Effect of Environmental Temperature on Ultraviolet Irradiated PP and its Composite
M IN Q IAO ,1S HI -S HAN W U 1,*AND J IAN S HEN 1,2
1School of Chemistry and Chemical Engineering
Nanjing University,Nanjing 210093,P.R.China
2College of Chemistry and Environment Science
Nanjing Normal University,Nanjing 210097,P.R.China
Q IAN -P ING R AN
Jiangsu Institute of Building Science Co.Ltd
Nanjing 210008,P.R.China
ABSTRACT:Some oxygen-containing groups such as C–O and C ?O were introduced onto the molecular chains of polypropylene (PP)through ultraviolet irradiation at different environmental temperatures in air.The concentration of the oxygen-containing groups was increased with the increasing environmental temperature after the same ultraviolet irradiation time.After irradiation at different environmental temperatures,there was no gel formed in PP.The crystal shape of irradiated PP kept unchanged,which was still monoclinic crystal.After the same ultraviolet irradiation time,the melt temperature of the irradiated PP decreased and its crystallinity was increased with the increasing environmental https://www.doczj.com/doc/552784209.html,pared with those of PP,the melt flow rate and hydrophilicity of the irradiated PP was improved,and their variation ranges was expanded with the increasing environmental temperature.The mechanical properties of PP/CaCO 3composite compatibilized by irradiated PP at different environmental temperatures were enhanced compared with those of PP/CaCO 3composite.Besides,the compatibiliza-tion of PP (irradiated at high environmental temperature for short time)was equivalent with that of PP (irradiated at low environmental temperature for long time).
KEY WORDS:polypropylene,composite,ultraviolet irradiation,compatibilization.Journal of T HERMOPLASTIC C OMPOSITE M ATERIALS,Vol.23—January 2010
137
0892-7057/10/010137–12$10.00/0DOI:10.1177/0892705708096573?SAGE Publications 2009Los Angeles,London,New Delhi and Singapore
*Author to whom correspondence should be addressed.E-mail:shishanwu@https://www.doczj.com/doc/552784209.html, Figure 3appears in color online https://www.doczj.com/doc/552784209.html,
138M.Q IAO ET AL.
INTRODUCTION
P OLYOLEFINS ARE A class of hydrophobic and inert polymers,so the compatibility between polyolefins and polar materials(for example, inorganic fillers)is poor.Therefore,the mechanical properties of their blends are often poorer than those of the parent polymers.The most common way to improve compatibilization between them is to introduce a third component as a compatibilizer,such as polymer attached with some functional groups,which can promote interfacial interaction between the matrix and the dispersed phase.In general,the active functional groups can be introduced onto the molecular chains of polymer by graft copolymeriza-tion with monomers containing desired functional groups.But this approach has some disadvantages,such as complex processing and chemical pollution.Furthermore,the residue of graft monomers and other auxiliaries may bring about negative effect on the thermal,electrical,and mechanical properties of the blends.Recently,Lei et al.[1–3]adopted ultraviolet irradiation to functionalize polyolefin[polyethylene(PE)and polypropylene (PP)]at room temperature in air without adding any monomers or auxiliaries.In this approach,some oxygen-containing groups were success-fully introduced onto the molecular chains of PE and PP,the compatibility between polyolefin and CaCO3or sericite-tridymite-cristobalite was improved,and the mechanical properties of the polyolefin composite were increased.However,the functionalization of polyolefin by ultraviolet irradiation at room temperature in air had the disadvantages of long time and low efficiency.
In this paper,we discussed the effect of environmental temperature on the structure and properties of ultraviolet irradiated PP,and the compatibilization of the irradiated PP in PP/CaCO3composite was also investigated.
EXPERIMENTAL
Materials
PP powder(grade045)with a melt flow index of5.2g/10min and a density of0.90g/cm3was manufactured by Nanjing Plastics Factory(China). PP granule(grade F401)with a melt flow index of1.8g/10min and a density of0.91g/cm3was manufactured by Yangzi Petrochemical Stock Co.Ltd (China).CaCO3with an average particle size of1.2m m,a specific surface area of7.63m2/g,and a density of2.70g/cm3was manufactured by Lanyang Chemical Co.(China).
Ultraviolet Irradiation of PP Powder
The ultraviolet irradiation of PP powder was performed at light intensity of114W/m2in air by an ultraviolet lamp manufactured by Chengdu Lamp Factory(China)with wavelength in the range of340–370nm.The ultraviolet irradiated PP powder was denoted as uvPP and the ultraviolet irradiated PP for40min was denoted as uv40PP.
Preparation of Composites
The PP(F401)/CaCO3and PP(F401)/uvPP/CaCO3composite was prepared with a twin roller(blending temperature:1708C,blending time: 10min),respectively.The composite was molded to plates with a thickness of1and4mm,respectively.The plates were then cut into the required specimens according to the test standards.
Measurement and Characterization
FTIR analysis was carried out on a VECTOR22spectrometer(Germany). The sample was scanned from4000to400cmà1with a resolution of4cmà1. XPS analysis was performed using an ESCALAB MK-II spectrometer (UK)with AlK a source(1486.6eV).The C1S peak was fitly resolved according to Gauss distribution.
Gel content measurement was determined by means of a soxhelet extractor.The sample was exposed to refluxing xylene for168h.
XRD measurement was made using a XD-3A X-ray diffractometer (Japan)with CuK a irradiation source.
DSC analysis was carried out on a LABSYS thermal analyzer(France). The sample was heated from room temperature to2008C at a heating rate of108C/min.The crystallinity(C)was calculated from C?H f/H f?100%,
where,H f is the melt enthalpy of sample;H0
f is the melt enthalpy at100%
crystallinity of PP,which is209.3J/g.
Melt flow rate measurement was carried out using an XNR-400A tester (China)under2308C and2.16kg load.
Water contact angle measurement was carried out with a RAMHAR-100 contact angle tester(USA)at room temperature.
SEM was carried out using a HITACHI-X650tester(Japan).
Tensile test was performed using an INSTRON-4466all-purpose tester (USA)according to ASTM D268.
Notched Izod impact test was performed using a XJ-40A impact tester (China)according to ISO180-1993E.
Effect of Environmental Temperature on Ultraviolet Irradiated PP139
RESULTS AND DISCUSSION
Chemical Structure of uvPP
The FTIR spectra of PP and uvPP at different environmental temperatures are shown in https://www.doczj.com/doc/552784209.html,pared with that of PP,the absorption peak around1725cmà1of uvPP was increased because of the introduction of the oxygen-containing groups such as C?O onto the molecular chains of PP. After the same ultraviolet irradiation time,the absorption peak around 1725cmà1of uvPP was increased with the increasing environmental temperature.That indicated the introduction rate of the oxygen-containing groups was increased with the increasing environmental temperature.
The PP and uvPP were investigated by XPS.The C1S peak was resolved into component peaks at binding energy of285.0,286.4,and287.8eV, corresponding to the carbon in C–H,C–O,and C?O.The C1S spectra of PP and uvPP at different environmental temperatures are shown in Figure3. XPS data of PP before and after ultraviolet irradiation are listed in Table1. The oxygen-containing groups introduced onto the molecular chains of PP were C–O and C?O,and their contents were increased with the increasing environmental temperature after the same ultraviolet irradiation time.
35003000250020001500
Wavenumber (cm?1)1000500
c
b
a
1725
Figure1.FTIR spectra of PP(a),uvPP at708C for30min(b),and60min(c).
140M.Q IAO ET AL.
The gel determination results indicated that the PP chains were not cross-linked after ultraviolet irradiation at different environmental temperatures (Table2),which was different to the state of ultraviolet irradiated PE[4–8] but the same to the state of beam irradiated PP and PE[9,10].
Crystal Structure of uvPP
The XRD spectra of PP and uvPP at different environmental temperatures are shown in Figure4.The XRD results of PP before and after ultraviolet irradiation are listed in https://www.doczj.com/doc/552784209.html,pared with those of PP,corresponding (110),(040),(130),(111),and(131)diffraction peak positions of uvPP were not changed,indicating that the crystal shape of uvPP was a-monoclinic crystal structure and the space of crystalline plane of uvPP was the same with that of PP.
The melting temperature and crystallinity of PP before and after irradiation at different environmental temperatures are listed in Table4.The melting temperature of uvPP was lower than that of PP because of the crystal lattice defects caused by ultraviolet irradiation[3],but the crystallinity of uvPP was higher than that of PP because of the scission of the molecular chains of
1725c b a
3500300025002000
Wavenumber (cm?1)
150******** Figure2.FTIR spectra of PP(a),uvPP at908C for30min(b),and60min(c). Effect of Environmental Temperature on Ultraviolet Irradiated PP141
289
288287286285284283282281280
289
288287286285284283282281280
289288287286285Binding energy (eV)
284283282281280
(a)(b)(c)Figure 3.C 1S spectra of PP (a),uvPP at 708C for 60min (b),and uvPP at 908C for 60min (c).
142
M.Q IAO ET AL .
PP followed by subsequent recrystallization of the broken molecular chains
[3,11].With the increasing environmental temperature,the melting temper-ature of uvPP decreased and crystallinity was increased after the same irradiation
time.
c
b
a
10152025302θ (degree)
354045
Figure 4.XRD spectra of PP (a),uvPP at 708C for 60min (b),and uvPP at 908C for 60min (c).Table 2.Effect of environmental temperature
on gel content of uvPP.
Irradiation
Gel content (%)time (min)
708C 908C 0
0030
006000
Table 1.XPS data of uvPP for 60min.
Environmental
temperature (8C)
C–H C–O C ?O Unirradiated
97.9 1.30.870
97.0 1.8 1.29096.1 2.3 1.6Effect of Environmental Temperature on Ultraviolet Irradiated PP
143
Properties of uvPP
The melt flow rates (MFR)of PP before and after ultraviolet irradiation at different environmental temperatures are listed in Table https://www.doczj.com/doc/552784209.html,pared with that of PP,the melt flow rate of uvPP was increased,and its fluidity was improved because of the degradation of the molecular chains of uvPP.After the same irradiation time,the melt flow rate of uvPP was increased with the increasing environmental temperature due to the increasing degradation of the molecular chains of uvPP.
The water contact angle of PP and uvPP at different environmental temperatures are listed in Table 6.Water contact angle of uvPP was lower than that of PP,indicating improved hydrophilicity.
Mechanical Properties of PP/uvPP/CaCO 3Composite
The mechanical properties of PP/CaCO 3composite and PP/uvPP/CaCO 3composite are listed in Tables 7and 8.Since PP was nonpolar and CaCO 3was polar,the compatibility and dispersion of PP/CaCO 3composite were therefore poor,which caused the low tensile strength and low notched impact strength.
The PP/uvPP/CaCO 3composite was prepared by adding a little of uvPP in PP/CaCO https://www.doczj.com/doc/552784209.html,pared with that in PP/CaCO 3composite,the compatibility between compositions and dispersion of CaCO 3particles in PP/uvPP/CaCO 3composite were greatly improved and meanwhile the
Table 4.Effect of environmental temperature on melting
temperature and crystallinity of uvPP for 60min.
Environmental
temperature (8C)
T m (8C)C (%)Unirradiated
166.722.070
166.122.690165.523.3
Table 3.XRD data of uvPP for 60min.
Environmental
Face space (A ?)temperature (8C)
110040*********Unirradiated
6.31 5.27 4.79 4.21 4.0870
6.29 5.26 4.78 4.20 4.0890 6.30 5.25 4.76 4.18 4.09
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M.Q IAO ET AL .
Table 7.Mechanical properties of PP/uvPP*/CaCO 3(64/6/30)composite.
Irradiation
time (min)
Tensile strength (MPa)Impact strength (J/m)0
29.73530
31.14340
31.3606031.562
*Environmental temperature:708C.
Table 8.Mechanical properties of PP/uvPP*/CaCO 3(64/6/30)composite.
Irradiation
time (min)
Tensile strength (MPa)Impact strength (J/m)0
29.73530
31.55840
31.7636031.356
*Environmental temperature:908C.
Table 6.Effect of environmental temperature
on water contact angle of uvPP.
Irradiation
Contact angle (degree)time (min)
708C 908C 0
939330
919040
8988608785
Table 5.Effect of environmental temperature
on melt flow rate of uvPP.
Irradiation
MFR (g/10min)time (min)
708C 908C 0
5.2 5.230
13.614.540
17.520.16028.732.8Effect of Environmental Temperature on Ultraviolet Irradiated PP
145
146M.Q IAO ET AL.
(a)(b)
Figure5.SEM photographs of liquid nitrogen frozen fractured surface of PP/CaCO3(70/30) composite(a)and PP/uv40PP(908C)/CaCO3(64/6/30)composite(b).
tensile strength and the notched impact strength of PP/uvPP/CaCO3 composite were increased.The tensile strength and notched impact strength of PP/CaCO3composite compatibilized by uvPP(irradiated at708C)were increased with the increasing irradiation time.The tensile strength and notched impact strength of PP/CaCO3composite compatibilized by uvPP (irradiated at908C)were first increased with the increasing irradiation time, reached a maximum value after irradiated for40min,and then decreased with further increasing irradiation time because of fulsome degradation of the molecular chains of uvPP.
Within irradiation time of40min,the compatibilization of uvPP at higher environmental temperature was better than that of uvPP at lower environmental temperature.The tensile strength and the notched impact strength of PP/CaCO3composite compatibilized by uvPP(irradiated at908C for40min)were31.7MPa and63J/m,respectively,which were equivalent with that of PP/CaCO3composite compatibilized by uvPP(Irradiated at708C for60min),respectively.
SEM of PP/uvPP/CaCO3Composite
The SEM photographs of liquid nitrogen frozen fractured surface of PP/ CaCO3composite and PP/uvPP/CaCO3composite are shown in Figure5. For PP/CaCO3composite,the CaCO3particles were congregated in the PP matrix,showing poor dispersion of the CaCO3particles.On the other hand, some CaCO3particles in the PP/uvPP/CaCO3composite were wrapped with PP,indicating that the dispersion of CaCO3particles was improved.
Effect of Environmental Temperature on Ultraviolet Irradiated PP147 (a)(b)
Figure6.SEM photographs of impact fractured surface of PP/CaCO3(70/30)composite (a)and PP/uv40PP(908C)/CaCO3(64/6/30)composite(b).
As shown in Figure6(a),there were some big holes on impact fractured surface of PP/CaCO3composite,which was due to the abscission of aggregated CaCO3particles from PP matrix,indicating the poor dispersion of CaCO3particles and the weak interfacial interaction between the CaCO3 particles and the PP matrix in PP/CaCO3composite.As shown in Figure 6(b),there were some holes and CaCO3particles on the fractured surface of PP/uvPP/CaCO3composite and the size of holes was smaller than that on the fractured surface of PP/CaCO3composite,indicating that the dispersion of CaCO3and the compatibility of the PP/uvPP/CaCO3composite were improved compared with those of the PP/CaCO3composite.
CONCLUSIONS
Some oxygen-containing groups such as C–O and C?O were introduced onto the molecular chains of PP by ultraviolet irradiation at different environmental temperatures in air.The concentration of the oxygen-containing groups was increased with the increasing environmental temperature after the same ultraviolet irradiation time.There was no gel in irradiated PP at different environmental temperatures.The crystal shape of the irradiated PP was a monoclinic crystal structure and its space of crystalline plane was not https://www.doczj.com/doc/552784209.html,pared with that of PP,the melting temperature of the irradiated PP decreased,while its crystallinity,melt flow rate and hydrophilicity was increased and their variation range was expanded with the increasing environmental temperature after the same
148M.Q IAO ET AL.
ultraviolet irradiation https://www.doczj.com/doc/552784209.html,pared with those of PP/CaCO3(70/30) composite,the tensile strength and notched impact strength of PP/irradiated PP/CaCO3(64/6/30)composite was increased due to the compatibilization of the irradiated PP.The tensile strength and notched impact strength of PP/uvPP(irradiated at908C for40min)/CaCO3(64/6/30)composite were equivalent with that of PP/uvPP(irradiated at708C for60min)/CaCO3 (64/6/30)composite,respectively.
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