Effect of various triazine derivatives on the thermal oxidative degradation of isotactic polypropylene

A number of triazine derivatives, mostly aryloxy-s-triazines, were prepared, and the effects of these compounds on the thermal oxidative degradation of isotactic polypropylene were examined by conventional oxygen uptake. Almost all triazine derivatives prepared showed a more or less inhibitive effect on the degradation of the polymer. Among them, α- and β-napthyloxy-s-triazines were found to be excellent inhibitors. On the basis of the results obtained, the relationship between inhibitive effect and the structure of the triazine derivatives is discussed.     

Radiation-induced oxidative degradation of poly(vinyl chloride)

Gas evolution and oxygen consumption in the γ-irradiation of PVC were studied. The gas evolution and the oxidative degradation are retarded by the presence of plasticizers and stabilizers. The G(HCI) and G(H₂) and 8 and 0.24 for the irradiation of pure PVC under vacuum and 0.02 and 0.14 for that of plasticized PVC, respectively. Gas evolution increases in the presence of oxygen, specially for the pure PVC. The G(–O₂) values for the pure and plasticized PVC are 30 and 12, respectively. The dependence of gas evolution and oxygen consumption on the oxygen pressure is more pronounced for the plasticized PVC than pure PVC because the oxygen diffusion is controlled.     

Thermooxidative degradation of isotactic polypropylene prepared on metallocene catalyst and its sorption capacity

The sorption capacity and resistance to thermooxidative degradation are comparatively studied for isotactic polypropylene (PP) produced in the medium of the liquid monomer on homogeneous metallocene catalytic systems and on a heterogeneous titanium–magnesium catalyst. These polymers are characterized by different sorption capacities with respect to the phenyl‐β‐naphthylamine antioxidant and different induction periods of oxidation by molecular oxygen. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99: 808–811, 2006     

Luminescence emission of isotactic polypropylene

In order to elucidate the origin of luminescent species in unstabilized commercial isotactic polypropylene (IPP), effects of hexane extraction and exposure of the extracted IPP film to the atmosphere on both fluorescence and phosphorescence emissions were examined. Fluorescence emission from the unextracted IPP film disappeared by the extraction, and only a very weak phosphorescence emission was found. During the exposure of the extracted IPP film to the atmosphere, both fluorescence and phosphorescence emissions appeared again. The intensity of the spectra increased with the exposure time and finally almost reached that from the unextracted IPP film. The results indicated that main fluorescent species in IPP are foreign impurities originating from an ambient atmosphere, and that contribution of a very minor amount of phosphorescence species such as carbonyl groups incorporated with the polymer was scarce.     

Environmental degradation of isotactic polypropylene plates as studied by positron annihilation lifetime spectroscopy

Outdoor degradation of isotactic polypropylene (PPI) plates was studied by means of positron annihilation lifetime spectroscopy (PALS), absorption infrared spectroscopy, differential scanning calorimetry (DSC) and density measurements. Infrared spectra reveal the presence of oxygenated species into the exposed polymer induced by external agents. Results from thermal and density analysis suggest an increase of crystallinity of the sample with exposure time. Positron data strengthen such a conclusion, showing a reduction of the amorphous zones as monitored by the corresponding decrease of positronium (Ps) formation. Furthermore, an estimation of the average sizes of the free volume holes and of the defects in the crystalline regions was obtained.     

Thermo-oxidative degradation of isotactic polypropylene film: Structural changes and its correlation with properties

Degradation of isotactic polypropylene has been studied by ageing the film samples at 70°, 80° and 90°C in air. Reactions involved in changing the molecular structure and formation of oxygenated and unsaturated groups, during thermo-oxidative degradation, are discussed. The increase in molecular weight ($\text{M}\text{?}{}_{\mathrm{v}}$) suggests molecular enlargement mainly by recombination of alkyl and alkoxy radicals which produces non-radical products. Tensile strength has been found to increase initially and then decreases with ageing time. Increase in isotacticity and density of polypropylene may be due to the cleavage of the backbone chain in the amorphous intercrystalline region, facilitating poorly ordered molecular segments into a more ordered helical form.     

低等规聚丙烯的研制Ⅴ.粘性聚合物的分离技术

采用液相本体法生产的粘性低等规聚丙烯在排放输送和分离回收时易堵塞阀门和管道。模试结果表明：控制聚合时丙烯转化率为20％～50％,同时预先在闪蒸釜中加人表面分散剂质量分数约0．3％的液体介质及预先充人丙烯单体可以有效地解决这一问题。介绍了采用乙醇-水溶液作为分散介质的分离技术特征,并可用深度冷冻法或吸附极性分子法从回收体系中除去乙醇。     

Physical aging in isotactic polypropylene

Physical aging studies were made using commercial and laboratory samples of isotactic polypropylene. Linear and nonlinear viscoelastic responses were measured after quenching the glass from above the glass transition temperatures to below the glass transition. Results show that aging is not eliminated by large mechanical deformations; rather, the time required for the glass to age into equilibrium is independent of the applied stress. Results obtained are purely kinetic and interpreted as the effects accompanying the process of glass formation in a semicrystalline polymer. © 1996 John Wiley & Sons, Inc.     

Radiation-induced reactions of syndiotactic polypropylene

Summary The radiation-induced reaction of highly syndiotactic polypropylene was examined by following the changes in limiting viscosity, molecular weight distribution, and stereoregularity. The degree of syndiotacticity clearly decreased even when there was no apparent change in molecular weight. Irradiation at an elevated temperature caused a marked decrease in molecular weight and formation of unsaturated residues.     

Dependence of tacticity distribution in thermal oxidative degradation of polypropylene

Summary Thermal oxidative degradation behavior of two kinds of polypropylene (PP) with different tacticity distribution was investigated based on the data obtained by NMR, temperature rising elution fractionation (TREF) and thermogravimetric analysis (TGA). Although these PPs have similar molecular weights and tacticity, the behavior of degradation was considerably different. The differences were found to be due to the tacticity distribution by TREF measurement. In order to investigate the effect of tacticity distribution on the degradation in more detail, the more stable PP having a broad tacticity distribution was divided into four kinds of tacticity fraction by TREF, and each of degradation behavior was investigated by TGA. The results indicated that the rate of degradation systematically depended on the tacticity. The higher stability of PP with the broader tacticity distribution would be originated from the abstraction reaction of tertiary hydrogen, which was the rate-determining step in PP degradation reaction.     

Influence of β nucleation on the mechanical properties of isotactic polypropylene and rubber modified isotactic polypropylene

The tensile and fracture behaviour of neat α and β nucleated isotactic polypropylene and rubber-modified α and β nucleated isotactic polypropylene has been investigated at test speeds of 0.0001-10 ms⁻¹ in the temperature range −30 to +60 °C. The presence of the β phase had little effect at low temperature. However, at +25 and +60 °C, it increased the speeds corresponding to the ductile-brittle transition in the neat polymer by more than three decades. This behaviour has been linked to changes in microdeformation mechanisms observed at the lamellar and spherulitic level, an increase in cavitational deformation in tensile tests and an increase in the strength of the β relaxation in dynamic mechanical spectra. In the blends, the presence of the β phase led to somewhat higher energy dissipation in regimes of ductile fracture. However, the ductile-brittle transitions were not significantly affected. The modifier phase was therefore inferred to control the initiation and propagation of the plastic zone ahead of the crack tip during fracture.     

聚丙烯复合材料的非等温结晶动力学

采用差示扫描量热仪研究了β成核剂和水滑石(LDH)/β成核剂复配的成核剂对聚丙烯(PP)非等温结晶动力学及熔融行为的影响。结果表明:加入成核剂后,PP中晶体分布不均匀且分散度增大。莫志深方法采用F(θ)表征聚合物在单位时间内达到某一结晶度时所需的冷却(或加热)速率,结晶度达到40%时,纯PP的F(θ)为3.82,加入β成核剂的PP的F(θ)为3.30,加入LDH/β成核剂的PP的F(θ)为2.49。与纯β成核剂相比,LDH/β成核剂能更好地提高PP的结晶温度、结晶速率,增强PP的β晶熔融峰,减弱β晶和α晶共存熔融峰和α晶熔融峰。     

固相氯化法氯化等规聚丙烯结构分析

借助ＤＳＣ,ＩＲ,＾１Ｈ－ＮＭＲ方法对搅拌式固相氯化制备的氯化等规聚丙烯的宏观氯原子分布和微观氯原子分布进行了分析。结果表明,搅拌式固相氯化法能够迅速破坏等规聚丙烯的结晶,从而得到宏观氯原子分布均匀的ＣＩＰＰ。此方法制备的ＣＩＰＰ主要为等丙烯分子链上的仲氢原子被取代的产物。     

The physical aging of isotactic polypropylene

The microstructural changes in isotactic polypropylene (PP), subsequent to quench from the melt to around T_g were studied using dynamic mechanical loss, volume dilatometry, small and wide angle X-ray scattering, infrared and NMR spectroscopy. The β-transition loss tangent and the specific volume decreased linearly with logarithm of aging time. Dynamic mechanical loss and NMR spectroscopy results established that amorphous chain mobility reduced during aging. X-ray and IR techniques showed that the crystallinity, the crystalline density, and the average chain conformation do not change during aging. Tensile tests indicated that diffusion of air or moisture into the polymer is not a competitive mechanism for the aging phenomenon. A simple free-volume model is quantitatively consistent with these observations. The fraction of the material which cannot age increased as the quench temperature decreased. Further, at lower temperatures a portion of the nonageable fraction is shown to reside in the amorphous fraction.     

Radiation-induced graft polymerization of acrylonitrile onto isotactic polypropylene and poly(tetrafluoroethylene–ethylene) copolymer films

Direct radiation-induced grafting of acrylonitrile (AN) onto both isotactic polypropylene (IPP) and (tetrafluoroethylene–ethylene) copolymer (ET) films has been studied. The effect of grafting conditions such as inhibitor and monomer concentrations and irradiation dose on the grafting yield was investigated. Homopolymerization of acrylonitrile was reduced to a minimum using ferric chloride (FeCl₃), and the suitable optimum concentration of the inhibitor was found to be 0.1 wt%. The higher the monomer concentration, the higher the degree of grafting obtained. It was observed that the degree of grafting onto IPP was higher than onto ET, at given grafting conditions. The effect of aging on IPP was also examined. IR spectroscopy showed that IPP was susceptible to photooxidation by aging. The swelling behaviour and electrical conductivity of the graft and hydrolysed graft films were investigated. The electrical conductivity was improved by hydrolysis of polyacrylonitrile in the graft chains.     

Uniaxial roll-drawing of isotactic polypropylene sheet

The process described as “roll-drawing” has been applied to commercial extruded sheets of isotactic polypropylene (M?_n = 70,900). Preheated billets were drawn into thin, clear, transparent sheets in a single pass, producing uniaxial orientation of the polymer molecules in the draw direction. At the maximum draw ratio of 20, the ultimate tensile strength and Young's modulus in the draw direction were 0.5 GPa and 20 GPa respectively. The mechanical properties transverse to the draw direction were virtually unchanged. The theory of fiber reinforcement for unidirectional anisotropic plates was applied to interpret the orientation dependence of the stress-strain behavior of the drawn sheets. From these results, it was estimated that the mechanical properties of biaxially laminated polypropylene sheets equaled the performance of aramid and carbon fiber composites, The roll-drawing process appears to be economically attractive for the production of ultra-high modulus crystalline thermoplastics in sheet form having excellent uniaxial or biaxial properties.     

The morphology of irradiated isotactic polypropylene

The research in this article explores the response of semicrystalline isotactic polypropylene to gamma radiation in air, and relates the morphological changes of the polymer to corresponding changes in mechanical properties. The effect of the initial morphology of the polymer on its response to irradiation is considered using infrared spectroscopy (FTIR), small‐ and wide‐angle X‐ray scattering, dynamic mechanical thermal analysis (DMTA), and mechanical testing. The extent of chain scission and crosslinking is dependent on the dose but not the initial starting morphology. These chemical changes cause the crystallinity to increase slightly, and the glass transition temperature to rise by a few degrees in all samples, but the overall morphology is only subtly changed. In contrast, a major deterioration in mechanical properties is caused. The effects of the irradiation observed under these conditions are similar in each material and the ultimate properties determined by the properties seen in the original material. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 2234–2242, 1999     

Thermal stability of additivated isotactic polypropylene

Summary Isotactic polypropylene stabilised with fullerene [C60], its adduct with methyl levopimarate, carbon black, p-t-butylcalix[4]arene, p-t-butylcalix[6]arene, Irganox 1076 or Topanol OC was investigated by means of oxygen uptake method under isothermal (165^°C) and isobaric (normal pressure) conditions. Oxidation investigations were performed in air as degradation environment. Additive concentration was 0.25 % (w/w). Kinetic parameters, oxidation induction and oxidation rate are compared with similar characteristics of additive-free i-PP. Effect of γ-irradiation on thermal oxidation is also presented. Three γ-exposure doses (50, 100 and 150 kGy) were selected. The influence of radiation treatment on the efficiency of studied compounds and some mechanistic aspects are also presented. Received: 5 June 2002/Revised version: 10 August 2002/ Accepted: 12 September 2002 Correspondence to Traian Zaharescu     

Some crystallization kinetics of isotactic polypropylene

Infra-red evidence is presented that the building of helices in the crystallization process from the glassy (or smectic) phase or from the melt are second order or zero-th order respectively. The observation coupled with data from density and X-ray diffraction measurements is interpreted in molecular structural terms.     

Crystallization features of oxidized isotactic polypropylene

The effect of the initial molecular weight parameters of polypropylene on the kinetics of isothermal polymerization is shown. It is found that the feed polymer with a wider molecular weight distribution (P-1) is characterized by lower values of the half-crystallization time as compared to the polymer with a narrower molecular weight distribution (P-2). Comparison between the crystallization parameters and the kinetics of accumulation of oxidation products showed that as the degree of oxidation of the polypropylene increases, the crystallization rate for both samples decreases and the concentration of the oxidation products increases. In this case, the degradation of tie chains accelerates the formation of crystallites. It is shown that P-1 has a higher nucleation energy as compared with P-2 and that this parameter increases during the oxidation of both polymers.