Effects of Macromolecular Compatibilizers Containing Epoxy Groups

Ind. Eng. Chem. Res. 2010, 49, 6291–6301

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Effects of Macromolecular Compatibilizers Containing Epoxy Groups on the Properties of Linear Low-Density Polyethylene/Magnesium Hydroxide Composites Zhen Yang,† Chengang Zhou,† Jun Cai,† Han Yan,† Xin Huang,† Hu Yang,*,† and Rongshi Cheng†,‡ Key Laboratory for Mesoscopic Chemistry of MOE, Department of Polymer Science and Technology, School of Chemistry and Chemical Engineering, Nanjing UniVersity, Nanjing 210093, P. R. China, and College of Material Science and Engineering, South China UniVersity of Technology, Guangzhou 510641, P. R. China

The effects of two kinds of macromolecular compatibilizers, poly(ethylene-co-glycidyl methacrylate) (PE-co-PGMA) and poly(ethylene-co-methyl acrylate-co-glycidyl methacrylate) (PE-co-PMA-co-PGMA), both containing epoxy groups, on the properties of linear low-density polyethylene (LLDPE)/magnesium hydroxide (MH) composites were studied in this work. On the basis of the experimental results from the mechanical test, thermal stability analysis, and scanning electron microscopy (SEM) observation, both PE-co-PGMA and PE-co-PMA-co-PGMA were demonstrated to be efficient compatibilizers. In order to investigate the compatibilization mechanism, further characterization by particle size and a particle size distribution analyzer, SEM-energy dispersive X-ray spectroscopy (EDX), and attenuated total reflectionFourier transform infrared (ATR-FTIR) were carried out, respectively. It was found that the epoxy groups on the compatibilizers played a very important role in modification of the LLDPE/MH system. The compatibilizers conglutinated tightly on the surface of MH though ring-open reactions between the epoxy group and hydroxyl of MH; furthermore, the long organic chains of compatibilizers entwisted with LLDPE through van der Waals force. The fracture morphology observation of LLDPE/MH composites also showed that MH particles were closely united with polymer matrix through the compatibilizers. Therefore, the compatibility between MH and LLDPE was enhanced, which improved the final performances of the LLDPE/MH composites further. 1. Introduction Recently, halogen-free flame retardants have been paid more attention, since the usage of traditional halogen-base ones have been limited due to the issues such as corrosiveness, smoke emission, and toxicity of the combustion products.1,2 Therein, magnesium hydroxide (MH), a kind of important halogen-free flame retardants, is more promising, since its endothermic decomposition temperature is higher than the processing temperature of many polymer materials, in addition to its characteristics of environment-benefit, smoke suppression, and filling.1-7 Therefore, preparation of polymer/MH composites is greatly meaningful to improve the fire retardancy of polymer materials. However, high loading of MH (usually about 60 wt %)8 is generally necessary to achieve an acceptable level of flame retardancy. Such a high loading level must result in the serious deterioration of mechanical properties of composites for the poor compatibility between inorganic and organic phases.3-5,9 Furthermore, it is well-known that good dispersibility of inorganic particles in a polymer matrix is a determining factor for getting satisfactory mechanical and thermal properties of composites.10 However, agglomeration of MH particles always counteracts the homogeneous dispersion of inorganic particles into the polymer matrix. These drawbacks restrict the application range of the inorganic/organic composites. In order to inhibit agglomeration of MH particles and improve the compatibility between the inorganic particles and polymer matrix further, surface modification to MH particles have been carried out. Surface modifiers including macromolecular11-28 * To whom correspondence should be addressed. Tel.: 86-2583686350. Fax: 86-25-83317761. E-mail: [email protected]. † Nanjing University. ‡ South China University of Technology.

and low-molecular weight29,30 compatibilizers have been both applied. Compared to low-molecule-weight ones in which hydrophobic chains are too short to entangle with the polymer matrix tightly, macromolecular compatibilizers are more beneficial to improve the mechanical properties of the composites in virtue of their longer organic chains.11 Therefore, more and more attentions have been paid to macromolecular compatibilizers in recent years. As for the polyolefin/inorganic filler systems, researchers have tried many different kinds of macromolecular compatibilizers11-28 based on various functional groups on the hydrophobic chains. Chiang et al.12 employed matrix graft modification using polypropylene-graft-acrylic acid (PP-g-AA) on PP/MH composites and found that mechanical properties and thermal resistance were improved. Mai et al.13,14 also used acrylic acid modified PP as a compatibilizer to PP/MH composites based on a mechanical properties test and fracture morphology observation, and they believed that addition of compatibilizers improved the interfacial interaction and enhanced the interface adhesion between MH and the matrix. Jancar15 tried PP-g-maleic anhydride (MAH) as a compatibilizer to PP/MH composites and indicated PP-g-MAH enhanced the interfacial adhesion. Fang et al.16 used maleic anhydride-graft-thylene-propylene rubber (EPR-g-MAH) as an additive in very low-density polyethylene (VLDPE)/MH composites. SEM images showed that the MH particles were totally embedded in the additive phase. Shen et al.17,18 studied the effects of PP-g-MAH and POE-g-MAH on thermal stability and crystallization behavior of PP/MH composites, respectively, and gave a depth explanation about compatibilization of macromolecular compatibilizers. Uotila et al.19 found that hydroxyl functionalized copolymers (PE-coOH and PP-co-OH), which they prepared by themselves, were unsuccessful in improving the toughness of PP/elastomer/

10.1021/ie100610j  2010 American Chemical Society Published on Web 06/25/2010

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Ind. Eng. Chem. Res., Vol. 49, No. 14, 2010

Table 1. Compositions of Various Composites compositions (wt %) sample code LLDPE M0 M1-2 M1-6 M1-10 M2-2 M2-6 M2-10

compatibilizer

PE-co-PGMA PE-co-PMA-co-PGMA

compatibilizer MH*a LLDPE 0 0 2 6 10 2 6 10

0 55 55 55 55 55 55 55

100 45 43 39 35 43 39 35

a MH* represents pure MH mixed with 5 wt % zinc borate and 1 wt % stearic acid (i.e., charge ratio of MH/zinc borate/stearic acid ) 100/5/ 1 by weight).

microsilica composites because the nature of the functional groups of the copolymer might have hindered its miscibility with the PP matrix. In addition to the macromolecular compatibilizers as mentioned above, many other novel compatibilizers were also reported in the literature, such as PE grafted with dibutyl maleate (PE-g-DBM),20 maleanised polybutadiene (MPBD),21 m-phenylenebismaleimide (BMI),22 maleic anhydride grafted poly[styrene-b-(ethylene-co-butylene)-b-styrene] (SEBS-g-MAH),23-25 poly(ethylene-co-glycidyl methacrylate),26 poly(ethylene-co-propylene) elastomer,27 acrylonitrile butadiene ultrafine fully vulcanized powdered rubber (NB-UFPR)11 and PP modified with vinyltriethoxysilane (PP-VTES).28 All of them improved mechanical and/or thermal properties more or less. As an important kind of polyolefin, linear low-density polyethylene (LLDPE) has been already applied widely in housing, transportation, electrical engineering, and many other fields.5 However, there has been little work related to LLDPE/ MH composites modified by macromolecular compatibilizers. Moreover, our previous work30 about the effects of several various silane coupling agents on LLDPE/MH composites have shown that, among five applied silane coupling agents, KH560 showed the best performances, and the epoxy groups on KH-560 played a key role. Therefore, in this work, poly(ethyleneco-glycidyl methacrylate) (PE-co-PGMA) containing epoxy groups also has been tried to LLDPE/MH composites as macromolecular compatibilizers first. Furthermore, poly(methyl acrylate) (PMA) showed nice flexibility, and additional soft segments were believed to be helpful for improvement of the elongation of composites. Poly(ethylene-co-methyl acrylate-coglycidyl methacrylate) (PE-co-PMA-co-PGMA) has been used as another compatibilizer here, which had an equivalent content of PGMA segment with PE-co-PGMA for further comparison. The influences of two macromolecular compatibilizers as mentioned above to the performances of LLDPE/MH compos-

Figure 1. TG curves of LLDPE and LLDPE/MH composites modified by the different content of (a) PE-co-PGMA and (b) PE-co-PMA-co-PGMA measured under air flow. Insert figure: TG curves of pink s, pure LLDPE; black s, LLDPE/MH composite without any compatibilizer.

ites and their compatibilization mechanisms were studied, respectively. 2. Experimental Section 2.1. Materials. LLDPE (type DFDA-7042, d ) 0.92 g/cm3; melt flow index, 1.7-2.3 g/10 min at 190 °C with a pressure of 2.16 kg, respectively) was supplied by Sinopec Yangzi Petrochemical Co., Ltd. (Nanjing, China). MH (BET surface area, 6.79 m2/g) was supplied by Chuangye Co. (Yixing, China). Poly(ethylene-co-glycidyl methacrylate) (8 wt % content of glycidyl methacrylate; d ) 0.94 g/cm3 at 25 °C; softening point, 87 °C; melt point, 99 °C; melt flow index, 5 g/10 min at 190 °C with a pressure of 2.16 kg, respectively) and poly(ethylene-

Table 2. Mechanical and Thermal Properties of Various LLDPE/MH Composites mechanical properties

a

thermal properties

sample code

tensile strength (MPa)

elongation at break (%)

main peak temperature in DTG curves of thermal oxidative degradation (°C)

LLDPE PE-co-PGMA PE-co-PMA-co-PGMA M0 M1-2 M1-6 M1-10 M2-2 M2-6 M2-10

18.5 ( 0.3 12.9 ( 0.3 4.1 ( 0.3 9.4 ( 0.1 13.9 ( 0.2 14.3 ( 0.2 16.3 ( 0.2 10.3 ( 0.2 12.7 ( 0.1 13.1 ( 0.2

1089.1 ( 37.6 717.3 ( 29.9 337.2 ( 12.8 10.4 ( 0.4 15.2 ( 0.4 21.7 ( 0.9 30.4 ( 0.8 9.7 ( 0.4 20.0 ( 0.6 36.2 ( 1.0

377.4/461.0a 440.5 439.9 471.4 472.0 468.2 475.8 467.7 485.2 485.2

Two peaks in the DTG curve of neat LLDPE.


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Figure 2. DTG curves of LLDPE and LLDPE/MH composites modified by the different content of (a) PE-co-PGMA and (b) PE-co-PMA-co-PGMA measured under air flow. Insert figure: TG curves of pink s, pure LLDPE; black s, LLDPE/MH composite without any compatibilizer.

co-methyl acrylate-co-glycidyl methacrylate) (8 wt % content of glycidyl methacrylate and 25 wt % content of methyl acrylate, d ) 0.94 g/cm3 at 25 °C; softening point, lower than 40 °C; melt point, 39 °C; melt flow index, 6 g/10 min at 190 °C with a pressure of 2.16 kg, respectively) were both purchased from Sigma-Aldrich Corporation. Two compatibilizers were marked as PE-co-PGMA and PE-co-PMA-co-PGMA, respectively. Stearic acid (A.R.) was supplied by Huakang Technology Co. (Nanjing, China). Zinc borate was supplied by Wenhua Flameretardant materials Co. Ltd. (Wenzhou, China) as a synergist, and the chemical formula for this grade was 2ZnO · 3B2O3 · 3.5H2O. 2.2. Preparation of LLDPE/MH Composites. According to the formulations described in Table 1, the MH powder, compatibilizer and other synergic agents, including stearic acid for better processing ability5,31 and zinc borate as the synergist,5,6,32 were mixed in a high-speed mixer (Type FW100; Taisite Instrument Co. Ltd.; Tianjin, China) with a rotor speed of 24 000 r/min for 20 min first. Then, the LLDPE/MH composites were prepared by melt-blending on a twin-roll open mill (Type XK-160; New Jinling Rubber Machinery Co.; Nanjing, China) at ∼125 °C for 5 min. After LLDPE melted, the modified MH was added into the mill. At last, the composites with a standard size for further testing were prepared in a lamination of plastic press tester (Type GT-7014-P; GOTECH Testing Machine Co., Ltd.; Dongguan, China), and the mold of 100 mm × 100 mm × 2 mm was used for each sample. The detailed preparing process is the following: the composites were compressed in a heat press for 5 min at 3.45 MPa and 150 °C

Figure 3. DTG and DSC curves of (a) LLDPE, (b) MH, and (c) composite M0 measured under air flow (black s, DTG curve; red s, DSC curve).

Figure 4. Scanning electron micrograph of fracture surface of composite M0.

at the first step; then in the heat press for another 5 min at 7.59 MPa and 150 °C; finally in a cold press at 2.07 MPa until the samples reached room temperature.

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Figure 5. Scanning electron micrographs of fracture surface of composites: (a) M1-2, (b) M1-6, and (c) M1-10.

Figure 6. Scanning electron micrographs of fracture surface of composites: (a) M2-2, (b) M2-6, and (c) M2-10.


2.3. Mechanical Properties Measurements. The testing specimens were stamped with an ASTM D1078-06 standard die. The mechanical properties (tensile strength and elongation at break) were measured at a tensile speed of 50 mm/min at 25 °C under the humidity of 60% by a universal material tester (Type Instron-4466; Instron Test Machine Trading Co., Ltd.). Five specimens were tested for each sample. 2.4. Thermal Analysis. Thermogravimetric (TG) and differential scanning calorimetric (DSC) analysis of composites (about 10 mg) were carried out under air atmosphere purge (30 mL/min) from 20 to 600 °C at a scanning rate of 10 °C/min by an integrative thermal analyzer instrument (Type STA-449C; NETZSCH Instrument Co. Ltd.; Germany). The temperature error of thermal analysis was less than 1 °C, and the mass error was less than 0.1 mg. 2.5. Scanning Electron Microscope (SEM) and Energy Dispersive X-ray (EDX) Spectroscopy. The composites were broken after cooled below their glass transition temperature by liquid nitrogen for keeping the original morphologies. The morphologies of the fracture surfaces after being sputter coated with gold were observed directly with a scanning electron microscope (type SSX-550; Shimadzu Co.; Japan) using an acceleration voltage of 25.0 kV. The EDX images and element analysis of MH particles, as well as the SEM images, were obtained by the same scanning electron microscope using 15.0 kV acceleration voltage. 2.6. Particle Size and Particle Size Distribution Analysis. Particle size and particle size distributions of dried modified MH samples were analyzed by particle size and the particle size distribution analyzer (type MasterSizer 2000; Malvern Instruments Co. Ltd.; U.K.). In the statistical analysis for the particle size and particle size distribution, the particle was assumed to be an equivalent spherical particle structure, which had the same volume as the original particle. 2.7. Attenuated Total Reflectance-Fourier Transform Infrared Spectroscopy (ATR-FTIR). In order to make comparison with the modified MH samples prepared in section 2.2, simple mixtures of MH* and compatibilizer were manually prepared with the same dose as preparation of modified MH in section 2.2 by a mortar. Both modified MH samples and simple mixtures of MH and compatibilizers were packed with filter paper and extracted using CHCl3 as solvent in the Soxhlet apparatus for 60 h to remove free compatibilizers. Finally, the samples were dried at 50 °C in a vacuum oven for 48 h. ATR-FTIR spectra were recorded using a Fourier transform infrared spectrometer (type IFS 66/ S; Bruker Co.; Germany) with Pike MIRacle ATR accessory. The interval of tested wave numbers was 650-4000 cm-1. 3. Results and Discussion 3.1. Mechanical Properties. Table 2 listed the tensile strength and elongation at break data of various LLDPE/MH composites. From Table 2, it was found that the tensile strength and the elongation at break of sample M0, without any compatibilizer, both decreased sharply after loading 55 wt % of MH* into the LLDPE matrix, which was ascribed to the poor compatibility between the MH and polymer matrix. Besides, at such a high loading level of MH, the rigid particles contributed very much to reduce the elongation of the composites. However, the mechanical properties were improved efficiently when PE-co-PGMA or PE-co-PMA-co-PGMA was incorporated into the composites. On the basis of Tables 1 and 2, the mechanical properties of composites, whether modified by PEco-PGMA or PE-co-PMA-co-PGMA, became better and better

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Figure 7. Particle size distribution curves of MH samples modified by (a) PE-co-PGMA and (b) PE-co-PMA-co-PGMA. Table 3. Molar Percentage of Elements on the Surface of Various MH Particles by EDX Element Analyses elements samples MH* MH* modified by PE-co-PGMAa MH* modified by PE-co-PMA-co-PGMAa a

carbon (%)

magnesium (%)

oxygen (%)

7.62 16.25

29.66 20.20

59.60 57.06

12.95

23.48

52.98

Charge ratio of MH*/compatiblizer ) 55/10 by weight.

with the increase of the contents of macromolecular compatibilizers. When the content of compatibilizers reached to 10 wt %, the tensile strength of sample M1-10 and M2-10 increased near 7 and 4 MPa, as well as the elongation at break were about 3.0 and 3.6 times higher than the corresponding values of sample M0, respectively. Moreover, according to the preparation formulations listed in Table 1, the content of compatibilizers increased from 2% to 10%, and nearly 20% of the LLDPE resin was replaced by the macromolecular compatibilizers. However, from Table 2, both the tensile strength and the elongation at break of two pure macromolecular compatibilizers themselves were lower than those of neat LLDPE. Therefore, the increase of the mechanical properties of composites was fully ascribed to the improvement of the compatibility between MH and LLDPE substantially by compatibilizers. In addition, the lower tensile strength and higher elongation at break in the case of M2-10 in comparison with M1-10 were

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Figure 8. SEM-EDX images of the untreated MH* sample. (a) Scanning electron micrograph, distribution of elements: (b) carbon, (c) magnesium, and (d) oxygen on the MH particle surface.

observed in Table 2 also, which might be due to the presence of a soft PMA segment of PE-co-PMA-co-PGMA compatibilizer in the M2-10 formulation. Furthermore, compared to the LLDPE/MH composites modified by KH-560,29,30 which also contained epoxy groups, those composites modified by macromolecular compatibilizers showed better mechanical performances for a more tight entanglement between the longer hydrophobic chains of the compatibilizers and the polymer matrix. 3.2. Thermal Analysis. Then, further thermal stability of the composites in air was investigated by thermogravimetric analysis (TG). TG and DTG curves of various samples were shown in Figures 1 and 2, respectively. (TG and DTG curves of two pure macromolecular compatibilizers were shown in the Supporting Information, Figures S1 and S2 as reference). Main peak temperatures in DTG curves of various samples were also calculated and summarized in Table 2. It was found that there were two large peaks in the DTG curve of neat LLDPE corresponding to the degradation of LLDPE with low and high molecular weight, respectively. In addition, according to Table 2, two pure macromolecular compatibilizers both showed lower thermal stability than neat LLDPE. However, after MH was filled into LLDPE, the thermal stability of polymer was increased evidently. In the DTG curve

of each LLDPE/MH composites as shown in Figure 2, both degradation peaks shifted to higher temperature and the lower degradation peak turned smaller. For detailing the thermal behaviors of various composites, differential scanning calorimetric analysis (DSC) was measured. The DSC curves of LLDPE, MH, and composites of M0 without any compatibilizer were supplied in Figure 3, respectively. With the comparison with DSC curves of LLDPE (Figure 3a) and MH (Figure 3b), the small exothermic peak (around 380 °C) and small endothermic peak (around 410 °C) of composites M0 in Figure 3c obviously corresponded to the decomposition of LLDPE with low molecular weight and MH, respectively. In addition, from the TG curve of M0 as shown in Figure 1, nearly 18% weight loss before 420 °C has been observed, which was corresponding to the first step of M0 degradation as shown in Figure 2. Furthermore, it could be calculated that the decomposition of all MH in M0 would cause 16.5% weight loss. So after MH has been added into the polymer matrix, the original lower degradation peak of neat LLDPE, as shown in the insert of Figure 2, was delayed and combined with the higher one, and only a very small amount of LLDPE with low molecular weight degraded around 380 °C. Moreover, on the basis of the results of DSC, TG, and DTG as shown in Figures 1, 2 and 3 and Supporting Information Figures S3 and


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Figure 9. SEM-EDX images of MH* sample modified by PE-co-PGMA (charge ratio of MH*/PE-co-PGMA ) 55:10 by weight). (a) Scanning electron micrograph, distribution of elements: (b) carbon, (c) magnesium, and (d) oxygen on the MH particle surface.

S4, the composites modified by various macromolecular compatibilizers had similar thermal behaviors to the composite of M0 without any compatibilizer. Therefore, the small peaks of DTG curves at lower temperature (about 400 °C) in Figure 2 were corresponding to the degradation of almost all MH and a very small amount of LLDPE with low molecular weight. On the other hand, the large peaks of DTG curves in Figure 2 were corresponding to the degradation of residual LLDPE. Furthermore, according to Figure 2 and Table 2, although neither the lower peak nor the higher peak temperatures in DTG curves showed linear dependence with the contents of compatibilizers, composites modified by 10 wt % of PE-co-PGMA as well as PE-co-PMA-co-PGMA, both had higher thermal stability. It was fully due to better dispersion of MH in the LLDPE matrix. In addition, composites M2-10 had a slightly higher peak temperature than M1-10 in DTG curves. It was inferred that the MH particles might facilely gravitate toward the soft PMA phase,19 which was more advantageous for uniform dispersing of MH in the polymer matrix. Therefore, in terms of the mechanical and thermal properties of LLDPE/MH composites, PE-co-PMA-co-PGMA and PE-coPGMA both showed good performances as efficient compatibilizers. However, in comparison with PE-co-PGMA, PE-coPMA-co-PGMA did not shown obvious improvement. Hence

it could be concluded that the PGMA segment, rather than PMA, played the key role in compatibilization. 3.3. Scanning Electron Microscope Measurement of Fracture Surface of the Composites. In order to study the macroscopic properties of composites as mentioned above, micromorphology investigation of the LLDPE/MH composites was carried out by SEM. The SEM images of the fracture surface of various composites were shown in Figures 4, 5, and 6, respectively. It was found from Figure 4 that the MH particles in M0 sample were not dispersed well in the polymer matrix without any compatibilizer. Many debonded MH particles occurred clearly on the fracture surface. Furthermore, there were many large gaps between LLDPE and MH, which all indicated poor adhesion and compatibility between MH and polymer matrix. However, for the composites modified by PE-co-PGMA (M1) and PE-co-PMA-co-PGMA (M2) as shown in Figures 5 and 6, respectively, the gaps became less and less, the surface looked more and more homogeneous wholly, and the dispersion of MH appeared better and better as the content of the compatibilizers increased. Moreover, when the content of the compatibilizers increased to 10 wt %, no clear interfaces between MH and polymers could be observed and most of MH particles in the

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Figure 10. SEM-EDX images of MH* sample modified by PE-co-PMA-co-PGMA (charge ratio of MH*/PE-co-PMA-co-PGMA ) 55:10 by weight). (a) Scanning electron micrograph, distribution of elements: (b) carbon, (c) magnesium, and (d) oxygen on the MH particle surface.

composites were encapsulated well in the polymer matrixes as shown in Figure 5c and 6c. The micromorphology analysis of LLDPE/MH composites was fully coincident with the results of mechanical properties measurement and thermal oxidative stability analysis, which indicated that both PE-co-PGMA and PE-co-PMA-co-PGMA acted as efficient compatibilizers for LLDPE/MH composites. 3.4. Particle Size and Particle Size Distribution Analysis. For investigation of the compatibilization mechanisms of both PE-co-PGMA and PE-co-PMA-co-PGMA in the LLDPE/MH system, further characterizations for the modified MH particles, by particle size and the particle size distribution analyzer, SEM-EDX, and ATR-FTIR, were carried out, respectively. The curves of particle size distribution of various MH samples modified by PE-co-PGMA and PE-co-PMA-co-PGMA, respectively, were shown in Figure 7. It was similarly manifested that, in both parts a and b of Figure 7, as the content of the compatibilizers increased, a new peak corresponding to the larger particle size of modified MH particles appeared and the proportion of the new peak turned larger and larger. When the content of the compatibilizers increased to 10 wt %, the smaller peak corresponding to original particle size of unmodi-

fied MH nearly disappeared, and the shape of the curves for the particle size distribution of MH almost turned into a single peak again. From Figure 7, another interesting fact was found that the average size of MH modified by either compatibilizers was nearly 10 times larger than that of unmodified ones, which indicated that the original individual MH particles agglomerated to form larger size particles after surface modification. For the characteristics of long chains, it was believed that, on the backbone of the macromolecular compatibilizers, there were many active sites suitable to adsorb MH particles through certain interaction between compatibilizers and MH, which might induce agglomeration of MH particles during the modification process. Furthermore, it could be inferred that the agglomerated MH particles were encapsulated by macromolecular compatibilizers to form a core-shell structure.19 On the basis of Figure 7, it was obvious that nearly all of the individual MH have been induced to agglomerate, and encapsulated, when the content of compatibilizers reached 10 wt %. Moreover, the encapsulated MH particles had good compatibilization with LLDPE matrix, though the size of modified MH turned bigger. Furthermore, in comparison with KH-560,29,30 the average particle size of MH modified by macromolecular compati-


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Figure 11. ATR-FTIR spectra of (a) MH*, (b)PE-co-PGMA, (c) the simple mixture of MH* and PE-co-PGMA (charge ratio of MH*/PE-co-PGMA is 55:10 by weight), and (d) MH* modified by PE-co-PGMA (charge ratio of MH/PE-co-PGMA is 55:10 by weight).

Figure 12. ATR-FTIR spectra of (a) MH*, (b)PE-co-PMA-co-PGMA, (c) the simple mixture of MH* and PE-co-PMA-co-PGMA (charge ratio of MH*/ PE-co-PMA-co-PGMA is 55:10 by weight), and (d) MH* modified by PE-co-PMA-co-PGMA (charge ratio of MH/PE-co-PMA-co-PGMA is 55:10 by weight).

bilizers was much larger, which might to be ascribed to longer hydrophobic chains of macromolecular compatibilizers and different compatibilization mechanisms. 3.5. Scanning Electron Microscope and Energy Dispersive X-ray Spectroscopy of MH Particles. Followed by for investigating the encapsulated core-shell structure of modified MH particles further, SEM-EDX was applied for element analysis of MH particle surfaces. The molar percentages of carbon, magnesium, and oxygen on the surface of MH particles untreated and treated by macromolecular compatibilizers were listed in Table 3, respectively, and the concurrent SEM-EDX images of these samples were shown in Figures 8, 9, and 10, respectively. Compared to the rough surface of untreated MH particles as shown in Figure 8a, it was found that modified MH particles exhibited more smooth and well-defined surfaces as shown in Figure 9a and Figure 10a. Moreover, on the surface of untreated sample as shown in Figure 8b, the

element distribution of carbon was random, which was contrasted to the element distribution of magnesium (Figure 8c) and oxygen (Figure 8d). Furthermore, according to Table 3, the molar ratio of the oxygen to magnesium element was equal to 2:1 corresponding to the stoichiometric proportion of oxygen to magnesium element in Mg(OH)2. Whereas, Figure 9b and Figure 10b demonstrated that carbon was enriched on the surface of modified MH particles. In addition, the molar ratio of oxygen to magnesium element on the surface of modified MH particles was both higher than 2:1, which sufficiently proved that compatibilizers were enriched on the surface of MH due to a certain interaction between the compatibilizer and MH. 3.6. ATR-FTIR Analysis. For further investigation of the molecular coupling mechanism, ATR-FTIR analysis was applied to study which kind of interactions was between the compatibilizers and MH, chemical bond (strong interaction) or physical adsorption (weak interaction).

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Figure 11 and Figure 12 gave the ATR-FTIR spectra of various MH samples modified by two macromolecular compatibilizers, respectively. For unmodified MH particles as shown in Figure 11a and 12a, there was a sharp and intense peak at 3693 cm-1, which was attributed to the O-H vibration of MH. The ATR-FTIR spectrum of PE-co-PGMA shown in Figure 11b represented the characteristic peaks of methylene (>CH2, 2916 and 2848 cm-1), carbonyl in ester (sCdO, 1734 cm-1), ether (sCsOsC, 1144 cm-1), and epoxy group (910 cm-1)33 on PE-co-PGMA, respectively. For comparison, a simple mixture of MH and compatibilizers with the same dose as modified MH has been prepared, and the absence of the characteristic peaks of compatibilizers, in Figure 11c, indicated that the compatibilizer was not able to be detected, which meant that the compatibilizers could not enrich and enwrap on the surface of MH particles just by simple mixing. However, as for modified MH, the presence of absorptions at 2916, 2848, and 1734 cm-1, in Figure 11d, was fully coincident with SEM-EDX analysis that there was enriched PE-co-PGMA on the surface of MH. Moreover, the absence of absorptions at 1144 and 910 cm-1 in Figure 11d provided clear evidence that chemical reaction has taken place on the surface of MH, and the compatibilizers grafted tightly on the surface of MH by the ring-open reactions between epoxy group and the hydroxyl of MH. As for the compatibilizer PE-co-PMA-co-PGMA, the ATR-FTIR spectra were shown in Figure 12, which illustrated the similar results to PE-co-PGMA. It can be concluded that epoxy groups as the active sites in the compatibilizers played a very important role in modification of the LLDPE/MH system. 4. Conclusions Above all, two macromolecular compatibilizers, PE-coPMA-co-PGMA and PE-co-PGMA, which contained epoxy groups, both showed good performances in LLDPE/MH composites. On the one hand, the epoxy ring of the macromolecular compatibilizers was facile to open and link with the hydroxyl of MH as the active sites, which formed a core-shell structure. On the other hand, the long organic chains of compatibilizers on the shell entwisted with polymers through van der Waals forces. The two effects enhanced the compatibility between inorganic fillers and polymer matrixes and improved the final performances of the composites. Supporting Information Available: TG and DTG curves of PE-co-PGMA and PE-co-PMA-co-PGMA and DSC curves of LLDPE/MH composites modified by different contents of PE-co-PGMA and PE-co-PMA-co-PGMA. This material is available free of charge via the Internet at http://pubs.acs.org. Literature Cited (1) Li, X.; Ma, G. B.; Liu, Y. Y. Synthesis and Characterization of Magnesium Hydroxide Using a Bubbling Setup. Ind. Eng. Chem. Res. 2009, 48, 763. (2) Marosfoi, B. B.; Garas, S.; Bodzay, B.; Zubonyai, F.; Marosi, G. Flame retardancy study on magnesium hydroxide associated with clays of different morphology in polypropylene matrix. Polym. AdV. Technol. 2008, 19, 693. (3) Horrocks, A. R., Price, D., Eds. Fire Retardant Materials; Woodhead Publishing Ltd: Cambridge, U.K., 2001. (4) Hornsby, P. R. Fire retardant fillers for polymers. Int. Mater. ReV. 2001, 46, 199. (5) Weil, E. D.; Levchik, S. V. Flame retardants in commercial use or development for polyolefins. J. Fire Sci. 2008, 26, 5.

(6) Zhang, Y. X., Ed. Manual of Optimal Design of Flame Retardants Production Formula and Application of New Materials; Yinsheng AudioVideo Publishing House: Changchun, China, 2005. (7) Rothon, R. N.; Hornsby, P. R. Flame retardant effects of magnesium hydroxide. Polym. Degrad. Stab. 1996, 54, 383. (8) Wang, Z. Z.; Qu, B. J.; Fan, W. C.; Huang, P. Combustion characteristics of halogen-free flame-retarded polyethylene containing magnesium hydroxide and some synergists. J. Appl. Polym. Sci. 2001, 81, 206. (9) Nie, S. B.; Song, L.; Guo, Y. Q.; Wu, K.; Xing, W. Y.; Lu, H. D.; Hu, Y. Intumescent Flame Retardation of Starch Containing Polypropylene Semibiocomposites: Flame Retardancy and Thermal Degradation. Ind. Eng. Chem. Res. 2009, 48, 10751. (10) Poovarodom, S.; Hosseinpour, D.; Berg, J. C. Effect of Particle Aggregation on the Mechanical Properties of a Reinforced Organic-Inorganic Hybrid Sol-Gel Composite. Ind. Eng. Chem. Res. 2008, 47, 2623. (11) Gui, H.; Zhang, X. H.; Dong, W. F.; Wang, Q. G.; Gao, J. M.; Song, Z. H.; Lai, J. M.; Liu, Y. Q.; Fan, H.; Qiao, J. L. Flame retardant synergism of rubber and Mg(OH)2 in EVA composites. Polymer 2007, 48, 2537. (12) Chiang, W. Y.; Hu, C. H. Effect of matrix graft modification using acrylic acid on the PP/Mg(OH)2 composites and its possible mechanism. J. Polym. Res. 2000, 7, 15. (13) Mai, K. C.; Qiu, Y. X.; Lin, Z. D. Mechanical properties of Mg(OH)2/polypropylene composites modified by functionalized polypropylene. J. Appl. Polym. Sci. 2003, 88, 2139. (14) Qiu, Y. X.; Lin, Z. D.; Mai, K. C. Fracture morphology of Mg(OH)2/polypropylene composites modified by functionalized polypropylene. J. Appl. Polym. Sci. 2003, 88, 2148. (15) Jancar, J. Influence of the Filler Particle-Shape on the Elastic-Moduli of PP/CaCO3 and PP/Mg(OH)2 Composites, 2. Enhanced Interfacial Adhension. J. Mater. Sci. 1989, 24, 4268. (16) Fang, Z. P.; Hu, Q. L. Influence of interfacial adhesion on stressstrain properties of highly filled polyethylene. Angew. Makromol. Chem. 1999, 265, 1. (17) Shen, H.; Wang, Y. H.; Mai, K. C. Effect of compatibilizers on thermal stability and mechanical properties of magnesium hydroxide filled polypropylene composites. Thermochim. Acta 2009, 483, 36. (18) Shen, H.; Wang, Y. H.; Mai, K. C. Non-isothermal crystallization behavior of PP/Mg(OH)2 composites modified by different compatibilizers. Thermochim. Acta 2007, 457, 27. (19) Uotila, R.; Hippi, U.; Paavola, S.; Seppala, J. Compatibilization of PP/elastomer/microsilica composites with functionalized polyolefins: Effect on microstructure and mechanical properties. Polymer 2005, 46, 7923. (20) Wang, Z. Z.; Qu, B. J.; Fan, W. C.; Hu, Y. A.; Shen, X. F. Effects of PE-g-DBM as a compatiblizer on mechanical properties and crystallization behaviors of magnesium hydroxide-based LLDPE blends. Polym. Degrad. Stab. 2002, 76, 123. (21) Liauw, C. M.; Dumitru, P.; Lees, G. C.; Clemens, M. L.; Rothon, R. N. Interfacial modification of polystyrene-block-polybutadiene-blockpolystyrene/magnesium hydroxide composites, 1-Effect on rheological properties. Macromol. Mater. Eng. 2003, 288, 412. (22) Liauw, C. M.; Khunova, V.; Lees, G. C.; Rothon, R. N. The role of m-phenylenebismaleimide (BMI) in reactive processing of poly(propylene)/magnesium hydroxide composites, 3 - Analysis of interphase structure development. Macromol. Mater. Eng. 2000, 279, 34. (23) Liu, S. P.; Ying, J. R.; Zhou, X. P.; Xie, X. L.; Mai, Y. W. Dispersion, thermal and mechanical properties of polypropylene/magnesium hydroxide nanocomposites compatibilized by SEBS-g-MA. Compos. Sci. Technol. 2009, 69, 1873. (24) Chang, S. Q.; Xie, T. X.; Yang, G. S. Morphology and flameretardancy properties of ternary high-impact polystyrene/elastomer/ polystyrene- encapsulated magnesium hydroxide composites. J. Appl. Polym. Sci. 2008, 108, 2488. (25) Chang, S. Q.; Xie, T. X.; Yang, G. S. Interfacial modification of high impact polystyrene magnesium hydroxide composites effects on flame retardancy properties. J. Appl. Polym. Sci. 2008, 110, 578. (26) Hippi, U.; Mattila, J.; Korhonen, M.; Seppala, J. Compatibilization of polyethylene/aluminum hydroxide (PE/ATH) and polyethylene/magnesium hydroxide (PE/MH) composites with functionalized polyethylenes. Polymer 2003, 44, 1193. (27) Wang, Z. Z.; Shen, X. F.; Fan, W. C.; Hu, Y.; Qu, B. J.; Gui, Z. Effects of poly(ethylene-co-propylene) elastomer on mechanical properties and combustion behaviour of flame retarded polyethylene/magnesium hydroxide composites. Polym. Int. 2002, 51, 653. (28) Nachtigall, S. M. B.; Miotto, M.; Schneider, E. E.; Mauler, R. S.; Forte, M. M. C. Macromolecular coupling agents for flame retardant materials. Eur. Polym. J. 2006, 42, 990. (29) Yang, Z.; Cai, J.; Zhou, C. G.; Zhou, D.; Chen, B. F.; Yang, H.; Cheng, R. S. Effects of the Content of Silane Coupling Agent KH-560 on

Ind. Eng. Chem. Res., Vol. 49, No. 14, 2010 the Properties of LLDPE/Magnesium Hydroxide Composites. J. Appl. Polym. Sci. 2010, DOI: 10.1002/app.32600. (30) Yang, Z.; Zhou, C. G.; Zhou, D.; Chen, B. F.; Yang, H.; Cheng, R. S. Modification of Linear Low Density Polyethylene-Magnesium Hydroxide Flame Retardant Composites. Chin. Petrochem. Technol. 2010, 39, 315. (31) Zweifel, H., Ed. Plastic AdditiVes Handbook, 5th ed.; Carl Hanser Verlag: Munich, Germany, 2001. ¨ lku¨, S. Effect of Temperature and (32) Eltepe, H. E.; Balko¨se, D.; U Time on Zinc Borate Species Formed from Zinc Oxide and Boric Acid in Aqueous Medium. Ind. Eng. Chem. Res. 2007, 46, 2367.

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(33) Li, C. H.; Ge, Z. S.; Fang, J.; Liu, S. Y. Synthesis and SelfAssembly of Coil-Rod Double Hydrophilic Diblock Copolymer with Dually Responsive Asymmetric Centipede-Shaped Polymer Brush as the Rod Segment. Macromolecules 2009, 42, 2916.

ReceiVed for reView March 13, 2010 ReVised manuscript receiVed June 1, 2010 Accepted June 11, 2010 IE100610J

Effects of Macromolecular Compatibilizers Containing Epoxy Groups

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