Morphology and Orientation of PP-Structural Foam Moldings

Abstract

An experimental study was conducted to investigate the interaction between the macrostructure and morphology of PP-structural foam moldings made by gas-counter pressure process by egression of foamed melt from the core of the molding. The structural foam moldings, center-gated cylindrical plate “disc” (diameter 1800 mm. high 11 mm) were produced on an in-line injection molding machine KuASY 800/250, varying the shot weight and melt temperature. The polymer used was isotactic polypropylene “Buplen” 7523 with 1 wt% chemical blowing agent (azodicarbonamide) added. The morphology, orientation, and processes of non isothermal phase transition have been studied using polarized optical microscopy, SALS, DSC and birefringence. Samples were cut from the discs at different distances from the gate. The presence of a two-layered structure was observed in the solid skin: an outer smectic layer and an inner particular crystalline layer. The thickness of the smectic layer and size of spherulites from skin to the foamed core were determined. The orientation in radical and tangential direction of the flow and perpendicular to the disc surface were studied in mold filling and egression stage. The fixed orientation in final moldings is a complex picture of bubble growth, bubble orientation and shear flow. It was found that the radical orientation decreases with the distance from the gate. Maximum orientation is located in the solid skin, and minimum in the foamed core, and was shown by means of a birefringence profile.     

Base-cover paracompactness

Call a topological space base-cover paracompact if has an open base such that every cover of contains a locally finite subcover. A subspace of the Sorgenfrey line is base-cover paracompact if and only if it is . The countable sequential fan is not base-cover paracompact. A paracompact space is locally compact if and only if its product with every compact space is base-cover paracompact.

     

On base-cover metacompact products

Generalizing results of Yang Gao, Lei Mou and Shangzhi Wang, as well as a result of the author, we prove that a topological space is locally compact and metacompact if and only if its product with every compact space is base-cover metacompact.     

Site-resolved X-ray scattering studies,II the morphology in injection-molded PP foams

PP-structural foam moldings, composed of three co-axial cylinders were produced on an on-line injection molding machine in a pre-pressurized mold cavity by the classical low-pressure process and an alternative low-pressure process. Melt temperature, injection direction and sprue diameter were varied. Cross-sections cut from the middle of the small cylinder in longitudinal orientation were investigated by site-resolved X-ray scattering techniques in three different experiments: (i) wide-angle scans of the cross-sections, resulting in two-dimensional intensity maps; (ii) measurements of azimuthal intensity distributions of the principal PP reflections, for selected positions in the cross-sections; (iii) again for selected positions, small-angle measurements interpreted in terms of long periods. The comparison of the results derived from the different samples in the different experiments allows far-reaching statements about the influence of melt temperature, sprue dimension and position, and the type of process on the morphology and texture in the smallest cylinder of the moldings.     

( m,n)-Equidista nt Sets i n $\ mathbb{R}^{k},\ mathbb{S}^{k}$ , a nd ℙk

We call a metric space X (m,n)-equidistant if, when A⊆X has exactly m points, there are exactly n points in X each of which is equidistant from (the points of) A. We prove that, for k≥2, the Euclidean space ℝ ^k contains an (m,1)-equidistant set if and only if k≥m. Although the sphere is (3,2)-equidistant, and ℝ⁴ contain no (4,2)-equidistant sets. We discuss related results about projective spaces, and state a conjecture about analogous to the Double Midset Conjecture.     

Conductive Composites Based on Metallocene Isotactic Poly(propylene): Preparation and Properties

Summary: The research deals with the preparation and the further comprehensive characterization of metallocene polypropylene-based composite materials by incorporation of carbon black nanoparticles. Composites containing up to 10 wt% of carbon black were prepared by direct melt mixing in a single screw extruder Brabender Extrusiograph type 30/25D with attached static mixer at melt temperature of 200 °C and a screw speed of 30 rpm, according to a two-step process. Some composites were treated with 3 wt% maleic anhydride grafted polypropylene (MAH-PP). The rheological behaviour of the miPP nanocomposites was determined by cone/plate rheological measurements at 180 °C. The composites were characterized by SEM for morphological details and uniaxial stress-strain measurements for determining the mechanical parameters. Electric conductivity of injection molded plates from these composites was investigated. The different miPPs studied are ranked in an ascending order according to their increasing molecular weight concerning the magnitude of their rheological parameters. The maleic anhydride compatibilizer leads to lower viscosity values even at high shear gradients and to better homogenization of the nanofiller in the polymer matrix. The processing conditions, carbon black concentration and viscosity of the virgin polymer have an impact on the final conductivity of the miPP/carbon black composites.     

Development of <Emphasis Type="Italic">β</Emphasis> and <Emphasis Type="Italic">α</Emphasis> isotactic polypropylene polymorphs in injection molded structural foams

Structural foam moldings, composed of three co-axial cylinders differing in diameter (10 mm, 20 mm, and 30 mm) and length, were produced from isotactic polypropylene (PP) and 0.5 mass % 1,1′-azobisformamide on an in-line injection molding machine in a mould cavity pre-pressurized with nitrogen by the classical low-pressure process combined with egression of foamed melt from the core. Injection-molding conditions were as follows: melt temperature, 220°C, mold temperature, 20°C, cooling time, 5 min, gas-counter pressure, 0.5 MPa. The sprue gate was at the end of the smallest cylinder and its diameter was varied from 4 mm to 7 mm. To investigate the development of β-PP modification in terms of phenomena due to the phase change in the mould cavity (expansion), appropriate specimens (cross-sections) were cut from the middle of each cylinder in parallel and perpendicular orientation to the flow direction and were investigated by WAXS, DSC, and POM. As revealed by WAXS, β-PP is present in all cylinders, always concentrated in certain regions of the cross-section — mainly in the surface layers of the smallest cylinder (D1) and in the foamed core of the other two cylinders (D2 and D3). Its concentration was found to change with the sprue dimensions. High β-PP concentration is associated with a preferred orientation in the skin of the smallest cylinder and with better expansion conditions in larger cylinders. Presence of the β-phase in the surface layers and in the core of the moldings was proved by DSC and POM.     

Modification of Recycled Polymer Blends with Activated Natural Zeolite

The growing interest in the natural zeolite is based on some specific peculiarities of its structure, which after dehydration enables adsorption processes of some polymer molecules and/or segments to take place on the zeolite surface. The main goal of the study is to investigate the effect of dehydrated zeolite on the flow behavior, mechanical properties and morphology of immiscible blends from unsorted polymer wastes. A tetra-component blend consisting of 40 wt.% polypropylene (PP), 40 wt.% high-density polyethylene (HDPE), 15 wt.% low-density polyethylene (LDPE) and 5 wt.% polystyrene (PS), was studied as a model system of commingled plastic wastes. Compositions from recycled blend and dehydrated zeolite in a wide concentration range (from 0 to 20 wt.%) were prepared using a twin-screw extruder Brabender DSE 35/17D in the temperature range from 140 to 190 °C. The compositions were characterized by capillary rheometry, differential scanning calorimetry (DSC), site-resolved wide-angle X-ray scattering (WAXS) and mechanical tests. The results show a compatibilizing effect of dehydrated zeolite at low concentration levels (1-2 wt.%) and open wide possibilities for utilization of dehydrated zeolite in the recycling of unsorted polymer wastes.     

Flow behaviour of gas-containing LDPE/i-PP melts

An experimental study was conducted to investigate the rheological behaviour and extrudate swell of polyolefin blends based on two grades of low-density polyethylene (LDPE) and an isotactic polypropylene (i-PP). Blending was carried out on a twin-screw extruder “Brabender” at different composition ratios in the temperature range from 140 to 190°C. The LDPE/i-PP blends mixed with 0.5 wt.% blowing agent were extruded by means of “Brabender” extrusiograph at melt temperature of 200°C and different extrusion rates. The influence of composition content on the viscosity and extrudate swell was considered. The foam structure and morphology are discussed in terms of shear rate, molecular characteristics and composition content. The presence of layered structure was observed: an outer smectic layer and an inner partially crystalline layer. The thickness of smectic layer and size of spherulites were determined.