EoW July 2010

technical article

2 Experimentation 2.1 Materials used Commercial EVA (DuPont Elvax ® 550) containing 15% by weight vinyl acetate was used as received. ATH grade C-33 with a mean particle size of 50μm, density of 2.42g/cm 3 and containing 35% chemically combined water, was supplied by Almatis Inc. The free flowing powder was not chemically modified during manufacture, and was used as received. Low molecular weight liquid polybutadienes, containing vinyl, maleic anhydride, epoxy or amine functionality, were supplied by Sartomer Company. Table 1 illustrates the relevant properties of each of the liquid polybutadienes (LPBD) used in this study. The polybutadiene materials can be considered bi-functional, as Table 1 indicates both a primary functionality and pendant vinyl content. Materials containing 70% vinyl are considered cure active, and susceptible to crosslinking in the presence of free radicals. The 28% vinyl polybutadienes, conversely, are considered more stable. Grafting of maleic anhydride occurs in the cis-trans moiety of the polybutadiene backbone, and consequently the higher vinyl content forces the functionality to reside in much closer proximity. In addition to Mn, this is a differentiating characteristic between LPBD-3 from LPBD-4. Introducing the liquid polybutadienes directly into the melt stream is prohibitive due to their physical form. The coupling agents were pre-dispersed onto the ATH in a dry liquid carrier (DLC) in a high shear blender. The result is a 50% active free flowing powder that can easily be side-fed into the extruder. Previous work has demonstrated that incorporation of a di-acrylate functional ionic monomer into polyolefins results in the formation of an ionic crosslinked structure.

Elongation (%) Elongation (%)

Tensile strength (MPa)

Figure 1 ▲ ▲ : Tensile strength results of functional versus non-functional LPBD compared to the base EVA. All products plasticised the EVA, however the MA LPBD to a lesser extent

Figure 2 ▲ ▲ : Elongation results of baseline study demonstrating that the anhydride functional LPBD influenced the EVA the least

Tensile strength (MPa)

The mechanism relies on free radicals generated by heat and shear during compounding. An ionic monomer, grade SR-732, was supplied as a means to increase the mechanical properties in the ethylene regions of the EVA. 2.2 Sample preparation A Brabender TSE-20 was used to melt blend each of the formulations examined in this study. The co-rotating twin-screw extruder has an L/D of 40:1, and a screw design configured to homogenise high loadings of filler. Additives were pre-dispersed onto the ATH and fed downstream at 20D. Experiments were carried out using a flat temperature profile of approximately 50ºC over the Vicat softening temperature, Figure 3 ▲ ▲ : Tensile results for ATH containing systems demonstrating that anhydride functional LPBD least reduces tensile strength

and 80rpm. A single strand extrudate was pulled through a water trough and pelletised. All formulations contained 60% by weight ATH, and 4% by weight of an LPBD. Baseline formulations were run to establish the effect of LPBD on EVA. ASTM tensile specimens were moulded using a Boy Machines XS 11-T micro- injection moulder. A temperature profile analogous to extrusion was employed. Specimens were pulled on a Thwing-Albert tensile tester in accordance with ASTM D-638. Tensile strength at yield and elongation at break data was collected. 3 Results A thorough understanding of the influence the LPBDs have on the EVA was imperative to understanding their influence on the ATH filled systems. Figures 1 and 2 illustrate the effect of a representative sample of LPBDs on the base EVA. Both Figures 1 and 2 demonstrate that the LPBDs have a deleterious influence on the tensile strength at yield, and the elongation at break. The LPBDs were not compatible with EVA, and served to plasticise it. Unfunctionalised LPBDs 1 and 2 had an equal impact on the EVA properties, which suggested that Mw and vinyl content were not influential variables. Figure 4 ▲ ▲ : Elongation results for baseline study in EVAATH system demonstrating an ability to re-establish the elongation using LBPD

Table 1 ▼ ▼ : Properties of liquid polybutadienes used in this investigation, highlighting the functionality type and loading, molecular weight and vinyl content, * internally epoxidized polybutadiene, ** tertiary amine grafted polybutadiene

ID

Mn (g/mol)

Functionality (type/%)

Vinyl (%)

LPBD-1 LPBD-2 LPBD-3 LPBD-4 LPBD-5 LPBD-6 LPBD-7

1400 4500 2500 5500 4700 4500 5000

- -

70 28 70 28 28 28 28

MA/17% MA/17% MA/5%

Epoxy*/5% Amine**/5%

51

EuroWire – July 2010