Crystalline Melting Point Research Articles

Phase morphology and mechanical properties of the electrospun polyoxymethylene/polyurethane blend fiber mats

Polyoxymethylene/thermoplastic polyurethane (POM/TPU) blends containing 10–30 wt % of TPU were electrospun using hexafluoroisopropanol as the solvent. The average fiber diameter increases with the increase in TPU content from 0.68 μm for neat POM fibers to 0.92 μm for POM/TPU 7:3 blend fibers due to the increase in solution viscosity. Core/sheath structure with the major component POM as the core and the minor component TPU as the sheath was observed by transmission electron microscopy and further confirmed by surface N contents of the blend fiber mats. The crystalline melting point and the degree of crystallinity of POM have no obvious change by coelectrospinning with TPU due to lack of interaction between POM and TPU as revealed by Fourier transform infrared spectroscopy. Tensile tests showed that the unusual high ductility of POM fiber mat could be further increased by coelectrospinning with 10 or 20 wt % TPU without significantly decreasing the stiffness and strength. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 1853–1859, 2009

The development of rubber-thermoplastic blends from ground tyre rubber and waste polypropylene

Ground Tyre Rubber (GTR) from scrap automotive and truck tyres was blended with Waste Polypropylene (WPP) from injection moulded products to prepare GTR/WPP blends . The blends were prepared in a Haake Rheocord PolyLab System, operating at 180 0 C and 30 rpm for 8 minutes. The degree of crystallinity of the WPP in the GTR/WPP blend was found to be unchanged up to a GTR level of 60 % by weight. Crystalline melting point and re-crystallization temperature showed a significant decrease with GTR content. Optical micrograph of the blends containing up to 60 wt% GTR showed a similar morphology, in which the GTR was dispersed in a continuous WPP phase. The GTR dispersed phase grew in size with GTR content until at 70 wt%, it changed to a continuous phase. However, all blends showed a mixture of cohesive, adhesive and ductile failures. The response to tensile loading ranged from a ductile plastic response with WPP-rich blends to a high extension-rubbery response with GTR-rich blends. Under impact loads, brittle fracture occurred in blends containing up to 40 wt% GTR, with ductile fracture thereafter. Hardness, tensile strength, secant modulus at 7% strain and tear resistance decreased with increase in GTR content, while % elongation at break and impact failure energy increased.

Inclusion polymerization of isoprene in deoxycholic acid

The radiation-induced polymerization of isoprene was made on its inclusion (or clathrate) complex with deoxycholic acid (DOCA) at 150 and 300 kGy. The microstructure of the resulting polyisoprene (PIP) was studied by FTIR spectroscopy and found fully comparable to that of PIP prepared by emulsion polymerization by a free radical initiator. Thus, the 1,4-trans content was found to be 48% and that of 1,4-cis units was 28% of the polymer structure; the remaining are being 1,2 and 3,4 units. The PIP irregular microstructure was justified in terms of monomer dynamics inside the DOCA channels. PIP from inclusion polymerization is fully amorphous as studied by differential thermal analysis (DTA) in comparison to an authentic sample of trans-1,4-polyisoprene, which instead has a crystalline melting point of 71.5 °C. The inclusion complex of PIP with DOCA (PIP@DOCA) shows a DTA melting point of 194.4 °C, 12.4 °C higher than the melting point of pure DOCA. PIP isolated from inclusion polymerization from DOCA and its complex PIP@DOCA was studied also by thermogravimetry (TGA) and differential thermogravimetry (DTG). Isoprene does not form inclusion complexes with urea and thiourea. When irradiated with these two compounds it produces an oily PIP oligomer whose microstructure was found by FTIR spectroscopy analogous to that of PIP prepared by emulsion polymerization by a free radical initiator.

Production and characterization of curdlan by Agrobacterium sp.

Agrobacterium sp. was studied for the production of curdlan by conventional one-factor-at-a-time technique and response surface methodology. Factors such as initial pH, urea concentration, sucrose concentration having the greatest influence on the curdlan production were identified. By using response surface methodology (RSM), the curdlan production by Agrobacterium sp. was increased significantly by 109%, from 2.4 g/L to 5.02 g/L when the strain was cultivated in the optimal medium developed by RSM as compared to conventional one-factor-at-a-time technique. The curdlan production rate of 0.84 g/(L h) was obtained when Agrobacterium sp. was cultivated in the optimal medium developed by RSM, which was the highest curdlan production rate reported to date. The infrared (IR) and NMR spectra, the thermogram of DSC and pattern of X-ray diffraction for the curdlan of the present study were almost identical to those of the authentic curdlan sample (from Alcaligenes faecalis; Sigma). The purified curdlan was a linear polysaccharide composed of exclusively β-(1,3)-glucosidic linkages with the molecular weight of 160,000 Da by GPC. The crystalline melting point (Tm), glass transition temperature (Tg) and X-ray diffraction of the sample indicated low crystallinity in the structure.

Finite element analysis of the thermoforming of Polypropylene

Polypropylene (PP) is typically solid phase thermoformed at temperatures close to its crystalline melting point, usually in the 150° to 160° Celsius range. In such conditions the mechanical properties of the material rapidly decline with temperature and these large changes in properties make Polypropylene one of the more difficult materials to process by thermoforming. This paper presents the findings of a study into the thermoforming behaviour of an industrial thermoforming grade of Polypropylene. Practical tests were performed using custom built thermoforming equipment at Queen’s University Belfast. Numerical simulations of these processes were similarly constructed to replicate thermoforming processes using industry standard Finite Element Analysis software.

Synthesis of highly crystalline poly(dimethylbutadiene) (PDMB) by radiation-induced inclusion polymerization: A comparison with PDMBs synthesized by bulk and emulsion polymerization

Poly-2,3-dimethylbutadiene (DMBD) has been synthesized by the radiation-induced inclusion polymerization technique. 2,3-DMBD was included as a clathrate in the channels of thiourea crystals and polymerized with 300 kGy into a crystalline high trans-1,4-polydimethylbutadiene (PDMB) in high yield. For comparison 2,3-DMBD was also polymerized by bulk radiolysis in high vacuum at 150, 300 and 600 kGy. The resulting PDMB was obtained in very low yields and had a microstructure completely different from that observed on PDMB synthesized by inclusion polymerization and more similar to the structure of an emulsion-PDMB prepared by a free radical initiator. Trans-PDMB prepared by inclusion polymerization was characterized by a crystalline melting point at 272 °C. The radiation chemical yield for the PDMB obtained by inclusion polymerization was found G=212 monomer units (in PDMB)/100 eV. This value is 23.5 times higher that measured in PDMB prepared by bulk radiolysis of the monomer.

Construction of thermoresponsive SCKs through tuning the crystalline melting point of the core domain.

Shell cross-linked knedel-like (SCK) block copolymer micellar nanoparticles were prepared from poly(acrylic acid-b-octadecyl acrylate-co-decyl acrylate) and studied as unique systems, having tunable core melting transition temperatures (Tm). Tm depression was accomplished by diluting octadecyl acrylate with the co-monomer decyl acrylate in the construction of the hydrophobic block segment of amphiphilic block copolymers of similar lengths and chemical compositions. Organization of those block copolymers into micelles and cross-linking throughout the shell then afforded a series of SCKs that exhibited core Tm values ranging from 3 to 40 °C. Confinement of the side-chain crystalline polymer chains within the core of the SCKs resulted in depression and broadening of the Tm values, which increased by ca. 5 °C when the shell was hydrated, as determined by differential scanning calorimetry measurements in the dry and 30 % (w/w) hydrated states. Passage through the melting transition was also observed for the SCKs dispersed in water, by dynamic light scattering experiments, which revealed an expansion and then collapse in hydrodynamic diameter over the temperature range of core melting. As the crystalline-amorphous core behaviors could be tuned over physiological temperature ranges, these nanoparticles are expected to be of utility as tunable drug delivery devices, with control over the kinetics and conditions of packaging and release.

Effect of recycling on the thermal properties of polymers

The continuous increase in the utilization of polymeric materials in many useful short-life applications has demanded the attention of researchers worldwide concerning the solid waste generation and, as an immediate consequence, the generalized environmental pollution. The main alternative for controlling this environmental impact is the polymer recycling process. However, one of the biggest challenges of this process is to keep the polymer performance within levels, which permit their reuse in the same or in other specific important technological applications. In this work, the laser flash technique is employed to study the effect of recycling on the thermal properties of some selected polymers. Since the thermal diffusivity expresses how fast heat propagates across a bulk material and the thermal conductivity determines the working temperature levels of a material, it is possible to assert that those properties are important when a polymer is used as an insulator and also when it is used in applications where heat transfer is desirable. Five sets of virgin and recycled commercial polymers widely used in many applications, including food wrapping, were selected for this study. Disc-shaped samples 10 mm diameter and 0.3–1 mm thickness were prepared by hot pressing the polymer pellets or powder, or by cutting discs from long cylindrical bars. Measurements were carried out from room temperature up to approximately 50 °C above the polymer crystalline melting point. Experimental results show different behavior for the thermal diffusivity of recycled polymers when compared with the corresponding virgin material.

Screening, characterization and flocculating property of carbohydrate polymer from newly isolated Enterobacter cloacae WD7

A total of 188 carbohydrate polymer-producing bacterial strains were isolated from recycled sludge of five seafood processing plants. Among three selected isolates, identified as Enterobacter cloacae WD7, Enterobacter agglomerans WD50 and Pseudomonas alcaligenes WD22. E. cloacae WD7 generated a viscous culture broth exhibiting the highest flocculating activity and a crude polymer yield of 2.27 g/L after 3 days cultivation. Partial purification of this polymer was performed by precipitation with 95% ethanol, dialysis and freeze-drying. It was characterized as an acidic heteropolysaccharide, composed of neutral sugars (29.4%), uronic acids (14.2%) and amino sugars (0.93%). The functional group analysis by FT-IR spectroscopy showed the presence of hydroxyl, carboxyl, carbonyl and methoxyl groups. Thermal analysis by DSC showed the crystalline transition and the crystalline melting point (Tm) at 300 °C. This polysaccharide was soluble in water and insoluble in any organic solvents tested; gelation occurred under alkaline conditions in the presence of divalent cations in which copper as CuSO4 gave the best result. Studies on the flocculation property revealed that this polysaccharide was stable at 4–60 °C and pH 5–7. The optimal concentrations for the flocculating activity were 2 mg/L polysaccharide and 40 mM CaCl2 which played the synergistic effect on kaolin flocculation. Moreover, this polysaccharide could flocculate the kaolin suspension over a wide range of pH (pH 2–8) and temperature (4–50 °C) tested in the presence of CaCl2.

Sorption of Organic Solvents in Poly(Dimethyl Siloxane) Membrane. II. Effect of Sorption on the Polymer Crystals upon Cooling

Polymer crystalline properties in poly(dimethyl siloxane) (PDMS) film after solvation by various solvents was determined using low temperature differential scanning calorimetry (DSC). At various solvent uptake levels, the crystalline thermal properties of the solvated polymer were modified to different extents as revealed by the shifts in crystalline melting point (Tm) and its enthalpy (ΔHm). Water uptake in PDMS was very limited (<0.01 g/g) and Tm did not significantly change during the sorption process. For toluene and cyclohexane penetrants, Tm moved toward a much lower temperature depending on the sorption levels. At low solvent uptakes, the Tm values decreased linearly with solvent uptakes due to formation of a miscible phase. Beyond a threshold, the Tm remained stable and an additional penetrant fusion peak appeared, implying the onset of a microphase separation phenomenon. The ΔHm values for the swollen membranes were decreased, with the exception of the water penetrant. This indicates that a lower percentage of polymer chains were involved in the crystalline domain for swollen PDMS.

Some aspects of the ozone degradation of poly(vinyl alcohol)

Poly(vinyl alcohol) (PVAL) forms a strong hydrogen-bond complex with ozone. The interaction energy is of the order of 47.3 kJ/mol as calculated from the blue shift undergone by the ozone absorption band in the UV after its complexation with PVAL. This fact may have many important practical implications in the application of PVAL in wastewater treatment both in terms of O 3 dissolution and persistence in water. Furthermore, PVAL is easily biodegradable but it is also slowly degraded by ozone. It is shown by viscometry, electrical conductimetry and by pH measurements that PVAL is degraded by ozone attack with extensive chain breaking. By FT-IR spectroscopy it has been shown that the final product is a PVAL oligomer with numerous ketonic groups along the main oligomer backbone and with carboxylic end groups. A mechanism of ozone degradation of PVAL has been presented and discussed. The chain scission is based on the ozone oxidation of the alcoholic groups of PVAL with formation of ketonic groups which in turn are the source of a keto–enol tautomerism which leads to random chain scission by further O 3 attack. Viscometric measurements show that the main viscosity drop of PVAL is achieved when a nominal stoichiometric ratio of O 3/PVAL < 0.05 is reached which means one ozone molecule for every >20 PVAL monomeric units. For comparison PVAL has been oxidized also with paraperiodic acid. Ozonized PVAL has been studied by thermal analysis (TGA, DTG and DTA) in comparison to a reference untreated PVAL under N 2. The oxidation of PVAL causes its complete amorphization since the crystalline melting point of PVAL at 235 °C is no longer detectable in the case of ozonized PVAL. In any case ozonized PVAL shows a better thermal stability which can be confirmed for instance by a higher maximum decomposition rate temperature as measured by DTG. This result is in agreement with theoretical calculations made by group increments according to Van Krevelen's method which predicts a higher decomposition temperature for a PVAL having ketonic groups in place of alcoholic moieties in the main polymer backbone.

Effect of Pre-Melting Time on Crystallization of Poly(ethylene terephthalate)

In this study poly(ethylene terephthalate) (PET) was melted at 300°C, approximately 46°C above the crystalline melting point, T m, for different times, i.e., Δt m,=5, 8, and 10 min, and then quenched to different isothermal crystallization temperatures, T c, ranging from 190°C to 230°C. The effect of pre-melting time, Δt m, at 300°C on the degree of crystallinity and on crystalline morphology were investigated by differential scanning calorimetry (DSC) and polarized-light microscopy (PLM). After crystallization at low T c, PLM data revealed the PET contained usual, positive, and unringed spherulites. After crystallization at high T c PET contained unusual, ringed, and double-extinction spherulites. The experimental results reveal that increasing the pre-melting time Δt m at 300°C causes an increment in T c for usual–unusual, unringed–ringed, and positive–double-extinction transitions of the PET spherulites. The experimental results also show that PET with a pre-melting time Δt m=8 min had higher crystallinity than those with pre-melting times Δt m=5 and 10 min. These crystallization phenomena were attributed to the different numbers of residual unmelted PET crystallites as a result of the variation in pre-melting time, Δt m, at 300°C.

Evaluation of vinylidene fluoride polymers for use in space environments: Comparison of radiation sensitivities

Poly(vinylidene fluoride) and copolymers of vinylidene fluoride with hexafluoropropylene, trifluoroethylene and chlorotrifluoroethylene have been exposed to gamma irradiation in vacuum, up to doses of 1 MGy under identical conditions, to obtain a ranking of radiation sensitivities. Changes in the tensile properties, crystalline melting points, heats of fusion, gel contents and solvent uptake factors were used as the defining parameters. The initial degree of crystallinity and film processing had the greatest influence on relative radiation damage, although the cross-linked network features were almost identical in their solvent swelling characteristics, regardless of the comonomer composition or content.

Thermal properties of melt polymers by the hot wire technique

Over recent years mathematical modelling has become an established tool for improving process control and product quality in polymer processing. As models become more sophisticated, there is an increasing need for reliable thermophysical properties data. Those properties are observed when heat is added or removed from a material, and they become important in any project that must function in any thermal environment. Thermal conductivity, thermal diffusivity and specific heat, namely the thermal properties, are the three most important physical properties of a material that are needed for heat transfer calculations. Reliable thermal properties values are essential for polymers, both in steady and non-steady state situations. Recently, transient techniques have become the preferable way for measuring thermal properties of materials. In this work, the hot wire parallel technique is employed in the experimental determination of the thermal properties of polymers. Samples are prepared through the extrusion process starting from the powder or pellets of the solid polymer. A special mould of stainless steel in the shape of a rectangular parallelepiped provided with ceramic insulators between the hot wire, thermocouple and the mould is employed to store the melt extruded polymer whose thermal properties will be measured. Measurements are carried out from room temperature up to approximately 50 °C above the crystalline melting point. Thermal conductivity, specific heat and thermal diffusivity experimentally determined are checked against data found in literature and those furnished by the manufacturers.

Estimation of Thermal Parameters of Halogenated Polymers Based on Group Additive Methods

The thermal parameters such as, glass transition temperature (Tg), crystalline melting point (Tm), initial thermal degradation temperature (Td,0), and coefficient of thermal expansion (Eg) of some halogenated polymers have been estimated employing two different relations such as the Van Krevelen method and the Askadskii method based on the group additive principle. The estimated parameters were compared with the experimental values. The estimated thermal parameters by the Van Krevelen method are found to be more accurate, rapid, and simple than the Askadskii method, except for a crystalline melting point.

Hydrostatic Extrusion of Poly(L‐Lactide)

AbstractPoly‐L‐Lactide(PLLA) has been used as a bone fracture fixation material for several years. However, its mechanical properties are still not satisfied. To improve its mechanical properties, we examined the hydrostatic extrusion procedure on the PLLA rods made by Injection Molding process. The extrusion ratio was adjusted to 3, 6, 9, and 12. The molecular weight of the PLLA decreased from 260,000 to 200,000 after injection molding process, but it did not change during the hydrostatic extrusion procedure. The melting point of PLLA hydrostatic extrusion products were increased with the extrusion ratio, but the increment was not obviouse. Extrusion products having low extrusion ratio had α‐form crystal in them, extrusion products having high extrusion ratio had both of α and β‐form crystall in them. At extrusion temperature of 145°C, PLLA rods showed the best flowing trends in the pressure medium of PEG 400. Extrusion temperature is placed in the range of crystalline transition temperature and melting point of PLLA. At extrusion ratio 9∼12, the extrusion products showed the best mechanical properties. The highest bending strength of the extrusion product was over than 350MPa. It is far stronger than that of the human cortical bone (200MPa). SEM observations showed that the fiber structure began to appear at an extrusion ratio ER=3, and at the extrusion ratio ER=6, the chain axes of PLLA became aligned to the extrusion direction. The structure of extrusion products at the high extrusion ratio showed highly oriented fiber structure composed of micro‐fibril. At high extrusion ratio tranformation from α‐crystal to β‐crystal was also observed.

Influence of the Casting Solvent on the Thermotropic Alignment of Thin Liquid Crystalline Polyfluorene Copolymer Films

The morphology of a conjugated polymer thin film determines how it will behave as an active layer in optoelectronic devices. The liquid crystalline phase present in some conjugated polymers offers a unique way of controlling the film morphology. For example, films in which the chains are aligned in a single direction can be fabricated by processing films on a templating layer and annealing them above the liquid crystalline melting point of the polymer. However, the ability to align to a templating layer will be influenced by the character of the as-cast film. This effect was examined by casting poly(9,9-dioctylfluorene-co-benzothiadiazole) (F8BT) films from a range of both aromatic and chlorinated solvents on top of rubbed polyimide layers and aligning via the thermotropic melt. Measurements of the dichroic ratio as a function of annealing time revealed that films cast from high boiling point aromatic solvents like isodurene (ISO) and o-xylene (OXY) aligned well with a maximum dichroic ratio over 10. Film...

Phase morphology, crystallisation behaviour and mechanical properties of isotactic polypropylene/high density polyethylene blends

The phase morphology, crystallisation behaviour and mechanical properties of isotactic polypropylene (iPP)/high density polyethylene (HDPE) blends were investigated. It was found that the properties are intimately related to each other. The morphology of the blends showed a two phase structure in which the minor phase was dispersed as domains in the major continuous matrix phase. The domain size of the dispersed phase increased with increasing concentration of that phase due to coalescence. It was also found that the domain size of the dispersed phase depends on the viscosity difference between the two phases. For a given HDPE/iPP blend, where HDPE is the matrix and iPP is the dispersed phase, the iPP domains were smaller than HDPE domains of the corresponding iPP/HDPE blend where iPP is the matrix and HDPE is the dispersed phase. A co-continuous morphology was observed at 50/50 PP/HDPE composition. Crystallinity studies revealed that blending has not much effect on the crystalline melting point of polypropylene and high density polyethylene. The crystallisation enthalpy and heat of fusion values of HDPE and PP in the blend were decreased as the amount of the other component increased. The variation in percent crystallinity of HDPE and PP in the blend was found to depend on the morphology of the blend. All the mechanical properties except Young's modulus and hardness showed negative deviation from the additivity line. This is due to the incompatibility of these blends.

Radiolytic unsaturation decay in polyethylene. Part II—the effect of irradiation temperature, thermal history and orientation

The decay rate of vinyl unsaturation in high-density polyethylenes irradiated at temperatures from about 310 to 450 K, changes significantly in the melting range up to the crystalline melting point as does free radical mobility and the polymer crystallinity. However, orienting the polymer, or slow cooling or quenching from the melt, prior to irradiation, do not alter the decay process or its rate, although they do alter the rate of increase of insoluble gel and of elastic modulus in the molten state. It is suggested that, below ∼340 K, the marked deviations from a first-order decay result from the limited mobility of polymeric free radicals in the crystalline phase and from scavenging, by vinyl groups, segregated into the amorphous phase, of radiolytic hydrogen atoms (H). In the melting range, the mobility of polymeric free radicals increases as the crystallinity decreases, reducing the importance of scavenging, so vinyl decay approximates more closely to a first-order relation. In the melt, the vinyl decay relation is not changed qualitatively by H atom scavenging, but the effective vinyl concentration is lower, so the decay rate drops sharply.

Preparation and characterization of polypropylene/mesoporous silica nanocomposites with confined polypropylene

AbstractPolypropylene (PP)/Ti‐MCM‐41 nanocomposites were prepared by isospecific propylene polymerization with Ti‐MCM‐41/Al(i‐C4H9)3 catalyst. The cross polarization/magic angle spinning (CP/MAS) 13C NMR spectrum of the composite was similar to that of the conventional isotactic PP, and the decrease in the pore volume of Ti‐MCM‐41 in the nanocomposites, as measured by N2 adsorption, was consistent with the value calculated from the weight loss in the thermogravimetric analysis (TGA) curve; both these facts attest to propylene polymerization within the mesopores of Ti‐MCM‐41. Alkali treatment followed by extraction with o‐dichlorobenzene allows us to extract the confined PP out of the Ti‐MCM‐41 mesopores. Although the PP/Ti‐MCM‐41 nanocomposites do not exhibit a crystalline melting point, the same PP when extracted from the mesopores showed a clear melting point at 154.7 °C; this indicates that the crystallization of PP confined in mesopores is strongly hindered. For the PP polymerized within the confinement, the molecular weight (Mw) and molecular weight distribution (Mw/Mn) were 84,000 and 4.3, respectively; these values were considerably smaller than those of the PP polymerized concurrently outside the Ti‐MCM‐41 mesopores (Mw = 200,000–450,000, Mw/Mn = 40–75). Therefore, the confinement also has a marked effect on the molecular weight of the PP. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 3324–3332, 2003