The Effects of Chain Extender on Viscosity and Mechanical Properties of Poly (Buthylene Terephthalate) Blending with Recycled Poly (Ethylene Terephthalate)-glass Fiber Composite
Lee Tin Sin,
In this study, multi-functional styrene-acrylic oligomers was used as the chain extender in poly butylenes terephthalate/recycled glass-filled poly ethylene terephthalate (PBT/RGF-PET) blends. Normally, usage of recycled plastics is favourable but somehow, during the reprocessing causes loss of properties. Thus, chain extender was added to restore the viscosity and mechanical properties of PBT/PET blends due to the incorporation of recycled poly (ethylene terephthalate) has lowered viscosity and molecular weight. Chain extender at 0.50 and 0.65 wt.% was added into 50/50 PBT/RGF-PET using melt compounding method to compare viscosity and mechanical properties with virgin PBT and RGF-PET, respectively. Addition of chain extender has improved the viscosity of the PBT/RGF-PET which was in relation to the increment of molecular weight. When 0.50 wt.% of chain extender was added to PBT/RGF-PET blend at ratio of 50:50, the flexural modulus increased 9.6% to 3530 MPa compared to the original flexural modulus at 3220 MPa. This showed that a small amount of chain extender was successfully to improve the flexural modulus. The increment of molecular weight as induced by the addition of chain extender improved the impact resistance of the PBT/RGF-PET from 17 to 20.3 kJ m-2 for addition of 0.50 wt.% chain extender.
to cite this article:
A.R. Rahmat, P.S. Lim, Lee Tin Sin, Soo-Tueen Bee and Tiam-Ting Tee, 2012. The Effects of Chain Extender on Viscosity and Mechanical Properties of Poly (Buthylene Terephthalate) Blending with Recycled Poly (Ethylene Terephthalate)-glass Fiber Composite. Journal of Applied Sciences, 12: 296-300.
Received: October 31, 2011;
Accepted: December 24, 2011;
Published: February 22, 2012
Poly Ethylene Terephthalate (PET) is well known of its applications in fabrication
of beverage bottles, packaging containers or engineering materials in combination
with glass fibers (Kusuktham, 2011). It has simple processing
technology and attachable for extrusion moulding, blow moulding, injection moulding
and thermoforming methods. Although, PET is a semi-crystalline, PET possesses
slow crystallization rate which limits its application as injection moulding
resins before the nucleating agent was introduced to promote fast crystallization
rate of PET. On the other hand, Poly Butylene Terephthalate (PBT) has rapid
crystallization rate with fast moulding cycle (Scheirs and
Long, 2003). When PET and PBT are blended together, the blend can be well
moulded at normal mould temperature around 80°C without addition of compabilizing
However, the polycondensation thermoplastics such as PET and PBT tend to undergo
severe degradation when they are processed at high temperature, i.e., hydrolysis
and thermal cleavage regularly happens especially during recycling process (Frounchi,
1999; Omrani et al., 2005). Camacho
and Karlsson (2000) reported that it is very frequent for the recycled plastics
to undergo undesirable change of mechanical, physical and chemical properties
as compared to the original polymers due to excessive heat and shear effects.
For instance, Mark (2004) has reported the initial intrinsic
viscosity (IV) of the virgin PET resin (V-PET) dropped from 0.75-0.85 to 0.62-0.65
dL g-1 resulted from the postconsumer recycled recovery process and
Many study have reported the recycling effects on physical, mechanical, thermal,
or rheology properties of recycled PET (R-PET) by comparing to V-PET as well
as the chemical modification or chain extension to improve the intrinsic viscosity
and molecular weight of V-PET or R-PET (Shah and Gasaway,
2007; Haralabakopoulos et al., 1999; Villalobos
et al., 2006). Type of chain extenders such as hydroxyl chain extender,
diisocyanates, bis-oxazolines, diepoxides, polyepoxides, bis-N-acyllactam and
biscaprolactam have been studied in polycondensates polymers for typical PET
and PBT (Loontjens, 2003). On the other hand, recycled
glass-filled PET (RGF-PET) is seldom reused as compared to post-consumer PET.
This is due to R-PET has low viscosity and molecular weight with possible post-contamination
which might lead to inferior properties (Felix et al.,
2011). Hence, this study was focusing on comparing the flexural and impact
properties as well as the viscosity number of the chain extender effects on
the RGF-PET blending with PBT.
MATERIALS AND METHODS
Materials and preparation of blends: PBT resin, Ultradur® B2550 was supplied by BASF. Recycled glass-filled PET source was supplied by 3T Industrial Sdn. Bhd. Styrene-acrylic multi-functional oligomer, a polyepoxides type of chain extender, Joncryl ADR-4368, was supplied by BASF. PBT resins and recycled glass-filled PET (RGF-PET) were dried in air circulation oven at 120°C for 4 h to reduce moisture content prior dry blending and compounding. Several samples as listed in Table 1 were prepared to determine the effects of chain extender to the PBT/RFG-PET blends. Co-rotating twin screw extruder Berstorff ZE25 UTX (25 mm diameter and L/D 44), was used for melt compounding. The barrel temperatures were varied from 240 to 260°C and the melt temperature was controlled at 260°C. The extrudate was cooled at water bath and cut into pellet form. The pellet samples were dried in air circulation oven at 120°C for 4 h. Injection moulding machine Krauss-Maffei 130-380 CX was used to mould ISO 3167 Type 1A specimens. Barrel temperatures were varied from 240 to 265°C to achieve the melt temperature 260°C. Mould temperature was controlled to 80°C and total cycle time was 40 sec. The specimens were conditioned in environment 23°C and 50% relative humidity for minimum 88 h prior testing.
Determination of viscosity and mechanical properties: Viscosity number
was determined according to ISO 1628-5. Small amount of pellet sample was dissolved
in phenol/1,2-dichlorobenzene (1:1) to a 0.005 g mL-1 concentration
|| Blending formulation
An Ubbelohde viscometer type capillary Ic was used to determine the flow times
of the sample solution and solvent at a water bath temperature of 25°C.
On the other hand, mechanical properties were conducted in controlled laboratory
atmosphere with (23±2)°C and (50±10)% relative humidity. Meanwhile,
the Melt Volumetric Rate (MVR) of the molten blends was determined using Ray-Ran
Melt Flow Indexer according to ASTM D1238-10 at load 2.16 kg and temperature
260°C. Flexural properties were conducted using Zwick/Roell Universal Tester
Machine with 2.5 kN loadcell according to ISO 178, with testing speed of 2 mm
min-1. Unnotched Charpy impact strength was determined using Zwick/Roell
Pendulum Impact Tester with 2 J pendulum according to ISO 179-1, with striking
speed of 2.9 m sec-1.
RESULTS AND DISCUSSION
Viscosity behavior: As shown in Table 2, the viscosity
number of PBT has reduced after blending with RFG-PET. The low RFG-PET viscosity
is because reprocessing has caused chain cleavage and depolymerization. This
was also reported by Jabarin and Lofgren (1984) that
thermal oxidation was the main degradation approach of PET. In this study, it
was observed that the viscosity number of pre-processing RFG-PET has viscosity
number at 62 mL g-1 and dropped to 57 mL g-1 after subjected
to heat and shear effects in the extrusion process. In consequence, the PET-RGF
has lack of entanglement which directly promotes chain sliding lowered the viscosity.
Beside chain scission has caused dropped of macromolecular sizes, there was
possibility breakage of glass fibers during the shear effect in the extrusion
process. Repetitive processing is unfavourable because prolong exposure to extreme
conditions is the main cause of severe degradation.
In contrast, the MVR outcomes showed that the molten viscosity of the PBT/RGF-PET
has reduced at the higher composition of RGF-PET. The higher MVR indicates higher
flow ability thus lower in viscosity. This observation can explain that PET
has higher melting point (255°C) than PBT at 223°C. When measurements
were done at the similar temperature, inherently PET has higher viscosity that
||Viscosity number and MVR of PBT, RGF-PET and blends with the
addition of chain extender
This was well exhibited in the MVR of RGF-PET where it was four-fold lower
than the PBT when tested at 260°C. In fact, this temperature was slightly
above the melting point of PET. This observation was also important to decide
the melt temperature to be used in injection moulding process to enable good
processability by controlling the melt temperature at 260°C to avoid severe
degradation where virgin PBT can withstand temperature up to 275 °C (Samperi
et al., 2004; McNeil and Bounekhel, 1991).
In this study, it was found that viscosity number for sample 50/50-N was 81
mL g-1 before adding chain extender. After adding 0.50 wt% of chain
extender, the sample 50/50-E50 possessed viscosity number at 110 mL g-1
which was 36% higher than the viscosity number without chain extender. However,
there was no viscosity number result for sample 50/50-E65. It was because the
respective sample was not fully dissolved in the phenol/1,2-dichlorobenzene
solvent in the Ubbelohde viscosity test. During the test, polymer gel was observed
in the solution which means that the molecular weight of sample containing 0.65%
chain extender were very high with the expected viscosity number was more than
110 mL g-1. According to Guo and Chan (1999)
who have found that the polymer gel was formed when diepoxides chain extender
was added into PBT. The gel content was 8 and 15%, respectively when 1.4 and
1.6 wt% of chain extender was added. The branching and crosslinking have occurred
when the chain extender amount was high (Guo and Chan 1999;
Villalobos et al., 2006). In order to obtain
gelation free PBT/RGF-PET blend at ratio of 50:50, the chain extender should
be applied at the range 0.50 and 0.65 wt.% to achieve the optimum physical outcomes.
The limited dosage (maximum 0.65 wt.% in this study) of multi-functional styrene-acrylic
oligomers in PBT/RPET-GF blends may be due to the polymer blends has reached
high branching and crosslinking environment which caused the polymer gel to
form extensively. Although, the determination of viscosity number was difficult
for sample 50/50 E65, MVR measurement was another good indication of high viscosity
number of these both samples. It was observed that the MVR has reduced when
the amount of chain extender increased. This indicated that higher chain extender
remained in an increasing trend when the amount is >0.50 wt%. In other words,
the addition of chain extender increased the molecular weight of PBT/R-GF-PET
Flexural properties: Flexural modulus as summarized in Fig.
1 exhibited an increasing trend when the amount of RGF-PET was increased
in the blend system. From flexural strength results in Fig. 2,
it was found that sample 100/0 did not break when the preset 5% maximum deformation
||Flexural modulus of PBT, RGF-PET and blends with the addition
of chain extender
||Flexural strength of PBT, RGF-PET and blends with the addition
of chain extender
The non-break behavior in virgin PBT showed a good ductility. When RGF-PET
was added into PBT/RGF-PET blend system, the flexural strength was lowered indicated
the inferior of the RGF-PET. In contrast, the flexural modulus of chain extended
PBT/RGF-PET showed some increment after chain extender Joncryl ADR-4368 was
added to the blends. When 0.50 wt.% of chain extender was added to sample 50/50-E50,
the flexural modulus increased 9.6% to 3530 MPa, compared to sample 50/50 with
flexural modulus at 3220 MPa. It showed that a small amount of chain extender
was successfully to improve the flexural modulus. A slight increased in flexural
modulus also reported in Zhou and his co-workers study using epoxycyclohexyl
polyhedral oligomeric silsesquioxane (epoxy-POSS) as chain extender in PBT.
Moreover, addition of chain extender has shown improvement of flexural strength
of PBT/RGF-PET blend.
||Unnotched charpy impact strength of PBT, RGF-PET and blends
with the addition of chain extender
When the amount of chain extender increased up to 0.65 wt.%, the PBT/RGF-PET
did not break when the preset 5% maximum deformation has been reached (Fig.
2). It was further expected the chain extender treated PBT/RGF-PET having
equivalent flexibility as virgin PBT. Generally the branching and crosslinking
of polymer chains increase the deformation strength as the result of limited
chain mobility or flexibility. Such observation has been reported by Guo
and Chan (1999) work about the chain extender was the preferable method
to induce higher flexural strength when PBT was processed by reactive extrusion
Impact properties: As shown in Fig. 3, the sample
100/0-N consisted of virgin PBT did not break when subjected to the impact hammer
indicated that PBT has high ductility or toughness. When the amount of RGF-PET
was increased in the blend systems, the impact strength was decline. According
to Chivers and Moore (1994), the toughness of the polymers
is in relation to the molecular weight. The reduction of impact strength for
the blends of PBT/RGF-PET happened at high contain of RGF-PET was mainly attributed
to the affect of inferior characteristic of chain scissioning in recycled PET.
Meanwhile, the impact strength of the blends showed somewhat increment after
chain extender was added. The sample 50/50-E65 exhibited the highest strength
due to higher molecular weight built up by chain extender has improved the impact
resistance. The decrement in percentage of crystallinity and increment in toughness
explained the improvement of impact resistance whereby the cracks can propagate
more readily in the crystallite.
In conclusion, the blending of RGF-PET has caused inferior effects to PBT.
However, addition of chain styrene-acrylic polyepoxide type of chain extender
helps to improve the blending properties. Addition of chain extender has improved
the viscosity of the PBT/RGF-PBT which was in relation to the increment of molecular
weight. When PBT/RGF-PET blend at ratio of 50:50, the chain extender should
be applied at the range 0.50 and 0.65 wt.% to achieve the optimum physical properties.
When 0.50 wt.% of chain extender was added to PBT/RGF-PET blend at ratio of
50:50, the flexural modulus increased 9.6% to 3530 MPa compared to the original
flexural modulus at 3220 MPa. This shows that a small amount of chain extender
has successfully improved the flexural modulus. Meanwhile, 0.65 wt.% of chain
extender added PBT/RGF-PET has exhibited equal flexibility as virgin PBT. The
increment of molecular weight as induced by the addition of chain extender improved
the impact resistance of the PBT/RGF-PET from 17 to 20.3 kJ m-2 for
addition of 0.50 wt.% chain extender.
The authors would like to thank BASF Malaysia for supplying materials and generosity for providing equipments for compounding and testing in this research.
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