Melt Stability Research Articles

Preparation and properties of biodegradable poly(lactic acid)/poly(butylene adipate-co-terephthalate) blend with glycidyl methacrylate as reactive processing agent

Poly(lactic acid) (PLA) and poly(butylene adipate-co-terephthalate) (PBAT) were melt-blended in the presence of glycidyl methacrylate (GMA) by twin-screw extrusion. The physical properties, phase morphology, thermal properties, and melt rheological behavior of the blends were investigated by tensile tests, Charpy impact tests, scanning electron microscopy (SEM), differential scanning calorimetry (DSC), and advanced rheology expended system (ARES). With 2 or 5 wt% GMA, the tensile toughness of the PLA/PBAT blend was greatly increased without severe loss in tensile strength. The impact strength of the blend was also significantly improved at 1 wt% of GMA addition but ultimately trended to be saturated with increasing GMA. SEM micrographs revealed that better miscibility and more shear yielding mechanism were involved in the toughening of the blend. DSC results indicated that the blend is still a two-phase system in the presence of reaction agent and the addition of GMA was found to enhance the interfacial adhesion between PLA and PBAT. Rheological results revealed that the addition of T-GMA increased the storage moduli (G′), loss moduli (G′′) and complex viscosity of the blends at nearly all frequencies. The decreased shear-thinning tendency of the blends in the presence of T-GMA also implied improved melt stability during processing.

Melt stabilisation of Phillips type polyethylene, Part I: The role of phenolic and phosphorous antioxidants

The role of a phenolic and three phosphorous (phosphite, phosphonite and phosphine) antioxidants in the melt stabilisation of polyethylene was studied in a Phillips type polyethylene by multiple extrusions. The polyethylene was stabilised with a single antioxidant at 700 ppm and with phenolic/phosphorous antioxidant combinations containing 700 ppm of each component. The functional groups (methyl, vinyl, vinylidene, trans-vinylene and carbonyl) of polyethylene and the residual amount of phosphorous antioxidants were analysed quantitatively by FT-IR methods developed in our laboratory. The rheological characteristics, the colour and the residual thermo-oxidative stability of the polymer were determined and compared. Blown films were prepared and their mechanical strength measured by the Elmendorf and Dart-drop tests. The comparison of the different characteristics revealed that the chemical reactions taking place during the first processing of the nascent polymer powder, as well as the chemical composition of the antioxidants determine the reactions taking place in further processing operations. The changes in the characteristics of stabilised polyethylene during processing are controlled by the phosphorous stabiliser. The effect and final result depend on the chemical structure of the given antioxidant. The phenolic antioxidant itself does not hinder the formation of long chain branches. It reduces the rate of oxidation of the various phosphorous stabilisers, but does not modify the mechanism of stabilisation of the phosphonite and the phosphine. The reactions of the phosphite are significantly modified by the presence of a phenolic antioxidant.

Application of power expansion in the thermodynamics of compressible Markovian copolymers

The problem of constructing phase diagrams for a compressible melt of a binary Markovian copolymer is reduced to a set of nonlinear differential equations in partial derivatives with transcendental relationships. Using power expansions, the closed set of nonlinear differential equations is derived. This set allows its further analytical study. Eigenvalues of a linearized system are analyzed, and the boundaries of the thermodynamic stability of melts are defined. Nonlinear equations in normal coordinates are obtained; for symmetric melts, these equations are reduced to a single equation by adiabatic elimination of small-scale variables. Binodal curves are calculated for such solutions of this equation, which correspond to the free energy minimum of melts. Corrections reflecting the effect of melt nonsymmetry are found. The results are applied for copolymers, whose composition is similar to that of homopolymers, diblock copolymers, and random and regularly alternating copolymers. Spinodals and binodals corresponding to microphase separation are constructed.

Inhibition of Thermal Oxidation Destruction of PBT/HDPE Blends by Organic Compounds of Five-valent Phosphorus

Abstract Polybutylene terephthalate (PBT) and highy density polyethylene (HDPE) were blended and stabilized with four different stabilizers obtained from the organic derivatives of five-valent phosphorus. These stabilizers were cyclohexylphosphonic acid, its metallic salts of cyclohexyl phosponates of bivalent nickel, bivalent iron and trivalent iron. The stabilization improved the thermal stability of the PBT/HDPE blends and increased their mass loss temperature. The blend melts were thermally aged inside a viscometer barrel and the Melt flow Index (MFIs) was measured. All stabilizers increased the melt stability of the blends when used in low rates (< 0.2 % in mass). At higher stabilizer rates, some stabilizers further enhanced the thermal stability, while others decreased it. A melt parameter was introduced to determine the melt stability of the PBT/HDPE blends during extrusion. The best stabilization was obtained with cyclohexylphosphonic acid based on the metallic salts of bivalent nickel. The mechanisms that lead to the inhibition of thermal destruction of the blends were explained in terms of the stabilizers.

Stabilisation of metallocene ethylene-1-octene copolymers during multiple extrusions

The melt stabilising efficiency of antioxidants with different structures based on hindered phenols, phosphite esters, phosphonite and a lactone was examined during multi-pass extrusions at 265 °C in three metallocene ethylene-1-octene copolymers (m-LLDPE) having different extent of short chain branching (SCB) and one Zeigler copolymer (z-LLDPE) containing the same level of SCB corresponding to one of the m-LLDPE polymers. The effect of the different antioxidants, when used separately and in combination, was investigated by characterising the changes in the polymer's rheological behaviour, colour formation and structural changes based on unsaturated groups and carbonyl content during five multi-pass extrusions. The results showed that all stabilisation systems examined offered higher efficiency in the metallocene polymers compared to the Zeigler. The effect of the extent of SCB in the metallocene polymers on the stabilising efficacy of the antioxidant systems was also examined, and it was shown that it had a significant effect, with both single and combinations of antioxidants giving higher efficiency in the m-LLDPE polymer containing higher extent of SCB. The presence of the lactone HP136 in mixtures containing hindered phenol–phosphite antioxidant systems gave a higher melt stabilisation efficiency than in its absence and this has been attributed to a co-operative antioxidant reaction steps that take place between the antioxidants resulting in the possible regeneration of the lactone antioxidant through a redox reaction. In all the metallocene PE polymers examined, the biologically hindered phenol, Irganox E, was shown to be more effective than the conventionally hindered phenol Irganox 1076, when examined alone or in combination with phosphite esters.

Thermodynamic study of bulk metallic glass: Zr41.2Ti13.8Cu12.5Ni10.0Be22.5

Recently, multicomponent glass forming alloys have been found which exhibit extraordinary glass forming ability and cooling rates of less than 100 K/s are sufficient to suppress nucleation of crystalline compounds and consequently form a bulk metallic glass (BMG). The thermophysical properties of liquid metals and alloys in the undercooled state is become great interest of research in recent years. Due to the high thermal stability of undercooled melts of BMG glass formers the experimental data of the thermophysical properties of bulk metallic melts are available in the undercooled region. It is interesting to study the thermodynamics of such materials. The aim of the present work to discuss the thermodynamic behavior of BMG by estimating the Gibb’s free energy difference ΔG, enthalpy difference ΔH and entropy difference ΔS between the undercooled liquid and corresponding equilibrium solid phases. The study is made by estimating ΔG, ΔH and ΔS for BMG: Zr41.2Ti13.8Cu12.5Ni10.0Be22.5 in the entire temperature range T m (melting temperature) to T g (glass transition temperature).

Nonlinear optical properties of pyridinium-betaines of squaric acid: Experimental and theoretical study

The linear and nonlinear optical properties of six pyridinium-betaines of squaric acid were characterized by means of electro-optical absorption measurements (EOAM) in dioxane solution. All chromophores studied exhibit intense absorption bands in the visible region within 372–441 nm, accompanied with decrease in dipole moment upon excitation. The static hyperpolarizabilities of the NLO-phores studied depend strongly on the substituent in the pyridinium ring and increase significantly going from donor to acceptor substituent. Specifically, the noncentrosymmetrically crystallizing 4-benzoyl compound showed the highest static hyperpolarizability. These empirical trends were supported and verified by quantum-chemical calculations (DFT and ab initio RHF). Bulk crystal properties such as decomposition points within the high temperature range 480–665 K and improved thermal stability in melt demonstrate the advantage of these materials for nonlinear optical applications.

Role of non-stoichiometry in the cracking of oxide crystals

The cracking and stoichiometric deviations frequently observed in crystals of mixed oxides have generally been perceived to be unrelated phenomena. The present study pertains to the cracking in Czochralski grown crystals of three different materials, viz. CdWO 4, PbWO 4 and ZnWO 4. The results obtained on the single-crystal growth as well as on the thermal stability of melts of these materials and of their constituent oxides demonstrate, for the first time, that stoichiometric deviations manifest as cracks in the crystals. An important outcome of this investigation is that materials exhibiting a small degree of super-cooling with stable melting and solidification temperatures should be less prone to cracking.

Nanosize Polyacrylamide/SiO2 Composites by Inverse Microemulsion Polymerization

Nanosize polyacrylamide/silica (PAM/SiO2) composites were prepared by water- in-oil (W/O) microemulsion process. In this system, aqueous solution of acrylamide containing disperse 10 nm size silicon dioxide was used as the dispersed phase of the microemulsion while the dispersion medium was sodium bis (2-ethylhexyl) sulfosuccinate (AOT)/toluene solution. The size of the synthesized PAM/SiO2 nanocomposites was 38–76 nm as determined by dynamic light scattering (DLS). The incorporation of nanosize silica filler reduces the particle size of PAM latex. It had also been found that the size of composite particles decreases with increasing filler loading along with better polydispersity. The presence of silica particles in the polymer latex particles and interaction of polymer chains with silica particles in hybrid nanocomposites were characterized by Fourier transform infra red spectrophotometry (FTIR), thermogravimetry analysis (TGA) and differential scanning calorimetry (DSC). The TGA results showed improved thermoresistance and high thermal stability behavior of hybrid composites. The DSC measurements revealed that the incorporation of filler favors crystallization, increases the enthalpy of melting and thermal stabilization of the synthesized composite particles. A scanning electron microscope (SEM) was used to study the morphology and topography of the prepared nanocomposites.

Distribution coefficient of boron in Si crystal ingots grown in cusp-magnetic Czochralski process

Silicon single crystals are grown by the Czochralski method with various growing conditions. Effective segregation coefficient of boron is found to depend on the magnetic field in cusp-magnetic Cz method. Effects of zero-Gauss plane (ZGP), ZGP shape and magnetic intensity (MI) on the dopant concentration and its distribution in the crystal are experimentally investigated. The shape of ZGP is not only flat but also parabolic due to the magnetic ratio (MR), which is the ratio of the lower to upper electric-current densities in the configurations of the cusp-magnetic field. Equilibrium distribution coefficient of boron calculated by BPS model is 0.698. With the crystal rotation ( w) of 16 rpm and the crucible rotation of −0.5 rpm, the effective distribution coefficient ( k e) is 0.728 in zero magnetic intensity and increases up to 0.8093 in the parabolic ZGP shape. Although the magnetic strength near the crystal–melt interface decreases with increasing MR, it increases in the bulk melt, and hence k e increases. Flow stability in the bulk melt influences k e. At the magnetic field and growing conditions, k e increases with increasing initial charge size of the silicon melt. There is no significant influence of ZGP on the radial distribution of the boron concentration. Simulation results of melt flow in the presence of a parabolic ZGP are outlined, and the segregation results in the experiments are compared with published experimental data.

Synthesis and characterization of melt‐processable polyimides derived from 1,4‐bis(4‐amino‐2‐trifluoromethylphenoxy)benzene

AbstractA series of molecular‐weight‐controlled imide resins end‐capped with phenylethynyl groups were prepared through the polycondensation of a mixture of 1,4‐bis(4‐amino‐2‐trifluoromethylphenoxy)benzene and 1,3‐bis(4‐aminophenoxy)benzene with 4,4′‐oxydiphthalic anhydride in the presence of 4‐phenylethynylphthalic anhydride as an end‐capping agent. The effects of the resin chemical structures and molecular weights on their melt processability and thermal properties were systematically investigated. The experimental results demonstrated that the molecular‐weight‐controlled imide resins exhibited not only meltability and melt stability but also low melt viscosity and high fluidability at temperatures lower than 280°C. The molecular‐weight‐controlled imide resins could be thermally cured at 371°C to yield thermoset polyimides by polymer chain extension and crosslinking. The neat thermoset polyimides showed excellent thermal stability, with an initial thermal decomposition temperature of more than 500°C and high glass‐transition temperatures greater than 290°C, and good mechanical properties, with flexural strengths in the range of 140.1–163.6 MPa, flexural moduli of 3.0–3.6 GPa, tensile strengths of 60.7–93.8 MPa, and elongations at break as high as 14.7%. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2008

Meltable phenylethynyl-capped oligoimide resins derived from 1,4-bis(4-amino-2-trifluoromethylphenoxy)benzene and 3,4′-oxydianiline

A series of meltable oligoimide resins with controlled molecular weights by reactive phenylethynyl endcapping groups have been prepared by the thermal polycondensation of 3,3′,4,4′-biphenyltetracarboxylic dianhydride (s-BPDA) with the aromatic diamine mixtures consisting of different mole ratios of 1,4-bis(4-amino-2-trifluoromethylphenoxy)benzene (1,4,4-6FAPB) and 3,4′-oxydianiline (3,4′-ODA) in the presence of 4-phenylethynylphthalic anhydride (PEPA) as molecular weight-controlling and reactive endcapping reagent. Experimental results indicated that the molecular weight-controlled oligoimide resins were mixtures containing a series of biphenylethynyl-endcapped oligoimides with different chemical structures and different molecular weights. The typical oligoimide resins could be melted at temperatures of 300 °C to yield stable molten fluid with melt viscosity of 13.4 Pa s, which was suitable for melt processing. The molten oligoimide resins could be further polymer chain extended and crosslinked by thermal curing of the reactive phenylethynyl groups to give strong and tough thermosetted polyimides. Thus, the oligoimide resin with calculated molecular weight of 2500 exhibited not only good meltability with low melt viscosity, but also high melt stability and fluidability at temperatures of <300 °C. After thermal curing, the obtained thermosetted polyimide showed high glass transition temperature (>316 °C, DMA), excellent thermal stability with initial thermal decomposition temperature of 588 °C and good mechanical properties with flexural strength of 159.1 MPa, flexural moduli of 3.3 GPa, tensile strength of 94.7 MPa and elongation at breakage of 9.0%.

Particle distribution and interfacial reactions of Al–7%Si–10%B4C die casting composite

Aluminum–boron carbide particle reinforced composite is an advanced material which can be used in applications such as neutron-shielding components, aircraft, and aerospace structures. In the microstructural characterization of an Al–7%Si–10%B4C die casting, attention is particularly focused on particle distribution and interface reaction products between B4C particles and the aluminum matrix. The quantitative analysis results show that, in a cross-section of the cast part, more particles concentrate in the center and fewer particles are present in the wall regions. Moreover, some particle segregation bands have been observed. The mechanisms of the particle migration are proposed to describe the phenomenon. However, the average particle fraction in any cross-section of the cast part is almost the same. A barrier layer consisting of several sublayers was detected on the surface of B4C particles. Using electron diffraction in selected areas, it is found that these sublayers are composed of Al3BC crystals, TiB2 crystals, Si crystals, and coarse stick-shaped TiB2 particles. In addition, it is observed that Si plays an important role in the formation of a dense barrier layer. The barrier layer can limit B4C decomposition and improve B4C stability in the aluminum melt.

Thermal sensor control of the quality of welded joints on the basis of the criteria of thermodynamic stability of melting of metal during welding

Thermal sensor control of the quality of welded joints on the basis of the criteria of thermodynamic stability of melting of metal during welding

The preparation and properties of biodegradable polyesteramide composites reinforced with nano-CaCO 3 and nano-SiO 2

Composites were fabricated utilizing melt mixing aliphatic polyesteramide (PEA) with ordinary CaCO 3, nano-CaCO 3, and nano-SiO 2. The effect of filler on the matrix was studied by mechanical properties and hydrolysis rate measuring. The ordinary filler as well as the nano-filler had a negative effect on the stability of the polymer melt, and an improved mechanical property was obtained around a critical concentration of the filler where a percolation phenomenon appeared. When the composites underwent hydrolysis, the inert filler played a role as a mechanical obstacle in the matrix and retarded the hydrolysis; on the other hand, the interfacial area between the filler particle and the matrix resin increased with the filler, which would accelerate the hydrolysis. As a result of these two inverse effects, a minimum and a maximum value appeared in the plot of the degradation rate-filler content graph. For the ordinary filler filled polymer, the filler retarded the hydrolysis; in great contrast, the hydrolysis rate of nano-composites showed a maximum value around the critical concentration of the filler, and was much higher than the neat resin.

Enhanced Melt Stability of Star-Shaped Stereocomplexes As Compared with Linear Stereocomplexes

Enhanced Melt Stability of Star-Shaped Stereocomplexes As Compared with Linear Stereocomplexes

Polyurethane elastomers with amide chain extenders of uniform length

Toluene diisocyanate based polyurethanes with amide extenders were synthesized poly(propylene oxide) with a number average molecular weight of 2000 and endcapped with toluene diisocyanate was used as the polyether segment. The chain extenders were based on poly(hexamethylene terephthalamide): hexamethylene diamine, bisamine-diamide and bisamine-tetra-amide. The linear poly(ether bisurethane-bisurea-amide)s (PUA) were colorless transparent thermoplastic elastomers with a high molecular weight. The polymers were analyzed by IR and DSC, the morphology studied by TEM, the mechanical properties studied by DMTA and the tensile, the elastic properties by compression and tensile set and thermal stability by melt rheology. The phase separation with these amide extenders was by crystallization. Increasing the length of the amide chain extender increased the modulus and the melting temperature of the PUA without changing the good low temperature properties. Also the elastic properties improved with amide segment length. The fracture stress increases with amide extender length. At 200 °C, the melt stability of the PUA with the bisamine-diamide chain extender was good.

Stability of hydrous melt at the base of the Earth's upper mantle

Seismological observations have revealed the existence of low-velocity and high-attenuation zones above the discontinuity at 410 km depth, at the base of the Earth's upper mantle. It has been suggested that a small amount of melt could be responsible for such anomalies. The density of silicate melt under dry conditions has been measured at high pressure and found to be denser than the surrounding solid, thereby allowing the melt to remain at depth. But no experimental investigation of the density of hydrous melt has yet been carried out. Here we present data constraining the density of hydrous basaltic melt under pressure to examine the stability of melt above the 410-km discontinuity. We infer that hydrous magma formed by partial melting above the 410-km discontinuity may indeed be gravitationally stable, thereby supporting the idea that low-velocity or high-attentuation regions just above the mantle transition zone may result from the presence of melt.

Modification of melt, light, and heat stability of polyamide 6 by hindered piperidine amine and tertiary amine

Hindered piperidine amine (HPA) and tertiary amine (TA) were introduced into hydrolytic polymerization of caprolactam, and polyamide 6 (PA 6) modified by additives [HPA/TA = 1 : 1 (w/w)] was obtained. The effects of additives on the melt, light, and heat stability of PA 6 were studied. The results showed that with an increase in additive content, the viscosity of PA 6 increased and the elastic response decreased. Thus, the drawing property of PA 6 fibers during melt spinning was improved. With the addition of 0.1%–0.2% additives, the degree of variation in amino end group content and relative viscosity decreased during the process going from resin to fiber, indicating the modified PA 6 had improved melt stability. During light and heat aging, the ratio of retained fracture strength of PA 6 filament increased after modification by 0.1%–0.4% additives. Scanning electron microscopy showed that the surface morphology of the modified fiber remained almost the same, whereas that of the unmodified fiber was seriously destroyed when exposed to xenon light for 8 days or heated to 180°C in air for 1.5 h. The degree of variation of relative viscosity of the PA 6 fiber also decreased after modification by 0.1%–0.2% additives under oxidative degradation. All these results indicate PA 6 had better melt, light, and heat stability when modified by additives. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 538–544, 2007

Joule heating of solid wires in MAG welding

There are numerous studies1–12 concerning the melting rate of welding wire and various investigations have been carried out on welding current, welding current waveform, wire extension, polarity, chemical composition, wire diameter, arc length, shielding gas composition and melting rate. Joule heating of bulk wire has been a large contributory factor to the melting rate of solid wire for carbon steel (hereafter referred to as either wire or solid wire) and Joule heating is a crucial factor in aspects of melting stability. However, there are few case studies concerning the detailed measurement of Joule heating at the contacts between the contact tube and wire and the calculation of melting rate.