EoW July 2010

EuroWire – 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

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,

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.

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,

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

illustrate

the effect of a representative sample of

LPBDs on the base EVA.

Both

Figures 1

and

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.

(g/mol)

Functionality

(type/%)

Vinyl

(%)

LPBD-1

1400

LPBD-2

4500

LPBD-3

2500

MA/17%

LPBD-4

5500

MA/17%

LPBD-5

4700

MA/5%

LPBD-6

4500

Epoxy*/5%

LPBD-7

5000

Amine**/5%

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

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)

Figure 3

▲

Tensile results for ATH containing systems

demonstrating that anhydride functional LPBD least

reduces tensile strength

Figure 4

▲

Elongation results for baseline study

in EVAATH system demonstrating an ability to

re-establish the elongation using LBPD

Tensile strength (MPa)

Elongation (%)