were investigated for their thermal (DSC) and structural (FTIR) characteristics as well as their density, melt flow index, tensile properties and combustibility during ageing test. As FTIR results identified the different carbonyl groups in copolymer were created, the highest oxidation intensity was observed for neat copolymer. That process was accompanied by the scission of the polymer macromolecules, especially for first 700 h of thermal ageing. Thermo‐oxidative ageing resulted also in the reduction of flammability of the test materials. The highest reduction was observed for neat polymer. The changes in some properties as analysed both for the copolymer and for its composites after over 700 h of ageing were indicative for initiation of cross‐linking of copolymer molecules after that time. Copyright © 2014 John Wiley & Sons, Ltd.     

氢氧化镁/膨润土协同阻燃聚丙烯的研究

进一步探究了改性氢氧化镁与其他阻燃剂的协同使用对聚丙烯材料性能的影响。结果表明:阴离子改性膨润土与氢氧化镁具有良好的协同阻燃作用,两者的比例影响其协同效果。当氢氧化镁和膨润土的质量比为37:3时,协同效果最好,材料的阻燃性能和机械性能都有改善。当协同阻燃剂的填充量为45%时,材料极限氧指数达到27.8,拉伸强度达到29 MPa。     

Thermal processability and properties of highly filled poly(vinyl alcohol)/talc composite

Abstract

A highly filled PVA/talc composite was prepared through our invented thermal processing technology without using any coupling agent or compatibiliser. The results showed that compared with neat PVA, the melt temperature of the composite decreased and the degradation temperature increased, providing a big temperature window for thermal processing of PVA/talc composite. The composite melt exhibited shear thinning behaviour while its viscosity increased with increasing talc, still satisfied the requirement of thermal processing. The morphology analysis confirmed that talc was well dispersed in PVA, improving heat deflection temperature (HDT), tensile strength and modulus of PVA. When talc was 50 wt-%, the HDT, tensile strength and modulus of the composite were 115°C, 48 MPa, 1·23 GPa respectively, increased by 92, 16 and 150%, compared with PVA, and the elongation at break was 100% of the composite, confirming that the high filled PVA/talc composite was a novel PVA based material with excellent thermal and mechanical properties.     

The significance of capillary rheology testing temperature for predicting PVC extrudability

A rheological investigation of the saturated fatty acids as lubricants for PVC was made in a Sieglaff-McKelvey rheometer over a wide temperature range. Results reveal that with an increase in carbon chain, fatty acids became more effective in reducing the melt viscosity of PVC. It was also discovered that the maximum viscosity variation due to these materials was observed at 350°F. At test temperatures of 400°F and above, no major viscosity differences were observed. Furthermore, the changes in the melt viscosity were more pronounced at shear rates less than 200 sec^?1. The usefulness of the measured viscosity variations at the critical test temperature of 350°F was shown by extrusion. An excellent correlation between the apparent melt viscosity and extrusion melt temperature was found. The criticalness of the test temperature in assessing the effect of lubricants on PVC flow is discussed.     

Crystallization behavior and viscoelasticity of bamboo‐fiber composites

This article deals with the effect of the kneading temperature on the crystallization of a matrix polymer and the viscoelasticity of a bamboo‐fiber‐reinforced biodegradable polymer composite. Upon the investigation of poly(butylene succinate) after melt mixing, spherulite generation was observed with polarized light microscopy and differential scanning calorimetry measurements. An increase in the spherulite dimensions was observed at high kneading temperatures (>150°C) in both the neat polymer and the bamboo‐fiber composite. Spherulite growth was initiated from the bulk matrix polymer and not from the surface of the bamboo fibers. The kneading temperature influenced the melt viscoelasticity above the melting point of poly(butylene succinate) but did not influence the viscoelasticity below the melting point. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 603–612, 2005     

Polyethyleneterephthalate with increased viscosity by chemical crosslinking

An attempt is made to improve the processing and operation properties of polyethyleneterephthalate (PETP) containing chemically bound pentaerythrol as modifier by increasing its viscosity through slight chemical crosslinking in the solid state. It is established that thermal treatment in vacuum for 8 h at 240°C of PETP containing 0.3 mol-% pentaerythrol leads to an increase in its molecular weight from 20000 to 40000 mainly as a result of additional solid state polycondensation. Further more, annealing in vacuum for 6 h at 250°C of the polymer containing 0.4 mol-% pentaerythrol leads to the formation of a loose three dimensional network resulting from chemical crosslinking in the solid state. It is shown that this crosslinking material has improved processing behaviour during injection moulding due to the increased viscosity of the melt.     

瓶级聚酯质量对流变及加工性能的影响研究

研究和分析了加工温度、特性黏数、摩尔质量及其分布、间苯二甲酸含量(IPA)、二甘醇(DEG)含量等因素对瓶级聚酯流变性及加工性能的影响。结果表明,在低剪切速率下,温度的升高使熔体的切力变稀现象逐渐减弱,当剪切速率达到8 000 s-1以上时,温度及剪切速率都几乎对熔体的表观黏度没有影响;摩尔质量越高,熔体黏度的切变速率依赖性越大,摩尔质量分布宽有利于成型加工条件的控制;在相同剪切速率下,熔体的剪切黏度随着IPA含量的增大而逐渐降低;DEG含量低的聚合物熔体在低剪切速率下出现非牛顿性流动的现象比DEG含量高的要明显得多。