The 5th ISFR (October 11-14, 2009, Chengdu, China)

INVESTIGATION ON PROPERTIES OF RECYCLED GLASSFIBER REINFORCED FLAME RETARDANT PBTShui D. Zhang*,1 Qi Ban,2 Han X.Huang1,Yuan Z. Li2
1

Lab for Micro Molding and Polymer Rheology, College of Mechanical and Automotive
Engineering, South China University of Technology, Guangzhou 510640, China.
2
Xiamen Hongfa Electroacoustic Co.,Ltd, Jimei North Ind. Dist., Xiamen 361021, China
E-mail: starch@scut.edu.cn
Abstract: Due to its excellent comprehensive properties, glass fiber reinforced flame
retardant PBT was widely applied in electrical accessory. In this paper, the glass fiber
reinforced flame retardant PBT with five times mold-injection effect on its carboxyl content,
characteristic viscosity of PBT and microscopic appearance were studied. The properties ofrecycled glass fiber reinforced flame retardant PBT including mechanical, electrical andframe retardant properties were well investigated. The results demonstrated that when therecycled glass fiber reinforced flame retardant PBT were multiple processed, its carboxyl
content increased while the characteristic viscosity of PBT and the length of glass fiberdecreased. After five times mold-injection, all its physical properties decreased, especially thenotched impact strength, tensile strength, flexural strength drastically decreased from 75 J/m
to 33 J/m, 115.6 MPa to 54.9 MPa, 161.1 MPa to 95.2 MPa, respectively.
Keywords: glass fiber reinforced flame retardant PBT; mold-injection; physical properties;
recycle1. Introduction
Polyesters, especially poly(1,4-butylene terephthalate) (PBT), is one of the mostimportant engineering polymers with a wide range of applications because it possesses good
dimensional stability, low moisture absorption, high heat distortion temperature, goodchemical resistance, excellent electrical properties, creep resistance and high strength andrigidity. Due to its numerous virtues, PBT is one of the most frequently used engineering
thermoplastic materials. Halogen-containing additives were found to be very efficient fire
retardants in PBT, with the addition of brominated compounds, a great number of systems areavailable to make PBT flame retardant. Glass-fiber reinforced poly(butylene terephthalate)(PBT/GF), flame retarded with brominated styrene, brominated phenylethane, brominatedepoxy resin and brominated polycarbonate, are the rare halogen materials to achieve a V-0
classification in UL 94 test. PBT fiber-reinforced composite materials have been adapted to- 178 -PARTⅢ MECHANICAL RECYCLING
improve the mechanical properties of neat plastic materials. Today, glass fiber reinforced PBT
is used in various insulating parts for electrical engineering and electronics, such as electronic
relay, communication and automobile applications. Therefore, the investigation of theprocessing of fiber-reinforced PBT is becoming increasingly important [1-4]. When the glass
fiber reinforced flame retardant PBT (GFFRPBT) was mold-injected by five times, how themold-injection process effect on its carboxyl content, characteristic viscosity of PBT andmicroscopic appearance were unclear. The properties of recycled glass fiber reinforced flame
retardant PBT (RGFFRPBT) including, mechanical, electrical and frame retardant properties
were still unknown. In this paper, the RGFFRPBT with five times mold-injection effect on its
carboxyl content, characteristic viscosity of PBT and microscopic appearance were studied.
The properties of RGFFRPBT including mechanical, electrical and frame retardant properties
were well investigated to demonstrate the properties of RGFFRPBT affected bymold-injection times.
2. Experiment
2.1 Materials
PBT (the virgin PBT samples, having intrinsic viscosity of 1.25 dl/g, were kindly
supplied by Du Pont de Nemours (Luxembourg)) was reinforced with 30 wt% glass fibers(Vetrotex EC 10um) (PBT/GF). Portions of 14 wt% flame retardants were added, consistingof brominated phenylethane (USA Chemtura FM2100) and Sb2O3 (China Yueyang ChemistFactory), the content of each flame retardant (around 10.3 wt% for brominated phenylethaneand 3.7 wt% for Sb2O3) corresponds to the content in the combination.
2.2 Preparation of flame retardant PBT with 30 wt% glass fibers (GFFRPBT)
Before compounding, the PBT and brominated phenylethane were dried at 120 °C for 5
h in an air-circulating oven, then PBT, brominated phenylethane and glass fibers werecompounded in a twin-screw extruder(L/D=25/1) by two process at the temperatures andscrew speed was 250 °C, 25 rpm, respectively. The extruded strands were passed through awater bath and pelletized. The blends were further dried at 120 °C, for 4 h before injection
molding the test specimens for properties determination, all bars were injection molded(Germany, ARBUR 420M)at 275 °C , and the mold temperature was kept at 50 °C. The
recycled glass fiber reinforced flame retardant PBT collected by injection molding wasprocessed with five times.
2.3 Characterization
The glass fiber reinforced flame retardant PBT recycled (RGFFRPBT) from different
times mold-injection were crashed by high-speed knapper and samples with total 0.2 g withthe 56 wt% PBT resin was maintained in 25 ml mixture of phenol/1,1,2,2-tetrachloroethane(50/50, w/w) at 120°C for 24 h to achieve a complete solution. The solution then cooled to- 179 -The 5th ISFR (October 11-14, 2009, Chengdu, China)
room temperature and filtered through a disposable membrane filter made from Teflon, thenthe solution was diluted to 100.0 ml at 20 °C. Carboxyl end-group content (CC) of the PBT
was determined according to Pohl’s method [5] by titrating a solution of the resin in benzyl
alcohol/chloroform with standard NaOH in benzyl alcohol in the presence of phenol red asindicator. Intrinsic viscosity measurements were performed using an Ubbelohde viscometer at30 °C in a mixture of phenol/1,1,2,2-tetrachloroethane (50/50, w/w). The burnised surfaces ofthe mold-injection specimen were studied using optical microscope (Japan, OLYMPUS GX51)
and the length of GF were averaged. The mechanical properties of such as tensile (ASTMD638-03) and flexural ( (ASTM D790-07) properties evaluation were done on a Universal testmachine (Reger, RGT-20A). The notched impact strength (ASTM D 256) was performed using
a impact tester (Sans Tested, ZBC1400-2) at room temperature. The flammability of samples
was studied by UL 94 tests according to IEC 60695-11-10 [6].Glow-wire ignitability test on
materials was processed by IEC 60695-2-1/3(1994-03) and the test temperature was 750 °C.
To measure the tracking, 50 drops of 0.1% ammonium chloride solution are dropped on thematerial, and the voltage measured for a 3mm thickness is considered representative of thematerial performance.
1.Results and Discussion
3.1 Effect of mold-injection times on carboxyl content, characteristic viscosity and length ofglass fiber of RGFFRPBTTab. 1 Effect of mold-injection times on carboxyl content,
characteristic viscosity and length of glass fiber of RGFFRPBT
samples

Carboxyl content(mg/kg)Intrinsic viscosity

Average length ofGF (um)

GFFRPBTRGFFRPBT-1st
RGFFRPBT-2ndRGFFRPBT-3rd
RGFFRPBT-4th
RGFFRPBT-5th

72
135
203
244
263
294

0.95
0.68
0.56
0.52
0.46
0.4

895
767
616
590
480
430

Tab. 1 was the carboxyl content, characteristic viscosity and length of glass fiber of
RGFFRPBT changed by the mold-injection times. It could see that with the increase ofmold-injection times, the carboxyl content of RGFFRPBT increased from 72 mg/kg to 294
mg/kg, while the characteristic viscosity and length of glass fiber of RGFFRPBT decreasedwith the mold-injection ranged from one times to five times, due to the thermal degradation ofthe polyesters that takes place during heating [7-9]. These changes indicated that during thethermal-process with high pressure, the shear by mold-injection could snip both the molecular- 180 -PARTⅢ MECHANICAL RECYCLING
chain and GF, and the degree of damage increased with the mold-injection times. As a result,both the characteristic viscosity and length of glass fiber of RGFFRPBT decreased to rather
low value: the characteristic viscosity of samples with three times (presented byRGFFRPBT-3rd) and four times (presented by RGFFRPBT-4th) mold-injection was 0.52,0.46, respectively.
3.2 Effect of mold-injection times on mechanical properties of RGFFRPBTTab. 2 Effect of mold-injection times on mechanical properties of RGFFRPBTsamples

Notched impact
strength (J/m)

Tensile strength(MPa)

Flexural strength(MPa)

GFFRPBT75115.6

161.9

RGFFRPBT-1st67

109.3

143.4

RGFFRPBT-2nd54

96.1

128

RGFFRPBT-3rd

42

85.9

115.1

RGFFRPBT-4th3663.7

105.2

RGFFRPBT-5th33

54.9

95.2

The notched impact strength, tensile strength and flexural strength of RGFFRPBT wereshown in Tab.2. With increasing in the mold-injection times, the notched impact strength,
tensile strength and flexural strength of samples decreased. The first time recycled GFFRPBT(presented by RGFFRPBT-1st) have an acceptable properties though the mechanicalproperties have a few decrease. There was almost sudden decrease after twice mold-injection(presented by RGFFRPBT-2nd), and when the mold-injection was increased to five times(presented by RGFFRPBT-5th), the mechanical properties of sample show drasticallydecreased to 33 J/m (44% of original value), 54.9 MPa (47.5% of original value), 105.2 MPa(58% of original value), respectively. The RGFFRPBT exhibited brittleness, frommicrostructural point of view, there are several possible reasons for this decrease: lowmolecular weight, high degree of crystallinity and large spherulites can substantially reducethe ductility of polymeric material[10].According the Tab.1, it could be explained that thethermal degradation of PBT molecular chain and the length of glass fiber, caused themechanical properties of RGFFRPBT decreased with the increase of mold-injection times.

- 181 -The 5th ISFR (October 11-14, 2009, Chengdu, China)
3.3 Effect of mold-injection times on flammability and comparative tracking index (CTI) ofRGFFRPBTTab. 3 Effect of mold-injection times on flammability and CTI of RGFFRPBTsamples

UL94 classification

Glow-wire
ignitability time (s)CTI(V)GFFRPBT

V-0

8.4

225

RGFFRPBT-1st

V-0

15225

RGFFRPBT-2nd

V-0

18.7

225

RGFFRPBT-3rd

V-0

18.9

225

RGFFRPBT-4th

V-0

17.1

225

RGFFRPBT-5th

V-0

15.3

225

When GFFRPBT is used in various insulating parts for electrical engineering andelectronics, both the glow wire ignitability time and CTI should be evaluated. Tab. 3 was theflammability and CTI data of samples with different mold-injection times, it could be seenthat all the samples could obtain V-0 classification and CTI with 225 V show excellent flame
retardant properties [11]. The results illuminated that when the recycled glass fiber reinforced
flame retardant PBT were multiple processed, it had not influenced the flammability and CTI
properties significantly. The reason maybe that microtacticity of surface [12] and brominatedphenylethane had no changed by the mold-injection. The reduction in flammability of PBT isa major concern, especially in the domains of transportation, construction, civil and electricalengineering, where fire protection is required[13].The glow-wire ignitability time waschanged by mold-injection times, GFFRPBT show the shortest ignitability time about 8.4
second, while the RGFFRPBT-1st burns 15second, and the extinction time increased with theincrease of mold-injection times.With the degradation of PBT molecular chain and the lengthof glass fiber, the molecular force and thermal stability of PBT decreased[14]. When thesample was heated at 750 °C glow wire, it prolongs the ignitability time. Though that, it still
could be illuminated that the RGFFRPBT showed good flammability and CTI properties andit was suitable to use in the electrical accessory[14].
4. Conclusion
When the glass fiber reinforced flame retardant PBT were five times mold-injection, its
carboxyl content increased while the characteristic viscosity of PBT and the length of glass- 182 -PARTⅢ MECHANICAL RECYCLING
fiber decreased. After five times mold-injection, all its mechanical properties decreased,
especially the notched impact strength and tensile strength drastically decreased, while theflammability and CTI properties not exhibited significantly to change. The results
demonstrated that the RGFFRPBT-1st had an acceptance physical properties when it wasused in the field of electrical accessory, such as relay. Due to the lower mechanical properties,
when the mold-injection times was higher than two, RGFFRPBT was unsuitable to beadopted as engineering polymer solely.
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