PARTⅢ MECHANICAL RECYCLING

MODIFIED RECYCLED GLASS FIBER REINFORCED
FLAME RETARDANT PBT WITH IMPROVEDMECHANICAL PROPERTIES BY NANO-PARTICLES
Shui 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: To improve the mechanical properties of recycled glass fiber reinforced flame
retardant PBT(RGFFRPBT), three kinds of nano-particles including silicon dioxide (SiO2),
montmorillonite(MMT) and mica were blended with RGFFRPBT by twin-screw extruder,respectively. The effect of nano-particle contents on physical properties of nanocomposite
was investigated, including the mechanical properties, electrical and frame retardant
properties. The results illuminated that when the content of nano-SiO2 and nano-mica was 1%,
the notched impact strength, tensile strength and flexural strength of nanocomposites weremarkedly improved, once the content of nano-particles ranged from 2% to 5%, the mechanicalproperties decreased, while heat distortion temperature increased. The content of MMT had
not significantly enhanced on the mechanical properties of nanocomposite. The addition ofnano-particle did not significantly affect the electrical and frame retardanttproperties.
1. Introduction
It is known that polybutylene terephthalate (PBT) have excellent comprehensive
properties, such as good dimensional stability, thermal and arc tracking resistance and soon[1-3]. Today, glass fiber reinforced frame retardant PBT is used in various insulating partsfor electrical engineering and electronics, such as electronic relay, communication andautomobile applications[4-7], and the ratio of RGFFRPBT was higher than 35 wt%. The
improvement of recycled glass fiber reinforced flame retardant PBT (RGFFRPBT) is
becoming increasingly important [8]. Nano-particle-filled polymers have been a subject ofactive topic in the past decades due to their unique physical and chemical properties [9-11].
When filled in polymer, nano-particles can insert into the defects of the polymers in thenano-size. The phenomenon of stress concentration in the polymer can be conquered via thecross-linking interaction of polymer molecule chains and nano-particles, as well as the effectof interfacial energy transmission. Many attempts have been made to improve these properties
of PBT by blending it with various fillers [12-14]. It was found that nano-particles have
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The 5th ISFR (October 11-14, 2009, Chengdu, China)
obvious strengthening and toughening effects thus can improve largely the physical propertiesof the composite polymers. With the addition of only a few percent of nanocomposites,polymer nanocomposites exhibit thermal, mechanical, and barrier properties that are greatly
improved over those of the pristine polymers. Numerous methods for the preparation ofpolymer nanocomposites have recently been developed by several groups[15-18]. Nano-silica
was used to modify thermoplastics polybutylene terephthalate (PBT) to improve the thermal
stability, tensile strength, and notched impact strength of PBT. Clays such as MMT, mica, andso on were applied to increase the mechanical properties of nanocomposites [19] [20]. Li etal[12] [21] prepared PBT-clay nanocomposites by the method of melt intercalation withMMT, and investigated the influence factors on the mechanical properties ofnanocomposites[18]. mica is a different kind of clay that has been widely used as areinforcing filler in polymeric matrices because of its excellent mechanical, electrical andthermal properties[22]. When the glass fiber reinforced flame retardant PBT (GFFRPBT) was
mold-injected, the mold-injection process decreased the characteristic viscosity of PBT andthe length of glass fiber,caused the decreases of mechanical properties. Few lectures focusedon the modified the RGFFRPBT with an improved mechanical properties. In this paper, toimprove the mechanical properties of RGFFRPBT, nano-particles including silicon dioxide(SiO2), montmorillonite(MMT) and mica were chosen to blended with RGFFRPBT bytwin-screw extruder, respectively. The effect of nano-particle contents on properties ofnanocomposite was investigated, including the mechanical properties, electrical and frame
retardant properties.
2. Experiment
2.1 Materials
Flame retardant PBT with 30 wt% glass fibers was prepared by the paper[23], the recycled
glass fiber reinforced flame retardant PBT collected by injection molding was processed with
one times mold-injection( by ARBUR 420M, at 275 °C),The commercial organic
montmorillonite (MMT), 10 A, modified with dimethyl, benzyl, hydrogenated tallow
quaternary ammonium (2MBHT) was provided by Southern Clay Co., USA. Nano-silica wasprovided by Hai-Tai, Nanjing, China, with the specific area of 380 m2/g (N2, BET), anaverage diameter of 22 nm. Mica is a platy potassium aluminium silicate, and is supplied withno surface treatment with particle size of 100-150 nm was offered by Zhong Lan Chen Guang
Research Institute of Chemical Industry, Chengdu, China.
2.2 Preparation of nano-particles-filled with GFFRPBT
Nanocomposites were prepared by direct melt compounding SiO2, MMT, mica with
RGFFRPBT was mixed by high-speed stir and then compounded in a twin-screw extruder(L/D=25/1) at 250 °C and 25 rpm, and the nano-particle loading was 0 % (presented byEGFFRPBT), 1 wt% (presented by RGFFRPBT/SiO2-1, RGFFRPBT/MMT-1, RGFFRPBT/- 172 -PARTⅢ MECHANICAL RECYCLING
mica-1, respectively) %, 2 wt% (presented by RGFFRPBT/SiO2-2, RGFFRPBT/MMT-2,RGFFRPBT/mica-2, respectively), 5 wt% (presented by RGFFRPBT/SiO2-5, RGFFRPBT/MMT-5, RGFFRPBT/mica-5, respectively), respectively. The extruded strands were passed
through a water bath and pelletized. The nanocomposites were further dried at 120 °C, for 4 h
before injection molding the test specimens for properties determination.
2.3 Characterization
The mechanical properties of such as Tensile (ASTM D638-03) and flexural ( ASTM
D790-07) properties evaluation were done on a Universal test machine (Reger, RGT-20A). The
notched impact strength (ASTM D 256) was performed using a impact tester (Sans Tested,ZBC1400-2) at room temperature. Glow-wire ignitability test on materials was processed byIEC 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 the material, and the voltage
measured for a 3mm thickness is considered representative of the material performance. Heatdistortion temperature (HDT) of nanocomposite was characterized by the procedure given in
ASTM D-648. All the standard test bar were prepared by mold-injection. The morphologiesof the fractured surfaces of the standard test bar were investigated using a Hitachi S-3700
scanning electron microscope (SEM).
3. Results and Discussion
3.1 Effect of content of nano-particles on the mechanical properties of modified RGFFRPBT
Tab.1 shows the notched impact strength, tensile strength and flexural strength ofnano-particles-filled RGFFRPBT as a function of filling content, with the tensile strength ofthe original EGFFRPBT as control. For the original version EGFFRPBT modified by SiO2and mica, the mechanical properties initially increases until the filling content reaches 1%.
The reason was that nSiO2 and mica have high modulus and tensile strength. After being filledwith RGFFRPBT, the particles present good compatibility with the resin matrix through thepolymer. At the interface of the grafting polymer and the resin matrix, a thick gradient layer
can be formed for the rigid particles to pass their mechanical strength to the PBT resin matrix.
This makes the adhesion even stronger and provides an effective bridge for the organic resin
to pass the stress to the inorganic particles. Thus, the notched impact strength, tensile strengthand flexural strength can be improved. All of the notched impact strength, tensile strength andflexural strength decreases with the contentinstead, and their values are even lower than thatof EGFFRPB Twhen the content is higher than 5 wt%. This decrease in ultimate strength ismainly due to the agglomeration of nano-particles above nano-particles loading [24, 25] andthe uncompatibility of nanocomposite. However, for MMT-filled RGFFRPBT, mechanicalproperties sharp decreases and reaches its minimum when the content is 5 wt%, even lower
than those of original version RGFFRPBT. This indicates that the toughness was poor after
being filled with MMT. Different to SiO2 and mica, the figure of MMT is layered structure,- 173 -The 5th ISFR (October 11-14, 2009, Chengdu, China)
which restricted it to disperse in the matrix of RGFFRPBT, decreased the adhesion ofmolecule chains and a network structure forms [26]. As a result, the mechanical properties ofMMT-filled RGFFRPBT could not be improved due to the debonding around thepolymer-clay interfaces and void formation.
Tab. 1 Effect of content of nano-particles on the mechanicalproperties of modified RGFFRPBTSamples

Notched impact
strength (J/m)

Tensile strength(MPa)

Flexural strength(MPa)

EGFFRPBTRGFFRPBT/SiO2-1
RGFFRPBT/SiO2-2
RGFFRPBT/SiO2-5
RGFFRPBT/MMT-1RGFFRPBT/MMT-2
RGFFRPBT/MMT-5
RGFFRPBT/mica-1
RGFFRPBT/mica-2
RGFFRPBT/mica-5

40.2
52.1
45.3
39.3
33.3
29.7
28.8
49.9
42.5
36.8

62.6
73.1
69
66.3
55.1
45.3
36.3
72.4
68.8
60.4

115.2
138.1
126.2
117.1
110.3
101.3
96.2
129.5
118.4
110.1

3.2 Effect of nano-particles content on the flammability, comparative tracking index and Heatdistortion temperature of modified RGFFRPBTTab. 2 Effect of nano-particles content on the Glow-wire ignitability time,
CTI and HDT of modified RGFFRPBTSamples

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

HDT(°C)EGFFRPBTRGFFRPBT/SiO2-1
RGFFRPBT/SiO2-2
RGFFRPBT/SiO2-5
RGFFRPBT/MMT-1
RGFFRPBT/MMT-2
RGFFRPBT/MMT-5
RGFFRPBT/mica-1
RGFFRPBT/mica-2
RGFFRPBT/mica-5

18.7
19.6
20.5
21.3
17.6
16.3
15.2
20.1
21.3
22.5

225
225
225
200
225
200
200
225
225
200

191
192.5
194.3
196.6
188.6
190
186.9
194.1
194.2
194.4

Tab. 2 exhibited the nano-particles content influenced on the flammability properties,
CTI and HDT. The data demonstrated that with the increased of mica and SiO2 content from 1wt% to 5 wt%, respectively, the electrical and frame retardant properties of modified- 174 -PARTⅢ MECHANICAL RECYCLINGRGFFRPBT show a few degraded, while the HDT of SiO2 modified RGFFRPBT wasimproved from 192.5 °C to 196.6 °C, HDT of maci modified RGFFRPBT was unsignificant
changed and kept as 194 °C. The results illuminated that when the recycled glass fiber
reinforced flame retardant PBT were extruded with nano-SiO2, the nano-particle play as thereinforced material of RGFFRPBT. The reason was that even a small amount of nano-particle
was significant affected on the free volume of PBT, confinement of the intercalated polymer
chains, and would prevent the segmental motion of the polymer chains[27]. With increased ofMMT content from 1 wt% to 5 wt%, the glow-wire ignitability time decreased from 17.3
second to 15.2 second. The reason was that when MMT was filled in polymer, it show higher
thermal stability [28]. Due to MMT-filled RGFFRPBT could not be improved due todebonding around the polymer-clay intefaces and void formation[26], the HDT of modified
RGFFRPBT had not significantly improved, even with the MMTcontent increased to 5 wt%,
its HDT was lower than that of EGFFRPBT and was only 186.9 °C.
3.3 Characterization of SEM

Fig. 1 SEM micrographs of nano-particles modified RGFFRPBT with various contents:(a)RGFFRPBT/SiO2-1, (b)RGFFRPBT/SiO2-2, (c) RGFFRPBT/SiO2-5(d) RGFFRPBT/MMT-1, (e)RGFFRPBT/MMT-2, (f)RGFFRPBT/MMT-5(g)RGFFRPBT/mica-1, (h)RGFFRPBT/mica-2, (i)RGFFRPBT/mica-5
The morphologies of the extruded RGFFRPBT obtained from nano-particls with up to 1
wt%to 5 wt% in the PBT matrix were examined by observing their fracture surfaces with anSEM, and the results are shown in Fig. 1 . These micrographs show that there is an increase in
the roughness and crack of the fracture surfaces due to the addition of particles. Indeed, theapparent roughness and crack of the fracture surfaces varies significantly from one composite
to another: picture (a), (d) and (g)where the micrographs are of composites which all contain- 175 -The 5th ISFR (October 11-14, 2009, Chengdu, China)
1 wt% of nano-particls, RGFFRPBT/SiO2-1 and RGFFRPBT/mica-1 show smoother surface
than that of RGFFRPBT/MMT-1, indicated that the roughness varies significantly depending
upon the type of particl employed. Picture (a), (b) and (c) show the fracture surfaces of thesamples change in appearance as the nano-SiO2 content increased. At low nano-SiO2 contents,
the surface was relatively smooth and featureless, with the rougher areas being associatedwith the nano-SiO2 particles. As the loading increased, the smoother areas become smaller insize and roughness and crack of the fracture surfaces dominated[22]. Picture (e) and (i) for
example, the surface becomes uniformly rough and larger crack between the figure. The SEM
micrographs of nano-particles modified RGFFRPBTcould be explained when thenano-particles content was less than 1%, the mechanical properties of nano-particles modifiedRGFFRPBT improved, while when the nano-particles content was higher than 2%, it
decreased the mechanical properties. Picture (d), (e) and (f) show that most of MMT are
agglomerated at greater size, these agglomerated layers could not from polymer-clay
interfaces[26], as a result, the MMT modified RGFFRPBT show little improved mechanicalproperties.
4. Conclusion
When silicon SiO2, MMT and mica were extruded with RGFFRPBT to modified its
mechanical properties, it was found thatwhen the content of nano-SiO2 and nano-mica was 1%, the notched impact strength,
tensile strength and flexural strength of nanocomposites were markedly improved, once thecontent of nano-particles ranged from 2% to 5%, due to the agglomeration of nano-particles
above nano-particles loading and the uncompatibility of nanocomposite, the mechanicalproperties decreased, however. The content of MMT had not significantly enhanced on themechanical properties of nanocomposite. The addition of nano-particle did not significantly
affect the electrical and frame retardanttproperties. The results illuminated that when
RGFFRPBT was modified by nano-SiO2 and nano-mica in 1 wt% content, it could improvethe mechanical properties and HDT of RGFFRPBT.
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