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Viscosity and Flow

Polyamide Chain Extension

Cray Valley styrene maleic anhydride (SMA®) resins can be used as additives to promote reactive chain extension, mainly in polyamides, in order to improve the melt characteristics and mechanical properties. The function of the chain extender is to bridge two or more adjacent polyamide chains together thereby increasing the effective molecular weight, and branching structure. Altering the molecular architecture via reactive extrusion can increase the melt flow, and mechanical properties of both virgin and recycled* polyamides alike. Alternatively, low molecular weight polybutadiene additives offer a rubbery link between chains to promote flexibility.

Figure 1 demonstrates the typical improvement in melt strength produced by integrating a fractional loading of SMA into an unfilled, undried PA66. Incorporating 0.5 weight % SMA 9000P into the melt stream the processibility of the extrudate improved dramatically.

Productivity

One of the greatest challenges that polyamides present are exceptionally low melt viscosities, which can be inhibitive on productivity and applicability. Figure 1 illustrates the dramatic effect on melt flow rate for both virgin commodity polyamides, and recycled streams of PA6/6. Note how SMA 9000 Series concentrates permit the user to dial in to a prescribed melt flow rate as the application commands.

Chain Extension Figure 1 left

Chain Extension Figure 1

Figure 1: Example of enhanced melt strength with and without SMA.  Measure MFR on prime and recycled grades of commodity polyamides demonstrating the influence of SMA 9001.

Prime Polyamides

Widely used in many strenuous applications, polyamides in their many forms have become synonymous with performance. However, very little development has been made in industry to further differentiate polyamides. Leveraging a reactive species such as SMA 9001, new advances in augmenting melt strength, blending with other polymers, and key performance attributes can be tuned to penetrate new application spaces. Figure 2 & Figure 3 illustrate the influence of low fractions of SMA 9001 on neat PA6 & PA6/6 respectively.

Chain Extension Figure 2

Figure 2: Net influence on mechanical properties of PA6 using SMA® 9001.

Figure 3: Net influence on mechanical properties of PA6/6 using SMA® 9001.

Recycled Polyamides

Globally, there has been a shift to repurposing polyamide from a variety of sources, such as end of life carpet and automotive. Despite significant efforts in separation and cleaning technology, only a small fraction of recycled polyamide 6 and polyamide 6/6 can be re-introduced into their incumbent applications. Post-industrial and post-consumer polyamides tend to have lower properties than is desirable for injection molding. Figure 4 & Figure 5 outlines the effectiveness of SMA® 9001 & 9002 on a purified r-PA6/6 and contaminated r-PA6/6 respectively.

Chain Extension Figure 4

Figure 4: Physical & mechanical property enhancements on ‘clean’ recycled PA6/6 using SMA® 9001.

Chain Extension Figure 5

Figure 5: Physical & mechanical property enhancements on ‘contaminated’ recycled PA6/6 using SMA® 9002.

Summary

SMA® 9000 series concentrates are the ideal additive to effectively modify the property landscape of virgin, recycled, blended and filled polyamides. A formulated pellet provides a balance of productivity, efficiency and homogeneity when used in your existing setup. Look for additional next generation SMA® concentrates to impart tensile properties in addition to those shown above.