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Comparison of rheological, mechanical, electrical properties of HDPE filled with BaTiO3 with different polar surface tension
Accepted Manuscript Title: Comparison of rheological, mechanical, electrical properties of HDPE filled with BaTiO3 with different polar surface tension Author: Jun Su Jun Zhang PII: DOI: Reference:
S0169-4332(15)02575-1 http://dx.doi.org/doi:10.1016/j.apsusc.2015.10.156 APSUSC 31637
To appear in:
APSUSC
Received date: Revised date: Accepted date:
7-8-2015 29-9-2015 22-10-2015
Please cite this article as: J. Su, J. Zhang, Comparison of rheological, mechanical, electrical properties of HDPE filled with BaTiO3 with different polar surface tension, Applied Surface Science (2015), http://dx.doi.org/10.1016/j.apsusc.2015.10.156 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Comparison of rheological, mechanical, electrical properties of HDPE filled with BaTiO3 with different polar surface tension
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Jun Sua,b, Jun Zhang1a, a
Department of Polymer Science and Engineering, College of Materials Science and
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Engineering, Nanjing Tech University , Nanjing 210009, People’s Republic of China b
College of Mechanics Engineering, Nanjing Institute of Industry Technology, Nanjing, 210023,
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People’s Republic of China.
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Highlight (1) The non‐polar and short vinyl groups can greatly reduce G’ of HDPE composites. (2) Long chains on BaTiO3 surface enhance the interaction of BaTiO3 with HDPE. (3) Polar amino groups on BaTiO3 surface raise the interaction of BaTiO3 with HDPE. (4) Polar amino groups can boost the dielectric constant of HDPE composites. (5) The potential use in electronic equipment of the KH550 composites is obtained
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Abstract
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In this work, three types of coupling agents: isopropyl trioleic titanate (NDZ105),
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vinyltriethoxysilane (SG-Si151), 3-aminopropyltriethoxysilane (KH550) were applied to modify the surface tension of Barium titanate (BaTiO3) particles. The Fourier transform infrared (FT-IR)
spectra confirm the chemical adherence of coupling agents to the particle surface. The long
hydrocarbon chains in NDZ105 can cover the particle surface and reduce the polar surface tension of BaTiO3 from 37.53mJ/m2 to 7.51 mJ/m2, turning it from hydrophilic to oleophilic properties. The short and non-polar vinyl groups in SG-Si151 does not influence the surface tension of BaTiO3, but make BaTiO3 have both hydrophilic and oleophilic properties. The polar amino in
KH550 can keep BaTiO3 still with hydrophilic properties. It is found that SG-Si151 modified BaTiO3 has the lowest interaction with HDPE matrix, lowering the storage modulus of HDPE composites to the greatest extent. As for mechanical properties, the polar amino groups in KH550 on BaTiO3 surface can improve the adhesion of BaTiO3 with HDPE matrix, which increases the 1
Correspondence to: Jun Zhang ([email protected])
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elongation at break of HDPE composites to the greatest extent. In terms of electrical properties, the polar amino groups on surface of BaTiO3 can boost the dielectric properties of HDPE/BaTiO3 composites and decrease the volume resistivity of HDPE/BaTiO3 composites. The aim of this study is to investigate how functional groups affect the rheological, mechanical and electrical
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properties of HDPE composites and to select a coupling agents to produce HDPE/BaTiO3
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composites with low dielectric loss, high dielectric constant and elongation at break.
Keywords: High density polyethylene (HDPE); Barium titanate (BaTiO3); Surface tension;
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Rheology; Coupling agents; Mechanical and electrical properties
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1. Introduction
Dielectric polymer/ceramic composites have become much attractive in electric domain.[1] Among them, fluoride polymer/ceramic is commonly used to fabricate embedded and multilayer
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capacitors in electronic equipment, because of polar structure of matrix. [2] The presence of fluoride atom endows fluoride polymer/ceramic with the disadvantage of poor processability. [3] High Density Polyethylene (HDPE) is one of the widely used engineering materials with
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highly tactic structure. Such tactic structure can enhance the crystallinity of HDPE, which can
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both enhance the mechanical and electric properties of HDPE. [4, 5]What’s more, the crystal lattices can melt during process and then decrease the viscosity of HDPE, improving the processability at the meantime. The non-polar structure endows HDPE not only with good
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resistance to oxidation and solvents, but also with low dielectric constant and loss.[6] Because of high dielectric constant, Barium titanate (BaTiO3) is one of the most important
ceramic materials with perovskite structure and which is widely used in electronic applications.[7] The application of BaTiO3 has been limited because of its brittleness and high dielectric loss.[8, 9] So far, there are few reports about the incorporation of BaTiO3 into HDPE matrix to enhance
electrical properties of HDPE composites.[10] Thereby, it is interesting to incorporate BaTiO3 into
HDPE and obtain HDPE/BaTiO3 with high dielectric constant, low dielectric loss and improved toughness of BaTiO3.
The interface between BaTiO3 and HDPE is critical to the processability and overall properties of HDPE composites. [11] In literature, the application of coupling agents can improve the compatibility of inorganic fillers with polymer matrix. [12] In this study, BaTiO3 are modified by three types of coupling agents to introduce different functional groups on the surface of particles. The aim is to investigate how functional groups affect the rheological, mechanical and electrical properties of HDPE composites and to select a coupling agents to produce HDPE/BaTiO3 composites with low dielectric loss, high dielectric
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constant and elongation at break.
2. Experimental 2.1 Materials High Density Polyethylene (HDPE 4902T), used in this study, is purchased from Sinopec
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Yangzi Petrochemical company limited, China. The density of HDPE is 0.952g/cm3. The melt flow index of HDPE 4902T is 0.3g/10min at 190oC under 5kg. Barium titanate (BaTiO3) particles
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are supplied from Baosong electrically functional Co., Ltd. in Foshan, Guangdong province. The distribution of diameter of BaTiO3 particles is D10<0.6μm, D50<1.8μm, D90<5.0μm.
There are three types of coupling agents applied in this study. The chemical/commercial
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names and structures of these coupling agents are listed in Table 1. Isopropyl trioleic titanate (NDZ105), Vinyltriethoxysilane (SG-Si151), 3-Aminopropyltriethoxysilane (KH550), are
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obtained from Nanjing shuguang Chemical Group Co., Ltd, China.
(Table1)
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2.2 Sample preparation
2.2.1 Surface modification of BaTiO3
In this work, NDZ105, SG-Si151, and KH550 were utilized for surface modification of the
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BaTiO3 particles, respectively. The amount of coupling agents is 1% by weight (wt%) of BaTiO3
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amount. For instance, 1.0g of NDZ105 is mixed in 100ml isobutanol for 15min. BaTiO3 (100 g) is then added into such solution with a 30 min stirring. The treated BaTiO3 particles are then dried at
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60°C for 4h. Similarly, SG-Si151 and KH550 are applied to modify the BaTiO3 surface in the same procedure.
2.2.2 Extraction of modified BaTiO3 particles
The modified BaTiO3 is extracted in ether solvent by Soxhlet extractor for 4h at 70oC. Then,
the extracted BaTiO3 particles are dried at 40 oC for 6 h. 2.2.3 Compounding of HDPE/BaTiO3 composites
HDPE and three kinds of modified BaTiO3 are mixed by a two roll mixing mill (Shanghai
Rubber Machinery Works, China), respectively. The formulations of HDPE/BaTiO3 are shown in Table 2. Obtained HDPE composites are heat-pressed at 170°C. (Table 2 ) 2.3 Testing procedures 2.3.1 Fourier Transform Infrared Spectroscopy Fourier transform infrared spectroscopy (FT-IR) spectra of untreated, NDZ 105 modified, SG-Si 151 modified, KH550 modified BaTiO3 particles before and after extraction are measured
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with Nicolet spectrometer (model NEXUS 670, American) 2.3.2 Water contact angle and surface tension measurement Static water contact angle is measured in a drop shape analysis system (model: DSA 100 Krüss, Germany) at 24 oC. The surface tension is calculated by Owens and Wendt method, using
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the contact angles of both deionized water and diiodomethane solvent. 2.3.3 Rheological characterization
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Rheological properties of HDPE control and HDPE/BaTiO3 composites are characterized at 170°C in the range of frequency from 0.002 to 100 Hz by Rheo-Stress instrument (model
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MCR302, Anton Paar, Austria).
2.3.4 Differential Scanning Calorimetry (DSC) measurement
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The melting behaviors of HDPE control and HDPE/BaTiO3 composites are tested by DSC instrument (model Q20, TA, USA). Samples are firstly heated from 30 oC to 180 oC at 40 oC/min,
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and then are held at 180 oC for 5 min to eliminate the effect of thermal history. Secondly, the samples are cooled from 180 oC to 30 oC at 10 oC/min. Thirdly, the samples are heated again from
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30 oC to 180 oC at 10 oC/min. The relative crystallinity (Xc) of the HDPE/BaTiO3 composite is
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calculated according to Equation (1). [4]
ΔH ×100% (1) ϕ × ΔH *
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X c＝
Where ΔH* stands for the enthalpy of fusion of the perfect HDPE crystals and
ΔH stands for the fusion enthalpy of HDPE in HDPE/BaTiO3 composites. The ΔH* of HDPE is 277.1 J/g. φ is the weight fraction of HDPE in HDPE/BaTiO3 composites.
2.3.5 Scanning electron microscopy
The dispersion of BaTiO3 is detected by scanning electron microscopy (SEM) (model: JEOL
JSM-5900, Japan). 2.3.6 Mechanical properties The mechanical properties are measured by using electromechanical universal testing machine (model CMT 5254, Shengzhen SANS Testing Machine Co., Ltd. China), according to ISO 527. The Shore D hardness of the samples is measured by using a Shore D hardness degree tester (model LX-D Jiangsu Mingzhu Testing Machinery Co., Ltd., China).
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2.3.7 Electric properties 2.3.7.1 Volume and surface resistivity The volume and surface resistivity of HDPE/BaTiO3 composites are tested at 24oC by a high resistance meter , purchased from Shanghai Precision & Scientific Instrument Co., Ltd., China.
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2.3.7.2 Dielectric constant and dielectric loss
The dielectric constant and loss of HDPE/BaTiO3 composites are measured in the range of
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10k~10MHz with precision impedance analyzer (model 4294A, Agilent American) following
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IEC60243. 3. Results and discussion 3.1 FT-IR analysis
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FT-IR spectra are utilized to detect functional groups on BaTiO3 particles. Figure 1 and Figure 2 illustrate the spectra of coupling agents and modified BaTiO3 particles after soxhlet
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extraction, respectively. In Figure 1, it is shown that three coupling agents all have absorption peaks at 2922cm-1 and 2855 cm-1, assigned to asymmetric stretching vibration of methylene and symmetric stretching vibration of methylene, respectively. [12] Additionally, NDZ105 has
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absorption peak at 1733 cm-1, assigned to C=O stretching vibration of carboxyl group. SG-Si151
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has absorption peak at 1078 cm-1, assigned to Si-O-C rocking vibration. [11]The absorption peak
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of KH550 is at 1579 cm-1, assigned to transforming vibration of –NH. [13] Figure 2 shows FT-IR spectra of modified BaTiO3 after extraction. The coupling agents
which are physically adhered on the particle surface can be washed away by ether solvent during
the extraction. So the detection of absorption bands at 2922cm-1 and 2855 cm-1 after extraction can
prove the chemical adherence of three coupling agents to the surface of BaTiO3 particles. It is consistent with literature that alkoxy groups can alcoholize with hydroxyl groups on surface of inorganic particles and form chemical bonds between each other.[12, 14] (Fig.1) (Fig.2)
3.2 Water contact angle and surface tension measurement Water contact angles of HDPE resins and BaTiO3 are listed in Figure 3. It is apparent that the water contact angles of HDPE and untreated BaTiO3 is about 80o and 12o, respectively. The NDZ105 can greatly enhance the water contact angle of BaTiO3 from 12 o to about 130 o, while
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SG-Si151 and KH550 can slightly affect the water contact angle. The results of surface tension of modified BaTiO3 particles are shown in Table 3, which are calculated by Owens and Wendit method. The total surface tension ( γ s ) and polar surface tension
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( γ sp ) of inorganic BaTiO3 particles and HDPE follow the order: Untreated BaTiO3 ≈ KH550 modified BaTiO3 > SG-Si151 modified BaTiO3 > NDZ105 modified BaTiO3 > HDPE control.
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This reason is that the NDZ105 has non-polar and long hydrocarbon chains, which can cover the surface of BaTiO3 particles to the greatest extent, resulting in the fact that the surface of
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NDZ105 modified BaTiO3 particles changing from hydrophilic to hydrophobic properties. [15] By comparison, KH550 has polar amino groups, so the polar surface tension of BaTiO3
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particles is slightly varied.
Although vinyl groups in SG-Si151 are non-polar, they have short hydrocarbon chains. In
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this way, the surface of SG-Si151 modified BaTiO3 is only partially covered by non-polar vinyl groups, making the overall polar surface tension of BaTiO3 still high.[16]
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( Fig.3 )
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(Table 3)
3.3 Effect of coupling agents on dispersion properties of BaTiO3 in organic solvents
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Figure 4 shows dispersion of untreated BaTiO3 , NDZ105 modified, SG-Si151 modified and
KH550 modified BaTiO3 in two-phase solvent. Because of relatively high density, distilled water is at the bottom, while n-octane solvent is at the upper layer. It is shown from Figure 4 that the untreated BaTiO3 particles are suspended in bottom layer
of solvent, showing hydrophilic properties. In terms of modified BaTiO3 particles, NDZ 105 modified BaTiO3 particles disperse in the layer of n-octane, showing oleophilic properties;
SG-Si151 modified BaTiO3 particles disperse in the interface of two solvents, showing both hydrophilic and oleophilic properties; KH550 modified BaTiO3 disperse in the layer of water, showing hydrophilic properties.[17] Only the dispersion of SG-Si151 modified BaTiO3 is not as expected. Non-polar vinyl groups can only partially cover the surface of BaTiO3 and turn partial surface of BaTiO3 from hydrophilic to oleophilic properties. So, the rest of the BaTiO3 surface still has high polar surface tension and
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shows hydrophilic properties. In this way, SG-Si151 modified BaTiO3 particles show both hydrophilic to oleophilic properties and disperse in the interface of two solvents.
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(Fig.4)
3.4 Effect of coupling agents on rheological properties of HDPE composites
The storage modulus (G’) and loss modulus (G’’) of HDPE composites are
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shown in Figure 5A and 5B, respectively. It is obvious that G’ and G’’ of samples all
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increase with the grown frequency. The G’ and G’’ follow the order: HDPE with KH550 modified BaTiO3 > HDPE control ≈ HDPE with untreated BaTiO3 > HDPE with modified NDZ105 BaTiO3 > HDPE with SG-Si151 modified BaTiO3.
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Generally, filler can interact with the polymer matrix to increase the storage modulus of composites. But the incorporation of untreated BaTiO3 has little effect on
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the G’, because the content of BaTiO3 is less than 5vol%, and there is few functional groups on the surface of BaTiO3, which means less interaction between BaTiO3 and
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HDPE matrix.[18]
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Scheme 1 shows the possible dispersion models of BaTiO3 in HDPE matrix. It is shown that the modification can improve the aggregation and dispersion of BaTiO3.
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Coupling agent KH550 has polar amino groups which can restrict the motion of
non-polar HDPE chains. Thus, the interaction between HDPE matrix and BaTiO3
particles is strong, resulting in higher storage modulus. Coupling agent NDZ105 has non-polar and long hydrocarbon chains. The polar
surface tension of NDZ105 modified BaTiO3 (7.51mJ/m2) is close to that of HDPE
control (5.18mJ/m2), but the long hydrocarbon chains can entangle with HDPE matrix
to increase the interaction between BaTiO3 and HDPE matrix. In this way, the G’ of
HDPE with NDZ105 modified BaTiO3 is only a little lower than that of HDPE control. By comparison, SG-Si151 has non-polar vinyl groups with relatively shorter molecular chains. So SG-Si151 modified BaTiO3 can non only have excellent compatibility with HDPE matrix, but also have little physical entanglement with
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HDPE chains. Thereby, the interaction of BaTiO3 particles with HDPE matrix is the weakest, leading to the lowest value of storage modulus. It is illustrated in Figure 5C that with the increase of frequency, the curves of G’/G’’ ratios of all samples grow. Only the G’/G’’ of HDPE control and HDPE with
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SG-Si151 modified BaTiO3 are below 1 at low frequency. The non-polar vinyl groups
in SG-Si151 have great compatibility with HDPE matrix and slightly hinder the
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motion of HDPE molecular chains. Thus, their G’/G’’ is below 1 at low frequency.
For other three HDPE composites, the G’/G’’ are all above 1 in the range of test
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frequency, meaning the solid-like behavior of HDPE composites. This is due to the fact that the interaction of these modified BaTiO3 particles with HDPE matrix is
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strong. [19]
The G’/G’’ rations of these two specimens exceed 1 at higher frequency, meaning
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a rheological transition from liquid-like behavior to solid-like behavior at 0.193 Hz for both specimens. This transition is ascribed to the interconnected structures formed
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in HDPE control and HDPE with SG-Si151 modified BaTiO3, at high frequency. [20] Figure 5D shows the Van Gurp plot with the loss phase angle δ versus the
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absolute value of the complex modulus |G*|. [19]It is clear that when |G*| is lower
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than 25033 Pa, the phase angle of HDPE composites are all lower than that of HDPE control. In literature, loss angle is sensitive to long and branched structure of polymer and the Van Gurp curve can shift to lower value of the phase angle, with increased long branch content. [4, 21]It seems that only when |G*| is lower than 25033 Pa, the varied phase angle can show more branched structure content among HDPE matrix to some extent, caused by the incorporation of BaTiO3 particles. (Fig.5 ) (Scheme 1)
3.5 Effect of coupling agents on crystallization of HDPE composites Table 4 lists DSC characteristics of HDPE composites. It is found that the onset onset melting temperature ( Tm ) of all samples are almost the same. The peak melting peak
temperature ( Tm
final
), final melting temperature ( Tm
) and relative crystallinity (Xc) of
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HDPE/BaTiO3 composites are a little different. The addition of un-modified BaTiO3 particles can both reduce the melting enthalpy (ΔH) and the crystallization degree (Xc) of HDPE composites. Because BaTiO3 particles in HDPE composites do not absorb heat and release heat, the
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enthalpy of HDPE/BaTiO3 composite listed in Table 5 is the enthalpy of HDPE in
HDPE/BaTiO3 composites. In terms of HDPE/BaTiO3 composites, the mass ratio of
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HDPE to HDPE/BaTiO3 composite is 1:1.3, so the enthapy of HDPE in
HDPE/BaTiO3 composites is remarkably lower than enthalpy of HDPE control. When
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calculating the crystallinity degree (Xc), the ethalpy of HDPE in HDPE/BaTiO3 composites and HDPE control was used at the same amount, according to Equation 1.
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At the same HDPE amount, the ethalpy of HDPE in the HDPE with untreated BaTiO3 is 197.3J/g (151.8J/g multiplying 1.3), which is slightly lower than that of HDPE
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control. This is consistent with literature in which the incorporation of inorganic filler can decrease theΔH and Xc.of polyolefin. [4, 5] Generally, crystallinity is correlated
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with the chain’s ability to pack into crystal lattices. The addition of untreated BaTiO3
decrease of ΔH and Xc.
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particles can hinder the pack of molecular chains into the crystal lattice, leading to the
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The functional groups of coupling agents on surface of BaTiO3 particles can increase the interaction of BaTiO3 particles with HDPE matrix and facilitate the pack of molecular chains into the crystal lattice, resulting in relatively higher Xc value than that of HDPE with un-modified particles.[22]
(Table 4 )
3.6 Effect of coupling agents on filler dispersion in HDPE composites Scanning electron micrographs (Figure 6) shows the dispersion of BaTiO3 in HDPE matrix. It is found that after surface modification, modified BaTiO3 particles also aggregate, but the interface between BaTiO3 and HDPE matrix become ambiguous, meaning the improved interaction. This can be explained by the fact the surface treatment of BaTiO3 particles can increase the interaction of BaTiO3 with
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HDPE matrix but affect the aggregation a little. [17] (Fig. 6 )
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3.7 Effect of coupling agents on mechanical properties of HDPE composites
The data of mechanical properties of HDPE/BaTiO3 composites are shown in
elongation at break of HDPE control from 859% to 55%.
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Table 5. It is observed that the addition of untreated BaTiO3 can greatly lower the
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Compared to that of untreated BaTiO3, the addition of NDZ105 and KH550 modified BaTiO3 can improve the elongation at break of HDPE composites from 55%
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to 161% and 357%, respectively. The surface modification of BaTiO3 by SG-Si151 has little effect on the elongation of break of HDPE with untreated BaTiO3 composite.
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The reason is that the long hydrocarbon chains from NDZ105 on BaTiO3 surface can physically entangle with HDPE matrix and that polar amino groups from KH550 on BaTiO3 surface can increase interfacial adhesion between BaTiO3 particle and
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HDPE matrix. While SG-Si151 can only bring non-polar vinyl groups without other
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long chains and polar groups. Thereby, the elongation at break of HDPE with un-modified BaTiO3 only can be lifted by the use of NDZ105 and KH550 modified
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BaTiO3. In literature, the 1wt% BaTiO3 coated with polydopamine can enhance the
beta-phase of poly(vinylidene fluoride) (PVDF), resulting in improvement of both tensile strength and elogation at break. However, the polar F groups make PVDF
more difficult to process than HDPE which has excellent fluidiy during manufacuturing.[23]
Although the un-modified BaTiO3 can decrease the crystallinity of HDPE
composites to a little extent, it can slightly lift the hardness of HDPE composites at 24oC temperature. It is reported that the increased crystallinity and filler amount can both enhance the hardness of polymer composites.[24] It is seemed in this study, that the addition of un-modified BaTiO3 plays the dominant effect on the rise of composite hardness. It is observed that the incorporation of modified and un-modified BaTiO3
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particles can reduce the tensile strength of HDPE control. It has been proved that the addition of BaTiO3 particles can decrease the crystallinity of HDPE control. In literature, the crystalline lattices can provide strength for composites to resist outside
ascribed to the decreased crystallinity of HDPE composites. [25]
3.8 Effect of coupling agents on electric properties
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3.8.1 Effect of coupling agents on dielectric properties
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( Table 5 )
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forces.[5] In this study, the reduced tensile strength of HDPE control can be mainly
Figure 7 and 8 show curves of relative dielectric constant and loss of HDPE
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composites in the range of frequency from 10kHz to 10 MHz. The dielectric constants of HDPE composites follow the order: HDPE with KH550 modified BaTiO3 > HDPE
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with SG-Si151 modified BaTiO3 ≈ HDPE with untreated BaTiO3 > HDPE with NDZ105 modified BaTiO3 > HDPE control. It is consistent with literature that the
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increasing BaTiO3 can increase the dielectric constant of polymer composites.[26] In general, the relative dielectric constant is mainly correlated with the polarity
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of composites. [11] It is mentioned above that coupling agent KH550 has polar
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amino groups which can boost the entire polarity of HDPE composites. In contrast, SG-Si151 has non-polar vinyl groups which partially cover the
surface of BaTiO3, making partial surface of BaTiO3 are still responsive to cyclic electric excitation. [9]
What’s more, NDZ105 has non-polar and long hydrocarbon chains, which can
greatly cover the surface of BaTiO3, leaving less surface of BaTiO3 responsive to cyclic electric excitation. In this way, the dielectric constant of HDPE with NDZ105 modified BaTiO3 is lower than HDPE with non-modified BaTiO3. It is observed from Figure 8 that the relative dielectric loss of HDPE composites
decreases drastically in the range of 10kHz~40kHz, and further decreases gradually in the frequency range of 40kHz~10MHz. The addition of un-modified and modified BaTiO3 can enhance the dielectric loss of HDPE composites, meaning that the energy lost during cyclic electric excitation is
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boosted by surface modification. (Fig. 7 ) (Fig.8 )
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3.8.2 Effect of coupling agents on volume and surface resistivity Table 6 illustrates the volume resistivity and surface resistivity of HDPE
composites. It is observed that HDPE with KH550 modified BaTiO3 exhibits the
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lowest volume resistivity of HDPE.
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The addition of un-modified BaTiO3 particles can increase the resistivity of HDPE composites, meaning BaTiO3 is non-conductive particles. [12]In terms of KH550 modified BaTiO3, the polar amino groups can provide polarity for easy
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passage of current in HDPE with KH550 modified BaTiO3, leading to the decreased volume resistivity.
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The addition of particles has the trend to enhance the surface resistivity of HDPE composites. This may be due to the fact that surface resistivity is mainly correlated
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with the surface texture and material itself. It is shown that the coupling agents have
(Table 6 )
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little effect on surface resistivity of HDPE/BaTiO3 composites.
4. Conclusions
It is proved by FT-IR and contact angle measurements that the surface modification of
BaTiO3 by NDZ105, SG-Si151 and KH550 can attach chemically non-polar hydrocarbon groups,
non-polar vinyl groups and polar amino groups to the surface of BaTiO3 particles, respectively. The dispersion of powders in solvents shows NDZ105 modified, SG-Si151 modified and
KH550 modified exhibit oleophilic properties, both hydrophilic and oleophilic properties, and oleophilic properties, respectively. In terms of rheological properties, the polar amino groups from KH550 have remarkable interaction with HDPE matrix, and raise the storage modulus of HDPE composites. Although the non-polar long hydrocarbon chains from NDZ105 can greatly decrease the polar surface tension of BaTiO3, the long chains also can physically entangle with molecular chains in HDPE, leading to
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slight decrease of G’. Only non-polar and short vinyl groups from SG-Si151 can remarkably decrease the storage and loss modulus of HDPE/BaTiO3 composites. As for mechanical properties, the polar amino groups can improve the adhesion of BaTiO3 in HDPE matrix, which increases the elongation at break of HDPE composites to the greatest extent.
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By comparison, the NDZ105 modified BaTiO3 particles with long hydrocarbon chains can also increase the elongation at break of HDPE composites.
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The dielectric constant of HDPE with KH550 modified BaTiO3 is the highest among other composites, due to the presence of polar amino groups. What is more, the presence of polar amino
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groups on surface of BaTiO3 facilitates the passage of current in HDPE matrix and then lowers volume resistivity of HDPE with KH550 modified composite .
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In sum, KH550 is selected as the optimum coupling agents, because HDPE with KH550 treated BaTiO3 has the highest dielectric constant of HDPE composites. In addition, after
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incorporation of 30wt% BaTiO3, HDPE with KH550 treated BaTiO3 still has 357% elongation at
Acknowledgements
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break.
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The authors gratefully acknowledge the Priority Academic Program Development of Jiangsu
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Higher Education Institutions (PAPD).
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nanocomposites fabricated with ferroelectric polymer matrix and BaTiO3 nanofibers modified with
[10] J. Gonzalez‐Benito, J. Martinez‐Tarifa, M.E. Sepulveda‐Garcia, R.A. Portillo, G. Gonzalez‐Gaitano, dielectric properties, Polymer Testing, 32 (2013) 1342‐1349.
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Composites based on HDPE filled with BaTiO3 submicrometric particles. Morphology, structure and [11] J. Su, S. Chen, J. Zhang, Z. Xu, Combined effect of pH level and surface treatment of Sm2O3,
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SmBO3 and ATO particles on cure, mechanical and electric properties of EPDM composites, Polymer Testing, 28 (2009) 419‐427.
[12] J. Su, S. Chen, J. Zhang, Z. Xu, Comparison of cure, mechanical, electric properties of EPDM filled with Sm2O3 treated by different coupling agents, Polymer Testing, 28 (2009) 235‐242.
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[13] J. Su, S. Chen, J. Zhang, Z. Xu, Combined Effect of VA Content and pH Level of Filler on Properties of EPDM/SmBO3 and EPDM/ATO Composites Reinforced by Three Types of EVA, Journal of Applied Polymer Science, 117 (2010) 1741‐1749.
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[14] K. Nagata, Y. Takahashi, S. Shibusawa, Y. Nakamura, Interfacial structure in vulcanized EPDM filled with mercaptosilane‐treated Al(OH)(3) and its influence on the mechanical properties, Journal of
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Adhesion Science and Technology, 16 (2002) 1017‐1026. [15] S. Pongdhorn, S.B. Chakrit, K. Hatthapanit, U. Thepsuwan, Comparison of reinforcing efficiency
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between Si‐69 and Si‐264 in an efficient vulcanization system, Polymer Testing, 24 (2005) 439‐446. [16] P. Sae‐oui, C. Sirisinha, U. Thepsuwan, K. Hatthapanit, Comparison of reinforcing efficiency
between Si‐69 and Si‐264 in a conventional vulcanization system, Polymer Testing, 23 (2004) 871‐879.
[17] P. Sae‐Oui, U. Thepsuwan, K. Hatthapanit, Effect of curing system on reinforcing efficiency of
silane coupling agent, Polymer Testing, 23 (2004) 397‐403.
[18] M.V. Gurp, J. Palmen, Time–temperature superposition for polymeric blends, Rheologica Acta, 67 (1998) 5‐8.
[19] T. Stefan, F. Christian, Van Gurp‐Palmen‐plot: a way to characterize polydispersity of linear
polymers, Rheologica Acta, 40 (2001) 322‐328.
[20] T. Stefan, W. Philipp, F. Christian, Van Gurp‐Palmen Plot II ‐ classification of long chain branched polymers by their topology., Rheologica Acta, 41 (2002) 103‐1133. [21] J. Su, S. Chen, J. Zhang, Z. Xu, Reinforcement of Ethylene‐Propylene‐Diene Rubber/Samarium
Borate and Ethylene‐Propylene‐Diene Rubber/Sb‐doped SnO2 Composites by Three Types of Ethylene‐Acrylic Acid: Assessment of Acrylic Acid Content on Crystallinity, Cure, Mechanical, and Electric Properties, Journal of Reinforced Plastics and Composites, 29 (2010) 2946‐2960. [22] N. Yao, P. Zhang, L. Song, M. Kang, Z. Lu, R. Zheng, Stearic acid coating on circulating fluidized bed combustion fly ashes and its effect on the mechanical performance of polymer composites., Applied Surface Science, 279 (2013) 109‐115.
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[23] N. Jia, Q. Xing, X. Liu, J. Sun, G. Xia, W. Huang, R. Song, Enhanced electroactive and mechanical properties of poly(vinylidene fluoride) by controlling crystallization and interfacial interactions with low loading polydopamine coated BaTiO3, Journal of Colloid and Interface Science, 453 (2015) 169‐176. [24] J. Su, S. Chen, J. Zhang, Effect of hot‐air aging on properties of EPDM/SmBO3/EAA and EPDM/ATO/EAA composites, Journal of Composite Materials, 46 (2012) 589‐602.
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[25] J. Su, S. Chen, J. Zhang, Effect of Hot Air Aging on Properties of EPDM/SmBO3/EVA and EPDM/ATO/EVA Composites, Journal of Applied Polymer Science, 122 (2011) 3277‐3289.
[26] S.D. Vacche, F. Oliveira, Y. Leterrier, V. Michaud, D. Damjanovic, J.‐A.E. Manson, The effect of
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processing conditions on the morphology, thermomechanical, dielectric, and piezoelectric properties
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an
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of P(VDF‐TrFE)/BaTiO3 composites, Journal of Materials Science, 47 (2012) 4763‐4774.
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Figure captions Fig.1 Spectra of three coupling agents Fig.2 Spectra of treated BaTiO3 after extraction Fig.3 Water contact angle of HDPE and BaTiO3
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Fig.4 Dispersion of BaTiO3 in a two-phase solvent, the bottom layer solvent is distilled water and the upper layer solvent is n-octane: A. Untreated BaTiO3; B. NDZ105 modified BaTiO3;C.
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SG-Si151 modified BaTiO3;D. KH550 modified BaTiO3 .
Fig.5 Rheological properties of HDPE composites: A. Storage modulus; B. Loss modulus; C.
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Curves of G’/G’’ ratios; D. Van Gurp plot.
Fig. 6 SEM micrographs of HDPE with various coupling agents, A: HDPE with untreated BaTiO3;
with KH550 modified BaTiO3
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Fig.8 Dielectric loss of HDPE composites
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Fig. 7 Dielectric constant of HDPE composites
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B: HDPE with NDZ105 modified BaTiO3; C: HDPE with SG-Si151 modified BaTiO3; D: HDPE
Scheme1 Possible dispersion models of BaTiO3 in HDPE matrix: A: HDPE with untreated BaTiO3;
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B: HDPE with NDZ105 modified BaTiO3; C: HDPE with SG-Si151 modified BaTiO3; D: HDPE
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with KH550 modified BaTiO3
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Table1 Chemical/commercial name and structure of coupling agents used in this study Chemical/commercial name
Molecular formation and structure C57H106O7Ti
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Isopropyl trioleic titanate
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(NDZ 105)
C8H18O3Si
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Vinyltriethoxysilane
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(SG-Si 151)
C9H23NO3Si
3-Aminopropyltriethoxysilane
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(KH550)
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Table 2 Formulation of HDPE/BaTiO3 composites used in this study (phr)
A B C D E
100 100 100 100 100
Untreated BaTiO3
NDZ105 treated BaTiO3
SG-Si151 treated BaTiO3
30 30 30
KH550 treated BaTiO3
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HDPE
30
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Sample No.
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Table 3 Surface tension of HDPE, untreated and treated BaTiO3 Surface tension (mJ/m2)
γ sd 30.08 37.84 55.76 38.60 38.84
γs
HDPE Untreated BaTiO3 NDZ105 modified BaTiO3 SG-Si151 modified BaTiO3 KH550 modified BaTiO3
35.26 75.37 63.28 73.25 75.81
γ sp 5.18 37.53 7.51 34.65 36.97
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Sample
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γ s : solid surface tension; γ sd :dispersive solid surface tension; γ sp :polar solid surface tension.
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Table 4 DSC characteristics of HDPE composites
Tmpeak
121.4 121.6 121.9 121.8 121.2
Xc
C
J/g
%
136.0 135.0 134.9 134.9 134.3
200.5 151.8 154.0 154.7 155.1
72.4 71.2 72.2 72.6 72.8
o
C
HDPE Control HDPE with untreated BaTiO3 HDPE with NDZ105 treated BaTiO3 HDPE with SG-Si151 treated BaTiO3 HDPE with KH550 treated BaTiO3
ΔH
o
C
132.2 131.5 131.6 131.3 131.0
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o
Tmfinal
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Tmonsett
Sample
Tmonset, onset melting temperature; Tmpeak , peak position in melting temperature range; Tmfinal ,
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final melting temperature; ΔH, enthalpy of fusion; Xc, relative crystallinity
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Table 5 Mechanical properties of HDPE composites
HDPE with untreated BaTiO3 HDPE with NDZ105 treated BaTiO3
Elongation at
(Shore D)
break (%)
Tensile strength (MPa)
64
859±32
29.3±1.4
66
55±20
26.6±1.8
66
161±67
25.7±2.1
66
46±12
27.7±0.7
66
357±42
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HDPE with SG-Si151 treated BaTiO3 HDPE with KH550
27.9±1.0
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treated BaTiO3
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HDPE Control
Hardness
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Sample
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Table 6 Volume and surface resistivity of HDPE composites Volume resistivity
Surface resistivity
Ω·m
Ω 2.08×108
8.45×1014
7.70×108
2.44×1014
6.93×108
3.54×1014
1.08×109
1.90×10
HDPE with untreated BaTiO3 HDPE with NDZ105 treated BaTiO3 HDPE with SG-Si151 treated BaTiO3 HDPE with KH550 treated BaTiO3
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HDPE Control
14
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Sample
1.00×109
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9.45×1013
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Figure 1
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Figure 2
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Figure 3
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Figure 4
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Figure 5
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Figure 6
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Figure 7
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Figure 8
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scheme 1
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S0169-4332(15)02575-1 http://dx.doi.org/doi:10.1016/j.apsusc.2015.10.156 APSUSC 31637
To appear in:
APSUSC
Received date: Revised date: Accepted date:
7-8-2015 29-9-2015 22-10-2015
Please cite this article as: J. Su, J. Zhang, Comparison of rheological, mechanical, electrical properties of HDPE filled with BaTiO3 with different polar surface tension, Applied Surface Science (2015), http://dx.doi.org/10.1016/j.apsusc.2015.10.156 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Comparison of rheological, mechanical, electrical properties of HDPE filled with BaTiO3 with different polar surface tension
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Jun Sua,b, Jun Zhang1a, a
Department of Polymer Science and Engineering, College of Materials Science and
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Engineering, Nanjing Tech University , Nanjing 210009, People’s Republic of China b
College of Mechanics Engineering, Nanjing Institute of Industry Technology, Nanjing, 210023,
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People’s Republic of China.
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Highlight (1) The non‐polar and short vinyl groups can greatly reduce G’ of HDPE composites. (2) Long chains on BaTiO3 surface enhance the interaction of BaTiO3 with HDPE. (3) Polar amino groups on BaTiO3 surface raise the interaction of BaTiO3 with HDPE. (4) Polar amino groups can boost the dielectric constant of HDPE composites. (5) The potential use in electronic equipment of the KH550 composites is obtained
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Abstract
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In this work, three types of coupling agents: isopropyl trioleic titanate (NDZ105),
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vinyltriethoxysilane (SG-Si151), 3-aminopropyltriethoxysilane (KH550) were applied to modify the surface tension of Barium titanate (BaTiO3) particles. The Fourier transform infrared (FT-IR)
spectra confirm the chemical adherence of coupling agents to the particle surface. The long
hydrocarbon chains in NDZ105 can cover the particle surface and reduce the polar surface tension of BaTiO3 from 37.53mJ/m2 to 7.51 mJ/m2, turning it from hydrophilic to oleophilic properties. The short and non-polar vinyl groups in SG-Si151 does not influence the surface tension of BaTiO3, but make BaTiO3 have both hydrophilic and oleophilic properties. The polar amino in
KH550 can keep BaTiO3 still with hydrophilic properties. It is found that SG-Si151 modified BaTiO3 has the lowest interaction with HDPE matrix, lowering the storage modulus of HDPE composites to the greatest extent. As for mechanical properties, the polar amino groups in KH550 on BaTiO3 surface can improve the adhesion of BaTiO3 with HDPE matrix, which increases the 1
Correspondence to: Jun Zhang ([email protected])
Page 1 of 31
elongation at break of HDPE composites to the greatest extent. In terms of electrical properties, the polar amino groups on surface of BaTiO3 can boost the dielectric properties of HDPE/BaTiO3 composites and decrease the volume resistivity of HDPE/BaTiO3 composites. The aim of this study is to investigate how functional groups affect the rheological, mechanical and electrical
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properties of HDPE composites and to select a coupling agents to produce HDPE/BaTiO3
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composites with low dielectric loss, high dielectric constant and elongation at break.
Keywords: High density polyethylene (HDPE); Barium titanate (BaTiO3); Surface tension;
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Rheology; Coupling agents; Mechanical and electrical properties
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1. Introduction
Dielectric polymer/ceramic composites have become much attractive in electric domain.[1] Among them, fluoride polymer/ceramic is commonly used to fabricate embedded and multilayer
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capacitors in electronic equipment, because of polar structure of matrix. [2] The presence of fluoride atom endows fluoride polymer/ceramic with the disadvantage of poor processability. [3] High Density Polyethylene (HDPE) is one of the widely used engineering materials with
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highly tactic structure. Such tactic structure can enhance the crystallinity of HDPE, which can
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both enhance the mechanical and electric properties of HDPE. [4, 5]What’s more, the crystal lattices can melt during process and then decrease the viscosity of HDPE, improving the processability at the meantime. The non-polar structure endows HDPE not only with good
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resistance to oxidation and solvents, but also with low dielectric constant and loss.[6] Because of high dielectric constant, Barium titanate (BaTiO3) is one of the most important
ceramic materials with perovskite structure and which is widely used in electronic applications.[7] The application of BaTiO3 has been limited because of its brittleness and high dielectric loss.[8, 9] So far, there are few reports about the incorporation of BaTiO3 into HDPE matrix to enhance
electrical properties of HDPE composites.[10] Thereby, it is interesting to incorporate BaTiO3 into
HDPE and obtain HDPE/BaTiO3 with high dielectric constant, low dielectric loss and improved toughness of BaTiO3.
The interface between BaTiO3 and HDPE is critical to the processability and overall properties of HDPE composites. [11] In literature, the application of coupling agents can improve the compatibility of inorganic fillers with polymer matrix. [12] In this study, BaTiO3 are modified by three types of coupling agents to introduce different functional groups on the surface of particles. The aim is to investigate how functional groups affect the rheological, mechanical and electrical properties of HDPE composites and to select a coupling agents to produce HDPE/BaTiO3 composites with low dielectric loss, high dielectric
Page 2 of 31
constant and elongation at break.
2. Experimental 2.1 Materials High Density Polyethylene (HDPE 4902T), used in this study, is purchased from Sinopec
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Yangzi Petrochemical company limited, China. The density of HDPE is 0.952g/cm3. The melt flow index of HDPE 4902T is 0.3g/10min at 190oC under 5kg. Barium titanate (BaTiO3) particles
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are supplied from Baosong electrically functional Co., Ltd. in Foshan, Guangdong province. The distribution of diameter of BaTiO3 particles is D10<0.6μm, D50<1.8μm, D90<5.0μm.
There are three types of coupling agents applied in this study. The chemical/commercial
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names and structures of these coupling agents are listed in Table 1. Isopropyl trioleic titanate (NDZ105), Vinyltriethoxysilane (SG-Si151), 3-Aminopropyltriethoxysilane (KH550), are
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obtained from Nanjing shuguang Chemical Group Co., Ltd, China.
(Table1)
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2.2 Sample preparation
2.2.1 Surface modification of BaTiO3
In this work, NDZ105, SG-Si151, and KH550 were utilized for surface modification of the
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BaTiO3 particles, respectively. The amount of coupling agents is 1% by weight (wt%) of BaTiO3
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amount. For instance, 1.0g of NDZ105 is mixed in 100ml isobutanol for 15min. BaTiO3 (100 g) is then added into such solution with a 30 min stirring. The treated BaTiO3 particles are then dried at
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60°C for 4h. Similarly, SG-Si151 and KH550 are applied to modify the BaTiO3 surface in the same procedure.
2.2.2 Extraction of modified BaTiO3 particles
The modified BaTiO3 is extracted in ether solvent by Soxhlet extractor for 4h at 70oC. Then,
the extracted BaTiO3 particles are dried at 40 oC for 6 h. 2.2.3 Compounding of HDPE/BaTiO3 composites
HDPE and three kinds of modified BaTiO3 are mixed by a two roll mixing mill (Shanghai
Rubber Machinery Works, China), respectively. The formulations of HDPE/BaTiO3 are shown in Table 2. Obtained HDPE composites are heat-pressed at 170°C. (Table 2 ) 2.3 Testing procedures 2.3.1 Fourier Transform Infrared Spectroscopy Fourier transform infrared spectroscopy (FT-IR) spectra of untreated, NDZ 105 modified, SG-Si 151 modified, KH550 modified BaTiO3 particles before and after extraction are measured
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with Nicolet spectrometer (model NEXUS 670, American) 2.3.2 Water contact angle and surface tension measurement Static water contact angle is measured in a drop shape analysis system (model: DSA 100 Krüss, Germany) at 24 oC. The surface tension is calculated by Owens and Wendt method, using
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the contact angles of both deionized water and diiodomethane solvent. 2.3.3 Rheological characterization
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Rheological properties of HDPE control and HDPE/BaTiO3 composites are characterized at 170°C in the range of frequency from 0.002 to 100 Hz by Rheo-Stress instrument (model
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MCR302, Anton Paar, Austria).
2.3.4 Differential Scanning Calorimetry (DSC) measurement
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The melting behaviors of HDPE control and HDPE/BaTiO3 composites are tested by DSC instrument (model Q20, TA, USA). Samples are firstly heated from 30 oC to 180 oC at 40 oC/min,
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and then are held at 180 oC for 5 min to eliminate the effect of thermal history. Secondly, the samples are cooled from 180 oC to 30 oC at 10 oC/min. Thirdly, the samples are heated again from
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30 oC to 180 oC at 10 oC/min. The relative crystallinity (Xc) of the HDPE/BaTiO3 composite is
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calculated according to Equation (1). [4]
ΔH ×100% (1) ϕ × ΔH *
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X c＝
Where ΔH* stands for the enthalpy of fusion of the perfect HDPE crystals and
ΔH stands for the fusion enthalpy of HDPE in HDPE/BaTiO3 composites. The ΔH* of HDPE is 277.1 J/g. φ is the weight fraction of HDPE in HDPE/BaTiO3 composites.
2.3.5 Scanning electron microscopy
The dispersion of BaTiO3 is detected by scanning electron microscopy (SEM) (model: JEOL
JSM-5900, Japan). 2.3.6 Mechanical properties The mechanical properties are measured by using electromechanical universal testing machine (model CMT 5254, Shengzhen SANS Testing Machine Co., Ltd. China), according to ISO 527. The Shore D hardness of the samples is measured by using a Shore D hardness degree tester (model LX-D Jiangsu Mingzhu Testing Machinery Co., Ltd., China).
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2.3.7 Electric properties 2.3.7.1 Volume and surface resistivity The volume and surface resistivity of HDPE/BaTiO3 composites are tested at 24oC by a high resistance meter , purchased from Shanghai Precision & Scientific Instrument Co., Ltd., China.
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2.3.7.2 Dielectric constant and dielectric loss
The dielectric constant and loss of HDPE/BaTiO3 composites are measured in the range of
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10k~10MHz with precision impedance analyzer (model 4294A, Agilent American) following
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IEC60243. 3. Results and discussion 3.1 FT-IR analysis
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FT-IR spectra are utilized to detect functional groups on BaTiO3 particles. Figure 1 and Figure 2 illustrate the spectra of coupling agents and modified BaTiO3 particles after soxhlet
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extraction, respectively. In Figure 1, it is shown that three coupling agents all have absorption peaks at 2922cm-1 and 2855 cm-1, assigned to asymmetric stretching vibration of methylene and symmetric stretching vibration of methylene, respectively. [12] Additionally, NDZ105 has
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absorption peak at 1733 cm-1, assigned to C=O stretching vibration of carboxyl group. SG-Si151
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has absorption peak at 1078 cm-1, assigned to Si-O-C rocking vibration. [11]The absorption peak
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of KH550 is at 1579 cm-1, assigned to transforming vibration of –NH. [13] Figure 2 shows FT-IR spectra of modified BaTiO3 after extraction. The coupling agents
which are physically adhered on the particle surface can be washed away by ether solvent during
the extraction. So the detection of absorption bands at 2922cm-1 and 2855 cm-1 after extraction can
prove the chemical adherence of three coupling agents to the surface of BaTiO3 particles. It is consistent with literature that alkoxy groups can alcoholize with hydroxyl groups on surface of inorganic particles and form chemical bonds between each other.[12, 14] (Fig.1) (Fig.2)
3.2 Water contact angle and surface tension measurement Water contact angles of HDPE resins and BaTiO3 are listed in Figure 3. It is apparent that the water contact angles of HDPE and untreated BaTiO3 is about 80o and 12o, respectively. The NDZ105 can greatly enhance the water contact angle of BaTiO3 from 12 o to about 130 o, while
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SG-Si151 and KH550 can slightly affect the water contact angle. The results of surface tension of modified BaTiO3 particles are shown in Table 3, which are calculated by Owens and Wendit method. The total surface tension ( γ s ) and polar surface tension
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( γ sp ) of inorganic BaTiO3 particles and HDPE follow the order: Untreated BaTiO3 ≈ KH550 modified BaTiO3 > SG-Si151 modified BaTiO3 > NDZ105 modified BaTiO3 > HDPE control.
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This reason is that the NDZ105 has non-polar and long hydrocarbon chains, which can cover the surface of BaTiO3 particles to the greatest extent, resulting in the fact that the surface of
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NDZ105 modified BaTiO3 particles changing from hydrophilic to hydrophobic properties. [15] By comparison, KH550 has polar amino groups, so the polar surface tension of BaTiO3
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particles is slightly varied.
Although vinyl groups in SG-Si151 are non-polar, they have short hydrocarbon chains. In
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this way, the surface of SG-Si151 modified BaTiO3 is only partially covered by non-polar vinyl groups, making the overall polar surface tension of BaTiO3 still high.[16]
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( Fig.3 )
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(Table 3)
3.3 Effect of coupling agents on dispersion properties of BaTiO3 in organic solvents
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Figure 4 shows dispersion of untreated BaTiO3 , NDZ105 modified, SG-Si151 modified and
KH550 modified BaTiO3 in two-phase solvent. Because of relatively high density, distilled water is at the bottom, while n-octane solvent is at the upper layer. It is shown from Figure 4 that the untreated BaTiO3 particles are suspended in bottom layer
of solvent, showing hydrophilic properties. In terms of modified BaTiO3 particles, NDZ 105 modified BaTiO3 particles disperse in the layer of n-octane, showing oleophilic properties;
SG-Si151 modified BaTiO3 particles disperse in the interface of two solvents, showing both hydrophilic and oleophilic properties; KH550 modified BaTiO3 disperse in the layer of water, showing hydrophilic properties.[17] Only the dispersion of SG-Si151 modified BaTiO3 is not as expected. Non-polar vinyl groups can only partially cover the surface of BaTiO3 and turn partial surface of BaTiO3 from hydrophilic to oleophilic properties. So, the rest of the BaTiO3 surface still has high polar surface tension and
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shows hydrophilic properties. In this way, SG-Si151 modified BaTiO3 particles show both hydrophilic to oleophilic properties and disperse in the interface of two solvents.
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(Fig.4)
3.4 Effect of coupling agents on rheological properties of HDPE composites
The storage modulus (G’) and loss modulus (G’’) of HDPE composites are
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shown in Figure 5A and 5B, respectively. It is obvious that G’ and G’’ of samples all
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increase with the grown frequency. The G’ and G’’ follow the order: HDPE with KH550 modified BaTiO3 > HDPE control ≈ HDPE with untreated BaTiO3 > HDPE with modified NDZ105 BaTiO3 > HDPE with SG-Si151 modified BaTiO3.
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Generally, filler can interact with the polymer matrix to increase the storage modulus of composites. But the incorporation of untreated BaTiO3 has little effect on
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the G’, because the content of BaTiO3 is less than 5vol%, and there is few functional groups on the surface of BaTiO3, which means less interaction between BaTiO3 and
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HDPE matrix.[18]
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Scheme 1 shows the possible dispersion models of BaTiO3 in HDPE matrix. It is shown that the modification can improve the aggregation and dispersion of BaTiO3.
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Coupling agent KH550 has polar amino groups which can restrict the motion of
non-polar HDPE chains. Thus, the interaction between HDPE matrix and BaTiO3
particles is strong, resulting in higher storage modulus. Coupling agent NDZ105 has non-polar and long hydrocarbon chains. The polar
surface tension of NDZ105 modified BaTiO3 (7.51mJ/m2) is close to that of HDPE
control (5.18mJ/m2), but the long hydrocarbon chains can entangle with HDPE matrix
to increase the interaction between BaTiO3 and HDPE matrix. In this way, the G’ of
HDPE with NDZ105 modified BaTiO3 is only a little lower than that of HDPE control. By comparison, SG-Si151 has non-polar vinyl groups with relatively shorter molecular chains. So SG-Si151 modified BaTiO3 can non only have excellent compatibility with HDPE matrix, but also have little physical entanglement with
Page 7 of 31
HDPE chains. Thereby, the interaction of BaTiO3 particles with HDPE matrix is the weakest, leading to the lowest value of storage modulus. It is illustrated in Figure 5C that with the increase of frequency, the curves of G’/G’’ ratios of all samples grow. Only the G’/G’’ of HDPE control and HDPE with
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SG-Si151 modified BaTiO3 are below 1 at low frequency. The non-polar vinyl groups
in SG-Si151 have great compatibility with HDPE matrix and slightly hinder the
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motion of HDPE molecular chains. Thus, their G’/G’’ is below 1 at low frequency.
For other three HDPE composites, the G’/G’’ are all above 1 in the range of test
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frequency, meaning the solid-like behavior of HDPE composites. This is due to the fact that the interaction of these modified BaTiO3 particles with HDPE matrix is
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strong. [19]
The G’/G’’ rations of these two specimens exceed 1 at higher frequency, meaning
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a rheological transition from liquid-like behavior to solid-like behavior at 0.193 Hz for both specimens. This transition is ascribed to the interconnected structures formed
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in HDPE control and HDPE with SG-Si151 modified BaTiO3, at high frequency. [20] Figure 5D shows the Van Gurp plot with the loss phase angle δ versus the
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absolute value of the complex modulus |G*|. [19]It is clear that when |G*| is lower
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than 25033 Pa, the phase angle of HDPE composites are all lower than that of HDPE control. In literature, loss angle is sensitive to long and branched structure of polymer and the Van Gurp curve can shift to lower value of the phase angle, with increased long branch content. [4, 21]It seems that only when |G*| is lower than 25033 Pa, the varied phase angle can show more branched structure content among HDPE matrix to some extent, caused by the incorporation of BaTiO3 particles. (Fig.5 ) (Scheme 1)
3.5 Effect of coupling agents on crystallization of HDPE composites Table 4 lists DSC characteristics of HDPE composites. It is found that the onset onset melting temperature ( Tm ) of all samples are almost the same. The peak melting peak
temperature ( Tm
final
), final melting temperature ( Tm
) and relative crystallinity (Xc) of
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HDPE/BaTiO3 composites are a little different. The addition of un-modified BaTiO3 particles can both reduce the melting enthalpy (ΔH) and the crystallization degree (Xc) of HDPE composites. Because BaTiO3 particles in HDPE composites do not absorb heat and release heat, the
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enthalpy of HDPE/BaTiO3 composite listed in Table 5 is the enthalpy of HDPE in
HDPE/BaTiO3 composites. In terms of HDPE/BaTiO3 composites, the mass ratio of
cr
HDPE to HDPE/BaTiO3 composite is 1:1.3, so the enthapy of HDPE in
HDPE/BaTiO3 composites is remarkably lower than enthalpy of HDPE control. When
us
calculating the crystallinity degree (Xc), the ethalpy of HDPE in HDPE/BaTiO3 composites and HDPE control was used at the same amount, according to Equation 1.
an
At the same HDPE amount, the ethalpy of HDPE in the HDPE with untreated BaTiO3 is 197.3J/g (151.8J/g multiplying 1.3), which is slightly lower than that of HDPE
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control. This is consistent with literature in which the incorporation of inorganic filler can decrease theΔH and Xc.of polyolefin. [4, 5] Generally, crystallinity is correlated
d
with the chain’s ability to pack into crystal lattices. The addition of untreated BaTiO3
decrease of ΔH and Xc.
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particles can hinder the pack of molecular chains into the crystal lattice, leading to the
Ac ce p
The functional groups of coupling agents on surface of BaTiO3 particles can increase the interaction of BaTiO3 particles with HDPE matrix and facilitate the pack of molecular chains into the crystal lattice, resulting in relatively higher Xc value than that of HDPE with un-modified particles.[22]
(Table 4 )
3.6 Effect of coupling agents on filler dispersion in HDPE composites Scanning electron micrographs (Figure 6) shows the dispersion of BaTiO3 in HDPE matrix. It is found that after surface modification, modified BaTiO3 particles also aggregate, but the interface between BaTiO3 and HDPE matrix become ambiguous, meaning the improved interaction. This can be explained by the fact the surface treatment of BaTiO3 particles can increase the interaction of BaTiO3 with
Page 9 of 31
HDPE matrix but affect the aggregation a little. [17] (Fig. 6 )
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3.7 Effect of coupling agents on mechanical properties of HDPE composites
The data of mechanical properties of HDPE/BaTiO3 composites are shown in
elongation at break of HDPE control from 859% to 55%.
cr
Table 5. It is observed that the addition of untreated BaTiO3 can greatly lower the
us
Compared to that of untreated BaTiO3, the addition of NDZ105 and KH550 modified BaTiO3 can improve the elongation at break of HDPE composites from 55%
an
to 161% and 357%, respectively. The surface modification of BaTiO3 by SG-Si151 has little effect on the elongation of break of HDPE with untreated BaTiO3 composite.
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The reason is that the long hydrocarbon chains from NDZ105 on BaTiO3 surface can physically entangle with HDPE matrix and that polar amino groups from KH550 on BaTiO3 surface can increase interfacial adhesion between BaTiO3 particle and
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HDPE matrix. While SG-Si151 can only bring non-polar vinyl groups without other
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long chains and polar groups. Thereby, the elongation at break of HDPE with un-modified BaTiO3 only can be lifted by the use of NDZ105 and KH550 modified
Ac ce p
BaTiO3. In literature, the 1wt% BaTiO3 coated with polydopamine can enhance the
beta-phase of poly(vinylidene fluoride) (PVDF), resulting in improvement of both tensile strength and elogation at break. However, the polar F groups make PVDF
more difficult to process than HDPE which has excellent fluidiy during manufacuturing.[23]
Although the un-modified BaTiO3 can decrease the crystallinity of HDPE
composites to a little extent, it can slightly lift the hardness of HDPE composites at 24oC temperature. It is reported that the increased crystallinity and filler amount can both enhance the hardness of polymer composites.[24] It is seemed in this study, that the addition of un-modified BaTiO3 plays the dominant effect on the rise of composite hardness. It is observed that the incorporation of modified and un-modified BaTiO3
Page 10 of 31
particles can reduce the tensile strength of HDPE control. It has been proved that the addition of BaTiO3 particles can decrease the crystallinity of HDPE control. In literature, the crystalline lattices can provide strength for composites to resist outside
ascribed to the decreased crystallinity of HDPE composites. [25]
3.8 Effect of coupling agents on electric properties
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3.8.1 Effect of coupling agents on dielectric properties
cr
( Table 5 )
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forces.[5] In this study, the reduced tensile strength of HDPE control can be mainly
Figure 7 and 8 show curves of relative dielectric constant and loss of HDPE
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composites in the range of frequency from 10kHz to 10 MHz. The dielectric constants of HDPE composites follow the order: HDPE with KH550 modified BaTiO3 > HDPE
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with SG-Si151 modified BaTiO3 ≈ HDPE with untreated BaTiO3 > HDPE with NDZ105 modified BaTiO3 > HDPE control. It is consistent with literature that the
d
increasing BaTiO3 can increase the dielectric constant of polymer composites.[26] In general, the relative dielectric constant is mainly correlated with the polarity
te
of composites. [11] It is mentioned above that coupling agent KH550 has polar
Ac ce p
amino groups which can boost the entire polarity of HDPE composites. In contrast, SG-Si151 has non-polar vinyl groups which partially cover the
surface of BaTiO3, making partial surface of BaTiO3 are still responsive to cyclic electric excitation. [9]
What’s more, NDZ105 has non-polar and long hydrocarbon chains, which can
greatly cover the surface of BaTiO3, leaving less surface of BaTiO3 responsive to cyclic electric excitation. In this way, the dielectric constant of HDPE with NDZ105 modified BaTiO3 is lower than HDPE with non-modified BaTiO3. It is observed from Figure 8 that the relative dielectric loss of HDPE composites
decreases drastically in the range of 10kHz~40kHz, and further decreases gradually in the frequency range of 40kHz~10MHz. The addition of un-modified and modified BaTiO3 can enhance the dielectric loss of HDPE composites, meaning that the energy lost during cyclic electric excitation is
Page 11 of 31
boosted by surface modification. (Fig. 7 ) (Fig.8 )
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3.8.2 Effect of coupling agents on volume and surface resistivity Table 6 illustrates the volume resistivity and surface resistivity of HDPE
composites. It is observed that HDPE with KH550 modified BaTiO3 exhibits the
cr
lowest volume resistivity of HDPE.
us
The addition of un-modified BaTiO3 particles can increase the resistivity of HDPE composites, meaning BaTiO3 is non-conductive particles. [12]In terms of KH550 modified BaTiO3, the polar amino groups can provide polarity for easy
an
passage of current in HDPE with KH550 modified BaTiO3, leading to the decreased volume resistivity.
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The addition of particles has the trend to enhance the surface resistivity of HDPE composites. This may be due to the fact that surface resistivity is mainly correlated
d
with the surface texture and material itself. It is shown that the coupling agents have
(Table 6 )
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te
little effect on surface resistivity of HDPE/BaTiO3 composites.
4. Conclusions
It is proved by FT-IR and contact angle measurements that the surface modification of
BaTiO3 by NDZ105, SG-Si151 and KH550 can attach chemically non-polar hydrocarbon groups,
non-polar vinyl groups and polar amino groups to the surface of BaTiO3 particles, respectively. The dispersion of powders in solvents shows NDZ105 modified, SG-Si151 modified and
KH550 modified exhibit oleophilic properties, both hydrophilic and oleophilic properties, and oleophilic properties, respectively. In terms of rheological properties, the polar amino groups from KH550 have remarkable interaction with HDPE matrix, and raise the storage modulus of HDPE composites. Although the non-polar long hydrocarbon chains from NDZ105 can greatly decrease the polar surface tension of BaTiO3, the long chains also can physically entangle with molecular chains in HDPE, leading to
Page 12 of 31
slight decrease of G’. Only non-polar and short vinyl groups from SG-Si151 can remarkably decrease the storage and loss modulus of HDPE/BaTiO3 composites. As for mechanical properties, the polar amino groups can improve the adhesion of BaTiO3 in HDPE matrix, which increases the elongation at break of HDPE composites to the greatest extent.
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By comparison, the NDZ105 modified BaTiO3 particles with long hydrocarbon chains can also increase the elongation at break of HDPE composites.
cr
The dielectric constant of HDPE with KH550 modified BaTiO3 is the highest among other composites, due to the presence of polar amino groups. What is more, the presence of polar amino
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groups on surface of BaTiO3 facilitates the passage of current in HDPE matrix and then lowers volume resistivity of HDPE with KH550 modified composite .
an
In sum, KH550 is selected as the optimum coupling agents, because HDPE with KH550 treated BaTiO3 has the highest dielectric constant of HDPE composites. In addition, after
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incorporation of 30wt% BaTiO3, HDPE with KH550 treated BaTiO3 still has 357% elongation at
Acknowledgements
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break.
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The authors gratefully acknowledge the Priority Academic Program Development of Jiangsu
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Higher Education Institutions (PAPD).
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d
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Figure captions Fig.1 Spectra of three coupling agents Fig.2 Spectra of treated BaTiO3 after extraction Fig.3 Water contact angle of HDPE and BaTiO3
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Fig.4 Dispersion of BaTiO3 in a two-phase solvent, the bottom layer solvent is distilled water and the upper layer solvent is n-octane: A. Untreated BaTiO3; B. NDZ105 modified BaTiO3;C.
cr
SG-Si151 modified BaTiO3;D. KH550 modified BaTiO3 .
Fig.5 Rheological properties of HDPE composites: A. Storage modulus; B. Loss modulus; C.
us
Curves of G’/G’’ ratios; D. Van Gurp plot.
Fig. 6 SEM micrographs of HDPE with various coupling agents, A: HDPE with untreated BaTiO3;
with KH550 modified BaTiO3
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Fig.8 Dielectric loss of HDPE composites
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Fig. 7 Dielectric constant of HDPE composites
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B: HDPE with NDZ105 modified BaTiO3; C: HDPE with SG-Si151 modified BaTiO3; D: HDPE
Scheme1 Possible dispersion models of BaTiO3 in HDPE matrix: A: HDPE with untreated BaTiO3;
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B: HDPE with NDZ105 modified BaTiO3; C: HDPE with SG-Si151 modified BaTiO3; D: HDPE
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with KH550 modified BaTiO3
Page 16 of 31
Table1 Chemical/commercial name and structure of coupling agents used in this study Chemical/commercial name
Molecular formation and structure C57H106O7Ti
ip t
Isopropyl trioleic titanate
cr
(NDZ 105)
C8H18O3Si
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Vinyltriethoxysilane
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(SG-Si 151)
C9H23NO3Si
3-Aminopropyltriethoxysilane
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d
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(KH550)
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Table 2 Formulation of HDPE/BaTiO3 composites used in this study (phr)
A B C D E
100 100 100 100 100
Untreated BaTiO3
NDZ105 treated BaTiO3
SG-Si151 treated BaTiO3
30 30 30
KH550 treated BaTiO3
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HDPE
30
cr
Sample No.
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Table 3 Surface tension of HDPE, untreated and treated BaTiO3 Surface tension (mJ/m2)
γ sd 30.08 37.84 55.76 38.60 38.84
γs
HDPE Untreated BaTiO3 NDZ105 modified BaTiO3 SG-Si151 modified BaTiO3 KH550 modified BaTiO3
35.26 75.37 63.28 73.25 75.81
γ sp 5.18 37.53 7.51 34.65 36.97
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Sample
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γ s : solid surface tension; γ sd :dispersive solid surface tension; γ sp :polar solid surface tension.
Page 19 of 31
Table 4 DSC characteristics of HDPE composites
Tmpeak
121.4 121.6 121.9 121.8 121.2
Xc
C
J/g
%
136.0 135.0 134.9 134.9 134.3
200.5 151.8 154.0 154.7 155.1
72.4 71.2 72.2 72.6 72.8
o
C
HDPE Control HDPE with untreated BaTiO3 HDPE with NDZ105 treated BaTiO3 HDPE with SG-Si151 treated BaTiO3 HDPE with KH550 treated BaTiO3
ΔH
o
C
132.2 131.5 131.6 131.3 131.0
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o
Tmfinal
cr
Tmonsett
Sample
Tmonset, onset melting temperature; Tmpeak , peak position in melting temperature range; Tmfinal ,
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final melting temperature; ΔH, enthalpy of fusion; Xc, relative crystallinity
Page 20 of 31
Table 5 Mechanical properties of HDPE composites
HDPE with untreated BaTiO3 HDPE with NDZ105 treated BaTiO3
Elongation at
(Shore D)
break (%)
Tensile strength (MPa)
64
859±32
29.3±1.4
66
55±20
26.6±1.8
66
161±67
25.7±2.1
66
46±12
27.7±0.7
66
357±42
cr
HDPE with SG-Si151 treated BaTiO3 HDPE with KH550
27.9±1.0
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treated BaTiO3
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HDPE Control
Hardness
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Sample
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Table 6 Volume and surface resistivity of HDPE composites Volume resistivity
Surface resistivity
Ω·m
Ω 2.08×108
8.45×1014
7.70×108
2.44×1014
6.93×108
3.54×1014
1.08×109
1.90×10
HDPE with untreated BaTiO3 HDPE with NDZ105 treated BaTiO3 HDPE with SG-Si151 treated BaTiO3 HDPE with KH550 treated BaTiO3
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HDPE Control
14
cr
Sample
1.00×109
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9.45×1013
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te
d
M
an
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Figure 1
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Figure 2
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Figure 3
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Figure 4
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Figure 5
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Figure 6
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Figure 7
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Figure 8
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scheme 1
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