5-7 OCTOBER

ISFR

2011

163

TOLEDO (SPAIN)COMPATIBILIZATION OF POSTCONSUMER PET/HDPE BLENDS.
R. Navarro1, F. Parres1, J.E. Crespo1, S. Sánchez-Caballero1 and M.A. Sellés1
1 Department of Mechanical and Materials Engineering, Universitat Politècnica de Valencia, Plz Ferrandiz y Carbonell, s/n;

03801; Alcoy – Alicante (Spain)
e-mail: raunavi@dimm.upv.esAbstract
Presently the large amount of disposable bottles makes it imperative to search for recycling or reuse methods of thesematerials, because they are not biodegradable. The mechanical properties of postconsumer polyethylene terephthalate(PET) and high density polyethylene (HDPE) blends at different composition with and without compatibilizer were studied. Abinary blend (PET-HDPE 70/30% wt) was prepared on a twin-screw extruder at 200-280 ºC. Later ternary blends wereprepared using as compatibilizer styrene-ethylene-butylene-styrene (SEBS) in different proportions from 0% to 30% (wt%)..
The different properties were then analyzed using tensile strength and impact tests. The presence of HDPE in the binary
blens showed an important decrease in mechanical properties. The addition of SEBS to the binary system PET / HDPE
allowed us to recover some mechanical properties, as well as improving the processability of the blends.

Keywords: PET,HDPE, blend, compatibilization

1. Introduction

Characterization

The recycling of plastic materials is a topic of particularinterest in today's society. Plastics consumption has
been a huge increase in recent years, especially since
the 80's. Parallel to this increase in consumption, havebeen generating large amounts of waste.
Among the polymeric materials have attracted moreinterest in the recycling industry is the polyethylene
terephthalate. This is reflected in the evolution of theconsumption figures of recent times [1].
There is an important market in the supply of waste fromPET bottles produced by injection-blowing process.
Recover these waste by mechanical recycling is one of
the most interesting lines of research at present [2].
Generally, the PET waste show contamination in theform of Polyethylene, which comes from the bottle caps.
The incompatibility between the two materials results in asignificant deterioration of mechanical properties [3].
The objective of this study is to characterize PET– HDPE
blends and then to use SEBS as a compatibilizer torecover some of the mechanical properties.

The preparation of the mixtures was carried out using adouble screw extruder to ensure correct dispersion of thecomponents in the blend. A co-rotation extruder Collin ZK
25 (Collin extrusions Ltd, Warwickshire, UK) with 25 mm
diameter screw and a length – diameter ratio of 24 wasused.
Test samples were obtained in a injection machine
Mateu & Sole brand Meteor model 270/75.

3. Results and Discussion
PET-HDPE System
After a study of the preforms and caps on the market forthe manufacture of packaging, it was decided to use as amaximum of 30% HDPE by weight.
Impact and tensile tests have been made to observe theevolution of the mechanical properties of the system as
we add higher proportions of HDPE to PET.
Table 1. Mechanical properties of PET-HDPE blends.

2. Experimental
Materials
To study this type of system has been used a virgin PET
manufactured by SABIC (BC-112) specifically for themanufacture of containers by injection blow molding
process. The second system component is a high density
polyethylene manufactured by BP (Rigidex® HD5211EA)
specific for injection caps. As a compatibilizer, SEBS has
been employed manufactured by API (Megol® SV,
Applicazioni Plastiche Industriali, Italy).

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PETHDPE
5% HDPE
10% HDPE
20% HDPE
30% HDPE

TensileStrength,
MPa
58.51
18.11
53.54
47.94
39.78
24.71

Elongation
at break,%146.4225.10100.94
31.72
3.40
2.76

ImpactStrength,kJ m-2
3.94
5.06
2.44
2.25
1.19
1.00

In this case, two phases appear in the blends, causingchanges in mechanical properties, which depend largely

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6th International Symposium on Feedstock Recycling of Polymeric Materials

on the cohesion that have both phases together, as wellas the weight ratio that exists between both polymers.
Studying the evolution of the values of Tensile Strength,
we saw that with the addition of HDPE, a decrease ofvalues occurs until the value of 24.71 MPa for the blend
with 30% of HDPE.
In the case of Elongation at break, adding 5% of HDPE,
the values obtained are very similar to virgin PET,occurring a significant decrease in the values for higher
charge ratios, reaching nearly to zero deformation for theblends of 20 and 30% of HDPE.
Finally, after analyzing the influence of the HDPE in theshock absorption capacity of the mixtures it wasobserved as the Impact Strength values obtained
descend gradually as the proportion of HDPE isincreased.
The general mechanical behavior observed in blends
shows the typical behavior of systems formed byincompatible materials.
PET – HDPE – SEBS System
For this study the ternary blend of PET with 30% of
HDPE is used, since it is the worst case can be foundduring the recycling of PET.
The component added to the system is a SEBS which is
chemically compatible with much of the polar polymers
including PET. The maximum proportion added to thebinary system is 30% as the maximum percentage ofminor component of the blend.
As in the previous section, Impact and tensile tests havebeen made to observe the evolution of the mechanicalproperties of the ternary system as different percentagesof SEBS are added.

4. Conclusions
The results obtained in this work show the incompatibility
between the PET and HDPE, resulting in widespreadloss in mechanical properties of the blends, especially in
ductile mechanical properties.
The addition of SEBS allowed us a widespread recovery
of mechanical properties compared to the initialmaterials. In particular, have largely recovered the valuesof tensile strength and impact energy in the blends withhigh content of SEBS.

References[1] N. Torres, J. J. Robin and B. Boutevin. Study ofthermal and mechanical properties of virgin and recycledpoly(ethylene terephthalate) before and after injection
molding, European Polymer Journal, (2000) , 36,2075 .
[2] F. Awaja and D. Pavel. Recycling of PET, EuropeanPolymer Journal, (2005), 41,1453 .
[3] S. Hamzehlou and A. A. Katbab. Bottle-to-bottle
recycling of PET via nanostructure formation by meltintercalation in twin screw compounder: Improved
thermal, barrier, and microbiological properties, Journal
Of Applied Polymer Science, (2007), 106,1375 .

Acknowledgements
To the VIDI of the Universitat Politecnica de Valencia forthe help granted to the project: “Use of recycled
polyethylene terephthalate (PET-R) in the toy industry”,
Ref: 003-306 within the program of First Projects ofResearch (PAID 06-10).

Table 2. Mechanical properties of Blends in function ofSEBS content.

0% SEBS
2.5% SEBS
5% SEBS
10% SEBS
20% SEBS
30% SEBS

TensileStrength,
MPa
24.71
30.95
32.87
34.60
37.98
44.52

Elongation
at break,
%
2.76
3.41
4.00
4.53
5.25
6.16

ImpactStrength,kJ m-2
1.00
1.19
1.31
1.75
2.18
2.69

Studying the evolution of the values of tensile strength,
we found that with the addition of SEBS recover theoriginal values of PET for the blend reached 30% of
SEBS a value of 42.52 MPa.
In the case of elongation at break, we found that thevalues achieved without very significant, are clearlyhigher than the initial blend.
Finally, after studying the influence of SEBS on the shock
absorption capacity of the mixtures, we observed that theimpact strength values obtained are clearly higher than
the initial blend, reaching for the mixture of 30% ofSEBS, values very similar to those of PET.

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