Rheological and mechanical properties of recycled poly(ethylene terephtalate)/high density polyethylene blends

Abstract

Triphenylphosphite (TPP) has been used as a chain extender to regenerate polyethylene terephtalate (PET) and high density polyethylene (HDPE) wastes and to improve the properties of PET/HDPE system based on recycled materials. TPP incorporation in PET and HDPE showed a noticeable increase of the torque as a function of the mixing time and proved that the degradation reactions are considerably decreased. In the case of PET/ HDPE blends, the increase of the torque was strongly dependent on the composition of the homopolymers and on the time of mixing. TPP incorporation contributed to significant variations of the rheological and mechanical properties of the regenerated PET and HDPE and their blends.

Full text

MATEC Web of Conferences 5, 04026 (2013)
DOI: 10.1051/matecconf/20130504026
c
Owned by the authors, published by EDP Sciences, 2013
Rheological and mechanical properties of recycled poly(ethylene
terephtalate)/high density polyethylene blends
M. Guessouma, N. Medjdoub, S. Nekkaa and N. Haddaoui
Laboratoire de Physico-Chimie des Hauts Polym´
eres (LPCHP), D´
epartement de G´
enie des Proc´
ed´
es,
Facult´
e de Technologie, Universit´
e Ferhat Abbas, 19000 S´
etif, Algeria
Abstract.Triphenylphosphite (TPP) has been used as a chain extender to regenerate polyethylene terephtalate (PET) and high
density polyethylene (HDPE) wastes and to improve the properties of PET/HDPE system based on recycled materials. TPP
incorporation in PET and HDPE showed a noticeable increase of the torque as a function of the mixing time and proved that
the degradation reactions are considerably decreased. In the case of PET/ HDPE blends, the increase of the torque was strongly
dependent on the composition of the homopolymers and on the time of mixing. TPP incorporation contributed to significant
variations of the rheological and mechanical properties of the regenerated PET and HDPE and their blends.
1. INTRODUCTION
Nowadays, recycling is the most adapted solution to
overcome the inexhaustible amounts of plastic packages
threw every day after being used only once. Also,
face to the increased awareness of the environmental
protection and the larger consumption of plastic packages,
post-consumed plastics recycling is actually a must
alternative that is adopted and encouraged by all
the governments. Poly(ethylene terephtalate) (PET) and
polyethylene (PE) are widely used as packaging materials
such as containers, bottles and films. Their annual rates of
growth of production and consumption steadily increase.
Their recycling can reduce the resources needed for
manufacturing, conserve energy and decrease the impact
of their wastes on the environment [1,2].
Compared to the other post-consumed plastics, PET
recycling is a complicated process because it undergoes
simultaneously several degradation reactions during
processing. Indeed, melt reprocessing is difficult and
engenders generally a series of degradation mechanisms
especially hydrolytic and thermal reactions which cause
serious deterioration of PET performances. Thus, blending
with recycled PE can yield better properties since it may
reduce considerably the susceptibility to hydrolysis.
To reinforce PET/PE blends, chain extenders like
phosphites can also be incorporated to overcome the
decrease of viscosity noticed during recycling. Phosphites
react with hydroxyl and carboxyl end groups of PET to
diminish the possibility of their reaction via hydrolysis.
They can also reduce the hydroperoxides to alcohol in
polyolefins [3–6] according to the following reaction:
ROOH +P(OAr)3→ROH +O=P(OAr)3.
The aim of this work is to characterize the rheological
and mechanical properties of PET/PE blends based on
recycled materials as a function of the composition of the
blend and the concentration of triphenylphophites (TPP)
incorporated during melt mixing.
ae-mail: guessoum melia@yahoo.fr
2. EXPERIMENTAL
Recycled HDPE (R-HDPE) was prepared by extruding
HDPE Marlex HHM 5502 BN of Qatar Chemical
Company (Q-Chem) in a Controlab single screw extruder
for two cycles. Scraps of recycled PET (R-PET) were
obtained after grinding PET water bottles. Recycled PET
was melt mixed in an internal mixer alone and with HDPE
without TPP and in the presence of 1% of TPP at 30 rpm
and at a temperature of 270 ◦C for a mixing time of 15 min.
R-PET/R-HDPE ratios were 30/70, 50/50 and 70/30.
R-PET/R-HDPE (0/1OO) was mixed at 190 ◦C and at the
same conditions as the previous formulations.
During mixing, the torque was recorded as a function
of the mixing time. After granulating, the melt flow index
(MFI) of the blends was measured on a Melt-Indexer using
a load of 1.2 Kg. Films were realized to perform Fourier
transform infrared spectra (FTIR) with a Perkin Elmer
1000 spectrophotometer. Izod impact test was realized
on a Ceast apparatus on unnotched samples prepared by
compression molding according to the standard ISO 180.
Tension tests were performed on dumbbell compression
molded samples using a Zwick Roell apparatus and at a
tension rate of 10 mm/min.
3. RESULTS AND DISCUSSIONS
3.1. Infrared analysis
Infrared spectra of R-PET, R-HDPE and (50/50)
(R-PET/R-HDPE) melt blended without TPP and with
1% of TPP gave no evidence of the occurrence of
reactions between R-PET and TPP and R-HDPE and TPP
(Figure 1). The phosphorous compounds that may be
formed after the reaction of R-PET with TPP appear in the
region where the R-PET spectrum is rich in bands, which
do not allow the observation of new characteristic bands.
3.2. Torque and MFI variations study
The melt mixing of R-PET, R-HDPE and R-PET/R-HDPE
without TPP showed a sharp decrease of the torque as a
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MATEC Web of Conferences
Figure 1. FTIR spectra of R-PET, R-HDPE and (50/50)
(R-PET/R-HDPE) melt blended with and without TPP.
Figure 2. Torque variations versus time for: a/R HDPE,
b/ R-PET.
function of mixing time which means that the degradation
processes are very favored (Figures 2–3).
The reduction of the intrinsic viscosity or the molar
mass is especially pointed out for R-PET which undergoes
hydrolytic and thermal degradation at a higher extent
than HDPE which torque decrease is lower. This result
is supported by the MFI variations (Figure 4) which
prove that the higher the content of R-PET, the higher
is the MFI of the blends. When TPP is introduced
during mixing, a noticeable increase of the torque is
displayed for all the formulations. This result proves
that the degradation reactions responsible of the viscosity
reduction are considerably avoided.
It is also noticed that the torque increase for R-PET
and for the formulations with a high concentration of
Figure 3. Variations of the torque after 15 minutes versus the
composition and the concentration of TPP.
Figure 4. MFI variations as a function of R-PET concentration in
(R-PET/R-HDPE) blends.
R-PET is much more important than that showed by HDPE
and the formulations containing less R-PET. This result is
essentially due to the fact that TPP acts as an antioxidant
for HDPE but as a chain extender for PET. So, more there
is R-PET in the blend, the higher is the torque (Figure 3).
The increase of the torque is also evidenced by the decrease
of the MFI of the regenerated homopolymers and blends
(Figure 4).
3.3. Mechanical properties
The Melt mixing of R-PET, R-HDPE and their blends
without TPP produced materials with a low impact
strength due the reduction of the viscosity, and the
incompatibility of the blend (Figure 5).
The same trend is observed when studying the strain at
break variations versus the blend composition (Figure 6).
This brittleness is still observed when 1% of TPP was
added and the degradation processes diminished, because
these behaviors are practically governed by the situation at
the interface which weakness produce materials with poor
performances.
The stress at break and Young modulus values depend
strongly on R-PET concentration. After blending in
presence of TPP, the increase of the viscosity increases the
stress at break for the formulations with higher rates of
R-PET but do not affect the values of the modulus of the
materials.
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REMCES XII
Figure 5. Impact strength variations as a function of R-PET rate
and TPP concentration.
Figure 6. Variations of a/ Strain and b/ stress at break as a
function of R-PET rate and TPP concentration.
4. CONCLUSIONS
The effectiveness of triphenylphosphite in upgrading
R-PET, R-HDPE and their blends properties has been
Figure 7. Young’s modulus variations versus R-PET and TPP
concentrations.
revealed by the torque and the MFI increase as a function
of the composition. An improvement of the impact
strength was also pointed out after adding TPP which
permitted to limit the degradation reactions and provide
a safe processing of these formulations based on recycled
materials.
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