Effect of multiple extrusion on molecular structure of polypropylene impact copolymer

Neat and multiple processed polypropylene impact-copolymer (ICPP) were fractionated using series of hydrocarbon solvents with increasing solvent power. The analyses of the fractions obtained in successive extractions showed significant decrease in weight-average molecular weight (Mw) and narrowing the molecular weight distribution (MWD) of investigated samples after extrusions. Although the changes due to thermooxidation were observed in all phases of the system, the most intensive degradation was found in the prevailing PP homopolymer phase.     

A novel apparatus combining polymer extrusion processing and x-ray scattering

A novel apparatus was designed and constructed combining polymer extrusion processing and x-ray scattering. It allows direct, real time monitoring of structure and temperature development in polymer material during extrusion. The apparatus involves a vertical industrial extruder equipped with a four-roll stretching device to mimic the processing environments of uni-axially oriented films or sheets, a simultaneous small and wide angle x-ray scattering system and an infrared thermometer as detection unit. The charging barrel of the extruder and the stretching device can be moved upward and downward precisely. By moving the sample along the center line, structure and temperature development as a function of position can be obtained. The performance of the apparatus was verified by a test experiment, which allows us to establish the relationship between processing parameters and evolution of structure with different length scales, and may lead to a better understanding of the physics in polymer processing.     

聚氨酯的热分解研究进展

介绍了有关聚氨酯热性能研究的状况,着重阐述了聚氨酯在不同气氛下的热解机理及热解动力学的内容,同时也阐述了聚氨酯今后热解研究的发展方向。     

Study the effect of antioxidants on biological activity and on homopolypropylene; mechanical and physical properties

Exposure of polymers to temperature, atmospheric oxygen, or even light could result in some degradation of the polymer properties and features during processing (application), storage and end use. In hydrocarbon polymers, the polymer tend to free radical formation, eventually resulting in chain damage or crosslinking that leads to degradation. Antioxidants are used to terminate these chain reactions by removing radicals. Antioxidants are used in most hydrocarbon polymers including, polypropylene. a good addiction package must be existed to overcome the effect of degradation and save the polymer shape and characteristics. The practical experiment was carried out on a pure polypropylene (intermediate polypropylene resin without additives) and another practical experiment but with adding several types of additives with a certain concentration and study the behavior of polypropylene in all cases with successive extrusions. On other hand Flexible molecular docking on heme oxygenase, an important stress protein that is involved in cellular protection, antioxidant and anti-inflammatory activities, justified the antioxidant activity of the isolated compounds. From the binding energy 3114 and 1680 they could consider to be powerful and available antioxidant.     

Solubilization and conformational behavior of Zein in aqueous solution of dodecyldimethylethylammonium bromide (DDAB)

The solubilization and conformational behavior of Zein in the presence of cationic surfactant, dodecyldimethylethylammonium bromide (DDAB) have been studied. The colloidal properties of DDAB in the absence and presence of Zein have also been investigated using physico-chemical and spectroscopy methods. The surfactant appears to bind to Zein at concentrations below the critical micelle concentration (cmc) and the binding becomes weaker at concentrations above the cmc. The interaction between DDAB and Zein depends on the chemical structure and molecular parameters (conformation, molar mass, charge) of the protein. The schematic sketches of the molecular mechanisms of the complex formation between like-charged proteins and surfactants have been proposed.     

One Step Fabrication and Application of Antibacterial Electrospun Zein/Cinnamon Oil Membrane Wound Dressing via In situ Electrospinning Process

Antibacterial wound dressing can benefit the wound healing by preventing bacterial infection, especially for the electrospun ones due to their porous structures and easily loading antibacterial drugs. However, it is challenging to apply the antibacterial electrospun wound dressing to covering the wound conveniently and safely. Here, we presented one step fabrication and application of antibacterial electrospun zein/cinnamon oil wound dressing via a handheld electrospinning setup. The prepared zein/cinnamon oil wound dressing showed gas permeability of (76.1±5.45) mm/s, hydrophilicity with zero body fluid contact angle, swelling stability after 24 h as well as antibacterial zones over 5 cm against both E. coli and S. aureus bacteria. Moreover, in situ electrospinning process can deposit the electrospun zein/cinnamon oil fibers directly onto the wound, meantime forming a wound dressing. The mice cut-wound model experiment demonstrated that the one step in situ fabrication and application of zein/cinnamon oil wound dressing could nearly heal the wound within 11 d.     

Tracking lubricants during single screw extrusion of uPVC

Lubrication is one of the most important parameters in unplasticized polyvinyl chloride (uPVC) processing apart from the PVC resin and processing equipment. Lubricants are used in specific ratios to ensure effective fusion of PVC particles. The exact mechanism on how these lubricants interact is not yet fully understood. A widely accepted theory is the interaction mechanism proposed by Rabinovic et al. where lubricants are said to act as surfactants and slip agents. In this study a method for tracking lubricants, by simulating the extrusion process within a single screw extruder, was proposed. A three stage fusion simulation consisted of the feeding zone (stage 1), the compression zone (stage 2) and the metering zone (stage 3). The association interactions between the individual components of a typical uPVC formulation were followed throughout the three stages. External polar and nonpolar lubricants in combination with an internal lubricant was studied. Lubricants were successfully tracked using scanning electron microscopy coupled with energy dispersive spectroscopy (SEM-EDS). In conclusion it was found that the use of an internal lubricant promotes dispersion of external lubrication towards PVC. It was also found that there is a competition between the internal lubricant and polar external lubricant.     

Thermal properties of high density polyethylene composites with natural fibres: Coupling agent effect

High density polyethylene composites with curaua fibres were prepared using an intermeshing co-rotating extruder and two different coupling agents. The thermal stability of the components was studied by thermogravimetric and differential scanning analysis, as well as by the oxidation induction time. Maleic anhydride grafted polyethylene, used as coupling agent, affected the composite stability more markedly than did poly(ethylene-co-vinyl acetate). However, oxidation induction times were analogous for composites with and without coupling agents. Results also indicated that a higher fibre-matrix interaction precludes the crystallinity enhancement caused by the fibre.     

A novel online visualization system for observing polymer extrusion foaming

Cell nucleation and premature cell growth in extrusion foaming are critical to elaborate the morphology of final foams. These courses happen in the extrusion die which has been unknown for real extrusion foaming process. In this study, a novel visualization system was developed to online observe the cell nucleation and evolution behavior in the extrusion die. The cell evolution and real time pressure along the flow direction could also be obtained with the system. It was found that the solution pressure P_solution was influential to the critical nucleation radius R_cr and the nucleation rate N₀. The higher screw rotating speed corresponded to higher P_solution, lower in die N₀ and less premature cells, while higher cell density for extrude foams. In addition, premature cells with radius over critical break radius R_crb would break into several small cells under sufficient stress gradient in the extrusion flow field.     

Polystyrene prepared by reactive extrusion: kinetics and effect of processing parameters

The conversion and residence time were investigated during the bulk polymerization of styrene in a twin screw extruder. It was found that polymerization mainly occurred in the zone between 400 and 1000 mm along the screw axis in the extruder, corresponding to the residence time of the reactants ranging from 1 to 4 min in the extruder. Furthermore, the processing conditions (feed rate, screw rotation rate) and average molecular weight of the polymer have a great effect on the residence time. Based on dimensionless analysis, a model of the residence time has been built‐up, which has been confirmed by the results of realistic measurements. A kinetic model of the polymerization has also been established under the assumption that the screw extruder can be regarded as an ideal plug flow reactor. Copyright © 2004 John Wiley & Sons, Ltd.     

Solvent effect on thermal degradation of plasticized para-substituted polystyrenes

The thermal effect on stability of a series of para-substituted polystyrenes with methyl, methoxy and α-methyl substituents in various solvents was studied in the temperature range of 298-363 K. They gave a monomer fluorescence as a minor part and excimer fluorescence as a major part. Thermal heating of para-substituted polystyrenes shows a decrease in both monomer and excimer fluorescences in all used solvents. Thermal heating causes a small fluorescence quenching effect at lower temperatures in solution but becomes very dominant at higher temperatures. Added terephthalate and phthalate plasticizers to these para-substituted polystyrenes caused a quenching of both monomer and excimer fluorescences without the formation of exciplex emission. The thermal quenching processes of the plasticized polymers were accompanied by a change in the structure of the fluorescence spectra at high heating temperatures. This may indicate that thermodestruction of these polymers starts from a random chain scission. The change in solvent polarity has considerable effect on fluorescence quenching but it has a minor effect on the thermal degradation of these polymers. The binding energies for excimer formation were calculated in the used solvents.     

Degradation of poly(ethylene terephthalate)/clay nanocomposites during melt extrusion: Effect of clay catalysis and chain extension

Organoclays with various contents of hydroxyl groups and absorbed ammonium were prepared and compounded with poly(ethylene terephthalate) (PET), forming PET/clay nanocomposites via melt extrusion. Dilute solution viscosity techniques were used to evaluate the level of molecular weight of PET/clay nanocomposites. Actually, a significant reduction in PET molecular weight was observed. The level of degradation depended on both the clay structure and surfactant chemistry in organoclays. The composites, based on clay with larger amount of hydroxyl groups on the edge of clay platelets, experienced much more degradation, because the hydroxyl groups acted as Brønsted acidic sites to accelerate polymer degradation. Furthermore, organoclays with different amounts of absorbed ammonium led to different extents of polymer degradation, depending upon the acidic sites produced by the Hofmann elimination reaction of ammonium. In addition, the composite with better clay dispersion state, which was considered as an increasing amount of clay surface and ammonium exposed to the PET matrix, experienced polymer degradation more seriously. To compensate for polymer degradation during melt extrusion, pyromellitic dianhydride (PMDA) was used as chain extender to increase the intrinsic viscosity of polymer matrix; more importantly, the addition of PMDA had little influence on the clay exfoliation state in PET/clay nanocomposites.     

The effect of phosphorus content on the thermal and the burning properties of cotton fabric coated with an ultrathin film of a phosphorus-containing polymer

The effect of phosphorus content on thermal degradation and burning behavior of poly(acryloyloxyethyl diethyl phosphate) or PADEP-coated cotton was studied. The results showed that PADEP-coated cotton prepared by admicellar polymerization using hexadecyltrimethylammonium bromide (HTAB) as a surfactant has higher amounts of phosphorus than that prepared using dodecyltrimethylammonium bromide (DTAB). Higher phosphorus content led to lower decomposition temperatures and greater amounts of char formation after thermal degradation. The effectiveness of the amount of phosphorus on the burning behavior of the treated cotton was investigated by an ASTM flammabilty test. In the case of PADEP-coated cotton prepared with DTAB, the flame spread slowly and extinguished with char formation on the fabric. For untreated cotton however, the flame spread quickly and burned the fabric entirely without char formation. Cotton coated with PADEP using HTAB exhibited self-extinguishing behavior after removing the ignition source. Decrease in decomposition temperature, increase in char formation and the burning behavior of PADEP-coated cotton are all consistent with phosphorus content on the treated fabric.     

Melt flow behavior of polypropylene composites filled with multi-walled carbon nanotubes during extrusion

Polypropylene (PP) composites filled with multi-walled carbon nanotubes (MWCNTs) were prepared using a twin-screw extruder. The melt flow properties of the composites were measured with a capillary rheometer in a temperature range from 180 to 230 °C and at various apparent shear rates varying from 100 to 4000 s⁻¹. The results showed that the melt shear stress increased almost linearly while the melt shear viscosity decreased almost linearly with increasing shear rates in a bi-logarithmic coordinate system. The melt shear flow followed the power law relationship and the dependence of the melt shear viscosity on temperature obeyed the Arrhenius equation. The relationship between the melt shear viscosity and the MWCNT weight fraction was roughly linear under the investigated range of temperature or shear rate.     

部分水解聚丙烯酰胺降解研究进展

高分子量的水溶性聚丙烯酰胺 (PAM)在不同领域均有广泛的应用 ,但其分子量的降解行为直接影响到从生产、使用到最终处置的各个环节。本文将主要对各环节中涉及的降解作用研究进展进行综述 ,包括化学降解、生物降解、热降解和机械降解等。     

Rheological and single screw extrusion processability studies of isotactic polypropylene composites filled with basalt powder

The development of novel composite materials with beneficial mechanical, thermal and electrical properties often focus only on the final properties of the products. However, in many cases their significant application potential may be suppressed by limitations resulting from their rheological and processing properties. The isotactic polypropylene (iPP) composites filled with basalt powder (BP) are known for their good thermomechanical stability and stiffness. The paper presents the complex results of off-line rheological measurements (oscillatory, capillary and torque rheometry) related to processing behavior obtained in a laboratory conditions with the use of a processing machine (single screw extruder), which allow understanding the different manner of the processing behavior occurring during the melt processing of iPP-BP composites. It was found that the addition of BP may cause unusual, beneficial effect of lowered viscosity of the melt. While the addition of up to 5 wt% of BP results in a profitable reduction of the pressure in the barrel during extrusion without influence on the throughput, a higher amount of the filler may lead to significant processing limitations due to strong wall slip.     

Effect of residual contaminants and of different types of extrusion processes on the rheological properties of the post-consumer polypropylene

Rheological measurements were conducted to verify the influence of different mechanical recycling processes and the presence of contaminants on the degradation of post-consumer polypropylene. Firstly, polypropylene (PP) was contaminated to simulate a post-consumer material, following the protocol recommended by the FDA. PP was subsequently recovered (washed and dried) and the samples were submitted to different extrusion processes. The rheological data demonstrated that the different types of processing applied and the presence of contaminants altered the molecular structure of the samples. The contaminants acted as agents that accelerated the polymer degradation. The contaminated samples submitted to higher shear rates exhibited greater decrease in their molar mass and a slight narrowing in the molar mass distribution. Also, it was observed that the most degraded samples showed decrease in their molar mass, in the viscosity and in the level of their molecular entanglements. These samples also exhibited a more Newtonian behavior and their molar mass distribution showed a slight narrowing. By calculating the ratio of the molar mass it was possible to quantify the degree of degradation of PP samples, confirming the results obtained.     

Cavitation of polyethylene during extrusion processing instabilities

We present observations of cavitation that occur inside a capillary die during extrusion of polyethylene. This phenomenon was observed over the last 1.5 mm of the capillary tube immediately upstream of the exit. We observed spontaneous formation of voids near the wall that grew to a typical length and width of 150 μm, and then shrank and disappeared over a time frame of approximately 20 ms. From velocity measurements of these structures, we concluded that their width in the radial direction was smaller than in the axial and lateral directions, and they were near the wall. The shape of the cavities was highly irregular. We assessed the roles of extensional stress and shear stress at the exit region and concluded that they were not the direct cause of cavitation. Rather, cavitation occurs in conjunction with an upstream rupture of the polymer that occurs in the contraction region leading into the capillary tube (gross melt fracture). We argue that the exit region does, however, serve as the initiation point of the cavitation because of a combination of the reduced pressure and extensional stress. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 2791–2799, 2002     

Effect of solution extrusion rate on morphology and performance of polyvinylidene fluoride hollow fiber membranes using polyvinyl pyrrolidone as an additive

<正>Polyvinylidene fluoride(PVDF) hollow fiber membranes prepared from spinning solutions with different polyvinyl pyrrolidone(PVP) contents(1%and 5%) at different extrusion rates were obtained by wet/dry phase process keeping all other spinning parameters constant.In spinning these PVDF hollow fibers,dimethylacetamide(DMAc) and PVP were used as a solvent and an additive,respectively.Water was used as the inner coagulant.Dimethylformamide(DMF) and water(30/70) were used as the external coagulant.The performances of membranes were characterized in terms of water flux,solute rejection for the wet membranes.The structure and morphology of PVDF hollow fiber were examined by BET adsorption,dry/wet weight method and scanning electron microscopy(SEM).It is found that the increase in PVP content and extrusion rate of spinning solution can result in the increase of water flux and decrease of solute rejection.The improvements of interconnected porous structure and pore size are induced by shear-thinning behavior of spinning solution at high extrusion rates,which could result in the increase of water flux of hollow fiber membranes.The increase of extrusion rate also leads to the increase of membrane thickness due to the recovery effect of elastic property of polymer chains.     

Enhanced directional thermal conductivity of polylactic acid/polybutylene adipate terephthalate ternary composite filled with oriented and surface treated boron nitride

A combination of solution casting and melt extrusion technique was used to fabricate Boron nitride (BN)-filled Polylactic acid (PLA)/polybutylene adipate terephthalate (PBAT) blend composites. The BN particles were surface treated with a silane coupling agent and functionalization was confirmed via spectroscopic analysis. Field emission scanning electron microscopy confirmed that the BN surface treatment improved the particle adhesion with the polymer matrices and acted as a compatibilizer for the polymers. Moreover, changes in the particle orientation in the blend composite yielded improved thermal conductivity in different directions. The inclusion of the treated BN particles enhanced the in-plane (~1.1 W m⁻¹K⁻¹) and through-plane (~0.8 W m⁻¹K⁻¹) thermal conductivity of the composites as compared to the neat PLA. In addition, the storage modulus of the composite become more than 3 GPa that is twice that of the PLA/PBAT blend with a reasonable tensile property. In general, compared with the PLA/PBAT blend, the blend composites exhibited superior thermal and mechanical properties.