Foamed polypropylene

The advantage of a foamed structure arises when a part is subjected to flexural loading, for which case the stiffness is proportional to the cube of the 

Another way of creating a foam is to incorporate hollow sphere fillers such composites, known as syntactic foams, have a superior surface finish compared with conventional foams. Flammability can be reduced by additives, e.g. antimony trioxide plus chlorinated waxes such additives, while retarding the ignition, lead to increased smoke emission. The flammability of PP is a hazard restricting its widespread use in the interior of buildings. 

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Structural foam mouldings may also include fibres to enhance further the mechanical properties of the material. Typical performance data for foamed polypropylene relative to other materials is given in Table 1.1. 

Polypropylene Foams Polypropylene foams are comparatively recent entries into the structural foam field, supplanting hi -density polyethylene foams, but their use is increasing rapidly because of the extreme range of grades and properties available, plus a favorable price advantage, compared with other thermoplastic foams. Glass-reinforced (30% glass) polypropylene foams are commonly used (13). 

Polypropylene (G/F)/nylon 6,6 Polyurethane open/closed cell foam Polypropylene (mica filled/glass filled/mineral filled) Aluminum tube AA4343/AA3003 base Aluminum tube AA4343/AA3003 base Nylon 6,6/nylon 6/polypropylene Nylon 6,6/nylon 6 Polypropylene (GF)... 

If the modulus of a dispersed rubbery component is only 1/1000 that of the surrounding rigid matrix, an air-filled structure is approximated. The two experimental points for foamed polypropylene in Figure 1 fit fairly well into the theoretical curves. It is apparent from Figure 1 that the modulus of a composite of known volume composition reflects clearly the phase distribution, i.e.y it indicates which component forms the continuous phase. The moduli may differ up to two decades after reversal of the continuous and the dispersed phases when the ratio of the component moduli is about 1000 1. 

Chaudhary AK, Jayaraman K. Foaming polypropylene with nanoclays. ANTEC 2008, conference proceedings. Society of Plastics Engineers 2008. 

A two-step gear pump (Fig. 15) was used to introduce the gas into the hot-melt adhesive. Foamability was later found to vary with the polymers used. Polyethylene is excellent for foaming. Polypropylene, polyester, and 12-polyamide (Nylon 12) are also very good. Styrene-butadiene and ethylene-vinyl acetate are good and dimer acid polyamide is fair. ... 

Polypropylene is the only high-volume thermoplastic that is processable by all major fabrication methods molding, extrusion, film, and fiber. Many new polypropylenes with improved engineering properties have been developed. The most promising are glass-reinforced polypropylene, foamed polypropylene, heat-resistant-polypropylene, and oriented sheeting. 

Structural Components. In most appHcations stmctural foam parts are used as direct replacements for wood, metals, or soHd plastics and find wide acceptance in appHances, automobUes, furniture, materials-handling equipment, and in constmction. Use in the huil ding and constmction industry account for more than one-half of the total volume of stmctural foam appHcations. High impact polystyrene is the most widely used stmctural foam, foUowed by polypropylene, high density polyethylene, and poly(vinyl chloride). The constmction industry offers the greatest growth potential for ceUular plastics. 

TDA-derived polyols are made by alkoxylation. Polypropylene oxide adducts of I DA (14) and TDA-initiated polyether polyols (13,15) are used in rigid polyurethane foams and continue to be included in new formulations (62) as well as older appHcations. 

Water-borne adhesives are preferred because of restrictions on the use of solvents. Low viscosity prepolymers are emulsified in water, followed by chain extension with water-soluble glycols or diamines. As cross-linker PMDI can be used, which has a shelf life of 5 to 6 h in water. Water-borne polyurethane coatings are used for vacuum forming of PVC sheeting to ABS shells in automotive interior door panels, for the lamination of ABS/PVC film to treated polypropylene foam for use in automotive instmment panels, as metal primers for steering wheels, in flexible packaging lamination, as shoe sole adhesive, and as tie coats for polyurethane-coated fabrics. PMDI is also used as a binder for reconstituted wood products and as a foundry core binder. 

Compounds based on S—EB—S usually contain polypropylene, which improves solvent resistance and processibiUty and raises upper service temperatures. Compounds intended for use in the automotive industry are able to survive 1000 hours air exposure at temperatures of 125°C with only minor changes in properties (54). Very soft compounds have been developed to replace foam mbber for interior trim parts. In this and similar appHcations, these soft compounds are usually insert molded over polypropylene or metal and then coated with flexible polyurethane paint (55). Other automotive appHcations include products intended for sound deadening, flexible air ducts, and gear shifter boots, as weU as improving the properties of sheet mol ding compounds. 

The RIM process was originally developed for the car industry for the production of bumpers, front ends, rear ends, fascia panels and instrument housings. At least one mass-produced American car has RIM body panels. For many of these products, however, a number of injection moulding products are competitive, including such diverse materials as polycarbonate/PBT blends and polypropylene/EPDM blends. In the shoe industry the RIM process has been used to make soling materials from semi-flexible polyurethane foams. 

Foam plastic media are manufactured from polyvinyl chloride, polyurethane, polyethylene, polypropylene and the other polymer materials. The foam plastic media are economical. 

Polycarbonate, polypropylene and modified PPO are popular materials for structural foam moulding. One of the main application areas is housings for business equipment and domestic appliances because the number of component parts can be kept to the absolute minimum due to integral moulding of wall panels, support brackets, etc. Other components include vehicle body panels and furniture. 

Comparison of structural foams based on various grades of polypropylene with some traditional... 

Example 2.8 A polypropylene sandwich moulding is 12 mm thick and consists of a foamed core sandwiched between solid skin layers 2 mm thick. A beam 12 mm wide is cut from the moulding and is subjected to a point load, IV, at mid-span when it is simply supported over a length of 200 mm. Estimate the depth of a solid beam of the same width which would have the same stiffness when loaded in the same way. Calculate also the weight saving by using the foam moulding. The density of the solid polypropylene is 909 kg/m and the density of the foamed core is 6(X) kg/m. ... 

A rectangular section beam of solid polypropylene is 12 mm wide, 8 mm deep and 300 mm long. If a foamed core polypropylene beam, with a 2 mm solid skin on the upper and lower surfaces only, is to be made the same width, length and weight estimate the depth of the composite beam and state the ratio of the stiffness of the two beams, (p = 909 kg/m, p = 500 kg/m ). 

Meluch et al.10 reported that high-pressure steam hydrolyzes flexible polyurethane foams rapidly at temperatures of 232-316°C. The diamines are distilled and extracted from the steam and the polyols are isolated from the hydrolysis residue. Good results were obtained by using reclaimed polyol in flexible-foam recipes at file 5% level. Mahoney et al.53 reported the reaction of polyurethane foams with superheated water at 200°C for 15 min to form toluene diamines and polypropylene oxide. Gerlock et al.54 studied the mechanism and kinetics of the reaction... 

After 8 h of reaction, the reactor was allowed to cool. A two-layer liquid formed. The top layer was found to contain mostly polypropylene ether triols with about 20% by weight diethylene glycol and 5% by weight toluene diamines. The top layer was purified by vacuum distillation at 2 mm Hg and 200° C to produce 320 g of a light brown liquid residue. This residue (polyols) was used as a replacement for 5% by weight of the Pluracol 535 polyol in the formulation of a flexible polyurethane foam. A flexible foam which had good resiliency and a density of 2.2 Ib/ft3 was obtained. At higher replacement levels, lesser quality foams were obtained. 

About 60% of the propylene oxide made is polymerized to polypropylene glycol and other polyethers for use in polyurethane foams and adhesives. Propylene glycol is also widely used in polyester resins based on maleic anhydride. 

Most automobile and furniture seating, foam mattresses, carpet underlay-ment, and other similar products are made from polyurethanes based on polypropylene glycol (PPG). PPG is the preferred raw material for these type of polymers because of the wide variation of possible properties of the end product and the relatively low cost. 

Experiments pertaining to a new system for the application of bromine to flame retardant polypropylene and foamed polystyrene are described. The FR compound, ammonium bromide, is formed in the amorphous regions of the polymer phase by the interaction of bromine sorbed on the polymer and ammonia, sorbed subsequently. Gaseous nitrogen which is also produced, expands and brings about the rearrangement of the chains to produce a porous structure. The ammonium bromide produced is finely divided and imparts FR properties to the polymer. 

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