Extruded structural foams

Extruded structural foams are produced with conventional extruders and a specially designed die with an inner, fixed torpedo located at the center of its opening. The extrudate from this die is hollow. The outer layer of the extrudate cools and solidifies to form solid skin the remaining extrudate expands toward the interior of the profile. The Celuka process, developed by Ugine-Kuhlmann [93], is widely used commercially. 

There are many ways in which foams can be processed and used as slabs, blocks, boards, sheets, molded shapes, sprayed coatings, extruded profiles, foamed in place in existing cavities, in which the liquid material is poured and allowed to foam, and as structural foams (Chapter 6, STRUCTURAL FOAM). Conventional equipment such as extruders, injection, or compression machines is used. However specially designed machines are available to just produce foamed products. 

PBT-PC blends show increased melt strength allowing them to be easily processed by blow molding and profile extrusion. The PBT-PC blends have been extruded into sheet and thermoformed into parts. Enhanced melt strength allows PBT-PC blends to be foamed. Structural foam grades for injection molding (10-30% density reduction) are commercially available. 

A study was made of relationships between compound rheological properties, microwave vulcanisation parameters and accelerators on the quality of extruded EPDM foam seals for the automotive industry. The influence of these factors on cell size and structure, density and mechanical properties was investigated. Correlations were found between the chemical composition of the compound, variations in processing parameters and the quality of the finished product. 12 refs. 

Antec 96. Volume II. Conference proceedings. Indianapolis, 5th-10th May 1996, p.1941-7. 012 EFFECT OF BRANCHED STRUCTURE ON THE CELL MORPHOLOGY OF EXTRUDED POLYPROPYLENE FOAMS. I. CELL NUCLEATION... 

Cellular Polymers II. Conference proceedings. Edinburgh, 23-25th March 1993, paper 10. 6124 STRUCTURAL CHARACTERISATION OF EXTRUDED POLYOLEFIN FOAMS MADE USING A CHEMICAL EXPANSION SYSTEM Shishesaz M R Hornsby P R Brunei University (Rapra Technology Ltd.)... 

Examples are given of the use of extruded PE foam sections in conjunction with other polymeric materials in the production of triangular, semicircular, rectangular and trapezoidal profiles, e.g. beam-like structures in which the rigid support may be of GRP. The foam can be bonded with thermally-fusible adhesives or two-sided self adhesive tape affixed to the foam prior to fabricating. A standard range of the foam prodncts is available, but other types can be tailor-made. 

While unaffected by water, styrofoam is dissolved by many organic solvents and is unsuitable for high-temperature applications because its heat-distortion temperature is around 77°C. Molded styrofoam objects are produced commercially from expandable polystyrene beads, but this process does not appear attractive for laboratory applications because polyurethane foams are much easier to foam in place. However, extruded polystyrene foam is available in slabs and boards which may be sawed, carved, or sanded into desired shapes and may be cemented. It is generally undesirable to join expanded polystyrene parts with cements that contain solvents which will dissolve the plastic and thus cause collapse of the cellular structure. This excludes from use a large number of cements which contain volatile aromatic hydrocarbons, ketones, or esters. Some suitable cements are room-temperature-vulcanizing silicone rubber (see below) and solvent-free epoxy cements. When a strong bond is not necessary, polyvinyl-acetate emulsion (Elmer s Glue-All) will work. 

ABS structural foam can be processed by injection molding, through conventional or low pressure injection machines (Chapter 4) by expansion casting in rotational molding machines (Chapter 13) or conveyorized oven systems or it can be extruded into profiles through conventional extruders (Chapter 5). 

Of particular note to date are developments using ESI-based materials in foam applications. Novel foam structures offer attractive properties and characteristics including softness, esthetics and drape for a wide range of thermoplastic and crosslinked foam applications. Other product technologies of interest are as injection molded structural foams, as foamed layers in multilayer structures and as foamed blends of interpolymers with styrenic and olefinic polymers [77-79], Interpolymers also have potential for co-extruded film and sheet applications. 

Polystyrene (PS) Structural polystyrene foams are molded by injection and expansion-casting methods. They have a strong continuous skin and a foam cote. Their densities are quite high, ranging from 20 to 40 lb/ft3, in contrast to the 1 to 5 Ibs/ft range of the steam-molded and extruded polystyrene foams discussed below (11). Compared to other structural foams, however, the densities are relatively low (see Table 3-1). 

Many solid adsorbents liberate gas as a result of desorption of volatile liquids under the influence of heat. Typical adsorbents with microporous structures such as activated carbons, or precipitated silicas and renewable resources have been used as a coblowing agent in producing low-density extruded polystyrene foam boards. Incorporation of corn cobs or other renewable vegetable matter containing about 10% water together with a primary PBA into polystyrene in the extrusion process produced a low-density polystyrene foam board with bimodal cellular structures. This type of foam with bimodal cell structures has about 10-15% lower K-factor than similar foams without bimodal cellular structures. Similar results were obtained with a precipitated silica for producing a low-density extruded polystyrene foam with bimodal cellular structures. ... 

Santechem 21-21. [Santech] Azoduxu-bonamide cone. blowing agent fix polyolefins, extruded and inj. molded structural foam. 

FIGURE 2.61 Structural foam process, (a) Filling the accumulator. The blowing agent (usually nitrogen) is injected into the melt in the extruder before it is passed into the accumulator, (b) Filling the mold. The accumulator ram injects the melt into the mold where the reduced pressure allows the gas to foam the resin. 

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