Amorphous Phase Of Polypropylene Research Articles

Adhesion control for injection overmolding of elastomeric propylene copolymers on polypropylene. Effects of block and random microstructures

The influence of chemical compositions and microstructures of ethylene–propylene copolymers on its adhesion strength to polypropylene was studied. DSC, WAXS and Raman micro spectroscopy were used to examine details of three ethylene propylene copolymers chemical compositions with amorphous and semicrystalline microstructures. Copolymers microstructures include from random to tapered blocky comonomers distributions. Semicrystalline copolymers strips were injection overmolded on a core polypropylene base, and peeling tests were conducted at room temperature. Adhesion strength depending on copolymers composition and microstructure are discussed on the basis of two mechanisms: fingering along amorphous polypropylene phase and co-crystalization. Injection adhesion after overmolding cannot be easily controlled via interphase melt temperature, as done before for other ethylene copolymers, mainly because of the very favorable Flory interaction parameter values. The used copolymers are classified for use for specific purposes, from easy recycling to high tenacity.

Environmental fracture of polypropylene membranes used in membrane distillation process

The thermal and mechanical stability of different capillary polypropylene (PP) membranes used in the membrane distillation (MD) process were investigated. Membranes differed in storage time from the manufacturing (from 1 to 8 years). Small changes in polymers crystallinity, melting temperature (T m ) and crystallization temperature (T c ) were detected as the storage time of membranes increased. This can be assigned to the crystal growth in amorphous phase of PP. However, independently on the storage time the brand-new membranes were found to be flexible and elastic and capable to bending without fracture. The MD process was carried out either continuously or continuously/periodically. Distilled water and NaCl solutions were used as feeds in MD process. It was found that PP membranes are loosing their flexibility and become brittle during long-term usage in MD modules, and as a consequence, they show susceptibility to cracking and fracture. These effects were more significant when NaCl solutions were used as feeds.

EPDM/PP Thermoplastic Vulcanizates As Studied by Proton NMR Relaxation: Phase Composition, Molecular Mobility, Network Structure in the Rubbery Phase, and Network Heterogeneity

Proton solid-state NMR T2 relaxation analysis is used to study model oil-extended ethylene−propylene-diene rubber (EPDM) and thermoplastic vulcanizates (TPV) composed of polypropylene (PP), EPDM and oil. It is shown that the method allows selective characterization of crystalline and amorphous phases of PP, cross-linked EPDM, and oil in TPVs. The network density in the rubbery (EPDM) phase is determined in a wide range of the TPV compositions, as well as in the oil-extended EPDM vulcanizates containing different amount of oil. The entanglement density decreases with increasing oil content in oil-extended EPDM. This decrease can be described using a scaling approach. Molecular mobility of oil molecules decreases with increasing EPDM network density and is significantly lower than that of pure oil due to physical interactions with the host matrix. It is shown that the network density in the rubbery phase of TPV is composed of chemical cross-links, physical junctions at the EPDM/PP interface, and temporary and trapped chain entanglements. The density of chemical cross-links increases with the amount of cross-linker per weight unit of EPDM. The density of the physical junctions increases with increasing PP content. Crystallinity of PP in TPV is hardly affected by the TPV composition. A small fraction of oil molecules plasticizes the amorphous phase of PP and the plasticization effect is proportional to an oil:PP mass ratio in the TPV composition. Two NMR methods for improving the selectivity of the T2 relaxation analysis to different phases of TPV are evaluated. The methods are based on the inversion−recovery experiment and double-quantum (DQ) filtering of the decay of the transverse magnetization relaxation. The DQ filtered T2 relaxation experiment improves the selectivity of the method and could open new possibilities for characterization of the network heterogeneity in rubbery materials. Some relationships between the TPV composition, network density, and mechanical properties are shortly discussed.

Mechanical Properties of Nanocomposites from Ball Milling Grafted Nano-Silica/Polypropylene Block Copolymer

Nanocomposites consisting of ethylene-propylene block copolymer filled with nano-silica (pre-treated by ball milling aided graft polymerisation) were prepared by a conventional compounding technique. The mechanical performance of the nanocomposites and the morphological changes induced by the addition of the nanoparticles were investigated. It was confirmed that the copolymer chains were chemically bonded to the silica particles during mechanochemical grafting in the ball mill. Morphology observations revealed that strong interfacial interaction between the grafting polymer (i.e., poly(butyl acrylate)) and the matrix (i.e., ethylene-propylene block copolymer) is critical for bringing the reinforcing effect of the nanoparticles into play. Owing to the enhanced interfacial interaction, the grafted nanoparticles exhibited a nucleating effect and improved the crystallinity of the polymer matrix. In addition, the particles also had a toughening effect on the amorphous polypropylene phase because of entanglements between the grafting polymer and the matrix. Insufficient interaction between the nanoparticles and ethylene-propylene rubber phase of the copolymer matrix actually introduces restraints. As a result, the tensile strength and modulus of the nanocomposites can be significantly increased by using low loadings of the treated nanoparticles. The decrease in the notched Charpy impact strength was insignificant in comparison to that of conventional micron-scale inorganic particles filled composites. The technical route proposed is therefore feasible for fabricating polymer composites with inorganic nanoparticles.

Interlaminar fatigue crack propagation in continuous glass fiber/polypropylene composites

The mode II interlaminar fatigue crack propagation behavior of unidirectional continuous glass fiber (GF) composites with a polypropylene (PP) matrix obtained under three different molding conditions has been studied with the use of the end-notch flexure (ENF) geometry. The microstructure and mechanical performance, especially the interlaminar fatigue crack propagation, are strongly affected by the molding conditions. Comparative results reveal a major influence of the fiber–matrix interface and the matrix morphology on the crack propagation resistance. The distribution of the ductile amorphous PP phase in the semi-crystalline PP matrix appears to be the controlling parameter determining the fatigue crack propagation resistance of the PP/GF composite. Fractographic observations clearly showed the role of this phase.

Effect of the Molding Conditions on Mode II Interlaminar Crack Propagation in Continuous Glass Fiber/Polypropylene Composites

The effect of molding conditions on the resistance to Mode II interlaminar crack propagation under monotonic and cyclic loading of unidirectional continuous glass-fiber composites with a polypropylene (PP) matrix was studied. The distribution of the fibers and of the crystalline and amorphous components of the matrix phase, the melting temperature and the amount of crystallinity are related to the molding conditions employed and to the resulting flexural strength and modulus, apparent interlaminar shear strength and Young’s modulus. Mode II crack propagation, either cyclic or monotonic, is strongly affected by the fiber-matrix interface and matrix morphology. The distribution of the soft amorphous PP phase in the semi-crystalline PP matrix appears to be the controlling parameter determining the fracture and fatigue resistance of the composite. The fractographic features clearly show the role that this phase plays during crack propagation. A relationship between the shear cusp size measured on the fatigue surfaces and the cyclic strain energy release rate is proposed.

Influence of heterogeneous textures of polypropylene/ethylene–propylene–rubber blends on dynamic viscoelastic properties in the solid

Heterogeneous textures in phase separated, solid polypropylene (PP)/ethylene–propylene–rubber (EPR) blends were investigated in relation to their dynamic viscoelastic properties. The glass transition temperature (Tg) of amorphous PP phase in PP/EPR blend quenched from molten state varies with propylene content of EPR as well as EPR content in blend. The Tg depends on the concentration of EPR dissolved in the amorphous PP phase. On the other hand, the Tg of EPR phase in PP/EPR blend is about the same as that of pure EPR. This fact means that PP molecules were not dissolved in EPR phase. For the same blending composition, the EPR concentration in matrix PP phase was larger for EPR having more propylene units. When the same EPR was used, the EPR concentration in the matrix was larger for blends with larger EPR content. The EPR concentration in the amorphous PP phase of PP/EPR blend in solid state is about the same as that in molten state, indicating that the EPR concentration in solid state was essentially determined by the EPR concentration in molten state.

Effect of conditions of crystallization on molecular relaxation in polypropylene

It was shown that annealing “Moplen” isotactic polypropylene (PP) granules at temperature of 433–443°K and remelting reduced T g. Samples slowly cooled from melt have lower T g than quenched samples. By the crystallization of PP from 1% tetrachloroethylene solution samples were obtained with a ‘shish-kebab’ structure, which are characterized by a very low intensity β-maximum of radiothermoluminescence. Annealing ‘shish-kebab’ specimens at 433–453°K produces an intense β-maximum near 210°K. After heating these specimens to 455°K or higher temperatures spherulitic PP samples are obtained for which the shape of light emission curve agrees with that of the light emission curve of initial PP granules heated under the same conditions. It was shown that storing annealed PP speciments with a spherulitic structure at room temperatures is accompanied by a gradual increase of T g. It was assumed that the main cause of variation of T g of PP during heat treatment and storate is the formation of micropores and stressed sections in the amorphous phase of PP.