Synergetic effect of a reactive compatibilizer and OMMT on the

Subscriber access provided by UNIV OF NEW ENGLAND ARMIDALE

Materials and Interfaces

Synergetic effect of a reactive compatibilizer and OMMT on the dispersion of PA6/PDMS blend with a high viscosity ratio Di Wang, Lian-Fang Feng, Xue-Ping Gu, Jiajun Wang, Cailiang Zhang, and Aihua He Ind. Eng. Chem. Res., Just Accepted Manuscript • Publication Date (Web): 12 Feb 2019 Downloaded from http://pubs.acs.org on February 12, 2019

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 22 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Industrial & Engineering Chemistry Research

Synergetic effect of a reactive compatibilizer and OMMT on the dispersion of PA6/PDMS blend with a high viscosity ratio

Di Wang1, Lian-Fang Feng1, Xue-Ping Gu1, Jia-Jun Wang1, Cai-Liang Zhang1*, Ai-Hua He2*

1State

Key Laboratory of Chemical Engineering, College of Chemical and Biological

Engineering, Zhejiang University, Hangzhou, Zhejiang 310027, China 2Shandong

Provincial Key Laboratory of Olefin Catalysis and Polymerization, Key

Laboratory of Rubber-Plastics (Ministry of Education ), School of Polymer Science and Engineering, Qingdao University of Science and Technology, Qingdao, Shandong 266042, China.

*Corresponding author: [email protected] (CL ZHANG) and [email protected] (AH He)

ACS Paragon Plus Environment

Industrial & Engineering Chemistry Research 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Abstract: The synergetic effect of a reactive compatibilizer and organo-montmorillonite (OMMT) on phase morphology and properties of polyamide 6 (PA6)/polydimethylsilicone (PDMS) blend with a high viscosity ratio of dispersed phase and matrix was studied. A small amount of an amine-terminated copolymer of polyether amine (PEA) and PDMS (PDMS-b-PEA) as a reactive compatibilizer can decrease significantly the dispersed phase domain size. However, the dispersed phase domain size has still been above 2 μm even when the PDMS-b-PEA concentration reaches 5 wt%. OMMT as the second additive can further decrease dramatically the dispersed phase domain size due to the barrier effect for preventing effectively the coalescence of dispersed phase domain. Moreover, the presence of PDMS-b-PEA can promote the uniform dispersion of OMMT. The synergetic effect of PDMS-b-PEA and OMMT can also improve tensile properties and decrease water absorption.

Keywords: polyamide; PDMS; blend; reactive compatibilizer; OMMT


Page 2 of 22

Page 3 of 22 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


1. Introduction Polyamide 6 (PA6), as one of the most common engineering plastics, is widely applied in many industrial field such as automobile, building and electronic device due to its excellent resistance to mechanical fatigue, thermal and many chemical substances1-3. However, the drawbacks of PA6 such as high moisture absorption and low-temperature impact strength limit its further application4, 5. As we all know, blending with existing other polymers is a very attractive and inexpensive route to produce balanced properties for a specific end-use6-8. Polydimethylsilicone (PDMS) possessing excellent elasticity and hydrophobicity may be a good additive to make up for those shortcomings of PA69-11. However, since PA6 and PDMS are mutually immiscible, a compatibilizing technology is vital to promote the dispersion of PDMS in PA6 as well as to improve their properties. A constant approach for improving the compatibility of immiscible polymer blend is to add or in-situ form a block or graft copolymer whose segments are chemically identical to or having affinity with the polymer components as a compatibilizer12-16. A multi-block copolymer of PA6 and PDMS as a compatibilizer could reduce the dispersed phase size of PA6/PDMS (80/20 by mass) by two times17. However, the size of dispersed phase domain had still been above 10 μm, which seemed that the copolymer didn’t play a great role in improving their compatibility. Different from the conventional polymer blends, the viscosity ratio of dispersed phase and matrix for the PA6/PDMS blend under melting processing is very large because the viscosity of PDMS as a rubber only slightly decreases with temperature while that of PA6 dramatically decreases. It is usually accepted that a high viscosity ratio is adverse to the dispersion of polymer blend, which may weaken the compatibilizing performance of copolymer. Apart from the copolymers, nanoparticles such as graphene18, carbon nanotube19, organo-montmorillonite (OMMT)20, 21 were also proved to be an efficient additive to reduce the dispersed domain size of immiscible polymer blend. For example, Khutua et al.22 found that an incorporation of a small amount of organoclay caused a substantial reduction of the size of dispersed poly(ethylene-ran-propylene) rubber (EPR) domain in the PA6 matrix. Liu et al.23 further indicated that the coarsening rate of PA6/acrylonitrile-butadiene-styrene



(ABS) blend annealed at a high temperature decreased significantly with an introduction of nano-silica. A lot of efforts have been paid on trying to identify the mechanisms involved in the morphology stabilization against coalescence by nanoparticles. The majority of authors conclude that the most probable mechanism is a physical barrier or rheology effect rather than a decrease of interfacial tension. More specifically, rheological measurements had demonstrated that when the concentration of nano-silica was beyond 2 wt%, a particle network would be formed to inhibit the movement of polymer melt and thus suppressed the coarsening process24. Khatua et al.22 further found that those nanoparticles failed to enhance the compatibility and interfacial adhesion between two immiscible polymers. Moreover, nanoparticles may form some stacks resulting in a negative effect on properties of polymer blend. Therefore, a further introduction of copolymer as an interfacial compatibilizer might be required to make up for the above defects. Some research work25, 26 have proved that the combination of compatibilizer and nanoparticle can exhibit joint effect on the immiscible thermoplastic polymer blend. However, seldom work has been reported about the thermoplastic polymer/rubber blend with a high viscosity ratio of dispersed phase and matrix. In this study, the joint role of reactive compatibilizer and OMMT on immiscible PA6/PDMS blend with a high viscosity ratio was investigated. The rationale behind choosing OMMT as the nanoparticle is that the silicate layers are well-known to be completely exfoliated in PA6 matrix. The reactive compatibilizer contains a segment of polyether immiscible with PA6 and PDMS, which can be easier to migrate into the interface to react with PA6, and then stabilize at the interface to improve the interfacial adhesion.

2. Experimental Section 2.1. Materials Two types of PA6 used in this study were of commercial grade 1013B and 1030B from UBE Nylon Ltd., Thailand. The viscosity of the latter named as PA6-H is higher than that of the former. PDMS (Mw=650000 g/mol) as the dispersed phase were provided by Jiangsu Tianchen New Material Co., Ltd. Na+-montmorillonite was provided by Zhejiang Fenghong New Material Co., Ltd. Prior


Page 4 of 22

Page 5 of 22 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


to usage, it was modified by the ion exchange reaction to increase the domain spacing of Na+-montmorillonite. The modification procedure was as follow: 20 g of OMMT was first introduced into 2000 mL distilled water. After 10 min of stirring, 9 g of stearyltrimethyllammonium (C18M3) was introduced into the OMMT suspension. And then a vigorous stirring was carried out. After the occurrence of white precipitate, the suspension was filtered and flushed repeatedly by distilled water. Finally, the product was dried and ground into sieves with 200 meshes. Octamethylcyclotetrasiloxane (D4) (Jiangsu Tianchen New Materials Co.), polyether amine

(PEA,

Mw=900

g/mol)

(ED900,

Huntsman

Petrochemical

Co.),

1,1,3,3-tetramethydisiloxane (TMDS) (Jiangsu Tianchen New Materials Co.) and allyl glycidyl ether (AGE) (Aladdin Industrial Co.) were used to prepare the reactive compatibilizer. D4 is distilled over CaH2 before usage, and others were used as received.

2.2. Synthesis of the Reactive Compatibilizer As shown in Figure 1, the reactive compatibilizer synthesized in our lab is composed of PDMS chain and PEA chain, which denoted as PDMS-b-PEA. Basically, the route to synthesize the reactive compatibilizer consists of three steps. The first one is to prepare α, ω-dihydrogen terminated polydimethylsiloxane (H-PDMS). D4 (49.33 g), TMDS (0.67 g) and catalyst (cationic resin) (7.5 g) were in order introduced into a three-necked reactor and then reacted at 55 ºC. After 6 h, the resulting mixture was charged into methanol to separate H-PDMS by filtration, and then was dried in a vacuum oven at 60 ºC for 12 h. The number average molecular weight of as-obtained H-PDMS is 20000 g/mol. The second step is to produce α,ω-diepoxy terminated polydimethylsiloxane (E-PDMS). In the presence of Karstedt platinum catalyst (50 ppm latinum complex in isopropanol), the as-synthesized H-PDMS was reacted with allyl glycidyl in toluene at 70 ºC for 2 h followed by at 80 ºC for 5 h. And then, E-PDMS was precipitated in methanol and dried in a vacuum oven at 60 ºC for 12 h. The last step is to produce the desired reactive compatibilizer through the reaction between epoxy functional groups of E-PDMS and amine functional groups of PEA in isopropanol at 80 ºC for 6 h. The molar ratio of E-PDMS and PEA is 1:1.1. After isopropanol was removed by reducing pressure, the reactive compatibilizer PDMS-b-PEA was obtained.



CH3 PEA H2C CH O H2C H2C H2C Si O HO PEA: NH2

CH3 CH CH3

CH2

O

x

CH3

Page 6 of 22

CH3

Si O Si H2C H2C H2C O HC H2 C PEA n OH CH3 CH3

C2H4O

y

CH

CH2

CH3

O

z

CH2 CH NH2 CH3

Figure 1. Molecular structure of reactive compatibilizer PDMS-b-PEA. 2.3. Blend Preparation Polymer blends were prepared by mixing the components in a batch mixer (HL-200, Jilin University of science and education instrument plant) equipped with two counter rotating rotors in 50 cm3 mixing chamber. Prior to blending, PA6 was dried in a vacuum oven at 80 °C for 12 h. All blend components were introduced simultaneously into the mixing chamber and were mixed at 100 rpm and 230 °C. After 10 min of mixing, samples were taken from the mixing chamber and then quenched in liquid nitrogen to freeze-in their morphologies. 2.4. Quiescent Annealing Pieces of blend samples of about 20 mm thick were warped with coppery netting and then annealed in a silicone oil bath at 230 ºC. After a certain annealing time, they were taken out from the oil-bath and then quenched immediately in liquid nitrogen to freeze the morphologies. 2.5. Measurement Scanning electron microscope (SEM): Blend morphologies were observed by SEM of type SU3500. Before SEM observation, samples were first fractured in liquid nitrogen and then immersed in toluene at room temperature for 12 h to etch the PDMS domains. After being dried in a vacuum oven at 80 ℃ for 12 h, samples were sputtered with gold for 3 min. The voltage for SEM observation was 5 kV. A semiautomatic image analysis method was used to determine the dispersed phase domain diameter (di). The volume average diameter of dispersed phase domain, dv, can be calculated by Eq (1).


Page 7 of 22 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


dv

n d  n d

4

i i 3

(1)

i i

Transmission electron microscope (TEM): The dispersion and location of OMMT in the blend was studied by TEM of type JEM-1230 operating at an accelerating voltage of 90 kV. Samples were ultra-microtomed into a thickness of 100 nm under a cryogenic condition. Owing to different electron constrasts between PA6 and PDMS, staining was not needed. The OMMT appeared dark in TEM images due to much higher electron density than neat polymers. Rheological behavior: The rheological behaviors of polymer components and their blends were measured by HAAKE RS6000 with a dynamic mode. Samples were disks of 25 mm in diameter and about 2 mm in thickness. The strain amplitude was set 10%, which is in the range of the linear viscoelastic shear oscillation. The test was performed within the frequency range from 100 to 0.1 rad/s. Tensile property: Tensile properties of polymer components and their blends were tested using a universal test machine (UTM2102, Shenzhen Suns Technology Stock Co. LTD.) according to GB16421-1996. All tests were carried out at room temperature. Water absorption: Cubic samples with a length in 40 mm, width in 10 mm, and thickness in 4 mm were first dried in a vacuum oven at 80 °C for 12 h and cooled in a desiccator. The samples were weighed, m1, and immersed in pure water. After 24 h, the samples were taken out from distilled water and weighed, m2, the water absorption, w, was calculated according to the following equation: 𝑤=

𝑚2 ― 𝑚1 𝑚1

× 100%

(2)

3. Results Figure 2 presents SEM micrographs of PA6/PDMS (80/20 by mass) blends with various amounts of PDMS-b-PEA. When a very small amount of PDMS-b-PEA (0.25 wt%) is added, the dispersed phase domain size significantly decreases. This implies that amide groups of PDMS-b-PEA can react with carboxyl groups of PA6 to form the copolymer of PDMS and PA6 and reduce effectively the interfacial tension. This can be further confirmed from the



emulsification curve essentially following the evolution of the dispersed phase domain size with the PDMS-b-PEA concentration shown in Figure 3. More specifically, an introduction of 0.25 wt% PDMS-b-PEA into the PA6/PMDS (80/20 by mass) blend can dramatically decrease the dispersed phase domain size from 11.7 to 3.5 μm, and then a slowly gradual decrease in the dispersed phase domain size with further increasing the amount of PDMS-b-PEA. However, it should be noted that the dispersed phase domain size is still above 2 μm even when the PDMS-b-PEA concentration reaches 5 wt%.

Figure 2. SEM micrographs of microtomed surfaces of various PA6/PDMS (80/20 by mass) blends without and with PDMS-b-PEA as a reactive compatibilizer. The PDMS-b-PEA concentrations are 0% (a), 0.25% (b), 0.5% (c), 2% (d) and 5% (e), respectively.


Page 8 of 22

Page 9 of 22

12 Without OMMT 2% OMMT

9

dv (m)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


6

3

0

0

1

2

3

4

5

PDMS-b-PEA concentration (wt%)

Figure 3. Emulsification curve of PA6/PDMS (80/20 by mass) blends with and without 2 wt% OMMT in the presence of PDMS-b-PEA as a reactive compatibilizer. After adding 2 wt% OMMT, the emulsification curve of PA6/PDMS (80/20 by mass) blends with different amounts of PDMS-b-PEA as the reactive compatibilizer is also shown in Figure 3. On the one hand, a critical compatibilizer concentration (Ccrit), above which the dispersed domain size does not decrease any further but leveled off, drops down to 0.5 wt% comparing with that in absence of OMMT. On the other hand, for the PA6/PDMS (80/20 by mass) blend without PDMS-b-PEA, the dispersed phase domain size sharply decreases from 11.7 to 2.7 μm by adding 2 wt% OMMT. When a very small amount of PDMS-b-PEA (0.5 wt%) is used, the dispersed phase domain size further decreases to 1.0 μm which is about one third of that without OMMT. This indicates that the joint effect of OMMT and PDMS-b-PEA can reduce effectively the critical compatibilizer concentration and the dispersed phase domain size of PA6/PDMS blends. The joint effect of OMMT and PDMS-b-PEA can be further seen from the plots of the dispersed phase domain size of three blend systems vs the blending time shown in Figure 4. The dispersed phase domain size of PA6/PDMS (80/20 by mass) containing 2 wt% OMMT and 0.5 wt% PDMS-b-PEA simultaneously is far smaller than that of PA6/PDMS/OMMT (80/20/2 by mass) and PA6/PDMS/PDMS-b-PEA (80/20/0.5 by mass) blends. Moreover, the blending time reaching an equilibrium size for the former is shorter than that for the latter two. More specifically, for adding separately OMMT and PDMS-b-PEA into the PA6/PDMS



blends, the equilibrium size was not reached until about 15 min of blending time, while for using simultaneously OMMT and compatibilizer as additives, the dispersed phase domain size decreased sharply to a smaller equilibrium size (about 1 μm) within 5 min of blending time. Therefore, a synergetic effect of adding OMMT and PDMS-b-PEA plays an important role in the immiscible PA6/PDMS blends.

10

PDMS-b-PEA 0.5% OMMT 2% PDMS-b-PEA 0.5%/OMMT 2%

8

dv (m)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 10 of 22

6 4 2 0

0

5

10

15

20

Time (min)

Figure 4. Plots of the dispersed phase domain size of various PA6/PDMS (80/20 by mass) blends versus the blending time.

4. Discussion To investigate the synergetic effect mechanism of OMMT and PDMS-b-PEA on the PA6/PDMS blend, the OMMT dispersion was first considered. Figure 5 presents TEM images of PA6/PDMS/OMMT (80/20/2 by mass) blends with and without 0.5 wt% PDMS-b-PEA. The white dispersed domains correspond to the PDMS phases, and their size is in agreement with that obtained from SEM (Figure 2 and 3). As shown in Figure 5, there are not any discernible OMMT platelets in PDMS domains; in other words, almost all OMMT platelets exist in the PA6 matrix or the interface between PA6 and PDMS due to the difference miscibility between OMMT with polymer chains. PA6 chain is more polar than PDMS chain; thus, OMMT is easily exfoliated by PA6 domain compared with PDMS domain. Comparing TEM images of PA6/PDMS/OMMT blends with and without PDMS-b-PEA, it can be further noticed that the OMMT dispersion in those two blends is


Page 11 of 22 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


quite different. For the one without PDMS-b-PEA, OMMT aggregates together and forms large tactoids in the PA6 matrix. After introducing PDMS-b-PEA, large tactoids of OMMT turned into small stacks and dispersed uniformly in the PA6 matrix. It can be concluded that the introduction of PDMS-b-PEA can promote the dispersion of OMMT in the PA6 matrix. This may be because that PMDS-b-PEA is easier to intercalate into the interlayer of OMMT.

Figure 5. TEM micrographs of PDMS/PA6/OMMT (80/20/2 by mass) blends without (a, b) and with 0.5% PDMS-b-PEA as a compatibilizer (c, d).

Since exfoliated OMMT platelets are located in the PA6 matrix, the decrease in dispersed phase domain size of PA6/PDMS (80/20 by mass) blend by adding OMMT might be attributed to the reduction of the viscosity ratio of dispersed phase and matrix. From complex viscosities of PA6 and PDMS shown in Figure 6, it can be seen that the viscosity of PA6 is far lower than that of PDMS especially at a low frequency, that is, the viscosity ratio of PDMS and PA6 is very large. It is well known that the higher the viscosity ratio, the more the dispersed phase tends to aggregate into a large dispersed phase domain. Thus, it is likely that the large viscosity ratio of PDMS and PA6 leads to the dispersed phase domain size above 2 μm even in the presence of high concentration compatibilizer. After the addition of



OMMT, the exfoliated OMMT platelets dispersed in the PA6 matrix increases the viscosity of PA6 matrix, as shown in Figure 6. As a result, the decrease in the viscosity ratio could result in the reduction of dispersed phase domain size. To check this possibility, the blend morphology with another PA6 (PA6-H) whose viscosity is very close to the PA6/2 wt% OMMT blend is investigated, as shown in Figure 7. Comparing Figure 2a and Figure 7, it can be seen that the dispersed phase domain size of PA6-H/PDMS (80/20 by mass) blend is smaller than that of the blend with a lower viscosity PA6 matrix, which demonstrates that the reduction of viscosity ratio can decrease the dispersed phase domain size. However, from Figure 7, it can be further found that the dispersed phase domain size of PA6-H/PDMS blend is far larger than that of PA6/PDMS blend with 2 wt% OMMT. This indicates that the main effect of the decrease in dispersed phase domain size in the PA6/PDMS blend in the presence of OMMT is not due to the increased viscosity of the matrix polymer.

4000

* (Pa·s)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 12 of 22

PDMS PA6/2% OMMT PA6-H PA6

1000

400

100 0.1

1

10

100

Frequency (rad/s)

Figure 6. Complex viscosities of PA6, PA6-H, PDMS and PA6/2% OMMT blend at 230 ºC.


Page 13 of 22 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 7. SEM micrographs of microtomed surfaces of PA6-H/PDMS (80/20 by mass) (a) and PDMS/PA6/OMMT (80/20/2 by mass) (b) blends.

Beside as a filler to increase the viscosity of PA6 matrix, OMMT as a type of nano-thickness silicate sheet can act also as a barrier to prevent effectively the coalescence of dispersed PDMS domain. To study the barrier effect of OMMT, the morphology stability of PA6/PDMS (80/20) blends with and without OMMT and/or PDMS-b-PEA upon quiescent annealing at 230 ºC were investigated. As shown in Figure 8, for PA6/PDMS blend without OMMT and PDMS-b-PEA, the dispersed phase domain size drastically increased with annealing time, indicating that a significant coarsening process had taken place. After adding 2 wt% OMMT, the dispersed phase size sharply decreased from 11.7 to 2.7 μm, and did hardly increase at all over the entire annealing time (20 min), in other words, those blends did not exhibit any coalescence of dispersed phase domains. This clearly indicates that OMMT plays an important role in restraining the coalescence of dispersed phase domains. After further adding PDMS-b-PEA, the dispersed phase domain size decreased to 1.0 μm, and was also not subjected to any noticeable change during quiescent annealing. As shown in foregoing results, the introduction of PDMS-b-PEA can decrease the interfacial tension between PA6 and PDMS, and promote the exfoliation and uniform dispersion of OMMT in the PA6 matrix. Thus, the addition of PDMS-b-PEA is more efficient in the reduction of dispersed phase domain size and the improvement of morphology stability. These results clearly demonstrate that exfoliated platelets of OMMT locating inside the PA6 matrix act effectively as a barrier for preventing the coalescence of dispersed PDMS domains.



20

15

dv (m)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

10

PA6/PDMS PA6/PDMS/OMMT PA6/PDMS/OMMT/PDMS-b-PEA

5

0

0

5

10

15

20

Time (min)

Figure 8. Dispersed phase domain size of various blends versus annealing time at 230 ºC: (a) PA6/PDMS (80/20 by mass) blend; (b) PA6/PDMS/OMMT (80/20/2 by mass) blend; and (c) PA6/PDMS/OMMT/PDMS-b-PEA (80/20/2/0.5 by mass) blend.

One can argue that the decreased dispersed phase domain size and morphology stability by the addition of OMMT may be because OMMT plays a role of the compatibilizer similar to block or graft copolymers in immiscible polymer blend. Once this argument is right, it is expected that the coalescence of dispersed PA6 domain should be also restrained for another blend composition where PA6 acts as the dispersed phase and PMDS acts as the matrix by adding OMMT. In this scenario, OMMT cannot act as an effective barrier to prevent the coalescence of dispersed phase domain because almost all OMMT platelets are present in the dispersed PA6 domain or the interface between PA6 and PDMS. For this purpose, various PA6/PDMS (20/80 by mass) blends with and without OMMT and/or PDMS-b-PEA in which PA6 became dispersed phase were prepared. Their morphologies before and after quiescent annealing at 230 ºC are presented in Figure 9. It can be found that the dispersed phase morphology of PA6/PDMS (20/80 by mass) blend is almost unchanged after the introduction of PDMS-b-PEA while it is changed from sphere to rod after adding OMMT. This further demonstrates that OMMT platelets mainly exist inside dispersed PA6 domain or the interface between PA6 and PDMS that results in the rod structure. From Figure 9, it can be further noticed that the dispersed PA6 domain size of PA6/PDMS/OMMT (20/80/2 by mass) blend markedly increases with the quiescent annealing time at 230 ºC, which is very similar to that in absence of OMMT. Obviously, the addition of OMMT into PA6/PDMS (20/80) blend does


Page 14 of 22

Page 15 of 22 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


not inhibit the coalescence of dispersed phases as imagined. However, if 0.5 wt% PDMS-b-PEA as a compatibilizer was further introduced into the PA6/PDMS/OMMT (20/80/2 by mass) blend, the dispersed PA6 domain is significantly smaller than that without PDMS-b-PEA. Furthermore, the dispersed PA6 domain only slightly increased with quiescent annealing time. These results indicates that the addition of OMMT does not suggest the increase in the compatibility (or miscibility) between PA6 and PDMS. Thus, the reduction in the dispersed phase domain in PA6/PDMS (80/20 by mass) blend by the addition of OMMT does not resulted mainly from the compatibilization effect but the barrier effect for preventing the coalescence of dispersed PDMS domains.

Figure 9. SEM images of various PA6/PDMS blends after different annealing times at 230 ºC. PA6/PDMS (20/80 by mass) blend: 0 min (a), 5 min (b), 10 min (c), 20 min(d); PA6/PDMS/ PDMS-b-PEA (20/80/0.5 by mass) blend: 0 min (e), 5 min (f), 10 min (g), 20 min (h); PA6/PDMS/OMMT (20/80/2 by mass) blend: 0 min (i), 5 min (j), 10 min (k), 20 min (l); and PA6/PDMS/OMMT/PDMS-b-PEA (20/80/2/0.5 by mass) blend: 0 min (m), 5 min (n), 10 min (o), 20 min (p).



In summary, when OMMT was introduced into the PA6/PDMS (80/20) blend, OMMT platelets mainly exist in the PA6 matrix. The addition of PDMS-b-PEA can promote the uniform dispersion of OMMT for preventing effectively the coalescence of dispersed domains, resulting in the decreased domain size. On the other hand, PDMS-b-PEA can decrease interfacial tension between PA6 and PDMS to further decrease the dispersed phase domain size.

5. Water Absorption and Mechanical Performance PA6 is a kind of hydrophilic polymer due to the existence of the amide bond. Water absorption has an important effect on its stability, mechanical properties and so on. Figure 10 presents the water-absorption contents of PA6/PDMS blends with and without OMMT and/or PDMS-b-PEA. It can be found that the addition of PDMS-b-PEA has almost no effect on the water-absorption content. However, when OMMT is added into the PA6/PDMS (80/20 by mass) blend, the water-absorption content decreases from 2.6% to 2.0% because it can block the passage of water diffusion. Moreover, the further addition of PDMS-b-PEA can reduce the water-absorption content to 1.5% due to better dispersion of OMMT in PA6 matrix. 3.0

Water absorption (%)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

2.5 2.0 1.5 1.0 0.5 0.0

A

B

Sample

C

D

Figure 10. Water absorption of various PA6/PDMS blends. Sample A: PA6/PDMS (80/20 by mass) blend; sample B: PA6/PDMS/ PDMS-b-PEA (80/20/0.5 by mass) blend; sample C: PA6/PDMS/OMMT (80/20/2 by mass) blend; sample D: PA6/PDMS/OMMT/PDMS-b-PEA (80/20/2/0.5 by mass) blend.


Page 16 of 22

Page 17 of 22

Figure 11 presents the tensile properties of PA6/PDMS (80/20 by mass) blends without and with OMMT and/or PDMS-b-PEA. Both tensile module and tensile strength at break of PA6/PDMS (80/20 by mass) blend are much smaller than that with OMMT. The tensile properties can be further improved by adding PDMS-b-PEA. These results can further confirm the synergetic effect of PDMS-b-PEA and OMMT on properties of PA6/PDMS (80/20 by mass) blend. 8000

60 Tensile module Tensile strength

6000 40 4000 20 2000

0

A

B

Sample

C

Tensile strength (MPa)

Tensile module (MPa)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


0

Figure 11. Tensile module and tensile strength at break of various PA6/PDMS blends. Sample A: PA6/PDMS (80/20 by mass) blend; sample B: PA6/PDMS/OMMT (80/20/2 by mass) blend; sample C: PA6/PDMS/OMMT/PDMS-b-PEA (80/20/2/0.5 by mass) blend.

6. Conclusion This work showed a synergetic effect of reactive compatibilizer PDMS-b-PEA and OMMT play an important role in reducing dispersion domain sizes and improving properties of PDMS/PA6 blend with a high viscosity ratio of dispersed phase and matrix. The dispersed phase domain size significantly decreases from 11.7 to 3.5 μm by an addition of a very small amount of PDMS-b-PEA (0.25 wt%). However, the dispersed phase domain size is still above 2 μm even when the PDMS-b-PEA concentration reaches 5 wt% due to the high viscosity ratio of dispersed phase and matrix. OMMT as an additive mainly dispersing in the PA6 matrix can restrain the coalescence of dispersed phase. PDMS-b-PEA can further



promote the dispersion of OMMT in PA6 for preventing the coalescence of dispersed PDMS phase. The combination of the compatibilization effect of PDMS-b-PEA and the barrier effect of OMMT can not only reduce the dispersed phase domain size but also improve tensile properties and decrease water absorption.

Acknowledgment The authors thank the National Key Research and Development Program of China (2016YFC1100801), the Fundamental Research Funds for the Central Universities (2017FZA4024), and the State Key Laboratory of Chemical Engineering (SKL-ChE-13D) for their financial support.

Reference (1) Wang, Z. L.; Li, J. F.; Nie, J.; Yang, S. G. Effect of Hydrothermal Treatment on Structure and Properties of Polyamide 6 Fibers. Acta Polym. Sin. 2016, 1710-1716. (2) Lin, J. H.; Pan, Y. J.; Hsieh, C. T.; Huang, C. H.; Lin, Z. I.; Chen, Y. S.; Su, K. H.; Lou, C. W. Using Multiple Melt Blending to Improve the Dispersion of Montmorillonite in Polyamide 6 Nanocomposites. Polym. Test. 2016, 56, 74-82. (3) Liao, G. Y.; You, Q. L.; Xia, H.; Wang, D. S. Preparation and Properties of Novel Epoxy Composites Containing Electrospun PA6/F-MWNTs Fibers. Polym. Eng. Sci. 2016, 56, 1259-1266. (4) Zhou, S. T.; Luo, W.; Zou, H. W.; Liang, M.; Li, S. Z. Enhanced Thermal Conductivity of Polyamide 6/Polypropylene (PA6/PP) Immiscible Blends with High Loadings of Graphite. J. Compos. Mater. 2016, 50, 327-337. (5) Mahmood, N.; Islam, M.; Hameed, A.; Saeed, S. Polyamide 6/Multiwalled Carbon Nanotubes Nanocomposites with Modified Morphology and Thermal Properties. Polymers. 2013, 5, 1380-1391. (6) Gu, H. B.; Ma, C.; Liang, C. B.; Meng, X. D.; Gu, J. W.; Guo, Z. H. A Low Loading of Grafted Thermoplastic Polystyrene Strengthens and Toughens


Page 18 of 22

Page 19 of 22 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Transparent Epoxy Composites. J. Mater. Chem. C. 2017, 5, 4275-4285. (7) Wang, P.; Xu, P.; Wei, H. B.; Fang, H. G.; Ding, Y. S. Effect of Block Copolymer Containing Ionic Liquid Moiety on Interfacial Polarization in PLA/PCL Blends. J. Appl. Polym. Sci. 2018, 135, 46161. (8) Dikobe, D. G.; Luyt, A. S. Investigation of the Morphology and Properties of the Polypropylene/Low-Density

Polyethylene/Wood

Powder

and

the

Maleic

Anhydride Grafted Polypropylene/Low-Density Polyethylene/Wood Powder Polymer Blend Composites. J. Compos. Mater. 2017, 51, 2045-2059. (9) Heiner, J.; Stenberg, B.; Persson, M. Crosslinking of Siloxane Elastomers. Polym. Test. 2003, 22, 253-257. (10) Park, E. S. Mechanical Properties and Antibacterial Activity of Peroxide-Cured Silicone Rubber Foams. J. Appl. Polym. Sci. 2008, 110, 1723-1729. (11) Chen, L.; Lu, L.; Wu, D. J.; Chen, G. H. Silicone Rubber/Graphite Nanosheet Electrically Conducting Nanocomposite with A Low Percolation Threshold. Polym. Composite. 2007, 28, 493-498. (12) Munoz, M. P.; Werlang, M. M.; Yoshida, I.; Mauler, R. S. Blends of High-Density Polyethylene with Solid Silicone Additive. J. Appl. Polym. Sci. 2002, 83, 2347-2354. (13) Wang, L. J.; Lang, F. Z.; Li, S.; Du, F. L.; Wang, Z. B. Thermoplastic Elastomers Based on High-Density Polyethylene and Waste Ground Rubber Tire Composites Compatibilized by Styrene-Butadiene Block Copolymer. J. Thermoplast. Compos. 2014, 27, 1479-1492. (14) Lai, S. M.; Hung, K. C.; Kao, H. C.; Liu, L. C.; Wang, X. F. Synergistic Effects by Compatibilization and Annealing Treatment of Metallocene Polyethylene/PLA Blends. J. Appl. Polym. Sci. 2013, 130, 2399-2409. (15) Fu, Z.; Wang, H. T.; Zhao, X. W.; Horiuchi, S.; Li, Y. J. Immiscible Polymer Blends Compatibilized with Reactive Hybrid Nanoparticles: Morphologies and Properties. Polymer. 2017, 132, 353-361. (16) Sangroniz, A.; Chaos, A.; Garcia, Y. M.; Fernandez, J.; Iriarte, M.; Etxeberria, A. Improving the Barrier Character of Polylactide/Phenoxy Immiscible Blend



Using

Poly(Lactide-co-Epsilon-Caprolactone)

Block

Page 20 of 22

Copolymer

as

A

Compatibilizer. J. Appl. Polym. Sci. 2017, 134, 45396. (17) Mani, S.; Cassagnau, P.; Bousmina, M.; Chaumont, P. Morphology Development in Novel Composition of Thermoplastic Vulcanizates Based on PA12/PDMS Reactive Blends. Macromol. Mater. Eng. 2011, 296, 909-920. (18) Mao, C.; Zhu, Y. T.; Jiang, W. Design of Electrical Conductive Composites: Tuning the Morphology to Improve the Electrical Properties of Graphene Filled Immiscible Polymer Blends. Acs Appl. Mater. Inter. 2012, 4, 5281-5286. (19) Li, Y.; Shimizu, H. Conductive PVDF/PA6/CNTs Nanocomposites Fabricated by

Dual

Formation

of

Cocontinuous

and

Nanodispersion

Structures.

Macromolecules. 2008, 41, 5339-5344. (20) Huang, S. J.; Bai, L.; Trifkovic, M.; Cheng, X.; Macosko, C. W. Controlling the Morphology

of

Immiscible

Co-continuous

Polymer

Blends

via

Silica

Nanoparticles Jammed at the Interface. Macromolecules. 2016, 49, 3911-3918. (21) Liu, X. Q.; Li, R. H.; Bao, R. Y.; Jiang, W. R.; Yang, W.; Xie, B. H.; Yang, M. B. Suppression of Phase Coarsening in Immiscible, Co-continuous Polymer Blends Under High Temperature Quiescent Annealing. Soft Matter. 2014, 10, 3587-3596. (22) Khatua, B. B.; Lee, D. J.; Kim, H. Y.; Kim, J. K. Effect of Organoclay Platelets on Morphology of Nylon-6 and Poly(Ethylene-ran-Propylene) Rubber Blends. Macromolecules. 2004, 37, 2454-2459. (23) Liu, Y.; Xie, L. S.; Ma, Y. L.; Liu, H. T.; Zhao, H. L.; Wang, Y. X. Ultrasound Assisted Continuous-Mixing for the Preparation of PP/SEBS/OMMT Ternary Nanocomposites. J. Appl. Polym. Sci. 2014, 131, 41202. (24) Elias, L.; Fenouillot, F.; Majeste, J. C.; Alcouffe, P.; Cassagnau, P. Immiscible Polymer Blends Stabilized with Nano-Silica Particles: Rheology and Effective Interfacial Tension. Polymer. 2008, 49, 4378-4385. (25) Zhou, J. T.; Yao, Z. J.; Zhou, C.; Wei, D. B.; Li, S. Q. Mechanical Properties of PLA/PBS Foamed Composites Reinforced by Organophilic Montmorillonite. J. Appl. Polym. Sci. 2014, 131, 40773.


Page 21 of 22 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(26) Wu, Y. J.; Shi, Y. T.; Zhu, L. Z.; Shentu, B. Q.; Weng, Z. X. Joint Effect of Compatibilizer

and

Organo-Montmorillonite

Polyamide-6/Poly(phenylene

oxide)

Blend:

Polym-Plast. Technol. 2015, 54, 682-690.


on

Compatibilization

Morphology

and

of

Properties.


Graphical Abstract


Page 22 of 22

Synergetic effect of a reactive compatibilizer and OMMT on the

Recommend Documents