Nylon melt-strength modifier.
Rohm and Haas Co., Philadelphia, presented the first detailed discussion of the use of its Paraloid EXL-4151 reactive acrylic-imide copolymer as a modifier to improve the inherently poor melt strength of nylon 6 for blow molding, blown film and thermoforming. This modifier is one of at least four in the EXL-4000 series, commercial production of which began last June (see PT, Feb. '88, p. 23; Nov. '90, p. 76). The material, also described as a polyglutarimide, is commercially available at $1.75 lb/tl. It has a glass-transition temperature of 302 F and approximately 5% total acid functionality.
John B. De Vries, market development manager for engineering resins additives, says Paraloid EXL-4151 forms a compatible blend with nylon 6, as the acid and anhydride functionality of the imide reacts with the amide end groups of nylon. Capillary-rheometer tests were conducted at 527 F and shear rates from 100 to 10,000/sec, comparable to rates experienced in extruding a blow molding parison. A low-molecular-weight nylon 6 had a viscosity of 95 Pascal-seconds prior to modification with EXL-4151. A 10% addition of modifier raised the nylon's viscosity to 200 Pa-s; 20% addition raised it to about 450 Pa-s. Tests of blown film extrusion showed that 10% addition of Paraloid EXL-4151 gave low-viscosity nylon greater bubble stability than was exhibited by a high-viscosity, film-grade nylon. DeVries says that without the acrylic-imide additive, the low-viscosity nylon could not be blown into film.
DeVries did point out that Paraloid EXL-4151 is less effective as a modifier when added to a high-molecular-weight nylon, because the melt viscosity of the material becomes too high, making it difficult to process.
The modifier reportedly also increases nylon's flex modulus as much as 20%, and HDT increases almost linearly with increasing modifier addition. Paraloid EXL-4151 does not diminish the chemical resistance or barrier properties of the nylon, according to DeVries. In fact, moisture barrier is said to be increased.
Besides low melt strength, poor notched Izod impact strength is another traditional drawback of nylon 6 in blow molding. Kathy Chrien, market manager for engineering resins additives, recommends a reactive, butyl acrylate-based nylon toughener, Paraloid EXL-3387, to be used in concert with the EXL-4151 modifier to address this need (see PT, Feb. '88, p. 23).
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|Title Annotation:||Rohm and Haas Co.'s Paraloid EXL-4151 reactive acrylic-imide copolymer|
|Author:||Gabriele, Michael C.|
|Date:||Apr 1, 1991|
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