Melting Endothermic Peak Research Articles

Effect of the liquid-liquid phase separation on the crystallization behavior and mechanical properties of poly(ethylene-ran-vinyl acetate) and paraffin wax blend

The effect of liquid–liquid phase-separation (LLPS) on the crystallization behavior and mechanical properties of poly(ethylene-ran-vinyl acetate) (EVA) with various amounts of vinyl acetate and paraffin wax blend was investigated. The blend of EVA-H (9.5% vinyl acetate) and the wax became homogeneous at temperatures greater than its upper critical solution temperature (UCST) (98°C), and an LLPS was observed between UCST and the melting point of 88°C for EVA-H in the blend. The existence of the LLPS is attributed to the relatively large amount of the hydrophilic component of vinyl acetate in EVA, although the molecular weight of the wax was just 560. However, LLPS did not occur for the EVA/wax blend when the content of vinyl acetate in EVA was less than 3%. This behavior was explained by using the Flory–Huggins lattice model with an effective interaction parameter. The degree of crystallinity of EVA-H in the EVA-H/wax blend, judged from a melting endothermic peak in differential scanning calorimeter (DSC) thermograms obtained during heating runs, decreased with increasing duration time in the LLPS region. The flexural modulus of the EVA/wax blend became maximum at certain blend composition (about 30 ∼ 40 wt % EVA depending upon the amount of vinyl acetate). This behavior can be explained by the fact that this blend composition has the largest relative degree of crystallinity of EVA measured by DSC and wide-angle X-ray scattering method. We found that the flexural modulus of the binder itself is directly related to that of a feedstock consisting of larger amounts of metal powder and the binder, which can help someone to develop a suitable binder system for a powder injection molding process. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 1991–2005, 1999

Effect of the liquid–liquid phase separation on the crystallization behavior and mechanical properties of poly(ethylene‐ran‐vinyl acetate) and paraffin wax blend

The effect of liquid–liquid phase-separation (LLPS) on the crystallization behavior and mechanical properties of poly(ethylene-ran-vinyl acetate) (EVA) with various amounts of vinyl acetate and paraffin wax blend was investigated. The blend of EVA-H (9.5% vinyl acetate) and the wax became homogeneous at temperatures greater than its upper critical solution temperature (UCST) (98°C), and an LLPS was observed between UCST and the melting point of 88°C for EVA-H in the blend. The existence of the LLPS is attributed to the relatively large amount of the hydrophilic component of vinyl acetate in EVA, although the molecular weight of the wax was just 560. However, LLPS did not occur for the EVA/wax blend when the content of vinyl acetate in EVA was less than 3%. This behavior was explained by using the Flory–Huggins lattice model with an effective interaction parameter. The degree of crystallinity of EVA-H in the EVA-H/wax blend, judged from a melting endothermic peak in differential scanning calorimeter (DSC) thermograms obtained during heating runs, decreased with increasing duration time in the LLPS region. The flexural modulus of the EVA/wax blend became maximum at certain blend composition (about 30 ∼ 40 wt % EVA depending upon the amount of vinyl acetate). This behavior can be explained by the fact that this blend composition has the largest relative degree of crystallinity of EVA measured by DSC and wide-angle X-ray scattering method. We found that the flexural modulus of the binder itself is directly related to that of a feedstock consisting of larger amounts of metal powder and the binder, which can help someone to develop a suitable binder system for a powder injection molding process. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 1991–2005, 1999

The Crystallization Behavior and Mechanical Properties of Poly(ethylene-ran-vinyl acetate) and Paraffin Wax Blend.

The effect of liquid-liquid phase-separation (LLPS) on the crystallization behavior and mechanical properties of poly(ethylene-ran-vinyl acetate) (EVA) and paraffin wax blend was investigated. The blend of EVA and the wax became homogeneous at temperatures greater than its upper critical solution temperature (UCST) (371K), and an LLPS was observed between UCST and the melting point of 361 K for EVA in the blend. The degree of crystallinity of EVA in the blend, judged from a melting endothermic peak in differential scanning calorimeter (DSC) thermograms obtained during heating runs, decreased with increasing duration time in the LLPS region.The flexural modulus of the blend became maximum at the 35wt% EVA. This behavior can be explained by the fact that this blend composition has the largest relative degree of crystallinity of EVA measured by DSC. We found that the flexural modulus of the binder itself is directly related to that of a feedstock consisting of larger amounts of metal powder and the binder, which can help someone to develop a suitable binder system for a powder injection molding process.

Differential scanning calorimetric study of poly(3-hydroxyoctanoate) inclusions in bacterial cells

Medium chain length polyhydroxyalkanoates, MCL-PHAs, produced by bacteria as inclusion bodies or granules were analyzed in situ by differential scanning calorimetry (DSC) without isolation from the cells. The kinetic DSC study of PHA granules, which contained mostly 3-hydroxyoctanoate units (PHO), in Pseudomonas putida BM01 cells showed that the polymer within the granules existed in an amorphous state, but it crystallized after dehydration of the cells under freeze-drying condition (below −50°C) followed by annealing at ambient temperature. In this manner, PHO within the cells readily crystallized to the maximum degree of crystallinity within 24 h at room temperature, which was much faster than for the same polymer isolated by solvent extraction. This observation suggests that the polymer within the cellular granules may be well organized. The DSC endothermic melting peak areas for the room-temperature annealed polymers within the cells were directly proportional to the amount of polymer in the cell, and the results from this type of quantitative analysis were essentially identical to those obtained by gas chromatographic and gravimetric analysis of the polymers. X-Ray diffraction analysis of the polymer in the freeze-dried, whole cells and of the isolated, fully crystallized polymer showed that the two types of PHO samples had similar crystal structures, but the polymer in the granules exhibited better side-chain packing and higher crystallinity.

Synthesis and Characterisation of Branched Poly(ethylene terephthalate)

Branched poly(ethylene terephthalate)s (PET) were synthesised with a variety of molar masses and with a large range of degree of branching by introduction of mono-, tri-(glycerol) and tetra-functional (pentaerythritol) comonomers to dimethyl terephthalate and ethylene glycol. The monofunctional alcohols, dodecanol and benzyl alcohol, were used as terminating agents to minimise gelation. The effect of various reaction parameters, such as percentage glycerol or pentaerythritol and polymerisation time, on limiting viscosity number [η] and weight average molar mass (Mw) were investigated. The thermal behaviour of branched PET was studied by differential scanning calorimetry; all samples showed a characteristic double endothermic melting peak and the glass transition temperature was not observed. Some branched PETs were subjected to solid-state polymerisation to increase the molar mass of previously prepared branched polymers. The solid-state polymerisation technique showed that the process not only promoted the molar mass but, more importantly, it increased the crystallinity of the polymer. Overall, the solid-state reaction rate was governed by initial molar mass, crystallinity, reaction temperature and time. © of SCI.

Blends of poly(butylene terephthalate) with co[poly(ethylene terephthalate-p-oxybenzoate)]: Crystallization behaviors

Polyblends of poly(butylene terephthalate) (PBT) with four different types of co[poly(ethylene terephthalate-p-oxybenzoate)] copolyester, designated as P28, P46, P64, and P82, were prepared by melt-blending. The crystallization behaviors of the blends were then studied by differential scanning calorimetry and polarized optical microscopy (POM). Crystallization rate and temperature of neat PBT are increased when less than 10 wt% of P28 is blended. On the contrary, crystallization rate and temperature of neat PBT decrease when 10 wt% of P46, P64, or P82 copolyesters is blended. The crystallization behaviors of the blends are confirmed by the POM observations at the cooling cycles of the melts. On the other hand, melting endotherm onset temperature and melting peak width for all blends are comparable with those of neat PBT. These results imply that the stability and distribution of PBT crystallites in the blends are not significantly influenced by blending. The effects of POB content in the composition of the blends on the crystalline morphology were also presented. It is found that the structure of crystallites of the blends changed gradually with increasing the POB content in the composition of copolyester from lamellar to cross-like spherulite structures. © 1996 John Wiley & Sons, Inc.

Effects of chemical constituents on crystalline properties of ethylene ionomers

The effect of % methacrylic acid (%MAA), % neutralization (%N) and ion type (Na+ or Zn++) on the crystalline properties of neutralized ethylene-methacrylic acid copolymers (ionomers) were studied using differential scanning calorimetry (DSC). Two endothermic melting peaks were observed for all the nine ionomers studied, the lower melting point (LMP) due to ordered ionic clusters and the higher melting point (HMP) due to polyethylene crystallites. Effects of %MAA, %N and ion type on LMP and HMP for as-received, aged and annealed samples are compared. Effect of types of pretreatments on LMP and HMP of ionomers at high and low %MAA contents for both ion types are discussed. Most of these results are explained from the point of view of crystalline morphology of ionomers.

Infrared spectroscopic studies of melting behavior of poly(ethylene 2,6-naphthalenedicarboxylate)

The FTIR method was used to study the melting behavior of poly(ethylene 2,6-naphthalenedicarboxylate) (PEN) samples of different thermal history of crystallization. With subtraction of the spectra of PEN samples of different crystallinities and amorphous PEN, the spectra of crystalline trans conformers, amorphous trans conformers, and amorphous gauche conformers were obtained. By following the changes in intensity of various gauche and crystalline bands during heating, the phenomenon of multiple melting endothermic peaks was shown to be due to the melting of imperfect crystalline conformation formed during crystallization. For two-step annealed samples, the crystalline conformational defects change into a more perfect one during annealing at higher temperatures.

Preparation and properties of new polyimides derived from 1,6-diaminodiamantane

New polyimides containing diamantane units were prepared by a conventional two-step method starting from 1,6-diaminodiamantane and aromatic dianhydrides. The intermediate poly(amic acid)s had inherent viscosities of 0.33–0.55 dL/g. These polyimides did not decompose below 400°C in air or nitrogen atmosphere, and the temperature at 5% weight loss were above 491°C. The glass transition temperatures of the polyimides were found to be 375–429°C by DSC. These polyimides had almost the same semicrystalline patterns and exhibited crystalline diffraction peak (2 θ) at around 15°. The polyimide Vb exhibited a melting endothermic peak at 514°C. © 1996 John Wiley & Sons, Inc.

Effective of Viscosity Ratio on Structure of Polypropylene/Polyamide 6 Blend Fiber.

Blend fibers of polypropylene (hereafter PP) and polyamide 6 (hereafter PA6) having various molecular weights were prepared by the melt spinning and drawing processes. Effect of the viscosity ratio of the polymers on the structure of the blend fibers were examined. For the undrawn PP fibers, the crystal orientation was very low even at a draft ratio of about 6.0. On the contrary, the undrawn blend fibers having a viscosity ratio (ηPP/ η PA6) of 1 and lower was found to have the oriented PP crystals even at a draft ratio of 2.0 to 4.0. The drawn blend fibers having a viscosity ratio of 1 and higher exhibited stronger and more distinct X-ray diffraction peaks of the PA6 crystals as compared with the blend fibers having a viscosity ratio of 1 and lower. An unusual phenomenon was observed in the DSC measurement of the drawn blend fibers: two melting endothermic peaks of the PA6 component appeared for the fibers with a viscosity ratio of 1 and lower. It was speculated that the imperfect and small PA6 crystallites were formed because of the inflluence of the PP component. The significant changes observed in the crystal orientation and the melting endothermic behavior in the blend fibers was considered to depend largely on the dispersion state of the PP and PA6 phases: when the viscosity ratio was lower than 1, the two phases are finely dispersed. On the ohter hand, when the viscosity ratio is high than 1, the phases are coarsely dispersed and the interaction hetween two phases are relatively low.

Thermal and structural analysis of heparin–PEO–PDMS–PEO–heparin pentablock copolymers

AbstractABCBA‐type amphiphilic block copolymers comprising polydimethylsiloxane (PDMS), poly(ethylene oxide) (PEO), and heparin segments were synthesized by coupling reactions between end‐functionalized oligomers. These multiblock copolymers were characterized to examine bulk properties using 1H‐NMR, FTIR, end‐group analysis, and sulfur elemental analysis. Block copolymers were further characterized in bulk using differential scanning calorimetry and X‐ray diffraction measurements. The PDMS glass transition remains unchanged with increasing PEO content, indicating coexistence of pure PDMS with mixed phases. Furthermore, endothermic melting of the block copolymers shifts to higher temperatures and becomes more intense with increasing PEO molecular weight. Additionally, the crystallinity of the PEO segment in the block copolymers increases with increasing PEO molecular weight. The PEO melting endotherm peak shifts from near 318 to 323 K with annealing. In the cooling thermogram, the block copolymers exhibit two crystallization exotherms, one near 303 K and the other near 193 K, attributed to PEO and PDMS recrystallization and nucleation, respectively. © 1994 John Wiley & Sons, Inc.

Structural analysis of polyamide-6,6 reinforced with glass fibre by the use of Fourier transform infra-red spectroscopy with photoacoustic detection and differential scanning calorimetry

The effect of fibre reinforcement, industrial processing and subsequent annealing on the structure of polyamide-6,6 was analysed in this paper from the correlation between photoacoustic Fourier transform infra-red (PA FTi.r.) spectroscopic and differential scanning calorimetry (d.s.c.) thermal measurements. Using the band situated at 1650 cm −1 as an internal reference band, no spectral change was detected in the bands at 936 and 1146 cm −1. Furthermore, the bands centred at 1335 and 1224 cm −1, which are related to chain-folding, appear in the unannealed composite, whereas in the matrix these were only detected at the highest annealing temperatures. It seems that the manufacturing process used for the composite determines its microstructure and the subsequent annealing does not produce further conformational changes. On the other hand, the composite satisfies a two-phase conformational model, different from that of the matrix, which can be related to the strong interactions between the polymer and the glass fibres with surface treatment. In the thermal analysis, in contrast to the spectroscopic results, substantial changes in the endothermic melting peaks and in the degree of crystallinity can be noted. Up to an annealing temperature of ∼ 120–150°C, the composite crystallinity is constant and lower than the matrix crystallinity, but above this temperature the value rises and tends towards the values of the matrix. Furthermore, there was a more homogeneous crystalline distribution detected in the unannealed matrix, along with a greater size and perfection of the crystals than that seen in those of the unannealed composite. We suggest that the d.s.c. variation in the crystallinity can be attributed to an improvement in the fibre-matrix interface, in which the crystals of the interfacial phase change to more perfect ones as a result of the annealing treatment.

Bis(dialkylamino)‐substituted isopropenyltriazines: effect of the length of the alkyl chains on the polymerization as well as on the properties of the resulting comb‐like polymers

AbstractNew isopropenyltriazines, e.g., 2‐diethylamino‐4‐dimethylamino‐6‐isopropenyl‐1,3,5‐triazine (2a) and 2‐dimethylamino‐4‐dioctadecylamino‐6‐isopropenyl‐1,3,5‐triazine (2b) were prepared by the alkylation reaction of 2‐amino‐4‐dimethylamino‐6‐isopropyl‐1,3,5‐triazine (1) with corresponding alkyl halides in the presence of sodium hydride. In the free‐radical homopolymerization of these monomers, the polymerization yield of 2b was lower than that of 2a due to a lower ceiling temperature. Copolymerizations of these monomers with styrene and methyl methacrylate were carried out, and monomer reactivity ratios (r1 and r2) were determined. The monomer reactivity decreases by the introduction of two octadecyl groups into the monomer. Exothermic crystallization and endothermic melting peaks based on the octadecyl side chains were observed in differential scanning calorimetry of the resulting comb‐like polymers. The thermal stability of the polymers is not affected by the long alkyl groups.

Side-Chain Crystallization of Comb-Like Copolymers Obtained from Isopropenyltriazines with Comonomers Having Octadecyl Group

Copolymerizations of 2-amino-4-anilino-6-isopropenyl-1,3,5-triazine and 2-amino-4-(N-octadecylanilino)-6-isopropenyl-1,3,5-triazine with octadecyl acrylate, octadecyl methacrylate, N-octadecylacrylamide, and N-octadecylmethacrylamide were carried out in order to investigate the side-chain crystallization of the resulting comb-like copolymers. Crystallization exothermic and melting endothermic peaks due to the side-chains of the comb-like copolymers were observed in differential scanning calorimetry (DSC) thermograms. When the content of isopropenyltriazine unit in the copolymer was high, glass transition temperature was observed above the melting point of the side-chain crystallites. The influence of monomer structure and copolymer composition on the crystallinity of the side-chains and glass transition temperature are discussed.

DTA identification of polycaprolactone

Polycaprolactone (PCL) is a new material used in orthopedics. It is characterized by an endothermic melting peak at about 61‡C, an endothermic decomposition peak at about 380‡C and an exothermic peak at about 453‡C. These three observed phenomena and the corresponding thermodynamic data made it easily possible to identify PCL among the other polymers previously examined with Differential Thermal Analysis (DTA).

Synthesis and polymerization of isopropenyltriazines containing two alkyl groups and side-chain crystallization of the resulting polymers

2,4-Bis( N-ethylanilino)-6-isopropenyl-1,3,5-triazine (BEIT) and 2,4-bis( N-octadecylanilino)-6-isopropenyl-1,3,5-triazine (BOIT) were prepared by the alkylation reaction of 2,4-dianilino-6-isopropenyl-1,3,5-triazine with the corresponding alkyl halides in the presence of sodium hydride in dimethylsulphoxide. The homopolymerization of these monomers and their copolymerization with styrene or methyl methacrylate were carried out using azobisisobutyronitrile as the initiator in benzene. The monomer reactivity ratios ( r 1 and r 2) were determined for these monomers. The homopolymerization rate and the monomer reactivity in the copolymerization for BOIT were lower than those for BEIT. For the polymers from BOIT, exothermic crystallization peaks and endothermic melting peaks based on the side chains of the comb-like polymers were observed in differential scanning calorimetry thermograms. The crystallinity of the side chains decreased with increasing content of styrene or methyl methacrylate in the copolymers.

Melting behaviour of controlled rheology polypropylene

The melting behaviour of reactor-made isotactic polypropylene (PP) and various controlled rheology polypropylene (CR-PP) samples crystallized under both isothermal and non-isothermal conditions were studied by differential scanning calorimetry and the crystal structure of isothermally crystallized samples at 120°C was investigated using wide angle X-ray diffraction. Multiple endotherms were observed dependent on the molecular weight of the samples, heating rate and cooling rate, and method of crystallization. Recrystallization or reorganization occurred more easily for low molecular weight samples and also for fast cooled samples during the reheating and the melting process. The isothermally crystallized CR-PPs produced by peroxide controlled degradation showed a small melting endotherm peak at ∼143°C which is probably connected to the β form crystal, while unreacted PP showed the α form crystal only. The small endotherm peak was more prominent in one CR-PP sample of intermediate molecular weight. Attempts were made to explain this behaviour through the observed maximum in the half-time of crystallization versus molecular weight plot.

Comb-Like Copolymers Obtained by Copolymerization of 2-Amino-4-(N-alkylanilino)-6-isopropenyl-1,3,5-triazines

Copolymerizations of 2-amino-4-(N-alkylanilino)-6-isopropenyl-1,3,5-triazines with styrene, methyl methacrylate and methyl acrylate were carried out using azobisisobutyronitrile as an initiator. Alkyl groups were propyl, hexyl, octyl, decyl, dodecyl, tetradecyl, hexadecyl, octadecyl, and docosyl. Copolymerization parameters (r1, r2, Q, and e) were determined for these monomers. No significant effect of alkyl chain length on the copolymrization parameters could be observed. Relationships between glass transition temperatures and composition of the copolymers were investigated. Crystallization exothermic and melting endothermic peaks due to the side-chains were observed in the DSC thermograms of the comb-like copolymers containing octadecyl and docosyl groups. The crystallinity of the side-chains decreased with increasing content of styrene or methyl methacrylate in the copolymers.

Synthesis and Side-Chain Crystallization of New Comb-Like Polymers from 2-Amino-4-(N-alkylanilino)-6-isopropenyl-1,3,5-triazines

New isopropenyl-1,3,5-triazines, e.g., 2-amino-4-(N-propyl(N3), hexyl(N6), octyl(N8), decyl(N10), dodecyl(N12), tetradecyl(N14), hexadecyl(N16), octadecyl(N18), and decosyl(N22)anilino)-6-isopropenyl-1,3,5-triazine, were prepared by the reaction of 2-amino-4-anilino-6-isopropenyl-1,3,5-triazine with corresponding alkyl bromides in the presence of sodium hydride in dimethyl sulfoxide. The alkylation reaction proceeded selectively on the imino group, and the products were obtained in high yields. Polymerizations of these monomers were carried out using azobisisobutyronitrile as an initiator. Glass transition temperature of the polymers decreased with increasing the numbers of carbon atoms in alkyl side-chain. The crystallization of the alkyl side-chains in the comb-like polymers was investigated by differential scanning calorimetry (DSC). The crystallization exothermic and the melting endothermic peaks based on the side-chains of the polymers containing long alkyl groups in excess of 14 carbon atoms were observed in DSC thermograms.

Differential Scanning Calorimetry and Stress Relaxation of Partially Saponificated Poly(vinyl alcohol)-Dimethyl Sulfoxide-Water System

In order to clarify the relation between the structure and properties of poly(vinyl alcohol) (PVA) gel, differential scanning calorimetry (DSC) and stress relaxation measurements were carried out. A small and broad endothermic peak which appeared at about 45°C was attributed to the disentanglement of molecular chains. A sharp endothermic peak which appeared in the temperature range from 70°C to 110°C was attributed to the gel melting or transition from gel to sol. The endothermic enthalpy determined from the area enclosed by the melting endothermic peak and the beseline showed a maximum at a DMSO concentration around 0.277 mf, which was almost independent of the concentration of PVA. The relaxation spectrum of PVA gels showed a maximum as a function of DMSO concentration at 0.277 mf DMSO. It was suggested that the number and structures of junction zones and the conformations of flexible chains connecting junction zones are optimized to give maxima of the elastic modulus and the endothermic enthalpy of melting.