The morphology of 50% PET/PEN random copolymer as revealed by high resolution scanning electron microscopy and X-ray diffraction

The microstructure of 50% PET/PEN random copolymer crystallised by uniaxial drawing and subsequent annealing is investigated by two-dimensional wide angle X-ray diffraction and high resolution scanning electron microscopy. Chemical etching was used to reveal the structure after drawing and subsequent annealing. The structure observed was found to be in the order of 100 nm. The results showed fibrillar microstructure parallel to the draw direction that could be associated with the presence of the smectic-A liquid crystalline transient mesophase as a result of the drawing. There was evidence of banding perpendicular to the draw direction when crystallisation started to take place. This banded structure was explained in terms of buckling of the thin polymer film perpendicular to the direction of the draw in an analogy similar to that of liquid crystalline polymers. The wide range of microstructure observed microscopically and reported here are, however, associated with crystallisation.     

The occurrence of the hexagonal phase in two long chain monodisperse carboxylic acids at high pressure

High-pressure differential thermal analysis (DTA) experiments have allowed the pressure-temperature phase diagrams to be constructed for the monoacid CH₃-(CH₂)₁₉₀-COOH and the diacid HOOC-(CH₂)₁₉₂-COOH. The current work follows on from previous work concerning the high-pressure phase of various monodisperse n-alkanes. The use of a diamond anvil cell calibrated from DTA data has allowed the morphology of each sample to be investigated as a function of pressure and temperature and for the crystallization, melting and hexagonal/orthorhombic transitions to be examined directly. It was shown that the monoacid displayed a similar behaviour to the n-alkane of twice its chain length due to end group pairing, whereas the diacid shows a wider hexagonal stable region, which extends to pressures as low as 0.35 GPa. This enhanced stability is thought to be due to increased configurational entropy due to unlimited end group association.     

An electrochemical method to study scaling by calcium sulphate of a heat transfer surface

The main purpose of this investigation was to devise an electrochemistry-based method, using the assessment of the oxygen-reduction cathodic reaction, in order to evaluate the intensity of calcium sulphate scale formation on a heat transfer surface. For this purpose, an experimental device, permitting the simultaneous measurement of the surface temperature and the current intensity relative to electrochemical oxygen-reduction on the heat transfer surface during the fouling process, was built. From the chronoamperometric curves, it is possible to deduce the induction time. The results were confirmed by the simultaneous direct measurement of the surface temperature. This coupling of thermal and electrochemical measurement gave additional information regarding the growth and the porosity of the formed scale layer. By this chronoamperometric method, it was shown that the supersaturation coefficient of a saturated calcium sulphate solution must exceed a critical value Ω_c of the order of 4 to observe the crystallization of the gypsum layer. For the same saturation level, the salt concentration has a stronger effect than the temperature on the precipitation process.     

Evaporation in a capillary tube of square cross-section: application to ion transport

Modelling of evaporation of a pure liquid within a capillary tube of circular cross-section is a classic problem which has been the subject of many studies. Here we consider the case of tubes of polygonal cross-section. This case leads to quite different results owing to the liquid flow along the tube edges induced by the capillary forces. Various evaporation regimes can be distinguished depending on the competition between capillary, gravity and viscous forces. We concentrate on the regime dominated by the capillary forces. It is shown that the position z₀ of the bulk meniscus should scale as z₀∝t in this case. The prefactor depends on the liquid distribution within the entrance region of the tube. A simplified model for a tube of square cross-section is then presented and calibrated against data from three-dimensional simulations. The last part of the paper is devoted to an analysis of ion transport during evaporation in a tube of square cross-section. The results suggest that the ion transport by liquid film can be a very effective mechanism for explaining the formation of efflorescence at the surface of porous media.     

The effect of a morphology modifier on the precipitation behaviour of nickel powder

The effect of a morphology modifier on the precipitation process of nickel powder was investigated in order to develop an understanding of its mechanism of action. Experiments were conducted on a pilot-plant scale using a 75-L autoclave with modifier dosages in the range of 0.25-5 vol%. Samples were collected from each successive batch reduction within a cycle and the powder was separated from the liquor before being washed and dried for subsequent analysis.The active particle rate processes were identified by transforming the particle size distribution (PSD) data into moments and from the change in surface area as measured by the BET method. Scanning Electron Microscopy (SEM) micrographs of the powder were used to observe the powder morphology and to validate the proposed particle rate processes and mechanism of action of the modifier.Evolution of the first moment (m0) and third moment (m3), equivalent to the total number of particles and volume, respectively, indicated that growth and aggregation were the major particle rate processes at a modifier dosage of 0.25 vol%. Breakage became apparent at dosage levels above 0.25 vol%. A decrease in BET surface area was noted in each cycle, indicating the presence of aggregation. The magnitude of decrease in the surface area indicated that the extent of aggregation decreased with increasing modifier dosage.SEM micrographs revealed that the powder was compact and aggregated at modifier dosages between 0.25 and 3 vol% and that loose porous powder was produced at 5 vol%. The modifier was found to inhibit growth, resulting in the formation of weaker agglomerate bridges leading to shear-induced breakage. This led to an increase in the surface area available for reduction. However, the effect of increased surface area in promoting reduction was outweighed by growth inhibition above a modifier dosage of 1 vol%. Thus, the number of attainable batch reductions increased when the modifier dosage was increased from 0.25 to 1 vol% and decreased with further increases in modifier dosage.     

Step-scan alternating DSC study of melting and crystallisation in poly(ethylene oxide)

Step-scan alternating differential scanning calorimetry (SSA-DSC) method was applied to investigate the phase behaviour of well-characterised poly(ethylene oxide) (PEO). Influence of the three main measurement's parameters of SSA-DSC method: length of the isothermal segment (t_iso/s), temperature jump between two subsequent isothermal segments (step/deg) and linear heating rate in dynamic segments (b/K/min), on the shape of reversing and non-reversing components during the melting and crystallisation of PEO, has been evaluated. It was found that the reversing component during melting of PEO is increasing with an increase of the isothermal segment length. This effect is due to the existence of defected polymer crystal structures that form metastable regions between crystal phase and already melted polymer. Reversible recrystallisation in the presence of still existing polymer crystals is facilitated by longer isothermal segments. By increasing the step, the equilibrium of reversible processes is shifted towards products and activation of rate-controlled processes takes place; molecular nucleation is hampered and partial melting and/or recrystallisation proceed slower—this effect can be observed as a decrease of reversing signal with increasing step.     

The information content in NIR spectral data for slurries of organic crystals

Despite being widely used in agriculture, food production and environmental monitoring and regarded as on-line chromatograph in petrochemical and biochemical industries, near infrared spectroscopy (NIR) has found difficulties in its application to processes of particle formation through crystallisation or precipitation where solids suspended in solutions cause problems in instrumentation as well as distortion of the spectra. The research work reported here was motivated by the hypothesis that the effect of particles on the NIR spectra in effect brings an opportunity instead: the spectra might contain useful information of both the solid and liquid phases. Through carefully designed experiments using both glutamic acid solutions and slurries of varied solid concentrations and particle size and temperature ranges and with the help of chemometric data analysis, it was found that the NIR spectra clearly contain sensitive information about the size, solid concentration, liquid concentration as well as polymorphs of crystals, providing the possibility of using the instrument for simultaneous measurement of the multiple properties of both phases.     

Thermal analysis and mechanism of α-Zn2SiO4:Mn formation from zinc oxalate dihydrate under hydrothermal conditions

Reaction of zinc oxalate dihydrate in high-temperature water at 200–400 °C was investigated to understand the mechanism of α-Zn₂SiO₄:Mn²⁺ formation and specifically why zinc oxalate dihydrate forms α-Zn₂SiO₄ crystalline phase at a higher rate compared with other water soluble and insoluble zinc sources studied in our previous works. From experiments under hydrothermal conditions, it was determined that the dehydration of zinc oxalate dihydrate became suppressed as the temperature and pressure increased. From thermal analyses, zinc oxalate dihydrate, which dehydrates at 160 °C in air, was stable at conditions up to 300 °C in water and this resulted in the lack of formation of the intermediate phase, hemimorphite, which forms at 150–175 °C from other zinc compounds (e.g. ZnO). The stability of the zinc oxalate dihydrate under hydrothermal conditions can possibly be attributed to changes in the chemical equilibrium with temperature and pressure which leads to the compound having less reactivity with silica so that reaction paths to form hemimorphite and β-Zn₂SiO₄ become unfavorable. Zinc oxalate dihydrate as starting material provided α-Zn₂SiO₄ at a higher formation rate than other starting materials.     

Experimental study and modelling of the crystallization of a water droplet

Modelling the crystallisation of a water droplet into a cold humid airflow is the first step in modelling the behaviour of water droplets sprayed out of a snow gun. This modelling, which is based on an experimental study, deals with the behaviour of the droplet which is transformed successively from the supercooled liquid phase to the liquid–solid phase and then the solid phase. These three transformations are brought about by various exchanges: heat transfer with conduction and convection as well as mass transfer with evaporation and sublimation. The supercooling phenomenon is naturally observed during experiments and taken into account in the modelling.     

Thermal and crystallisation behaviours of blends of polyamide 12 with styrene-ethylene/butylene-styrene rubbers

Polyamide 12 (PA12)/styrene-ethylene/butylene-styrene (SEBS) and PA12/maleic anhydride grafted SEBS (SEBS-g-MA) blends were prepared in a twin-screw extruder followed by injection moulding. Thermal and crystallisation behaviours of these blends were evaluated. Thermal properties and morphology of the blends were estimated using thermo gravimetric analysis (TGA) and scanning electron microscopy (SEM), respectively. The phase structure of the blends was interpreted by dynamic mechanical thermal analyser (DMTA). In terms of temperature at maximum rate of degradation (T_max) and integral procedural decomposition temperature (IPDT), it was found that PA12/SEBS-g-MA (PM) blends possessed greater thermal stability than PA12/SEBS (PS) blends. The kinetics of degradation process of PA12 and its blends were studied using Coats-Redfern (CR) method. It was found that there is no appreciable change in the thermal stability of PA12 in the presence of small amount of rubber phase. A good correlation was observed between the thermal properties and phase morphology of the blends. Melting and crystallisation behaviours of the blends were analysed by differential scanning calorimetry (DSC). These results showed that the melting and crystallisation behaviours of PA12 were not significantly affected by blending with rubbers. It was also observed that the functional group present in the rubber phase has little effect on the melting and crystallisation behaviours of PA12.