Thermal degradation behaviour of isotactic polypropylene blended with lignin

The influence of lignin on the thermal degradation of isotactic polypropylene, investigated by thermogravimetric analysis, is reported in this article. Polypropylene blends containing 5 and 15 wt% of lignin were prepared by mixing the components in a screw mixer. An increase in the thermal degradation temperature of the blends was observed as a function of lignin content, in both oxidative and non-oxidative conditions. The increase is noticeably marked for the experiments carried out in air atmosphere, where the interactions between the polypropylene and the lignin lead to the formation of a protective surface able to reduce the oxygen diffusion towards the polymer bulk. Morphological analyses were carried out with optical and electronic microscopy, to evaluate the degree of dispersion of the lignin in the polypropylene matrix. X-ray techniques were employed to study the influence of lignin on the structure of the blended polypropylene.     

Shear-induced crystallization in phase-separated blends of isotactic polypropylene with ethylene-propylene-diene terpolymer

The compatibility between isotactic polypropylene(i PP) and ethylene-propylene-diene terpolymer(EPDM) in the blends was studied. SAXS analysis indicates that i PP and EPDM phases in the binary blend are incompatible. Isothermal crystallization behaviors of i PP in phase-separated i PP/EPDM were studied by in situ POM equipped with a Linkam shear hot stage. It was found that typical spherulites of i PP were formed both in neat i PP and in i PP/EPDM blends. The radial growth rate(d R/dt) of spherulites of i PP in the blend was not influenced by EPDM phases. Further investigations on isothermal crystallization of i PP in i PP/EPDM after shear with a fixed shear time showed that the crystallization rate of i PP in the blends increased with increasing shear rates, whereas, the crystallization rate was much lower than that of neat i PP. WAXD results showed that ?-crystal i PP was formed in neat i PP as well as in i PP/EPDM blends after shearing and the percentage of ?-crystal bore a relationship to the applied shear rate. The presence of EPDM resulted in lower percentage of ?-crystal in the blends than that in neat i PP under the same constant shear conditions. SAXS experiments revealed that shear flow could induce formation of oriented lamellae in i PP and i PP in the blends, and the presence of EPDM led to a reduced fraction of oriented lamellae.     

Interactions between polypropylene and photochromic dyestuffs

Polypropylene that contains photochromic dyestuffs ages faster than pure polypropylene. This influence strongly depends on the dyestuff type. Chemiluminescence measurements can be used as an indicator for the ageing of polypropylene and for researching the photochromic degradation.     

Crystallization kinetics of isotactic polypropylene blended with atactic polystyrene

Crystallization kinetic parameters, such as spherulitic growth rates, nucleation densities, and Avrami-exponents, have been determined by optical microscopy for isotactic polypropylene blended with atactic polystyrene. It is found that the crystallization of iPP is strongly influenced by the presence of polystyrene. With increasing PS concentration in the blend, the nucleation densities decrease, while the spherulitic growth rates as well as the positions of thermal peaks, measured by DSC, remain independent of sample composition. Due to the formation of interfaces as a consequence of increasing dispersion of polystyrene the nucleation changes from preferentially thermal to athermal.     

Irreversible deformation of isotactic polypropylene in the pre-yield regime

In the modeling of the mechanical response of a polymer over a large strain range, the nonlinear viscoelastic and viscoplastic behavior must be considered. For many polymers, nonlinear behavior is observed at low loads, e.g. by a stress-dependence of the creep compliance for stresses above 2 MPa in case of the polypropylene used in this study. Additionally, plastic deformation has been observed at strains below the yield point for several polymers. In this study, the irreversible deformation by cavitation and shear yielding of polypropylene are characterized in the pre-yield regime in uniaxial tensile tests using digital image correlation. The recovery of strain after unloading at a prescribed strain level is measured and used to identify the evolution of the plastic strain during uniaxial tension. An experimental technique for simultaneous determination of the true stress–true strain curve and the degree of stress whitening, which relates to the amount of cavitation, is introduced and the initiation of cavitation is compared to the plastic deformation detected in strain recovery at various temperatures.     

Advanced x-ray study on crystalline and amorphous components of as-polymerized isotactic polypropylene

The WAXS powder pattern profile analysis of as-polymerized high-yield isotactic polypropylene has been performed in order to evaluate the crystalline, the so-called amorphous, and the diffuse scattering components. The amorphous component has been interpreted in terms of microcrystallites.The intensity percentages of the sample components are: -crystalline =42.12%, -semimicrocrystalline=18.65%, and -microcrystalline=39.23%. The method allows a good evaluation of the anisotropic structural disorder as well as the crystallite dimensions anisotropy and crystallinity determination. Moreover, the contemporary occurrence of different crystalline modifications in the sample can be defined quantitatively.The crystallinity, expressed as the ratio between the integral intensities diffracted by the large -form crystallites plus the middle-size -form crystallites and the sum of the larger and smaller ones is 61%.     

Molecular fractionation in isotactic polypropylene during isothermal crystallization

The nucleation frequency of isotactic polypropylene shows for certain molecular weight distributions during isothermal crystallization a “stepwise” development of the nuclei as a function of time. The resulting curve can be fitted by a superposition of exponential functions assuming a separate nucleation density for each nucleation step. The multimodal nucleation is discussed as a consequence of molecular fractionation effects during crystallization. Received: 23 October 1997 Accepted: 12 May 1998     

The Synthesis of Isotactic Polypropylene with Spherical Morphology via Supported Metallocene Catalyst

Tile morphology control of polypropylene products is one of the technological obstaclesto the industrial polymerization of propylene via metallocene catalyst. One efficient wayto solve this problem had been proposed that the metallocene catalyst should besupported on suitable carrier. Although lots of work has been reported'-', up to date, nobreakthrough has been got yet. The stUdies on morphology control of supportedmetallocene catalysts will be of great value in either scientific or practice…     

Development and characterisation of flame-retardant fibres from isotactic polypropylene melt-compounded with melamine-formaldehyde microcapsules

Intumescent flame-retardant textiles have been developed from flame-retardant microcapsules. The work is based on the synthesis of different melamine-formaldehyde microcapsules containing di-ammonium hydrogen phosphate and/or poly(1,6-hexamethylene adipate) by in-situ polymerisation. Two types of shell have been produced, composed of melamine formaldehyde or melamine formaldehyde-poly(hexamethylene adipate glycol). The microcapsules obtained were melt-compounded at 5%-wt with an isotactic polypropylene matrix using a twin-screw extruder, and multi-filaments have afterwards been spun from the various extrudates. The manufactured fibres were mechanically characterized by measuring their tensile properties, and their thermal properties were investigated by DSC and TGA. Finally, knitted fabrics were processed from the multi-filaments: their flame-retardant properties were evaluated by performing a fire test with a cone calorimeter, and their thermal conductivity measured with a Hot Disk. The different thermal behaviours are discussed in terms of the influence of system formulation on the overall thermal degradation, due to interactions between the different components of the flame-retardant microcapsules. The results showed that for one of the structures, an intrinsic intumescent flame-retardant system has been achieved.     

Role of the interphase dynamics in the induction time of the thermo-oxidation of isotactic polypropylene

This work completes an earlier study on the influence of molar mass and microstructure on the thermal stability of low molar mass isotactic polypropylenes (iPP). The relative dependence of induction time (t_i) on both parameters has been assessed for new metallocene iPP samples (M-PP) with molar masses from 65,000 to 182,000. The new M-PP series includes one metallocene ethylene-propylene copolymer (M-EP) with an ethylene content of 2.6 mol%.When the new t_i data are considered together with those previously reported, neither the molar mass nor the microstructure, taken as sole parameters, is able to explain the global t_i evolution of the M-PP samples.On the basis of the results corresponding to the M-EP copolymer, it is proposed that local chain dynamics occurring at high free volume regions, associated to propylene segment interruptions, play a main role in the ability of the interphase to initiate the oxidation. The correlation of the characteristic interphase chain dynamics, as measured by DMTA, with t_i data supports this suggestion. This hypothesis provides a more unified insight about the actual origin of the iPP thermo-oxidation, as it integrates the influence of parameters which have been found to drive partially the thermal stability of iPP, in particular, molar mass and microstructure.     

Photo-oxidation of thick isotactic polypropylene films I. Characterisation of the heterogeneous degradation kinetics

Photo-oxidation kinetics of thick isotactic polypropylene films have been compared to thermal-oxidation kinetics of thin films, and noticeable differences have been found. The non-classical kinetic trend of the former can be described as a three step evolution: a typical induction/autoacceleration POOH build-up at the beginning, an intermediate slower POOH content increase and, finally, a gentler POOH increase, which can be better described by quadratic functions of the oxidation time than by a linear dependence. In addition, a series of oscillations appearing from the beginning of the photo-oxidation are found. This kinetic heterogeneity is suggested to be related to the progression of the oxidation to the inside of the strips. However, the FTIR analysis of the evolution of the POOH band position in both photo and thermal oxidation, enables the observed shape changes to be associated to kinetic stages.     

Irreversible structural changes in cryogenic mechanically milled isotactic polypropylene

The influence of cryogenic mechanical milling on the structure and the thermal behavior of isotactic polypropylene was investigated by means of wide-angle X-ray scattering, differential scanning calorimetry and transmission electron microscopy. The results presented show that structural changes caused by mechanical milling at cryogenic temperatures are only partly reversible. The decrease in the degree of crystallinity as determined by differential scanning calorimetry with increasing milling time is attributed to a reversible transformation of the initial morphology into a nanostructured morphology, consisting of small fragments of the original isotactic polypropylene lamellae. During recrystallization from the molten state, there still exists an influence of the previous milling treatment, leading to significantly changed crystallization behavior. The reason for this behavior might be a decrease in the molecular weight or a change in the molecular weight distribution or the formation of long-chain branched polypropylene molecules induced by cryogenic mechanical milling.

Enhanced mechanics in injection molded isotactic polypropylene/polypropylene random copolymer blends via introducing network-like crystal structure

The crystallization behavior, rheological behavior, mechanical properties and microstructures of injection molded isotactic polypropylene(i PP), polypropylene random copolymer(co-PP) and i PP/co-PP blends were investigated. Differential scanning calorimetry(DSC) and dynamic rheological analysis illustrated that i PP and co-PP were compatible in the blends and co-PP uniformly dispersed in the i PP phase. Polarizing optical microscope(POM) was adopted to observe the crystal size and morphology evolution. The results of mechanical properties and scanning electron microscopy(SEM) indicated that the crystal size of i PP in i PP/co-PP blends(10 wt% co-PP + 90 wt% i PP and 30 wt% co-PP + 70 wt% i PP) radically decreased after the incorporation of co-PP. During crystallization, the molecular chain segments of co-PP could penetrate i PP spherulites and form a network-like crystalline structure. The network-like crystal structure could effectively transmit stress and consume more energy to overcome intermolecular forces to resist stretching. In this way, the strength would improve to a certain degree. The impact fracture mechanism of i PP/co-PP blends is quasi ductile fracture by multiple crazes. Our work discovered that the blends containing 10 wt% and 30 wt% of co-PP exhibited prominent toughness and reinforcement.     

Nonisothermal crystallization behavior of isotactic polypropylene/ thermoplastic rubber blends

The morphology and crystallization behavior of blends of polypropylene (PP) and an ethylene-based thermoplastic elastomer (TPO) were investigated by scanning electron microscopy (SEM) and differential scanning calorimetry (DSC). The SEM images showed a two-phase morphology for these blends. As TPO was partially crystalline, two distinct peaks were observed in both heating and cooling scans of DSC. The crystallization temperature of TPO in blends was higher than pure TPO. In contrast, the crystallization temperature of PP in blends was lower than pure PP. The crystallization behavior of blends was modeled by Avrami equation. It was observed that the presence of TPO accelerated the growth rate of crystals of PP in PP/TPO blends.     

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.     

Fuming nitric acid treatment of isotactic polypropylene film

Fuming nitric acid treatment has been made on a melt-quenched and an annealed isotactic polypropylene film. The treated samples were characterized by measurements of weight loss, density, molecular weight, spin-lattice,T ₁, and spin-spin,T ₂, relaxation times. Concurrent with the increases in weight loss, density and a decrease in molecular weight, increases inT _1l andF _c , a fraction of crystalline region, and decreases inT _2a andF _a , a fraction of amorphous region, were observed as a consequence of the decrease in an amount of noncrystalline portions. However, unexpected fall inT _1l was also observed after about 2–3 hr of treatment time. These observations were discussed by the structural changes that took place during acid etching.     

Dilatometric studies of isotactic polypropylene with different morphology before and after thermal degradation in air

Summary Glass transition phenomenon in isotactic polypropylene has been studied in this paper basicly on dilatometric studies. New suggestions are made for explaining the occurrence of twoT _g values with their characteristic dependence on the degree of crystallinity of the samples having a different morphological structure. The effects produced by thermooxidation are discussed. T _g calledT _g1 is considered as the true glass transition temperature in the amorphous phase of IPP whereasTg2 is melting of a smectic phase in IPP,T _g2 >T _g1.Author thanks Prof. M. Kryszewski for useful discussion.     

Radiation resistant polypropylene blended with mobilizer,: antioxidants and nucleating agent

Post-irradiation storage of medical disposables prepared from isotactic polypropylene renders them brittle due to degradation. To avoid this, isotactic polypropylene [(is)PP] was blended with a mobilizer, dioctyl pthallate (DOP), three antioxidants (hindered amines and a secondary antioxidant) and benzoic acid to obtain radiation-resistant, thermally-stable and transparent material. Different formulations prepared were subjected to gamma radiation to doses of 25 and 50 kGy. Tests of breakage on bending after ageing in an oven at 70°C up to 12 months have shown that the addition of DOP and the antioxidants imparts improved radiation and thermal stability as compared to (is)PP alone or its blend with DOP. All the formulations irradiated or otherwise demonstrated excellent colour stability even after accelerated ageing at 70°C for prolonged periods.     

The influence of nucleus density on optical properties in nucleated isotactic polypropylene

The effect and efficiency of three nucleating agents, a sorbitol based clarifier, a traditional heterogeneous nucleating agent and poly(vinylcyclohexane) (PVCH) was studied in polypropylene (iPP) homopolymer. The nucleating agents were added to iPP in different amounts; PVCH in 0–200 ppm, while the other two in 0–2000 ppm. Optical and mechanical properties were determined on injection molded plates or bars, respectively. Nucleation efficiency was studied by thermal analysis, while structure was characterized by polarized light (PLM), scanning electron (SEM) and atomic force microscopy (AFM). Nucleus density was calculated using the method of Lamberti, which is based on the kinetic theory of the crystallization developed by Lauritzen and Hoffmann. The results proved that the nucleating agents modify properties in different ways and extent. PVCH is very efficient already at small concentrations and increases the stiffness of iPP considerably more than the other two compounds. On the other hand, the clarifier and the traditional nucleating agent induce better optical properties even at smaller efficiency. The structure developing in the presence of the three nucleating agents is also different. The clarifier forms a network in iPP and induces the formation of a microcrystalline structure according to the former literature data. Microspherulitic structure develops in the presence of the heterogeneous nucleating agent studied, while relatively large supermolecular units form in iPP nucleated by PVCH even under the conditions of injection molding. The calculation of nucleus density by existing models and the comparison of the results to optical properties proved that haze is determined by the size of the supermolecular units of the polymer and this latter depends on nucleus density.     

Preparation of polypropylene/poly(styrene-co-(butyl methacrylate)) nanoblends by diffusion and subsequent copolymerization of monomers in isotactic polypropylene pellets

The diffusion and subsequent copolymerization of styrene(St)/butyl methacrylate(BMA) mixed monomers in i PP pellets to prepare copolymer nanoblends were investigated. The diffusion step was carried out at 90 ℃ for 2 h in water, and the copolymerization was initiated by the addition of BPO with the aid of a small amount of St. The diametrical distributions of both St and BMA units and their ratio St/BMA were investigated by micro FTIR. Both St and BMA can diffuse into the centres of i PP pellets. The diametrical distribution of St/BMA ratio is constant in all the copolymer blends. The copolymer composition depends on the comonomer feed ratio. The molecular weights of the copolymers were measured by GPC after extraction with tetrahydrofuran. The phase morphology of the copolymer blends was investigated by FESEM, showing the average particle sizes of less than 100 nm. DSC measurements show that the diffusion and subsequent copolymerization of St/BMA monomers only occur in the amorphous regions of i PP pellets.