In order to improve elongational viscosity of polypropylene, allowing its use in a wide range of applications, different samples of branched polypropylene have been produced by reactive extrusion and evaluated by different techniques. It is known that the long chain branching (LCB) can act as a nucleating agent in the crystallization process. This is confirmed by differential scanning calorimetry (DSC), optical microscopy, and crystallization analysis fractionation (CRYSTAF), where an increase in the crystallization temperature can be observed when comparing linear and branched samples. In the chemical composition distribution profile of the analyzed samples, it is possible to see differences in the amount of crystallized material among the branched PP samples and it is possible to correlate it with the long chain branching content and distribution, measured by Triple Detector Gel Permeation Chromatography (3D-GPC), using the Mark-Houwink plot (MH Plot), conformation plot, and gpcBR methodology. A decrease in dissolution temperature, and an increase in soluble fraction is observed by temperature rising elution fractionation (TREF) at increasing LCB content in the polymer samples. These results indicate that the presence, amount, or distribution of long chain branching affects the crystallization kinetics and the crystal morphology. CRYSTAF and TREF show a good correlation with LCB content measured by GPC.

SbstractThe influence of three nucleating agents from different generations on the crystallization behavior of propylene homopolymer was studied by differential scanning calorimetry (DSC) and atomic force microscopy (AFM). The amount of nucleating agent used varied between 1000 and 2200 ppm. The new generation nucleating agent, Hyperform  HPN-68L, accelerates the crystallization more efficiently than the other nucleating agents tested. It was also possible to verify the effects of agglomeration and negative interaction between calcium stearate and sodium benzoate. Furthermore, AFM images allowed to differentiate the crystals generated by Millad  3988 through the observation of a fibrillar intertwining network structure, with characteristic spacing and length of crystals, justifying its excellent performance to improve polypropylene optical properties.

Studies about polypropylene nanocomposite foams are receiving attention because nanoparticles can change physical and mechanical properties, as well as improve foaming behavior in terms of homogeneous cell structure, cell density, and void fraction. In this research, the foaming behavior of polypropylene, polypropylene/long-chain branched polypropylene (LCBPP) 100/20 blend, and polypropylene/LCBPP/halloysite nanocomposites with 0.5 and 3 parts per hundred of resin (phr) is studied. The LCBPP was used to improve the rheological properties of polypropylene/LCBPP blend, namely the degree of strain-hardening. Transmission electron microscopy observation indicated that halloysite nanotube particles are well distributed in the matrix by aggregates. Subsequent foaming experiments were conducted using chemical blowing agent in injection-molding processing. Polypropylene foam exhibited high cell density and cell size as well as a collapsing effect, whereas the polypropylene/LCBPP blend showed a reduction of the void fraction and cell density compared to expanded polypropylene. Also, the blend showed reduction of the collapsing effect and increase of homogeneous cell size distribution. The introduction of a small amount of halloysite nanotube in the polypropylene/LCBPP blend improved the foaming behavior of the polypropylene, with a uniform cell structure distribution in the resultant foams. In addition, the cell density of the composite sample was higher than the polypropylene/LCBPP sample, having increased 82% and 136% for 0.5 and 3 phr of loaded halloysite nanotube, respectively. Furthermore, the presence of halloysite nanotube increased crystallization temperature (Tc) and slightly increased dynamic-mechanical properties measured by dynamic-mechanical thermal analysis. By increasing halloysite nanotube content to 3 phr, the insulating effect increased by 13% compared to polypropylene/LCBPP blend. For comparative purposes, the effect on foaming behavior of polypropylene/LCBPP was also investigated using talc microparticles.

Summary Heterophasic poly(propylene) copolymers obtained by sequential polymerization are multi‐component products formed by a crystalline matrix of poly(propylene) and an ethylene‐propylene rubber phase. Some crystalline polyethylene and poly(ethylene‐co‐propylene) are formed in the rubber synthesis step by copolymerization of ethylene and propylene. These multi‐component systems present a complicated microstructure and heterophasic morphology. In this study, two heterophasic copolymers with the same total amount of rubber but different composition and molecular weight, were thoroughly analyzed. The morphology was evaluated by SEM and AFM techniques. The complexity of the system required some attention in the fractionation methodology to perform an accurate interpretation of results and different methodologies of fractionation, especially for obtaining PE fractions as free of PP as possible, were performed in order to better characterize the crystalline polyethylene fractions in the copolymers. Preparative TREF was used to obtain fractions for further analysis by 13C‐NMR, DSC and GPC. Also samples were submitted to Cross Fractionation Chromatography (CFC). Results obtained by the different methodologies were compared.

Summary: Diolefins can be used as comonomers in propylene copolymerizations in order to modify some of the final properties of the obtained poly(propylene) (PP) resins. Although reduction of catalyst activity can be expected when such copolymerizations are performed with standard heterogeneous Ziegler-Natta catalysts, copolymers containing 1,5-hexadiene (HD) and 1,7-octadiene (OD) can be produced at high rates when the comonomer content is sufficiently low (below 2 mol%); however, the presence of very small amounts of 5-ethylidene-2-norbornene (ENB) leads to complete catalyst inhibition. It is shown that incorporation of dienes lead to decrease of the melting point of the final product, especially in presence of ENB. When compared to HD, addition of OD causes more pronounced modification of the melt flow index and weight-average molecular weight, although the xylene solubles is less sensitive to the comonomer feed when the comonomer composition is low. Obtained results indicate that small amounts of dienes can be used at plant site to modify the final properties of PP resins produced with standard heterogeneous Ziegler-Natta polymerizations.