Recovery of Terephthalic Acid from Alkali Reduction Wastewater by Cooling Crystallization

A process for the recovery and purification of terephthalic acid (TA) from alkali reduction wastewater is reported. TA was first precipitated from alkali reduction wastewater by acidification with sulfuric acid, and then the produced crude TA was dissolved in dimethylacetamide (DMA) so that crude TA could be purified from the solution by cooling crystallization. The results indicated that acidification could reduce the chemical oxygen demand of the wastewater by 83 %, and the purity of TA by crystallization could reach 99.91 %. A correlation was proposed in describing the solubility of crude TA in DMA from 303.4 to 358.65 K, which gives a mean relative discrepancy of less than 1.14 %. The cooling rate of the mother liquor had a large influence on the crystal size distribution. At an average cooling rate of 1.18 K min^–1, the particle size distribution of TA was narrow and the average size was about 100 μm. In a bench‐scale study, it was demonstrated that the crystallized product can be recycled as the raw material for polyethylene terephthalate production.     

碱减量废水中回收对苯二甲酸资源再用

从碱减量废水中回收对苯二甲酸,分析酸析工艺条件对回收产品的性能影响因素趋势;将得到的回收产品资源再用,作为原料制备聚酯涂膜,因回收产物纯度低于正规产品,试验加入甘油进行共聚合改性。在酸析回收工艺试验中确定了对回收资源性能的影响显著性大小依次为:酸析反应温度、废水碱度、搅拌速度、加酸速度、硫酸浓度。在最佳的工艺条件下,对苯二甲酸回收率为81%。在资源再用共聚合工艺试验中确定了加入官能度大于2的单体甘油,是产生支化和导致体型产物的根源,而多元醇的超量使用使得高分子聚合物在聚合过程中随着分子量增大不致产生凝胶化。实验表明,当原料酸醇比为1∶2.5,三元醇与二元醇摩尔比为1∶3时,资源再用产物的性能较为理想。     

Nonisothermal crystallization behavior of biodegradable poly(butylene terephthalate‐co‐butylene adipate‐co‐ethylene terephthalate‐co‐ethylene adipate) copolyester

A series of biodegradable aliphatic‐aromatic copolyester, poly(butylene terephthalate‐co‐butylene adipate‐co‐ethylene terephthalate‐co‐ethylene adipate) (PBATE), were synthesized from terephthalic acid (PTA), adipic acid (AA), 1,4‐butanediol (BG) and ethylene glycol (EG) by direct esterification and polycondensation. The nonisothermal crystallization behavior of PBATE copolyesters was studied by the means of differential scanning calorimeter, and the nonisothermal crystallization kinetics were analyzed via the Avrami equation modified by Jeziorny, Ozawa analysis and Z.S. Mo method, respectively. The results show that the crystallization peak temperature of PBATE copolyesters shifted to lower temperature at higher cooling rate. The modified Avrami equation could describe the primary stage of nonisothermal crystallization of PBATE copolyesters. The value of the crystallization half‐time (t_1/2) and the crystallization parameter (Z_c) indicates that the crystallization rate of PBATE copolyesters with more PTA content was higher than that with less PTA at a given cooling rate. Ozawa analysis was not suitable to study the nonisothermal crystallization process of PBATE copolyesters, but Z.S. Mo method was successful in treatingthis process. POLYM. ENG. SCI., 2011. © 2011 Society of Plastics Engineers     

碱减量废水残渣甲酯化反应动力学研究

为实现碱减量废水残渣有效利用,对碱减量废水残渣甲酯化反应条件与反应动力学规律进行了系统考察。论文首先考虑洗涤干燥等预处理方法对碱减量废水残渣组成的影响,然后通过改变醇酸比、初始水分含量及反应温度条件,进行了碱减量废水残渣甲酯化反应动力学实验研究。结果表明,预处理可有效去除残渣中的无机盐杂质提高对苯二甲酸纯度,但预处理会明显降低后续残渣甲酯化产物对苯二甲酸二甲酯(DMT)的收率以及对苯二甲酸(TA)甲酯化反应的转化。TA甲酯化两步反应均对温度敏感,采用典型的可逆平衡反应模型对实验数据进行拟合,得到动力学模型参数,并在此基础上对动力学模型进行检验,结果表明所建立的动力学模型是可靠的,能很好的预测各组分的浓度。研究所得可为碱减量废水残渣甲酯化工艺放大与设计提供依据。     

Effect of stoichiometric imbalances on the melt condensation polymerization of poly(dodecamethylene terephthalamide) studied by intrinsic viscosity and 13C‐NMR

Poly(dodecamethylene terephthalamide) (PA‐12,T) was synthesized by melt condensation polymerization of 12,T salt with 0, 1, 3, 5, or 10% molar excess of 1,12‐diaminododecane (DA), terephthalic acid (TA), or benzoic acid (BA). Intrinsic viscosities (IV) (0.5 g/dL in 96% H₂SO₄ at 25°C) were measured to determine relative molecular weight differences. IV was highest for reactions containing 1 and 3 mol % excess DA (1.36 and 1.31 dL/g, respectively), followed by the product of pure 1 : 1 salt (1.25 dL/g). For all concentrations of excess TA and BA, IV was decreased. ¹³C‐NMR chemical shifts for DA, TA, and BA end groups were identified and their concentrations determined by comparison with the intensity of main chain polymer peaks. A log–log plot of IV versus number average molecular weight calculated from ¹³C‐NMR data shows a linear trend with Mark‐Houwink constants of K = 55.8 × 10^?5 dL/g and α = 0.81. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Fast crystallization of liquid crystalline copolyesters based on poly(ethylene terephthalate)

Crystallization of a series of liquid crystalline copolyesters prepared from p‐hydroxybenzoic acid (HBA), hydroquinone (HQ), terephthalic acid (TA), and poly(ethylene terephthalate) (PET) was investigated by using differential scanning calorimetry (DSC). It was found that these copolyesters are more crystalline than copolyesters prepared from PET and HBA. Insertion of HQ–TA disrupts longer rigid‐rod sequences formed by HBA and thus enhances molecular motion and increases the crystallization rate. The effects of additives on the crystallization of the copolyesters were also studied. Sodium benzoate (SB) and sodium acetate (SA) increase the crystallization rate of the copolyesters at low temperature, but not at high temperature. It is most likely that liquid crystalline copolyesters do not need nucleating agents, and small aggregates of local‐oriented rodlike segments in nematic phase could act as primary nuclei. Chain scission of the copolyesters caused by the reaction with the nucleating agents was proved by the determination of intrinsic viscosity and by the IR spectra. Diphenylketone (DPK) was shown to effectively promote molecular motion of chains, leading to an increase in the crystallization rate at low temperature, but it decreased the crystallization rate at high temperature. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 79: 497–503, 2001     

Electricity generation from terephthalic acid using a microbial fuel cell

BACKGROUND: Pure terephthalic acid (PTA) is a petrochemical product of global importance and is widely applied as an important raw material in making polyester fiber and polyethylene terephthalate (PET) bottles. In this work, a single‐chamber microbial fuel cell (MFC) was constructed using terephthalic acid (TA) with a chemical oxygen demand (COD) concentration range from 500 mg L^?1 to 3500 mg L^?1 as the electron donor and strain PA‐18 as the biocatalyst. RESLUTS: In the single chamber MFC, several factors were examined to determine their effects on power output, including COD concentration and electrode spacing. The characteristic of the strain PA‐18 was further studied. Cyclic voltammetry showed that electrons were directly transferred onto the anode by bacteria in biofilms, rather than self‐produced mediators of bacteria in the solutions. Scanning electron microscopy (SEM) observation showed that the anodic electrode surface was covered by bacteria which were responsible for electron transfer. Direct 16s‐rDNA analysis showed that the PA‐18 bacteria shared 99% 16SrDNA sequence homology with Pseudomonas sp. CONCLUSIONS: Electricity generation from TA in MFC was observed for the first time. The maximum power density produced by TA was 160 mW m^?2, lower than that achieved using domestic wastewater. This novel technology provided an economical route for electricity energy recovery in PTA wastewater treatment. High internal resistance was the major limitation. To further improve the power output, the electron transfer rate was accelerated by overexpression of membrane the protein gene of the strain PA‐18 and by reducing the electrolyte and mass transfer resistance by optimizing reactor configuration. Copyright © 2008 Society of Chemical Industry     

Crystallization behavior of poly(N‐methyldodecano‐12‐lactam). IV. Nonisothermal crystallization

Nonisothermal crystallization of poly(N‐methyldodecano‐12‐lactam) (MPA) was investigated using DSC method at cooling rates of 2–40 K/min. With increasing cooling rate, crystallization exotherms decreased in magnitude and shifted toward lower temperatures. Subsequent heating runs (10 K/min) showed an exotherm just above T_g, which increased in magnitude with the rate of preceding cooling run, corresponding to the continuation of primary crystallization interrupted as the system crossed T_g on cooling. Kinetic evaluation by the Avrami method gave values of exponent n close to 2.0, suggesting two‐dimensional crystal growth combined with heterogeneous nucleation. The Tobin method, covering the intermediate range of relative crystallinities, provided n ? 2.20, suggesting possible partial involvement of homogeneous nucleation at later stages of nonisothermal crystallization. The crystallization rate parameter k^1/n showed a linear dependency on cooling rate for both methods, the Tobin values being slightly higher. The Ozawa approach failed to provide reasonable values of the kinetic exponent m of MPA. The Augis–Bennet method was used to determine the effective activation energy of the entire nonisothermal crystallization process of MPA. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 95: 564–572, 2005     

Poly(ethylene terephthalate) Recycling and Recovery of Pure Terephthalic Acid. Kinetics of a Phase Transfer Catalyzed Alkaline Hydrolysis

Poly(ethylene terephthalate) (PET) taken from post‐consumer soft‐drink bottles was subjected to alkaline hydrolysis with aqueous sodium hydroxide after cutting it into small pieces (flakes). A phase transfer catalyst (trioctylmethylammonium bromide) was used in order the reaction to take place in atmospheric pressure and mild experimental conditions. Several different reaction kinetics parameters were studied, including temperature (70–95°C), NaOH concentration (5–15 wt.‐%), PET average particle size, catalyst to PET ratio and PET concentration. The disodium terephthalate received was treated with sulfuric acid and terephthalic acid (TPA) of high purity was separated. The ¹H NMR spectrum of the TPA revealed an about 2% admixture of isophthalic acid together with the pure 98% terephthalic acid. The purity of the TPA obtained was tested by determining its acidity and by polymerizing it with ethylene glycol using tetrabutyl titanate as catalyst. A simple theoretical model was developed to describe the hydrolysis rate. The apparent rate constant was inversely proportional to particle size and proportional to NaOH concentration and to the square root of the catalyst amount. The activation energy calculated was 83 kJ/mol. The method is very useful in recycling of PET bottles and other containers because nowadays, terephthalic acid is replacing dimethyl terephthalate (the traditional monomer) as the main monomer in the industrial production of PET.     

Characterization and thermal‐oxidative degradation behavior of poly(ethylene terephthalate‐co‐4,4′‐bibenzoate) prepared via direct esterification technique

A series of poly(ethylene terephthalate‐co‐4,4′‐bibenzoate)s (PETBBs) were prepared via direct esterification from the monomers of terephthalic acid (TPA), 4,4′‐biphenyl dicarboxylic acid (BPDA), and ethylene glycol (EG) with different molar ratios. The chemical compositions of the obtained PETBBs, investigated by H¹‐NMR, were identical with the feed ratio, and the high molecular weights of PETBBs were confirmed by GPC analysis. The glass transition, crystallization, and melting behavior of them were measured by DSC; the results indicated that, in the range of 5–25 mol% of BPDA addition, the glass transition temperature (T_g) increased almost linearly and the melting temperature (T_m) decreased with increasing content of BPDA unit. As expected, the crystallization of PETBB became difficult with increasing introduction of BPDA, explained by higher crystallization temperature and smaller crystallization enthalpy from the glassy state. This decrease of crystallization rate may be beneficial to film processing. Moreover, owing to the introduction of rigid‐rod BPDA unit, the initial and maximum thermal‐oxidative decomposition temperatures were enhanced. The kinetic analysis of the thermal‐oxidative degradation indicated that the apparent activation energies of degradation for these PETBBs became higher than that of PET. POLYM. ENG. SCI., 2012. © 2012 Society of Plastics Engineers     

Isothermal crystallization kinetics and melting behaviors of poly(butylene terephthalate) and poly(butylene terephthalate‐co‐fumarate) copolymer

The isothermal crystallization kinetics and melting behaviors after isothermal crystallization of poly(butylene terephthalate) (PBT) and poly(butylene terephthalate‐co‐fumarate) (PBTF) containing 95/5, 90/10, and 80/20 molar ratios of terephthalic acid/fumaric acid were investigated by differential scanning calorimetry. The equilibrium melting temperatures of these polymers were estimated by Hoffman–Weeks equation. So far as the crystallization kinetics was concerned, the Avrami equation was applied and the values of the exponent n for all these polymers are in the range of 2.50–2.96, indicating that the addition of fumarate does not affect the geometric dimension of PBT crystal growth. Crystallization activation energy (ΔE) and nucleation constant (K_g) of PBTF copolymers are higher than that of PBT homopolymer, suggesting that the introduction of fumarate hinders the crystallization of PBT in PBTF. POLYM. ENG. SCI., 2013. © 2012 Society of Plastics Engineers     

Poly(propylene)–poly(propylene)‐grafted maleic anhydride–organic montmorillonite (PP–PP‐g‐MAH–Org‐MMT) nanocomposites. II. Nonisothermal crystallization kinetics

The nonisothermal crystallization kinetics of poly(propylene) (PP), PP–organic‐montmorillonite (Org‐MMT) composite, and PP–PP‐grafted maleic anhydride (PP‐g‐MAH)–Org‐MMT nanocomposites were investigated by differential scanning calorimetry (DSC) at various cooling rates. Avrami analysis modified by Jeziorny and a method developed by Mo well‐described the nonisothermal crystallization process of these samples. The difference in the exponent n between PP and composite (either PP–Org‐MMT or PP–PP‐g‐MAH–Org‐MMT) indicated that nonisothermal kinetic crystallization corresponded to tridimensional growth with heterogeneous nucleation. The values of half‐time, Z_c; and F(T) showed that the crystallization rate increased with the increasing of cooling rates for PP and composites, but the crystallization rate of composites was faster than that of PP at a given cooling rate. The method developed by Ozawa can also be applied to describe the nonisothermal crystallization process of PP, but did not describe that of composites. Moreover, the method proposed by Kissinger was used to evaluate the activation energy of the mentioned samples. The results showed that the activation energy of PP–Org‐MMT was much greater than that of PP, but the activation energy of PP–PP‐g‐MAH–Org‐MMT was close to that of pure PP. Overall, the results indicate that the addition of Org‐MMT and PP‐g‐MAH may accelerate the overall nonisothermal crystallization process of PP. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 3093–3099, 2003     

Non‐isothermal crystallization behavior of stereo diblock polylactides with relatively short poly(d‐lactide) segments from the melt

Stereo diblock polylactides (SDB‐PLAs) composed of relatively short poly(d ‐lactide) (PDLA) segments and relatively long poly(l ‐lactide) (PLLA) segments were synthesized to have a wide number‐average molecular weight (M_n) range of 2.5 × 10⁴–2.0 × 10⁵ g mol^?1 and d ‐lactyl unit content of 0.9–38.6%. The effects of incorporated short PDLA segments (M_n = 2.0 × 10³–7.7 × 10³ g mol^?1) on crystallization behavior of the SDB‐PLAs were first investigated during heating after complete melting and quenching or during slow cooling after complete melting. Stereocomplex (SC) crystallites can be formed at d ‐lactyl unit content as low as 4.3 and 5.8% for heating and slow cooling, respectively, and for M_n of PDLA segments as low as 2.0 × 10³ and 3.5 × 10³ g mol^?1, respectively. With decreasing M_n and increasing d ‐lactyl unit content, the cold crystallization temperature during heating decreased and the crystallization temperature during slow cooling increased. With increasing d ‐lactyl unit content, the melting enthalpy (ΔH_m) of SC crystallites during heating and the crystallinity (X_c) of SC crystallites after slow cooling increased, whereas ΔH_m of PLLA homo‐crystallites during heating and X_c of PLLA homo‐crystallites after slow cooling decreased. The total ΔH_m of SC crystallites and PLLA homo‐crystallites during heating and the total X_c after slow cooling became a minimum at d ‐lactyl unit content of 10–15% and gave a maximum at d ‐lactyl unit content of 0%. Despite the accelerated crystallization of some of SDB‐PLAs, the low values of total ΔH_m and X_c at d ‐lactyl unit content of 10–15% are attributable to the formation of two crystalline species of SC crystallites and PLLA homo‐crystallites.     

Synthesis and characterization of cassava starch graft poly(acrylic acid) and poly[(acrylic acid)‐co‐acrylamide] and polymer flocculants for wastewater treatment

Starch‐g‐poly(acrylic acid) and poly[(acrylic acid)‐co‐acrylamide] synthesized via chemically crosslinking polymerization were then each mixed with inorganic coagulants of aluminum sulfate hydrate [Al₂(SO₄)₃·18H₂O], calcium hydroxide [Ca(OH)₂], and ferric sulfate [Fe₂(SO₄)₃] in a proper ratio to form complex polymeric flocculants (CPFs). All CPFs exhibited low water absorbency than those of the uncomplexed superabsorbent copolymers. The color reduction by the CPFs was tested with both synthetic wastewater and selected wastewater samples from textile industries. The synthetic wastewater was prepared from a direct dye in a concentration of 50 mg dm^?3 at pH 7. The CPFs of poly[(acrylic acid)‐co‐acrylamide] with calcium hydroxide at a ratio of 1:2 is the most effective CPF for the wastewater color reduction. The CPF concentration of 500 mg dm^?3 could reduce the color of the synthetic wastewater containing the direct dye solution by 95.4% and that of the industrial wastewater by 76%. Starch‐g‐poly(acrylic acid)/Ca(OH)₂ CPF can reduce the synthetic direct dye and the industrial wastewater by 74% and 18%, respectively. Chemical oxygen demand, residual metal ion concentrations, pHs, turbidity of the wastewater were also investigated and the potential use of the complex polymer flocculants for textile wastewater treatment was indicated. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 2915–2928, 2006     

The effect of an enzymatic pretreatment on the hydrolysis and size reduction of fat particles in slaughterhouse wastewater

The effect of an enzymatic pretreatment, Pancreatic Lipase 250 (PL‐250), on the hydrolysis and size reduction of fat particles in slaughterhouse wastewater was characterised for enzyme doses ranging from 125 to 1000 mg dm^?3 and initial particle sizes (D_in) varying between 53 and 383 µm. Treatment with PL‐250 significantly reduced the size of pork fat particles in slaughterhouse wastewater. Particle size reduction increased with D_in, possibly due to the more filamentous and plate‐like configuration of the larger fat particles, which could be easily broken at weak points. The smaller particles were observed to be denser and more spherical. Size reduction also increased with enzyme concentration, but the benefit of adding more enzyme diminished greatly as enzyme dose was increased. The maximum long‐chain fatty acid (LCFA) concentration in filtered samples was detected after 4–7 h of treatment and ranged from 8.2 to 34.9 mg dm^?3. The linear rate of LCFA released in solution during enzymatic pretreatment ranged from 39.4 to 169.9 mg dm^?3 d^?1, and increased with enzyme concentration up to 500 mg dm^?3. At a PL‐250 concentration of 1000 mg dm^?3, the LCFA release rate decreased, maybe due to excessive layering of adsorbed enzyme on the fat particles or increased degradation of released LCFAs. The pretreatment appeared to be more efficient with beef than pork fat particles. However, the effect of an enzymatic pretreatment on a downstream anaerobic treatment of slaughterhouse wastewater containing fat particles remains to be tested. © 2001 Society of Chemical Industry     

Synthesis,physical properties,and crystallization of optically active poly(L‐phenyllactic acid) and poly(L‐phenyllactic acid‐co‐L‐lactic acid)

Optically active poly(L ‐phenyllactic acid) (Ph‐PLLA), poly(L ‐lactic acid) (PLLA), and poly(L ‐phenyllactic acid‐co‐L ‐lactic acid) with weight‐average molecular weight exceeding 6 × 10³ g mol^?1 were successfully synthesized by acid catalyzed direct polycondensation of L ‐phenyllactic acid and/or L ‐lactic acid in the presence of 2.5–10 wt % of p‐toluenesulfonic acid. Their physical properties and crystallization behavior were investigated by differential scanning calorimetry, thermogravimetry, and polarimetry. The absolute value of specific optical rotation ([α]) for Ph‐PLLA (?38 deg dm^?1 g^?1 cm³) was much lower than that of [α] for PLLA (?150 deg dm^?1 g^?1 cm³), suggesting that the helical nature was reduced by incorporation of bulky phenyl group. PLLA was crystallizable during solvent evaporation, heating from room temperature, and cooling from the melt. Incorporation of a very low content of bulky phenyllactyl units even at 4 mol % suppressed the crystallization of L ‐lactyl unit sequences during heating and cooling, though the copolymers were crystallizable for L ‐phenylactyl units up to 6 mol % during solvent evaporation. The activation energy of thermal degradation (ΔE_td) for Ph‐PLLA (200 kJ mol^?1) was higher than that for PLLA (158 kJ mol^?1). The ΔE_td for the copolymers increased with an increase in L ‐phenyllactyl unit content. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Dynamic crystallization of polypropylene and wood‐based composites

Thermoplastic composites made of an isotactic polypropylene (iPP) matrix and woodflour (WF) were prepared by melt‐blending, using twin‐screw extrusion and injection molding. Up to 20 wt % of the composite was composed of WF. The incorporation of an interfacial agent made of an ethylene/methacrylic acid copolymer to iPP and WF, PP/WF, binary blends causes a compatibilization effect that becomes evident due to a reduction in the crystallization temperature of PP. In both the binary composites and the compatibilized or ternary composites, the PP adopts an α or monoclinic structure when crystallization occurs from the melt under dynamic conditions at cooling rates between 1 and 20°C min^?1. On the other hand, X‐ray diffraction analysis using synchrotron radiation of the injection‐molded samples demonstrates the existence of a β or trigonal form in the binary as well as the ternary PP/WF composites. They reach k_β levels between 0.18 and 0.25, which can be interpreted as the co‐operation between a reduction of the crystallization rate and the shear effect induced during the injection. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 6028–6036, 2006     

PE/PE‐g‐MAH/Org‐MMT nanocomposites. II. Nonisothermal crystallization kinetics

The nonisothermal crystallization kinetics of high‐density polyethylene (HDPE) and polyethylene (PE)/PE‐grafted maleic anhydride (PE‐g‐MAH)/organic‐montmorillonite (Org‐MMT) nanocomposite were investigated by differential scanning calorimetry (DSC) at various cooling rates. Avrami analysis modified by Jeziorny, Ozawa analysis, and a method developed by Liu well described the nonisothermal crystallization process of these samples. The difference in the exponent n, m, and a between HDPE and the nanocomposite indicated that nucleation mechanism and dimension of spherulite growth of the nanocomposite were different from that of HDPE to some extent. The values of half‐time (t_1/2), K(T), and F(T) showed that the crystallization rate increased with the increase of cooling rates for HDPE and composite, but the crystallization rate of composite was faster than that of HDPE at a given cooling rate. Moreover, the method proposed by Kissinger was used to evaluate the activation energy of the mentioned samples. It was 223.7 kJ/mol for composite, which was much smaller than that for HDPE (304.6 kJ/mol). Overall, the results indicated that the addition of Org‐MMT and PE‐g‐MAH could accelerate the overall nonisothermal crystallization process of PE. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 91: 3054–3059, 2004     

Gel Composition and Strength Properties of Alkali‐Activated Oyster Shell‐Volcanic Ash: Effect of Synthesis Conditions

The gel composition and mechanical properties of alkali‐activated oyster shell‐volcanic ash were investigated at different NaOH concentrations (8, 12, and 15M) and curing temperatures (60°C and 80°C) in wet and dry conditions. XRD, FTIR, SEM‐EDS, and TGA‐DSC were used for microstructural characterization of the binder. The gel composition of the system was found to be influenced by NaOH concentration and was not affected when curing temperature was varied from 60°C to 80°C. The main phase was N,C–A–S–H for all alkali‐activated oyster shell‐volcanic ash, with C–S–H as secondary phase for some samples and contains high percentage of iron. The splitting at υ₃ = 1400–1494 cm^?1 on FTIR spectra corresponded to the elimination of the degeneracy due to the distortion of CO₃^2? group. The high degree of splitting indicated that this carbonate group is linked to Ca²⁺. The compressive strength was influenced by curing temperature and the formation of a secondary phase. The compressive strength in dry condition increased roughly between 28 and 180 d for some samples, while in wet condition, the partial dissolution of Si–O–Si bonds of some silicate phases resulted in a reduction of strength.     

Nonisothermal bulk crystallization of high‐density polyethylene via a modified depolarized light microscopy technique: Further analysis

The quiescent nonisothermal bulk crystallization kinetics of high‐density polyethylene was investigated with a modified depolarized light microscopy technique, which allowed for studies at average cooling rates of approximately 5–2500 °C min^?1. All of the samples crystallized at a pseudoisothermal temperature (i.e., the plateau or crystallization temperature), despite the nonisothermal nature of the cooling conditions. The rate of the crystallization process increased monotonically with increasing the cooling rate and decreasing the crystallization temperature. Moreover, the apparent crystallinity content was a certain decreasing function with the cooling rate. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 1009–1022, 2002