Natural and accelerated weathering of some polyblends

A weathering study has been carried out on a polyurethane elastomeric adhesive and its polyblends with the following vinyl polymers: poly(vinyl chloride), poly(vinyl alcohol), poly(vinyl acetate), and vinyl acetate—vinyl chloride copolymer. Stress-strain measurements were done on an Instron model 1125 testing machine after aging at normal room conditions, outside, and in an artificial weathering chamber. The observed modifications of the mechanical properties can be attributed to a decrease of the molecular weight of the polymers involved during the cryolysis process; this process is less significant for natural weathering than for artificial weathering. Results are discussed and conclusions drawn.     

Studies on phase separation in polyblends of block copolymers

The morphologies of polyblends of block copolymers of styrene and butadiene with similar composition but different molecular weights have been examined with an electron microscope. The micrographs show that some supramolecular features, with different morphologies to those in the matrix, are randomly dispersed. These results, we believe, provide evidence of the incompatibility of the block copolymers in spite of their chemical identity.     

Modification of the properties of some polyblends and reinforced polymers

In the present paper we shall deal with: (a) Polyblends made of a polyurethane (PU) based on a polyether and diphenyl-methane-diisocyanate and an acrylic terpolymer (AT) system and, (b) glass fibre reinforced poly-(organosiloxane), (SR). We now report some differential scanning calorimetry (d.s.c.) measurements and the effect of thermal cycling exposure on these polymers. Stress-strain tests were done on an Instron universal testing machine. The modification of the properties on the polymers after blending and reinforcing respectively are discussed. At certain ratio PU to AT the behaviour of the polyblend to thermal cycling exposure is better than that of PU. The presence of the reinforcing agent in the silicone polymer significantly improves its mechanical and thermal properties.     

Phase immiscibility induced enhanced fluorescence in spin-coated PVP/PPO polyblends

We report on the effect of phase immiscibility on the structure and optical properties of spin-coated polyvinylpyrrolidone (PVP) and polyphenylene oxide (PPO) polyblends using X-ray diffraction, IR absorption, optical absorption and florescence spectroscopic techniques. The broad diffraction halos in the X-ray diffraction patterns reveal the semi-crystalline nature for the synthesized polyblends. The change in q value for both the deconvoluted halos confirms the variation in the molecular interactions while the decrease in their fwhm values signify the enhancement in crystalline nature with the blending. The infrared absorption studies were used to elucidate the interaction of functional groups in the spin-coated polyblends. The position of three excitonic bands and the red shift in the optical absorption edge with the increase in the PPO content has been observed for these polyblends. The six time enhancement in fluorescence peak intensity in visible region (~500 nm) for immiscible blend (50/50) composition has been of importance for the design of low cost luminescent and photovoltaic devices.     

Aging of polyblends

Methyl methacrylate–styrene–acrylonitrile copolymers, alone and with polybutadiene modification, were examined for changes in impact strength and yellowness after thermal and light aging. The copolymer displayed no change in strength or clarity, while the butadiene-modified material showed increase in yellowness and loss in impact resistance. It is apparent that these changes are primarily due to the decomposition of the butadiene phase in the impact material, and this conclusion might be applied to diene-containing blends in general.     

Quantitative thermal analysis of polyblends

A new quantitative thermal analysis technique was attempted on ABS and Noryl-type polyblends. A particular component within a polyblend was identified by its glass transition temperature and the amount of the component was determined from the increase in specific heat at the glass transition temperature. Two commercial Noryl resins were determined to be blends of high impact polystyrene and polyphenylene oxide in 47-47 and 69-17 proportions by weight, respectively. Polystyrene appears to be cosoluble with polyphenylene oxide without the formation of any complex. The PS-PPO polyblends yield single sharp glass transitions which are a function of concentration.     

Phase separation in segmented polyurethanes

Phase separation in a segmented polyurethane has been studied by differential scanning calorimetry. The glass transition temperature of the soft phase decreases logarithmically with time to a limiting value at each annealing temperature. The magnitude of the decrease is larger at low annealing temperatures, but the normalized rate of logarithmic decrease is smaller. At high annealing temperatures, long sequences of hard segments are excluded from the soft phase in which short segments are still soluble. At low temperatures, even short hard segments separate from the soft phase. The exclusion of the hard segments from the soft phase is a relatively fast process, but the development of order in hard domains takes longer time to reach steady state.     

Phase separation behavior of rubber-modified epoxies

The compatibility and phase separation behavior of mixtures of the diglycidyl ether of bisphenol A and carboxyl-terminated butadiene-acrylonitrile copolymers were studied by means of light transmission, viscosity measurements, and optical microscopy. Cloud point measurements of the blends prior to curing showed a strong influence of acrylonitrile on the miscibility behavior, especially near the critical composition of the system. In addition, the cloud point curves showed a highly skewed shape which turned out to be particularly favorable to the formation of a rigid but tough two-phase structure. Blends subjected to isothermal cure at 120°C were found to begin phase separation at a progressively shorter time with increase in the copolymer content. Furthermore, while the phase domains tended to cease growing at the time of gelation, the composition within the sample continued to change well beyond the gel point.     

Compounding extruders for improved polyblends

An expanding application for compounding extruders is the production of materials with new and outstanding properties by blending two or more polymer components. Mixing is essential to control domain size and insure nongradient properties whether the components are miscible, multiphase with discreet domains, or multiphase with stratified structure. This paper will comment on important mechanisms for dispersion in single-screw and twin-screw compounding extruders. A theoretical model for mixing via kneading blocks in twin-screw corotating extruders is experimentally verified. The pigment distribution was found experimentally to agree generally with theory. The commercially interesting polyblend systems and compounder geometries are more complicated than the theoretical model. Practical compounder design considerations for miscible, rubber-toughened and two-phase stratified systems are presented.     

PET/PLA共混物的降解性

引言 随着高分子材料工业技术的迅速发展,高分子材料已渗透到国民经济各部门以及人们生活的各个领域,并和钢铁、木材、水泥并列成为四大支柱材料,而其蓬勃发展的同时也导致了塑料等大量高分子废弃物带来的日益严重的白色污染问题.     

无稳定剂体系下的双水相聚合相分离

以丙烯酰胺（AM）、季铵类阳离子甲基丙酰氧乙基三甲基氯化铵（DMC）和丙烯酰氧乙基二甲基苄基氯化铵（AODBAC）为单体,以2,2'-偶氮双[2-（5-甲基-2-咪唑啉-2-基）丙烷]二盐酸化物（VA044）为引发剂,在水溶液中进行无稳定剂体系下的双水相共聚。利用紫外分光光度仪在线观察体系的分相过程并测定体系的临界分相点。通过改进的溴化法测定临界转化率（X_c）。利用黏度法测定临界分子量（M_c）。并对各个因素对于X_c和M_c的影响进行研究。结果表明具有表面活性的阳离子单体AODBAC对体系的相分离具有较好的促进作用。引发剂的用量和AODBAC的摩尔分数（f_AODBAC）对于X_c的影响较小,反应温度升高会使X_c增大。总单体浓度和f_AM的升高会使X_c减小。引发剂用量的增加、反应温度和f_AODBAC的升高都会使M_c减小。f_AM和单体浓度的增加会使M_c显著增加。     

Phase separation in epoxy resins containing polyethersulphone

Scanning electron microscopy and dynamic mechanical spectroscopy have been used to study phase separation of dissolved polyethersulphone (PES) from trifunctional and tetrafunctional epoxy resins during curing. No phase separation was observed at high concentrations of the tetrafunctional resin. Observations of nodules on fracture surfaces, and of multiple peaks in the dynamic mechanical spectra provided evidence for a separate, crosslinked, PES-rich phase in the remaining materials. Despite the variety of morphologies obtained in mixtures of PES with different hardeners and resins, modulus and fracture toughness showed little dependence upon composition.     

Photopolymer morphology: Phase separation during polymerization

Morphology and phase structure were studied before and after photopolymerization for the binder–monomer system: poly(styrene/sec-butylmaleate)(50/50)–trimethylolpropane triacrylate (TMPTA)(75/25). Films supported on a suitable substrate were measured by dynamic mechanical analysis and by dielectric relaxation before and during photocrosslinking. Such film support techniques also allow a variety of physical and chemical treatments to be carried out to determine structure changes. Two phases and a secondary transition were identified. The shift in temperature of both T_g's during photopolymerization and concurrent, fracture-surface electron photomicrography were consistent with a mechanism involving phase separation of TMPTA during polymerization. Probable composition of the phases is discussed.     

Phase separation kinetics of rigid-rod polymers during coagulation

Kinetics of phase separation of poly(p-phenylenebenzobisoxazole) (PBO) in methanesulfonic acid are examined by the time-resolved small angle light scattering and turbidity measurements. Thin films of polymer solutions are spin-coated on microscope slides and observed in a controlled environment light scattering cell. These solutions appear to undergo a spinodal decomposition-like phase separation, following Cahn-Hilliard type phase separation kinetics upon exposure to water vapor. An exponential increase in the scattered light intensity at short times is found. Transmittance measurements are used to determine the effects of molecular weight and coagulation medium on the rate of coagulation.     

Phase separation in dispersions of weakly interacting particles

The close analogy is explored between the phase behaviour of colloidal dispersions of weakly interacting particles and that of conventional molecular systems. The analogues of all three states of matter and phase equilibria may be observed. Different behaviour is predicted depending on the range of attractive forces.     

Phase separation and phase inversion of polyurethane networks

A series of polyurethane networks were prepared from MDI (4,4¹-diphenyl methane diisocyanate), ethylene glycol and a polyoxyethylene-tipped polyoxypropylene triol. The phase separation and phase inversion phenomena of these polyurethane networks were investigated by differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA) and measurement of their tensile properties. The DSC and DMA data indicate that the segmented copolyurethanes possess a two-phase morphology comprising soft and hard segments. It can be found from DSC data that the polyether soft segments exhibit a T_g (glass transition temperature) of –60 °C, and the aromatic hard segments display a T_g of about 128 °C. Two T_gs corresponding to the comprised segments can also be found by DMA for some segmented polyurethanes. Varying the content of aromatic hard segments over the range from 0 to 80 wt% changes the material behavior from a soft rubber through a highly extensible elastomer to a brittle semi-ductile glassy material. Based on the property-composition plots, phase inversion appears to occur at a hard segment content of about 50 wt%.     

Phase separation of polymerized lipids in hybrid liposomes

Summary Hybrid liposomes were prepared from the mixture of dipalmitoyl phosphatidylcholine (DPPC) and di-2,4-octadecadiene phosphatidylcholine (DODPC), and their phase separation behaviours was analyzed. In hybrid liposome systems, two transition temperatures (18 and 41°C for DODPC and DPPC, respectively) were clearly observed by means of DSC and fluorescence techniques. These two transition temperatures were also found after polymerization of DODPC molecules in hybrid liposomes by the UV irradiation. These strongly suggest that DPPC and DODPC molecules do not dissolve well but form clusters in the membrane. This phase separation was directly confirmed by freeze-fracture TEM technique.     

Phase separation and mechanical responses of polyurethane nanocomposites

Nanocomposites of a diamine-cured polyurethane with nanofillers of different kinds, sizes, and surfaces were studied. Atomic force microscopy, scanning electron microscopy, X-ray diffraction, tensile tests, and dynamic mechanical thermal analysis were employed in the experiments. Experimental results suggest that mechanical properties are strongly correlated to polymer phase separation, which depends on the nature of the interface between the polymer and the nanoparticles. Two stages of phase separation were observed: the first stage involves the self-assembly of the hard segments into small hard phases of about 10 nm in width; the second stage involves the assembly of the 10 nm wide hard phases into larger domains of about 40-100 nm in width. In the case of polyurethane/ZnO nanocomposites with 5 wt% (less than 1 vol%) 33 nm ZnO nanoparticles, the covalent bonds that were formed between the polymer and ZnO surface hydroxyl groups constrain both stages of phase separation in polyurethane, resulting in approximately 40% decrease in the Young's modulus, 80% decrease in the strain at fracture, and 11 °C increase in the glass transition temperature of the soft segments. In the case of polyurethane/Al₂O₃ nanocomposites with 5 wt% 15 nm Al₂O₃ nanoparticles, hydrogen bonds between the particles and the polymer mainly constrain the second step of the phase separation, resulting in about 30% decrease in the Young's modulus and 12 °C increase in the glass transition temperature, but only a moderate decrease in the strain at fracture. The most striking results come from polyurethane/clay composites, where only van der Waals type interactions exist between polyurethane and the organically modified clay (Cloisite 20A). With the addition of 5 wt% surface modified clay (Cloisite 20A), both the Young's modulus and the strain at fracture decrease more than 80%, but the glass transition temperature increases by about 13 °C. Adding 10 wt% Cloisite 20A into polyurethane almost totally disrupts the phase separation, resulting in a very soft composite that resembles a “viscous liquid” rather than a solid.