Struktur und Eigenschaften von ABS-Polymeren. IV. Zum Einfluß der thermischen Vorbehandlung auf das Deformationsverhalten von ABS-Pfropfpolymerisaten

The influence of thermal history on the thermomechanical properties of a graft polymer (ABS) is investigated. The thermal pretreatments are: sharp quenching from above the glas-transition of the matrix resin, annealing below the glas transition. A first characterization of the influence of these two pretreatments is done by measuring density, probe length as function of temperature and by DTA. The less modulus in the region below the glas transition of the matrix resin is very sensitive to thermal pretreatment. Small but reproducible influences are observed in the glas transition region of the polybutadien particles. At room temperature stress-strain measurements are achieved until fracture happens. Crazing is observed (which is often called stress-whitening) in all cases, but the extent of craze growing is dependent on thermal history. The measurements are completed by scanning micrographs of the fracture surfaces. Annealing of the fracture surfaces gives additional informations. The results are discussed using the concept of free volume which is variated by thermal pretreatment. At room temperature the phase-boundary between polybutadion particle and matrix resin is considered as transition zone from high to small hole concentration. The sharpness of this zone is supposed to be a decisive parameter for the macroscopic deformation behaviour.     

Annealed segmented polyether ester—poly (vinyl chloride) blends

Hytrel, PVC and blends of these polymers containing, respectively, 75% and 45% by wt of Hytrel were annealed and the dynamic mechanical and sonic velocity behaviour of these annealed samples were compared with the unannealed materials. The annealed Hytrel showed evidence of enhanced segregation of the hard and soft segments, while for PVC there was a shift of the glass transition to a higher temperature. Annealing of the 75% by wt Hytrel blend resulted in increased phase separation of the constituent materials and a very broad tan δ—temperature dispersion. It was also concluded that the 45% by wt Hytrel blend again showed phase separation on annealing, but to a lesser extent.     

Mechanical spectroscopy connected to creep and stress relaxation in a high resistant silicon nitride

Silicon nitride processed by gas pressure sintering contains a very small amount of glassy phase and consequently exhibits a strong resistance to deformation until 1450 °C. Above this temperature, both relaxation kinetics and creep rate rapidly increase. To explain such a behaviour, the formation of a liquid phase by dissolution of YSiAlON phases was proposed. The present paper shows that mechanical spectroscopy argues for the existence of such a liquid phase at high temperature. The mechanical loss is very low in the as-sintered material. Nevertheless, the internal friction peak generally observed in silicon nitride, and attributed to the glass transition in the glassy pockets, is also observed in the gas pressure sintered silicon nitride. Moreover, the peak is much higher in annealed and “quenched” specimens and it increases with annealing time. These results show that the annealed and “quenched” material contains much more glassy phase and so argues for the dissolution of crystalline phases at high temperature.     

Stress optical studies of oriented poly(methyl methacrylate)

A series of samples of oriented poly(methyl methacrylate) was produced by hydrostatic extrusion at temperatures below the glass transition temperature. The development of orientation in the process was monitored by the measurement of birefringence which was shown to depend on the extrusion temperature as well as on the applied deformation. Additional information to characterize the oriented state was obtained by measuring the shrinkage force which developed when the oriented sample, constrained to constant length, was heated to a temperature just above the glass transition temperature; specimens free to contract all recovered to the isotropic state and original dimensions on annealing at this temperature. Most measurements were made on specimens ‘as extruded’ with additional studies made on specimens annealed at temperatures above the extrusion temperature but below the glass transition. The data, which have strong implications with regard to deformation mechanisms, are interpreted both at a molecular level in terms of deviations from an ideal rubber network, and at a more phenomenological level in terms of the Mooney-Rivlin equation.     

Quantitative study of the annealing of poly(vinyl chloride) near the glass transition

Poly(vinyl chloride) displays a normal DSC of DTA curve for the glass transition when quenched from above its T_g. However if cooled slowly or annealed near the glass transition temperature, a peak appears on the DSC or DTA curve at the T_g. In this paper quantitative studies of the time and temperature effects on the production of this endothermal peak during the annealing of PVC homopolymer and an acetate copolymer are presented. The phenomenon conforms to the Williams, Landell, and Ferry equation for the relaxation of polymer chains, the rate of the peak formation becoming negligible at more than 50°C below T_g. The energy difference between the quenched and annealed forms is small. For a PVC homopolymer annealed 2 hr at 68°C, which is T_g ?10°C, the difference is 0.25 cal/g. For a 13% acetate copolymer of PVC similarly annealed, the difference is 0.36 cal/g. The measured rates of the process give a calculated activation energy of 13–14 kcal/mole for PVC homopolymer and copolymer. This appearance of a peak on the T_g curve for a polymer when annealed near the glass temperature appears to be a general phenomenon.     

DSC and DMTA study of annealed cold-drawn PET: a three phase model interpretation

Cold-drawn poly(ethylene terephthalate) (PET) samples annealed at different undercoolings are studied by means of differential scanning calorimetry and dynamic mechanical thermal analysis. When heating from room temperature, the onset of the glass transition region in cold-drawn, un-annealed samples is found to be significantly lower than in the case of un-oriented PET. On the contrary, the presence of crystalline lamellae in oriented PET cause a shift (and spread out) of the glass transition region towards higher temperatures. The crystal thickening process caused by heating above the annealing temperature, is suggested to take place after a rigid amorphous phase linked to the basal surface of the lamellae has softened. It is found that the low-temperature (between 100 and 140 °C) annealed samples have a glass dispersion region ranging significantly above the annealing temperature itself. This circumstance leads to envisage vitrification as a possible mechanism able to limit lamellar thickening during the annealing process at these low temperatures.     

Effect of crystallinity on enthalpy recovery peaks and cold‐crystallization peaks in PET via TMDSC and DMA studies

Poly(ethylene terephthalate) (PET) sheets of different crystallinity were obtained by annealing the amorphous PET (aPET) sheets at 110°C for various times. The peaks of enthalpy recovery and double cold‐crystallization in the annealed aPET samples with different crystallinity were investigated by a temperature‐modulated differential scanning calorimeter (TMDSC) and a dynamic mechanical analyzer (DMA). The enthalpy recovery peak around the glass transition temperature was pronounced in TMDSC nonreversing heat flow curves and was found to shift to higher temperatures with higher degrees of crystallinity. The magnitudes of the enthalpy recovery peaks were found to increase with annealing times for samples annealed ≤30 min but to decrease with annealing times for samples annealed ≥40 min. The nonreversing curves also found that the samples annealed short times (≤40 min) having low crystallinity exhibited double cold‐crystallization peaks (or a major peak with a shoulder) in the region of 108–130°C. For samples annealed long times (≥50 min), the cold‐crystallization peaks were reduced to one small peak or disappeared because of high crystallinity in these samples. The double cold‐crystallization exotherms in samples of low crystallinity could be attributed to the superposition of the melting of crystals, formed by the annealing pretreatments, and the cold‐crystallizations occurring during TMDSC heating. The ongoing crystallization after the cold crystallization was clearly seen in the TMDSC nonreversing heat flow curves. DMA data agreed with TMDSC data on the origin of the double cold‐crystallization peaks. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Stress and Volume Relaxation in Annealing Flat Glass

Laboratory simulation of the industrial process of annealing sheet glass has yielded data on the genesis of stresses in initially stress-free glass. The experimental results differed from expectations based on classical annealing theory in that stresses began to develop in the annealing range even when the glass was being cooled at a constant rate, i.e. even in the absence of any changes of temperature gradients within the glass. Typically, these stresses account for 40% of the total residual stress in glass annealed according to a linear schedule. The remaining 60% are the well-known thermoelastic stresses that arise later in the annealing process from the decay of temperature gradients in the glass. The stresses observed to arise in glass as it is being cooled at a constant rate are attributed to volume relaxation effects which, in parts of the annealing range, generate stresses rapidly enough that they are not dissipated by stress relaxation. A mathematical model of annealing is proposed that takes account of both stress and structural relaxation. The model fits the experimentally observed evolution of stresses during linear cooling. It also suggests that (with the activation energies of stress and structural relaxation about the same) the actual rate, at any given temperature, of structural relaxation is about 4 times lower than that of stress relaxation.     

An anomaly in the necking behavior of polyethylene,part 4

It is shown that the annealing of a high molecular weight, high density polyethylene at different temperatures ranging from 393.2 to 405.2 K influences the density of the material, the lamellar structure as studied by differential scanning calorimetry and transmission electron microscopy, and the necking and fracture behavior at constant uniaxial tensile loading in air at 313 K. In previous reports, a marked transition in the necking and fracture behavior of high density, high molecular weight polyethylene under constant uniaxial tensile loading has been reported. The nominal stress and the maximum strain rate of this transition show minima for polyethylenes annealed at temperatures of about 401 K. By combining these data with data for the lamellar structure a hypothesis that explains the necking/fracture behavior is set up. The heat treatment at temperatures from 393.2 to 403.2 K of the original non-equilibrium lamellar structure causes a molecular fractionation preferentially of low molecular weight and branched material. These segregated parts may then act as fracture initiators and thus lower the resistance towards fracture. Other structural effects such as those proposed by McCready and co-workers may also be of importance. The fracture curves at nominal stresses below transition of the materials annealed at 396.7 and 401.2 K for 24 h are shifted to shorter times in comparison with that of the non-annealed material and this can also be explained by molecular fractionation. The time to necking at 14 MPa nominal stress seems to be related to the lamellar thickness of the samples.     

Plasticizer migration from plasticized into unplasticized poly(vinyl chloride)

There exist important industrial applications, such as hoses or plastic windows, dealing with closely combining plasticized and rigid poly(vinyl chloride). Nevertheless, migration of plasticizer causes severe variation of the mechanical performance of the end-products. This work comprises an effort to investigate and understand these phenomena, also as an extension of previous work of ours in migration to liquid environments. The common system plasticized PVC/dioctylphthalate/unplasticized PVC was studied under two-sided diffusion conditions, i.e., from a thin sheet of plasticized sheet. The whole assembly was placed between two glass plates and then was held in an oven at 64°C to simulate accelerated test conditions. Some pressure was also applied to ensure perfect contact between the plastic sheets. Three different levels of initial plasticizer concentration (48, 66, and 100 phr) have been considered for a period of about five months, until equilibrium was reached. During this period the migration process was monitored by weight changes. Plots of M_t/M_∞ vs. t^½, where M_∞ the amount migrated at equilibrium and M_t the amount lost at time t, resulted in evident linear relationship. Therefore, it was proved that the Fick's law approximation for short times can be used to describe the migration kinetics for this solid/solid system. On the other hand, macroscopic observations revealed that no plasticizer was accumulated at the interface, i.e. all plasticizer leaving the plasticized sheet entered the rigid ones. Finally, it seems that the controlling stage is the diffusion inside plasticized PVC while possible annealing of the plasticized polymer structure cannot be excluded.     

Biaxial orientation of poly(vinyl chloride) compounds Part 2 –Structure–property relationships and their time dependency

Abstract

X-ray diffraction and thermomechanical analysis have been used, respectively, to examine structural order and shrinkage behaviour for oriented samples of rigid and flexible poly(vinyl chloride) (PVC). Results were compared with previously measured tensile properties and structure–property relationships explored. X-ray diffraction showed that drawing produces planar crystallite orientation in PVC sheets. If drawing and subsequent annealing conditions are held constant, but draw ratio is varied, there is good correlation between structural order measured by X-ray diffraction and tensile strength. Increased annealing time and temperature improve crystallite order and dimensional stability, while tensile strength is unchanged. The greatest enhancement in tensile strength is achieved by stretching PVC towards its maximum draw ratio at 90°C, but optimum thermal stability of the oriented structure is achieved when higher annealing temperatures are used. Room temperature recovery is observed for flexible PVC when the material has a glass transition temperature below ambient. This can be delayed by increased annealing time and temperature, and by increased draw ratio.     

Polymeric systems for acoustic damping. I. Poly(vinyl chloride)–segmented polyether ester blends

A series of six Hytrel/PVC blends were prepared by solution blending Hytrel in methylene chloride and PVC in tetrahydrofuran. The samples were subsequently prepared in sheet form by hot pressing at 170°C. Physical and mechanical properties of the homopolymers and the blends were investigated. The copolyester homopolymer is a partly crystalline elastomeric material. The level of crystallinity was measured by x-ray diffraction and the sensitivity of this level to heat treatments and quenching determined by DSC. A Morgan pulse propagation meter was used to measure sonic velocity and, indirectly, acoustic impedance of the blends. Dynamic mechanical studies indicated that blends containing 25%–50% by weight of Hytrel were completely compatible in the sense that a single glass transition was observed; but as the Hytrel level was increased to 60% and 65%, a shoulder became apparent on the low-temperature side of the glass transition peak. At 80% Hytrel, two peaks were observed, indicating incompatibility. The glass transition temperatures of these blends were found to decrease linearly with added Hytrel.     

Effect of thermal pretreatment on the fracture behavior of polycarbonate in medium strain rate tensile tests

The fracture properties of as-received and annealed (48 h at 403 K) commericial polycarbonates (PC) were examined in tensile tests with an average strain rate of ? = 2 s^?1. Both materials were subjected to tensile tests at temperatures ranging from 223 to 423 K. The results were processed by a computer interfaced to the testing machine. The tensile strength of the annealed (pretreated) PC was superior to that of the as-received (untreated) material. The elongation at break and the fracture energy, then, decreased due to annealing at all temperatures, yet followed impact strength curves. Fracture analysis and fracture morphology revealed clear differences in the behavior of the materials. Fracture nucleation occurred commonly at several points in the pretreated specimens, whereas only one nucleation point was found in the untreated specimens. Shear yielding morphology, which indicated plastic deformation, started to appear at a lower temperature in the pretreated specimens than in the untreated ones.     

脆性材料哑铃形拉伸试样的应力分布及断裂位置研究

应用大型有限元分析软件ANSYS模拟分析了哑铃形拉伸试样在拉伸过程中的应力分布及应力集中的位置和应力集中系数,分析结果显示过渡圆弧处出现应力集中,应力集中系数达到了1.123。分别采用聚苯乙烯（PS）的压制和注射成型的两种哑铃形试样,研究了试样的拉伸断裂过程及断裂位置,并验证了模拟分析结果正确性。结果表明压制哑铃形试样是均质各向同性,其断裂发生在应力集中系数最大的圆弧过渡位置;对于各向异性的注塑哑铃形试样,断裂发生在表层和剪切层较薄的浇口远端平直段,应力集中对其影响较弱。     

Impact strength of polymers: 1. The effect of thermal treatment and residual stress

The effect of thermal annealing and quenching on the notched Izod impact strength of several polymers has been studied. Primary emphasis was placed on polycarbonate, but ABS, PVC, polysulfone, and polymethylmethacrylate were also studied. It was determined that residual stresses created by thermal quenching from above the glass transition temperature can have a great effect on impact strength for the polycarbonate, PVC, and polysulfone polymers studied. In fact, it is shown that the thickness transition observed in impact strength for polycarbonates is governed by the residual stresses and not by thickness. In polycarbonates, quenched sheets up to 3/8 in. in thickness have shown impact strengths of 18 ft-lb/in. whereas sheets 1/8 in. in thickness can be embrittled by annealing, showing an impact strength of 2 ft-lb/in. However, it has been shown that this embrittlement results from the absence of residual stress. Residual stresses having maximum values up to 3000 psi (in Compression) have been determined at the polycarbonate sheet surface using birefringence measurement techniques. The existence of these compressive stresses is postulated to restrict the extent of craze growth at the notch tip, and the impact specimen can yield rather than fail in a brittle manner if the stress state is sufficient.     

Effects of Recycling on the Mechanical Behavior of Polypropylene at Room Temperature Through Statistical Analysis Method

This article reports the effects of recycled material percentage, annealing conditions, and glass fiber percentage on the mechanical behavior of injection molded polypropylene samples. Specimens were prepared with different percentages of recycled material ranging from 0 to 100%. Two groups of samples, i.e., non‐annealed and annealed at 150°C, were tested to investigate annealing effects. The effects of adding fiber (0–7.5%) to specimens was also investigated. It was found that increasing the amount of recycled material improves the material properties in a non‐linear trend. Annealing had a significant positive effect on both non‐fiber‐added and fiber‐added samples: it improved the yield stress of non‐reinforced polypropylene samples by more than 10% and their Young's modulus by about 50%. Fiber‐added materials showed more variability, and adding fiber also improved the Young's modulus and the yield stress of the samples by about 50%. The results indicate that the three factors investigated improved toughness of the injected polypropylene samples; however the effects are not significant. The study findings reveal that using recycled polypropylene has no significant effect on the material properties of polypropylene. POLYM. ENG. SCI., 56:1283–1290, 2016 © 2016 Society of Plastics Engineers     

Influence of Thermal History on Crystal Nucleation in Silicon Carbide Amorphized with Neon Irradiation

Silicon carbide (SiC) specimens were amorphized with neon ions and annealed at 1273 K via transmission electron microscopy (TEM). Two types of annealing procedures were conducted: (i) continuous annealing for 60 min and (ii) annealing for 5 min, repeated 10 times. TEM observations revealed that crystal nucleation was more apt to occur in the SiC amorphized by repeated annealing than in the continuously annealed SiC.     

Structural order in oriented PVC mouldings

The structural changes occurring upon drawing and annealing of compression and injection mouldings of commercial poly(vinyl chloride) were studied by wide-angle X-ray diffraction. Low temperature drawing appears to lead to a reduction in 3-dimensional order and an increase in oriented 2-dimensional order. The degree of order of drawn and annealed PVC depends on draw ratio, annealing temperature and the restraint during annealing. The maximum in 2-dimensional order occurs on annealing at 110°C. Tensile yield stress is significantly increased by the drawing process and it was shown that the anisotropy of this mechanical property decreased upon annealing. This could not be explained by the reduction in amorphous orientation alone. Electron microscopy of the fracture surfaces shows a structure which appears to be related to the drawing and annealing process.     

Energy Release in Isothermally Stretched Silicate Glass fibers

Three types of silicate glass fibers are annealed, simultaneously stretched in the glass transition region for certain time lengths, then slowly cooled to room temperature under load, and subsequently scanned by differential scanning calorimetry (DSC). During the DSC scanning, a broad exothermic peak (representing energy release) occurs in the stretched fibers well below the glass transition temperature, while it does not occur in the non-stretched fibers. The peak indicates that mechanical stretching can result in an energy enhancement in the fibers. It also confirms that the energy released during reheating of the fibers formed using an industrial continuous fiber drawing process originates not only from thermal quenching but also from mechanical stretching. However, the mechanical stretching-induced energy is much lower than the thermal hyperquenching-induced energy in glass fibers. The effect of annealing temperature and time on the energy release behavior is discussed in terms of viscoelasticity.     

Gold nanolayer and nanocluster coatings induced by heat treatment and evaporation technique

The paper is focused on the preparation and surface characterization of gold coatings and nanostructures deposited on glass substrate. Different approaches for the layer preparation were applied. The gold was deposited on the glass with (i) room temperature, (ii) glass heated to 300°C, and (iii) the room temperature-deposited glass which was consequently annealed to 300°C. The sheet resistance and concentration of free carriers were determined by the van der Pauw method. Surface morphology was characterized using an atomic force microscopy. The optical properties of gold nanostructures were measured by UV–vis spectroscopy. The evaporation technique combined with simultaneous heating of the glass leads to change of the sheet resistance, surface roughness, and optical properties of gold nanostructures. The electrically continuous layers are formed for significantly higher thickness (18 nm), if the substrate is heated during evaporation process. The annealing process influences both the structure and optical properties of gold nanostructures. The elevated temperature of glass during evaporation amplifies the peak of plasmon resonance in the structures, the surface morphology being significantly altered.