Back SearchTitle: ACOUSTICS AND FORMING OF NOVEL POLYOLEFIN BLEND FOAMS
Page Range: p.349-367
Author(s): Subramonian S; Remy L; Schroer D
File size: 306K
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Issue Year: cp
Volume: 23
Issue No: No. 6
Abstract
Acoustic materials based on macrocellular thermoplastic foams made from blends of PE and PP were developed for applications in sound absorption and insulation. The closed-cell foams exhibited good acoustic performance over a broad frequency range and were particularly effective at low frequencies. They were able to withstand high service temperature environments in industrial applications. Other advantages, relative to conventional acoustic media, included resilience, structural integrity, ease of fabrication, moisture resistance and recyclability. Attempts were made to improve the acoustic performance by profiling the foam with Helmholtz resonators and quarter wave attenuators. Forming, i.e. shaping by application of heat and pressure, was used to manufacture acoustic parts with the desired shape and size for space-constrained applications such as appliance and automotive applications. This process could also be used to modify the skin quality and surface aesthetics of the foam. Studies were conducted using laboratory-scale equipment to determine the process conditions for forming polyolefin foams and to evaluate the effect on cell structure, foam properties and acoustics. Techniques for preservation of the acoustic performance of the foam during the forming process were examined. 9 refs.
Title: EXTRUSION OF MICROCELLULAR FOAMS USING PRE-SATURATED PELLETS AND SOLID-STATE NUCLEATION
Page Range: p.369-385
Author(s): Kumar V; Nadella K; Branch G; Flinn B
File size: 369K
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Issue Year: cp
Volume: 23
Issue No: No. 6
Abstract
A microcellular extrusion process using pre-saturated pellets of PVC and solid-state nucleation was developed. The process could be conducted on existing extrusion equipment without modifications. This was in contrast to the supercritical process in which, typically, gas at several tens of MPa was introduced in the melt and significant modifications to the standard extrusion equipment were required. Innovative gas delivery and cell nucleation strategies were proposed and demonstrated. Implementation of these strategies required the addition to the production line of only a pressure vessel in which the polymer pellets were saturated with carbon dioxide. The results showed that, as the die and barrel temperatures and thus the melt temperatures decreased, the relative density of the PVC foam increased and the bubble size decreased. The extrusion was conducted at temperatures of 20 to 30 degrees C below the normal temperature for PVC extrusion. Microcellular structure with cell size in the range 20 to 80 micrometres was achieved in the PVC-carbon dioxide system. 19 refs.
Title: ANALYSING THE EFFECT OF MOLD TEMPERATURE ON FOAM DENSITY AND FOAM SURFACE TEXTURE
Page Range: p.387-402
Author(s): Abdul-Rami A M; Hopkinson N; Dickens P M
File size: 483K
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Issue Year: cp
Volume: 23
Issue No: No. 6
Abstract
The effects of mould temperature on the average density and surface texture of high-resilience cold-cure flexible PU foams were studied. It was shown that higher mould temperatures produced lower density foams and that mould temperature had a significant and repeatable effect, particularly on the macro surface texture. Variations in surface roughness were observed at varying mould temperatures due to voids, shrink marks, scaling, knit lines and mottling. These variations were sufficiently large to warrant careful consideration of mould temperature management when forming foams in the mould. It was shown that the temperature of a production mould should be held at close tolerance to maintain a uniform surface texture. Temperature variations across the surface of foam tools, especially larger tools, are probably one of the main reasons why foam parts have varying surface texture which often leads to scrap. In the flexible foam moulding process, particularly cold-cure flexible foam moulding, temperature control was very important. The process required uniform surface temperature throughout the mould to ensure a uniform foam density and uniform surface texture. 12 refs.
Title: PHYSICAL PROPERTIES OF POLYPROPYLENE FOAMS - HOW TO PREDICT AND CONTROL THEM
Page Range: p.403-415
Author(s): Stadlbauer M; Folland R
File size: 229K
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Issue Year: cp
Volume: 23
Issue No: No. 6
Abstract
The desired PP foam properties for food packaging, protective packaging, automotive applications, building and construction, and display panels are discussed. Resin requirements for achieving the target foam properties are considered, including low density (foamability), stiffness and thermal conductivity at given density and cell structure. Available models for description of the relationship between resin properties, foam structure, foam density and final foam properties are described. A predictive tool for selecting material combinations, which will enable the desired foam properties to be achieved by foam producers and end-users, is presented. 16 refs.