Fabrication of Smart Shape Memory Fluorosilicon Thermoplastic

Jul 29, 2019 - To expand the application of shape memory materials in situations where elevated temperature and corrosion resistance are required, nov...
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Article Cite This: Ind. Eng. Chem. Res. 2019, 58, 15199−15208

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Fabrication of Smart Shape Memory Fluorosilicon Thermoplastic Vulcanizates: The Effect of Interfacial Compatibility and Tiny Crystals Jianfeng Fan, Mengwen Yan, Jiarong Huang, Liming Cao, and Yukun Chen* Lab of Advanced Elastomer, School of Mechanical and Automotive Engineering, South China University of Technology, 381 Wushan Road, Tianhe District, Guangzhou 510640, China Downloaded via DUKE UNIV on August 23, 2019 at 16:27:01 (UTC). See https://pubs.acs.org/sharingguidelines for options on how to legitimately share published articles.

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ABSTRACT: To expand the application of shape memory materials in situations where elevated temperature and corrosion resistance are required, novel heat-triggered shape memory (HSM) fluorosilicon thermoplastic vulcanizates (TPVs) were designed via core−shell dynamic vulcanization. When the fluororubber (FKM)/silicone rubber (SR) ratio reached 1:1, excellent shape fixity (Rf ∼ 96%) and shape recovery ratios (Rr ∼ 98%) were achieved at the suitable switching transition temperature (Ttrans) of 160 °C. The influence of core−shell structure on shape memory behavior mainly comes from the following aspects: the improvement of interfacial compatibility promoting stress delivery between polyvinylidene fluoride (PVDF) and SR/FKM phases in the shape fixing and shape recovery process and the reduced numberaverage rubber particle size caused by the appropriate interfacial compatibility facilitating the increasing of interface area, which improved the nucleation density and induced abundant tiny crystals in the blends. Additionally, the formation of core−shell structure also endowed the TPVs with improved mechanical properties.

1. INTRODUCTION Currently, heat-triggered shape memory polymers1,2 (SMPs) that can subsequently recover to their original shape after being induced to certain external heat are attracting increasingly attention from academic and industrial researchers. However, in order to extend their potential applications in harsh environments3−5 with high humidity, elevated temperature, and corrosion resistance, ongoing efforts are required to develop fluorosilicon materials. Generally speaking, the prerequisite to fabricate a SMP involves two aspects: two separated phases6−10 and excellent interfacial compatibility. For the phase separation morphology, a fixed phase was used to maintain the deformed shape, whereas the reversible phase plays an important role in storing and releasing internal stress. Interestingly, the synthesized ABA (where A = hard block and B = soft block) triblock copolymers11,12 that combine the phase separation with good compatibility between two phases are one of the ideal candidates for shape-memory polymers. However, a complicated synthetic process is inevitable for intrinsically thermoresponsive SMPs, which may hinder their development. Compared with the de novo synthesis, the strategy of blending two or more polymers could combine desired properties of individual components directly and effectively, which provides a new way to solve the current problem. Furthermore, dynamic vulcanization of the blending method13−15 permits fabricating thermoplastic vulcanizates (TPVs) with microphase-separated © 2019 American Chemical Society

morphology and strong shape recovery driving force, which exhibits great potentiality in the fabrication of HSM materials. For HSM TPVs, the glass transition temperature16−19 (Tg, higher than room temperature) or melting temperature14,20,21 (Tm) of plastic phase was used to fix the temporary shape of polymer systems. As for Tg, for example, PLA has been blended with various rubbers and elastomers, such as natural rubber (NR),22 nitrile butadiene rubber (NBR),23 polyurethane (PU),24 etc., to prepare SMPs, where the fixing of the temporary state is realized by Tg of PLA. While for Tm, several crystalline polymer-based SMPs have been reported where the crystallization behavior of plastic served as a fixed phase.14,25,26 For example, Li25 et al. reported that tiny crystals and the amorphous regions exploited as the switch phase and the reversible phase, respectively, in the thermoplastic polyvinylidene fluoride (PVDF)/acrylic copolymer SMP during the mechanical deformations. Xu14 et al. designed ethylenepropylene-diene rubber/polypropylene (EPDM/PP) TPVs manifesting a typical sea−island structure via in situ compatibilization, in which the crystallization of PP acted as the fixed phase to prevent the deformed molecular chains from sliding. Meanwhile, their results were confirmed that the Received: Revised: Accepted: Published: 15199

June 4, 2019 July 17, 2019 July 29, 2019 July 29, 2019 DOI: 10.1021/acs.iecr.9b03028 Ind. Eng. Chem. Res. 2019, 58, 15199−15208

Article

Industrial & Engineering Chemistry Research Table 1. Characteristics of Materials Used in This Study polymer (abbreviation)

grade (supplier)

specifications

poly(vinylidene fluoride) (PVDF) methylvinyl silicone rubber (SR)

PVDF 502 (Guangzhou Li Chang Fluoroplastics. Co. Ltd., China) KE 571-U (Shin-Etsu, Japan)

fluororubber (FKM)

2463 (Zhonghao Chenguang Research Institute of Chemical Induatry, China)

dicumyl peroxide (DCP) bisphenol AF (AF) benzyltriphenylphosphonium chloride (BPP) N,N-dimethylformamide (DMF)

CP (Shanghai Aladdin Bio-Chem Technology Co., Ltd., China) AR (Zigong Tianlong Chemical Co. Ltd., China) AR (Zigong Tianlong Chemical Co. Ltd., China)

MFI (190 °C, 2.16 kg) = 10 g/10 min molecule weight = 5.2 × 105 g/mol and density = 1.22 g/cm3 vinylidene fluoride content = 40%; hexafluoropropylene content = 25%; tetrafluoroethylene content = 35% purity ≥98% purity ≥99.5% purity ≥99.5%

AR (Shanghai Richjoint Chemical Reagents Co., Ltd., China)

purity ≥99.5%

excellent interfacial compatibility played critical role in transferring stress between the phase in both shape fixing and shape recovering process. Similarly, Guo et al.27 found that the generation of links at the interface was beneficial to transfer stress. Therefore, the profound interfacial compatibility is another important factor for fabricating SMPs. Inspired by the previous research and achievements, we design and prepare a kind of fluorosilicon HSM TPVs based on the commercially available PVDF and silicone rubber (SR). The chemically cross-linked rubber phase with high elasticity is regarded as the reversible phase and the crystallization of PVDF is regarded as the temporary fixed phase to stabilize the deformed shapes. But PVDF and SR exhibit poor compatibility. Fortunately, a novel PVDF/fluororubber (FKM)/SR TPV with core−shell structure was reported in our previous work,28 where the FKM molecule chains were migrated into the interface between PVDF and SR to tune their interfacial compatibility due to the thermodynamic factor. Consequently, further results confirmed that the FKM molecules facilitated more interfacial crystallization of PVDF than SR molecules due to more oriented chains of PVDF at the interface assisted by the excellent compatibility of PVDF and FKM/SR particles. Meanwhile, the enhanced interfacial compatibility facilitated the increase of interface area, thereby raising the nucleation density, and inducing abundant tiny crystals in the blend.29−31 And Li’s25,32 research indicated that tiny crystals contributed to the realization of the appropriate shape fixing and excellent shape recovery. With the development of shape memory TPVs obtained by core−shell dynamic vulcanization, a new material was added to the existing library of these thermadaptive shape memory polymers.

Table 2. Compounding Formulations of Different Samples code

PVDF

FKM

SR

DCP

AF/BPP

Ca(OH)2/MgO

P6F4S0 P6F3S1 P6F2S2 P6F1S3 P6F0S4

60 60 60 60 60

40 30 20 10 0

0 10 20 30 40

0 0.2 0.4 0.6 0.8

0.8/0.4 0.6/0.3 0.4/0.2 0.2/0.1 0/0

0.8/1.2 0.6/0.9 0.4/0.6 0.2/0.3 0/0

respectively. For brevity, the sample codes were defined according to the weight ratio of PVDF/FKM/SR, e.g. P6F2S2 represents the sample of the PVDF/FKM/SR TPV with the weight ratio of 60/20/20. The core−shell dynamic vulcanization was performed using a torque rheometer (RTOI-55/20, POTOP, China), equipped with two rotors at 190 °C and the rotor speed of 90 rpm. PVDF was first melted in the chamber for about 3 min, then the FKM/SR blend with predetermined quantity was added into the mixing chamber. Finally, DCP and AF/BPP were used to initiate the dynamic vulcanization of SR-core and FKMshell, respectively. After the melt reached the final stable torque, the blending process was ended. The samples were hot pressed at 190 °C into a sheet with a thickness of about 1 mm. 2.3. Mechanical Property Measurements. The tensile strength and elongation at break were measured on a computerized tensile strength tester (UT-2080, U-CAN Dynatex Inc., Taiwan) under a tensile mode with a strain rate of 500 mm/min at room temperature. At least five specimens were tested for each sample, and the values were averaged. Then the toughness of PVDF/FKM/SR TPVs were evaluated by calculating the area underneath the stress−strain curves,33,34 which represent the energy of mechanical deformation per unit volume prior to fracture. 2.4. Scanning Electron Microscope (SEM). The phase morphology of cryogenically fractured PVDF/FKM/SR TPVs before and after being annealed, and after being extracted to remove the PVDF phase were carried out by S1530 microscopy (Japan). The static annealing process for the cryo-fractured surfaces was completed in a vacuum oven at 140 °C for 1 h, whereas the selective extraction was carried out with hot N,N-dimethylformamide (DMF, ∼110 °C) for 72 h. Notably, before morphological observation, both cryofractured surfaces were gold sputter-coated for good conductivity. Since the dispersion state of the dispersed phases is related with the compatibility between the phases, the number-average particle size (Dn) was determined from more than 300 particles in five independent SEM images, using the Image-Pro Plus 4.5

2. EXPERIMENTAL SECTION 2.1. Materials. The other chemicals were used as received. 2.2. Preparation of PVDF/FKM/SR TPVs via Core− Shell Dynamic Vulcanization. The raw materials and some specifications are displayed in Table 1. Prior to blending, the FKM compound was prepared by mixing with acid scavenger of Ca(OH)2/MgO on a two-roll mill at room temperature. And then, the FKM/SR blends were prepared by mixing the FKM compound and masticated SR at room temperature in a torque rheometer (RTOI-55/20, POTOP, China). The detailed compounding formulations of different samples are shown in Table 2. For all TPVs, the weight ratio of PVDF/ rubber (FKM+SR) was fixed at 60/40. The loading amount of DCP was fixed at 2% weight of the SR component, the loading amount of AF was fixed at 2% weight of the FKM component (where AF/BPP weight ratio was fixed as 2/1). The Ca(OH)2 and MgO loading were fixed at 2 and 3 wt % of FKM, 15200

DOI: 10.1021/acs.iecr.9b03028 Ind. Eng. Chem. Res. 2019, 58, 15199−15208

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Industrial & Engineering Chemistry Research

Figure 1. Schematic diagram depicting the shape fixing and shape recovery ratios of the heat-triggered SM behavior.

software. Dn was determined using the following eq 1, wherein ni is the number of particles with the diameter Di. Dn =

θf × 100 180 θ − θf shape recovery ratio (%), R r = r × 100 θf shape fixity ratio (%), R f =

∑i niDi ∑i ni

(1)

(2)

3. RESULTS AND DISCUSSION 3.1. Preparation of PVDF/FKM/SR TPVs with Core− Shell Structure. According to our previous report,28 we fabricated a novel fluorosilicone TPV with bicrosslinked SRcore/FKM-shell structure. For a ternary blend, the spreading coefficient is a widely accepted index37 to predict the structure of the PVDF/FKM/SR ternary system. The spreading coefficients derived from the surface tension (as shown in Table S1) of the thermodynamics view are calculated based on the equation:

2.5. Transmission Electron Microscopy (TEM). To observe the structure of the TPVs prepared via core−shell dynamic vulcanization, transmission electron microscopy (TEM) was performed for P6F2S2. The ultrathin samples (about 100 nm in thickness) were prepared via an ultramicrotome (Leica EMUC6, Germany) and then observed through JEM-100CX II transmission electron microscope (JEOL, Japan) with an accelerating voltage of 100 kV. 2.6. Polarized Optical Microscopy (POM). The crystallization morphology of PVDF in PVDF/FKM/SR TPVs during the nonisothermal crystallization process were observed by using an Axioskop 40 polarized optical microscopy (POM) (ZEISS, Germany) coupled with a hot stage under crossed polarizers. A hot stage was employed for controlling the temperature. The samples were first melted at 190 °C for 5 min and then quickly cooled down to the temperature of 110 °C. The reduction of spherulites size of PVDF was affirmed by POM, this information confers the unique opportunity to understand the reason for the excellent shape fixity. 2.7. Differential Scanning Calorimeter (DSC). The Tm values of the PVDF phase in TPVs were obtained via the DSC (240 F1, NETZSCH, Germany) technique under a flowing nitrogen atmosphere. Weighed samples were subjected to the following heat−cool−heat cycles: they were heated from 30 to 220 °C at a rate of 20 °C/min, were maintained at 220 °C for 5 min to eliminate previous heat history, then underwent a nonisothermal crystallization by cooling down to 30 °C at a rate of 5 °C/min, and subsequently heated up again to 220 °C at a rate of 5 °C/min to record the data. 2.8. Dynamic Mechanical Analysis (DMA). The Tg of the components in the TPVs was obtained by a dynamic mechanical thermal analyzer (METTLER DMA 1) using tensile mode. Temperature sweep was performed from −140 to 50 °C at a heating rate of 2 °C/min and a frequency of 1 Hz. The loss tangent (tan δ) was recorded as a function of temperature. 2.9. Heat-Induced Shape Memory Characterization. The PVDF/FKM/SR TPVs were cut into rectangular strips of dimensions ca. 5 cm (length) × 0.7 cm (width) × 1 mm (thickness). And then, a fold-deploy test10,35,36 was employed to characterize the heat-triggered shape memory effect (SME). To further depict the experimental process intuitively, the schematic diagram is shown in Figure 1. Based on the shape fixing angle (θf) and shape recovery angle (θr), the shape fixing (Rf) and shape recovery (Rr) ratios were calculated using the following equations:

λPVDF/FKM/SR = γPVDF/SR − (γPVDF/FKM + γFKM/SR ) λFKM/PVDF/SR = γFKM/SR − (γPVDF/SR + γFKM/SR ) λPVDF/SR/FKM = γPVDF/FKM − (γPVDF/SR + γFKM/SR )

(3)

where γPVDF/SR, γPVDF/FKM, and γFKM/SR are the interfacial tension between PVDF and SR, PVDF and FKM, and FKM and SR, respectively. Furthermore, these interfacial tensions were calculated based on harmonic-mean equation, and thereby estimating the spreading coefficient between the phases, as shown in Table 3. In the case of only one positive Table 3. Interfacial Tension and Spreading Coefficient of the Main Experimental Raw Materials interface tension (mN/m)

spreading coefficient (mN/m)

γPVDF/FKM = 1.93 γFKM/SR = 1.22 γPVDF/SR = 4.55

λPVDF/FKM/SR = 1.40 > 0 λFKM/PVDF/SR = −5.26 < 0 λPVDF/SR/FKM = −3.84 < 0

spreading coefficients of λPVDF/FKM/SR, the FKM phase will completely wet the interface of PVDF and SR to form the core−shell structure.37,38 Because of the similar natural properties of FKM and PVDF, as well as the restraint effect of the core−shell structure on the intimate contact between PVDF and SR, minimization of the surface free energy of the TPV was obtained. To ascertain the encapsulation function of FKM on SR particles, TEM was performed for P6F2S2 and the result is shown in Figure 2. It is clearly observed that a black phase was enclosed by a bright annular area. In the TEM image, the bright annular area relates to the FKM-shell, while the black phase is the SR-core. Therefore, SR particles are encapsulated by FKM phase in PVDF matrix, and the formed core−shell structure would correspond to the lowest free energy.39 Owing to accurate design, the FKM chains could provide strong interaction to prevent the destruction of the poor PVDF-SR interface during the mechanical deformation,40−42 which contributed to the improvement of PVDF/SR toughness. 15201

DOI: 10.1021/acs.iecr.9b03028 Ind. Eng. Chem. Res. 2019, 58, 15199−15208

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Industrial & Engineering Chemistry Research

Figure 2. TEM micrograph of P6F2S2 with SR-core/FKM-shell structure. Figure 3. Rf of TPVs obtained at various Ttrans.

Compared with the P6F0S4, as shown in Figure S1, the tensile strength, elongation at break, and tensile toughness were significantly increased from 8.49 MPa, 12.82%, and 0.87 MJ/ m3 up to 21.67 MPa, 174.62%, and 36.14 MJ/m3 of P6F2S2 and slightly increased with a further increase in the content of FKM. This result is attributed to the fact that the perfect core− shell structure for FKM/SR was improved gradually with an increasing FKM/SR ratio. The excellent interfacial compatibility and phase-separated structure will endow the PVDF/ FKM/SR TPVs with excellent shape memory behaviors which will be discussed in the subsequent parts. 3.2. Origination of the Shape Fixity Ratio: Crystallization Behavior of PVDF. Inspired by the PP-based HSMPs,6,14 PVDF/FKM/SR TPVs can also be considered as an ideal candidate for a shape memory fluorosilicon elastomer, wherein core−shell rubber particles and the semicrystalline PVDF served as the recovery driving force providers and the fixing phase, respectively. As a semicrystalline polymer, shape fixing is closely related to the crystallization behavior of PVDF. Therefore, the choice of the switching transition temperature (Ttrans), which is directly associated with the crystallization of PVDF, is surmised as the priority factor to achieve high performance of SM behavior of TPVs.43 In order to ascertain their memory temperature range, DSC characterization was performed to evaluate thermal properties of PVDF/FKM/SR TPVs. Figure S2 shows the nonisothermal crystallization curves and nonisothermal heating curves of PVDF in TPVs. As can be seen, the maximum crystallization temperature (Tc) and the maximum Tm of TPVs are ca. 140 and 175 °C, respectively. And each sample exhibited broad crystallization and melting transition of PVDF due to the intrinsic characteristic of polymers. Therefore, a series of Ttrans (110, 130, 140, 160, and 170 °C) were employed to study the SM behaviors of TPVs. The SM properties, Rf and Rr, of TPVs were characterized by fold-deploy tests. As shown in Figure 3, all of the TPVs were found to have low Rf at Ttrans of 110 and 130 °C. This is because the slightly melted crystalline in the plastic zone is insufficient to transfer stress efficiently, indicating that appropriate content of melted crystalline of PVDF was the precondition for the SM process. Furthermore, the specimens were further deformed at 140 and 160 °C to activate more of the crystalline PVDF to melt. It is observed that the fixing rate remarkably increased with the increase of Ttrans (≥140 °C) regardless of the morphology of TPVs. However, when Ttrans improved to 170 °C, almost all crystalline phases were melted and lost their shape during the shape recovery process. That is because the real maximum

Tc is higher than the experimental value and the real maximum Tm is lower than the experimental value due to the test error determined by the test method itself. As discussed above, we confirmed that the crystallized portion of PVDF polymer chains was used to stabilize the temporarily deformed shapes, and increasing temperature could improve shape fixing and shape recovery of TPVs while facilitating the delivery of internal stress in the rubber phase. On the other hand, according to Li’s25 study, tiny crystals could help TPV realize high performance with respect to shape memory. For PVDF/FKM/SR TPVs, the sequentially increasing Rf with the addition of FKM at Ttrans of 140 and 160 °C would be ascribed to the numerous tiny crystals. To further study the shape fixing mechanism, POM characterization was performed to observe the crystallization behavior of TPVs during the nonisothermal crystallization; the results of this are shown in Figure 4. In this process, the black cross extinction phenomenon was observed for all samples, which indicated that the crystalline structure of the PVDF phase was spherulite. And the spherulite diameter was effectively reduced by the increasing content of FKM. That is because the introduction of FKM improved the interfacial compatibilization of PVDF/SR (see section 3.4 for detailed discussion), thereby reducing the rubber particles size, which not only served as an active nucleating agent, but also hindered the growth of PVDF crystals.43 Meanwhile, the decreased SR/ FKM particle size, under the same PVDF proportion, turned out the increased number of cross-linked PVDF/SR particles. This directly led to the increased number of small spherulites,44 corresponding to fixed points, which contributed to the fixing of the deformed shape. A detailed analysis of dispersed particle size will be undertaken further in this article. Considering the improved interface mentioned above, PVDF chains were trapped within the SR/FKM particles, assisting the formation of oriented chains of PVDF at the interface, which could act as the interfacial nucleating agent, as shown in Figure 5b. Since the FKM-shell was gradually improved as the core−shell ratio decreased to 1, it is clearly observed that the peak of crystallization temperature (Tc) significantly increased from 138.4 to 140.8 °C for the PVDF phase, as shown in Figure S2a. The schematic for the interfacial crystallization in PVDF/FKM/SR TPV with and without core−shell structure is illustrated in Figure 5b. Furthermore, because SR can be perfectly wrapped by FKM when the SR/ FKM ratio < 1, similar Tc values were observed for DP6F2S2, DP6F3S1, and DP6F4S0. In addition, the efficient nucleation 15202

DOI: 10.1021/acs.iecr.9b03028 Ind. Eng. Chem. Res. 2019, 58, 15199−15208

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Industrial & Engineering Chemistry Research

Figure 4. POM images of P6F2S2 during isothermal crystallization at 160 °C.

Figure 5. (a) Plots of relative crystallization versus crystallization time. (b) Schematic for the interfacial crystallization for TPVs.

3.3. Origination of the Shape Recovery Ratio: Interfacial Compatibility. Aside from Rf, Rr is another important parameter in assessing the SM properties of TPVs. For all TPVs as shown in Figure 6B, no significant change in Rr was observed as the temperature increased from 110 and 130 °C. Nonetheless, a great increase in Rr of all TPVs was observed at elevated temperatures of 140 and 160 °C. This is due to the fact that the improved temperature contributed to the storage and release of elastic resilience of the rubber phase. Moreover, at Ttrans of 160 °C, all of the TPVs containing FKM displayed excellent shape recovery as shown in Figure 6B, which is obviously superior to P6F0S4 without any FKM. Considering that the extensive PVDF molecular chains are mobile at temperatures of 160 °C, it can be reasonably supposed that shape fixing and shape recovery are predominated by the interface compatibility. For PVDF/FKM/SR TPVs, on account of the similar molecular architecture of FKM and PVDF as well FKM’s encapsulation function on SR

effect of core−shell particles moved up the appearance time of the PVDF spherulite crystallize in the blends, as shown in Figure 5a, relative crystallinity versus time. Therefore, from Figure 3, it is clearly observed that P6F2S2 possesses a nearly similar Rf to P6F4S0. It is generally believed that nucleation contributes to the advanced Ti (as shown in Figure 5a), which thereby facilitated the shape fixing behavior of blends. Based on the above results, after transferring the stress from the PVDF phase to the core−shell particles via the interface, the deformed shape may be fixed by the timely crystallization due to the improved core−shell structure in the cooling and programming process. Therefore, P6F2S2 possesses excellent shape fixing behavior, which is extremely close to that of P6F4S0, and synchronously combines the properties of silicone rubber and fluororubber. Therefore, the strategy of core−shell dynamic vulcanization paves the way for advanced fluorosilicone TPVs with SM behavior. 15203

DOI: 10.1021/acs.iecr.9b03028 Ind. Eng. Chem. Res. 2019, 58, 15199−15208

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Industrial & Engineering Chemistry Research

further increasing FKM content (SR/FKM ratio < 1) on the shape recovery behavior of the blends is limited, and that in turn suppresses the functional performance of SR in TPVs. In the light of the above results, the interfacial compatibility is the key indicator of the SM efficiency. Notably, the prepared P6F2S2 that simultaneously possesses dual functional performances of SR and FKM exhibited an apparent SM effect. 3.4. Improvement of Interfacial Compatibilization via Core−Shell Dynamic Vulcanization. On the basis of the above analysis, we prepared fluorosilicone TPVs that simultaneously integrate high mechanical strength and perfect SM properties. Our design strategy of achieving SM effect for blends is to fix the temporary shape by the crystallization of PVDF and generate charming recovery ratios by stress transfer of the FKM/SR phase. In our work, the admirable interface simultaneously served as fluctuation-assisted nucleating agent and the interfacial compatibilizer, which made the dominating contributions to the mechanical and SM properties as discussed above. Moreover, the excellent interfacial compatibility was ascribed to the intrinsic characteristics and the encapsulation function of the formed FKM−shell structure, which were supported by the thermodynamic view and TEM results. To investigate the miscibility between components, SEM and DMA were performed. Figures 7 and S3 show the cryogenically fractured surface before and after adding FKM in PVDF/SR TPVs. The obvious interface debonding is observed in Figure 7a, which would be due to the weak interfacial wetting between the PVDF and SR phases in these cases. Compared with P6F0S4, it is clearly seen that P6F1S3, P6F2S2, P6F3S1, and P6F4S0 showed a gradual smooth surface, which indicates the enhanced interfacial compatibility and improved bonding strength45−47 owing to the addition of FKM. It ought to be noted that the prefect shell structure of P6F2S2 and P6F3S1 prevent the contact between PVDF and SR, showing similar excellent interfacial adhesion. Furthermore, in order to verify the bridging function of FKM between PVDF and SR, the samples of P6F0S4, P6F2S2, and P6F4S0 were statically annealed48,49 at 140 °C for 1 h. And their corresponding SEM images are provided in Figure 7a′, b′, and c′. As seen, the annealing process drastically coarsens the cryogenically fractured surface of P6F0S4, and a

Figure 6. Snapshots of “U” shape recovery sequence at 160 °C (A) and Rr of TPVs obtained at various Ttrans (B).

particles, the formed FKM-shell structure strengthened the interaction between PVDF and SR domains. Consequently, the improved interface contributed to the stress transfer between SR/FKM particles and PVDF phase in shape recovery and deformation process. To further understand the influential factor of interface compatibility on shape memory behavior, snapshots of the “U” sequence upon shape recovery processes under the selected Ttrans of 160 °C were recorded in real time with a digital camera, as shown in Figure 6A. It is clearly presented that the TPVs containing FKM show approximately full recovery with a fast shape recovery rate compared with P6F0S4 without any FKM. For example, P6F2S2 completed the shape recovery process in 30 s and showed a remarkable shape recovery ratio (Rr > 95%). Meanwhile, it is noticed that the effect of the

Figure 7. SEM images of the cryogenically fractured surface of the P6F0S4 (a, a′), P6F2S2 (b, b′), and P6F4S0 (c, c′) before and after being annealed at 140 °C for 1 h. 15204

DOI: 10.1021/acs.iecr.9b03028 Ind. Eng. Chem. Res. 2019, 58, 15199−15208

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Industrial & Engineering Chemistry Research

Figure 8. SEM images of the etched surface by DMF at 140 °C for 72 h: (a) P6F0S4, (b) P6F1S3, (c) P6F2S2, (d) P6F3S1, (e) P6F4S0, and (f) their number-average particle size.

disproportionate number of holes are observed in Figure 7a. The reason for this is that the poor adhesion between PVDF/ SR phases accelerated their separation during the annealing process. However, the cryogenically fractured surface of P6F2S2 and P6F4S0 still maintained uniform morphologies after the annealing process, as shown in Figure 7b and c, indicating the stable interfacial compatibilizing effect of the core−shell structure. It is expected that the excellent compatibilizing effect originates from two functionalities of the formed FKM-shell structure: the mandatory encapsulation preventing the intimate contact between PVDF and SR and the similar intrinsic characteristics of PVDF and FKM. Similar to other works,14,50,51 compatibility contributes to a size reduction of the dispersed vulcanized rubber particles. To further understand the dispersion of core−shell particles, the free PVDF was etched by DMF at 110 °C for 72 h. As seen in Figure 8, the rubber phases of all the samples dispersed in the continuous PVDF phase as spherical particles. During dynamic vulcanization process of the PVDF/SR immiscible system, the breakup and coalescence of the SR phase occurred simultaneously, leading to the formation of the larger number-average size (as shown in Figure 8f) and broader corresponding size distribution (as shown in Figure S4). With the incorporation of FKM, which acts as interfacial compatibilizer, the formation of FKM-shell at PVDF/SR interface prevents the coalescence of the SR particles, and thus decreasing trend of the number-average particle size of the dispersed SR/FKM domains from 2.15 to 1.39 μm was observed. A decrease in Dn led to a significant increase in the specific surface of dispersed particles,52 and their interface indicated the perfect compatibility. It is generally believed that the excellent interfacial compatibility improves the stress transfer, which plays an important role in determining the SM behavior of a multiphase polymer blend. In addition, DMA was used to assess the interfacial compatibility toward Tg in PVDF/FKM/SR ternary blends. The tan δ as a function of temperature for all the blends were shown in Figure 9. As seen, PVDF/FKM/SR blends show three distinct tan δ peaks at ∼−120, ∼−40, and ∼−15 °C, corresponding to the Tg of SR, PVDF, and FKM, respectively. Moreover, it is also observed that the tan δ peak of the PVDF phase is shifted from −41.53 to −38.79 °C, while it increased from −15.95 to −14.45 °C for the FKM phase, as shown in

Figure 9. Loss tangent as a function of temperature plotted for TPVs.

Table 4. Clearly, the results do not follow typical theory to confirm the impressive miscibility, in which the tan δ peaks of Table 4. Tg of Every Component of PVDF/FKM/SR TPVs code P6F4S0 P6F3S1 P6F2S2 P6F1S3 P6F0S4

Tg‑SR

Tg‑PVDF

Tg‑FKM

−125.14 −126.06

−38.79 −39.13 −39.29 −40.03 −41.53

−14.45 −14.87 −15.96 −15.95

both PVDF and FKM shift toward each other gradually with the increase of FKM content. That is because aside from the interaction between FKM and PVDF, the Tg of FKM is also determined by the volume fraction of the corresponding phase, which has been reported by other authors.53,54 In this PVDF/ FKM/SR system, the core−shell particles may be considered as a phase composed of FKM and SR, and Tg of the partial compositions, FKM, could be calculated using the Fox formalism:55,56 15205

DOI: 10.1021/acs.iecr.9b03028 Ind. Eng. Chem. Res. 2019, 58, 15199−15208

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Industrial & Engineering Chemistry Research

Figure 10. 3D illustration of action mechanism of core−shell structure in shape memory of fluorosilicon TPVs.

w w 1 = 1 + 2 Tg Tg1 Tg 2

deformation process. Finally, the compatibilized PVDF/SR interface contributed to the stress transfer between the PVDF phase and SR/FKM particles: the deformed rubber particles in the shaping process and the release of strong elastic force in the shape recovery process.

in which Tg1 and Tg2 are the glass transition temperature of pure FKM and SR, respectively; as well as w1 and w2 are their corresponding mass fraction in SR/FKM phase. Above calculations indicated that Tg of FKM in the SR/FKM phase shifted to the high temperature with increasing FKM/SR ratios. Therefore, in our work, the observation of the increasing Tg‑PVDF could confirm the enhanced miscibility between PVDF and SR via core−shell dynamic vulcanization. 3.5. SM Mechanism Analysis. In light of the abovementioned analysis, the results have confirmed that the formation of the core−shell structure can improve the SM behavior of the TPVs. Therefore, an action mechanism of SRcore/FKM-shell structure in SM behavior of fluorosilicon TPVs was illustrated in Figure 10. Based on detailed comparisons of the following illustrations between PVDF/ FKM/SR TPVs (Figure 10B) and PVDF/SR TPVs (Figure 10A), it becomes clear that the improved SM behavior of TPVs with core−shell structure might originate from (i) the abundant tiny crystals of PVDF and (ii) the improved interfacial compatibility between the PVDF and SR phases. It is clear that these PVDF/FKM/SR TPVs with core−shell structure showed strong interfacial compatibility due to the encapsulation function of FKM and excellent affinity between FKM and PVDF. On the one hand, the incorporation of FKM efficiently prevented the coalescence of the SR phase, leading to the reduction of Dn and the increment of particle number. More SR-core/FKM-shell particles dispersed in the PVDF matrix led to the increased number of small PVDF crystals in the blends, which indicated the increased number of fixed points. Thus, the abundant tiny PVDF crystals endowed the elastomers with good shape fixing and stored more entropy elasticity in the recovery phase. On the other hand, the powerful compatibilized interface also contributed to the concentration fluctuation, which facilitated the orientation of PVDF chains, hence accelerating the crystallization of PVDF. The consequent accelerated crystallization helped the SR/ FKM particles maintain their highly elongated shape in the

4. CONCLUSION In summary, we designed a thermoplastic shape memory fluorosilicon material with core−shell structure, in which the cross-linked rubber phase and the crystallization of the PVDF phase served as the reversible phase and the temporary fixed phase, respectively. We demonstrated the core−shell structure effects on the SM properties of immiscible PVDF/SR blends. It is found that the appropriate temperature and the excellent interfacial compatibilization are crucial for realizing the SM behavior. Aside from the effect of Ttrans on the SM behavior of TPVs, the improved the interfacial compatibilization induced abundant tiny PVDF crystals, which contributed to the realization of the high SM performance. Furthermore, the excellent interfacial compatibilization facilitated the deformation of rubber particles in the shaping process and the release of strong elastic force in the shape recovery process. The suitable mechanical properties and SM behavior were achieved by tailoring the FKM/SR ratio (1:1): enhanced tensile strength (∼21.67 MPa), elongation at break (∼174.62%), tensile toughness (36.14 MJ/m3), and improved Rf (∼96%) and Rr (∼98%). We envision that PVDF/FKM-shell/SR-core blends with considerable mechanical properties may open up new applications as thermoplastic shape memory fluorosilicon materials.

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ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.iecr.9b03028. Surface tension of the main experimental raw materials, mechanical properties, DSC characterization, SEM images, number-average particle size, and corresponding size distributions (PDF) 15206

DOI: 10.1021/acs.iecr.9b03028 Ind. Eng. Chem. Res. 2019, 58, 15199−15208

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excess zinc oxide nanoparticles. Compos. Sci. Technol. 2018, 167, 431− 439. (15) Huang, J. R.; Cao, L. M.; Yuan, D. S.; Chen, Y. K. Design of multi-stimuli responsive shape memory biobased PLA/ENR/Fe3O4 TPVs with balanced stiffness-toughness based on selective distribution of Fe3O4. ACS Sustainable Chem. Eng. 2019, 7, 2304−2315. (16) Yan, M. W.; Cao, L. M.; Xu, C. H.; Chen, Y. K. Fabrication of “Zn2+ Salt-Bondings” Cross-Linked SBS-g-COOH/ZnO Composites: Thiol−Ene Reaction Modification of SBS, Structure, High Modulus, and Shape Memory Properties. Macromolecules 2019, 52, 4329−4340. (17) Liu, C.; Huang, J. R.; Yuan, D. S.; Chen, Y. K. Design of high strength XSBR/Fe3O4/ZDMA shape memory composite with dual responses. Ind. Eng. Chem. Res. 2018, 57, 14527−14534. (18) Fu, L. H.; Wu, F. D.; Xu, C. H.; Cao, T. H.; Wang, R. M.; Guo, S. H. Anisotropic shape memory behaviors of polylactic acid/citric acid-bentonite composite with a gradient filler concentration in thickness direction. Ind. Eng. Chem. Res. 2018, 57, 6265−6274. (19) Wu, W. C.; Xu, C. H.; Zheng, Z. J.; Lin, B. F.; Fu, L. H. Strengthened, recyclable shape memory rubber films with a rigid filler nano-capillary network. J. Mater. Chem. A 2019, 7, 6901−6910. (20) Chung, T.; Romo-Uribe, A.; Mather, P. T. Two-way reversible shape memory in a semicrystalline network. Macromolecules 2008, 41, 184−192. (21) Du, J.; Armstrong, S. R.; Baer, E. Co-extruded multilayer shape memory materials: Comparing layered and blend architectures. Polymer 2013, 54, 5399−5407. (22) Yuan, D. S.; Chen, Z. H.; Xu, C. H.; Chen, K. L.; Chen, Y. K. Fully biobased shape memory material based on novel co-continuous structure in poly(lactic acid)/natural rubber TPVs fabricated via peroxide-induced dynamic vulcanization and in-situ interfacial compatibilization. ACS Sustainable Chem. Eng. 2015, 3, 2856−2865. (23) Wang, Y. P.; Zhang, C. H.; Ren, Y. R.; Ding, T.; Yuan, D. S.; Chen, Y. K. Shape memory properties of dynamically vulcanized poly(lactic acid)/nitrile butadiene rubber (PLA/NBR) thermoplastic vulcanizates: The effect of ACN content in NBR. Polym. Adv. Technol. 2018, 29, 2336−2343. (24) Jing, X.; Mi, H. Y.; Peng, X. F.; Turng, L. S. The morphology, properties, and shape memory behavior of polylactic acid/thermoplastic polyurethane blends. Polym. Eng. Sci. 2015, 55, 70−80. (25) You, J. C.; Fu, H.; Dong, W. Y.; Zhao, L. P.; Cao, X. J.; Li, Y. J. Shape Memory Performance of Thermoplastic Polyvinylidene Fluoride/Acrylic Copolymer Blends Physically Cross-Linked by Tiny Crystals. ACS Appl. Mater. Interfaces 2012, 4, 4825−4831. (26) Chatterjee, T.; Dey, P.; Nando, G. B.; Naskar, K. Thermoresponsive shape memory polymer blends based on alpha olefin and ethylene propylene diene rubber. Polymer 2015, 78, 180−192. (27) Zhang, X. H.; Liu, J.; Zhang, Z. Y.; Wu, S. W.; Tang, Z. H.; Guo, B. C.; Zhang, L. Q. Toughening Elastomers Using a MusselInspired Multiphase Design. ACS Appl. Mater. Interfaces 2018, 10, 23485−23489. (28) Chen, Y. K.; Wang, Y. H.; Xu, C. H.; Wang, Y. P.; Jiang, C. Y. New Approach to Fabricate Novel Fluorosilicone Thermoplastic Vulcanizate with Bicrosslinked Silicone Rubber-Core/FluororubberShell Particles Dispersed in Poly(vinylidene Fluoride): Structure and Property. Ind. Eng. Chem. Res. 2016, 55, 1701−1709. (29) Wang, Y. H.; Gong, Z.; Xu, C. H.; Chen, Y. K. Poly (vinylidene fluoride)/fluororubber/silicone rubber thermoplastic vulcanizates prepared through core-shell dynamic vulcanization: Formation of different rubber/plastic interfaces via controlling the core from “soft” to “hard. Mater. Chem. Phys. 2017, 195, 123−131. (30) Jin, J.; Du, J.; Chen, H. Y.; Han, C. C. Fluctuation-assisted nucleation in the phase separation/crystallization of iPP/OBC blends. Polymer 2011, 52, 6161−6172. (31) Tian, M.; Li, T.; Zhang, L. Q.; Tian, H. C.; Wu, Y. P.; Ning, N. Y. Interfacial crystallization and its mechanism in in-situ dynamically vulcanized iPP/POE blends. Polymer 2014, 55, 3068−3074. (32) Huang, M. M.; Zheng, L. C.; Wang, L. L.; Dong, X.; Gao, X.; Li, C. C.; Wang, D. J. Double Crystalline Multiblock Copolymers with

AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. ORCID

Yukun Chen: 0000-0001-5523-3942 Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work was supported by the Key Projects of Basic Research and Applied Basic Research in Colleges and Universities in Guangdong Province (2018KZDXM004) and Special project for innovation of high-end scientific research institutions in Zhongshan City (2019AG013). The authors also express thanks to the National Projects (61409220414/ JZX7Y2019026206860).

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REFERENCES

(1) Hager, M. D.; Bode, S.; Weber, C.; Schubert, U. S. Shape Memory Polymers: Past, Present and Future Developments. Prog. Polym. Sci. 2015, 49−50, 3−33. (2) Leng, J. S.; Lan, X.; Liu, Y. J.; Du, S. Shape-memory polymers and their composites: stimulus methods and applications. Prog. Mater. Sci. 2011, 56, 1077−1135. (3) Kim, C. L.; Lee, J. J.; Oh, Y. J.; Kim, D. E. Smart wearable heaters with high durability, flexibility, water-repellent and shape memory characteristics. Compos. Sci. Technol. 2017, 152, 173−180. (4) Liu, Y.; Du, H.; Liu, L.; Leng, J. Shape memory polymers and their composites in aerospace applications: a review. Smart Mater. Struct. 2014, 23, 1−22. (5) Yang, Z. H.; Wang, Q. H.; Wang, T. M. Tunable Triple-Shape Memory Binary Mixtures with High Transition Temperature and Robust Mechanical Properties. Macromol. Chem. Phys. 2016, 217, 1305−1313. (6) Cui, R.; Ding, J. P.; Chen, Y. K. Magnesium acrylate induced interfacial compatibilization of EPDM/PP thermoplastic vulcanizate and shape memory behavior. Composites, Part A 2019, 122, 27−35. (7) Liu, T. Z.; Zhou, T. Y.; Yao, Y. T.; Zhang, F. H.; Liu, L. W.; Liu, Y. J.; Leng, J. S. Stimulus methods of multi-functional shape memory polymer nanocomposites: A review. Composites, Part A 2017, 100, 20−30. (8) Shirole, A.; Nicharat, A.; Perotto, C. U.; Weder, C. Tailoring the Properties of a Shape-Memory Polyurethane via Nanocomposite Formation and Nucleation. Macromolecules 2018, 51, 1841−1849. (9) Zhu, Y. Q.; Radlauer, M. R.; Schneiderman, D. K.; Shaffer, M. S. P.; Hillmyer, M. A.; Williams, C. K. Multiblock Polyesters Demonstrating High Elasticity and Shape Memory Effects. Macromolecules 2018, 51, 2466−2475. (10) Ragin Ramdas, M.; Santhosh Kumar, K. S.; Reghunadhan Nair, C. P. Synthesis, structure and tunable shape memory properties of polytriazoles: dual-trigger temperature and repeatable shape recovery. J. Mater. Chem. A 2015, 3, 11596−11606. (11) Wang, G. Q.; Jiang, M.; Zhang, Q.; Wang, R.; Zhou, G. Y. Biobased multiblock copolymers: Synthesis, properties and shape memory performance of poly(ethylene 2,5-furandicarboxylate)-bpoly(ethylene glycol). Polym. Degrad. Stab. 2017, 144, 121−127. (12) Koosomsuan, W.; Yamaguchi, M.; Phinyocheep, P.; Sirisinha, K. High-Strain Shape Memory Behavior of PLA-PEG Multiblock Copolymers and Its Microstructural Origin. J. Polym. Sci., Part B: Polym. Phys. 2019, 57, 241−256. (13) Chatterjee, T.; Dey, P.; Nando, G. B.; Naskar, K. Thermoresponsive shape memory polymer blends based on alpha olefin and ethylene propylene diene rubber. Polymer 2015, 78, 180−192. (14) Xu, C. H.; Wu, W. C.; Zheng, Z. J.; Wang, Z. W.; Nie, J. D. Design of shape-memory materials based on sea-island structured EPDM/PP TPVs via in-situ compatibilization of methacrylic acid and 15207

DOI: 10.1021/acs.iecr.9b03028 Ind. Eng. Chem. Res. 2019, 58, 15199−15208

Article

Industrial & Engineering Chemistry Research Controlling Microstructure for High Shape Memory Fixity and Recovery. ACS Appl. Mater. Interfaces 2017, 9, 30046−30055. (33) Kim, S. M.; Jeon, H.; Shin, S. H.; Park, S. A.; Jegal, J.; Hwang, S. Y.; Oh, D. X.; Park, J. Superior toughness and fast self-healing at room temperature engineered by transparent elastomers. Adv. Mater. 2018, 30, 1705145. (34) Filippidi, E.; Cristiani, T. R.; Eisenbach, C. D.; Waite, J. H.; Israelachvili, J. N.; Ahn, B. K.; Valentine, M. T. Toughening elastomers using mussel-inspired iron-catechol complexes. Science 2017, 358, 502−505. (35) Chan, B. Q. Y.; Heng, S. J. W.; Liow, S. S.; Zhang, K.; Loh, X. J. Dual-responsive hybrid thermoplastic shape memory polyurethane. Mater. Chem. Front. 2017, 1, 767−779. (36) Yu, R.; Yang, X.; Zhang, Y.; Zhao, X. J.; Wu, X.; Zhao, T. T.; Zhao, Y. L.; Huang, W. Three-Dimensional Printing of Shape Memory Composites with Epoxy-Acrylate Hybrid Photopolymer. ACS Appl. Mater. Interfaces 2017, 9, 1820−1829. (37) Wang, J.; Reyna-Valencia, A.; Chaigneau, R.; Favis, B. D. Controlling the Hierarchical Structuring of Conductive PEBA in Ternary and Quaternary Blends. Ind. Eng. Chem. Res. 2016, 55, 12848−12859. (38) Shen, C.; Zhou, Y.; Dou, R.; Wang, W.; Yin, B.; Yang, M. B. Effect of the core-forming polymer on phase morphology and mechanical properties of PA6/EPDM-g-MA/HDPE ternary blends. Polymer 2015, 56, 395−405. (39) Li, L. P.; Yin, B.; Zhou, Y.; Gong, L.; Yang, M. B.; Xie, B. H.; Chen, C. Characterization of PA6/EPDM-g-MA/HDPE ternary blends: The role of core-shell structure. Polymer 2012, 53, 3043− 3051. (40) Chen, Y. K.; Wang, W. T.; Yuan, D. S.; Xu, C. H.; Liang, X. Q.; Cao, L. M. Bio-Based PLA/NR-PMMA/NR Ternary Thermoplastic Vulcanizates with Balanced Stiffness and Toughness: “Soft-Hard” Core-Shell Continuous Rubber Phase, In Situ Compatibilization, and Properties. ACS Sustainable Chem. Eng. 2018, 6, 6488−6496. (41) Huang, J. R.; Cao, L. M.; Yuan, D. S.; Chen, Y. K. Design of Novel Self-Healing Thermoplastic Vulcanizates Utilizing Thermal/ Magnetic/Light-Triggered Shape Memory Effects. ACS Appl. Mater. Interfaces 2018, 10, 40996−41002. (42) Huang, J. R.; Fan, J. F.; Yin, S. H.; Chen, Y. K. Design of remotely, locally triggered shape-memory materials based on bicontinuous polylactide/epoxidized natural rubber thermoplastic vulcanizates via regulating the distribution of ferroferric oxide. Compos. Sci. Technol. 2019, 182, 107732. (43) Ji, X. Y.; Chen, D. Y.; Zheng, Y.; Shen, J. B.; Guo, S. Y.; HarkinJones, E. Multilayered assembly of poly(vinylidene fluoride) and poly(methyl methacrylate) for achieving multi-shape memory effects. Chem. Eng. J. 2019, 362, 190−198. (44) Wei, X. F.; Bao, R. Y.; Cao, Z. Q.; Yang, W.; Xie, B. H.; Yang, M. B. Stereocomplex Crystallite Network in Asymmetric PLLA/ PDLA Blends: Formation, Structure, and Confining Effect on the Crystallization Rate of Homocrystallites. Macromolecules 2014, 47, 1439−1448. (45) Cao, L. M.; Huang, J. R.; Chen, Y. K. Dual Cross-linked Epoxidized Natural Rubber Reinforced by Tunicate Cellulose Nanocrystals with Improved Strength and Extensibility. ACS Sustainable Chem. Eng. 2018, 6, 14802−14811. (46) Cao, L. M.; Fan, J. F.; Huang, J. R.; Chen, Y. K. A robust and stretchable cross-linked rubber network with recyclable and selfhealable capabilities based on dynamic covalent bonds. J. Mater. Chem. A 2019, 7, 4922−4933. (47) Liu, Y. T.; Cao, L. M.; Yuan, D. S.; Chen, Y. K. Design of supertough co-continuous PLA/NR/SiO2 TPVs with balanced stiffnesstoughness based on reinforced rubber and interfacial compatibilization. Compos. Sci. Technol. 2018, 165, 231−239. (48) Ojijo, V.; Sinha Ray, S.; Sadiku, R. Toughening of Biodegradable Polylactide/Poly(butylene succinateco-adipate) Blends via in Situ Reactive Compatibilization. ACS Appl. Mater. Interfaces 2013, 5, 4266−4276.

(49) Wang, H. T.; Fu, Z. A.; Zhao, X. W.; Li, Y. J.; Li, J. Y. Reactive Nanoparticles Compatibilized Immiscible Polymer Blends: Synthesis of Reactive SiO2 with Long Poly(methyl methacrylate) Chains and the in Situ Formation of Janus SiO2 Nanoparticles Anchored Exclusively at the Interface. ACS Appl. Mater. Interfaces 2017, 9, 14358−14370. (50) Li, X.; Kang, H. L.; Shen, J. X.; Zhang, L. Q.; Nishi, T.; Ito, K.; Zhao, C. M.; Coates, P. Highly toughened polylactide with novel sliding graft copolymer by in situ reactive compatibilization, crosslinking and chain extension. Polymer 2014, 55, 4313−4323. (51) Wu, N. J.; Zhang, H.; Fu, G. L. Super-tough Poly(lactide) Thermoplastic Vulcanizates Based on Modified Natural Rubber. ACS Sustainable Chem. Eng. 2017, 5, 78−84. (52) Chen, Y. K.; Fan, J. F.; Wang, W. T.; Wang, Y. P.; Xu, C. H.; Yuan, D. S. Influence of size reduction of crosslinked rubber particles on phase interface in dynamically vulcanized poly (vinylidene fluoride)/silicone rubber blends. Polym. Test. 2017, 63, 263−274. (53) Marin, N.; Favis, B. D. Co-continuous morphology development in partially miscible PMMA/PC blends. Polymer 2002, 43, 4723−4731. (54) Mittal, V.; Akhtar, T.; Matsko, N. Mechanical, Thermal, Rheological and Morphological Properties of Binary and Ternary Blends of PLA, TPS and PCL. Macromol. Mater. Eng. 2015, 300, 423− 435. (55) Kim, W. N.; Burns, C. M. Blends of polycarbonate and poly(methyl methacrylate) and the determination of the polymerpolymer interaction parameter of the two polymers. Macromolecules 1987, 20, 1876−1882. (56) Brostow, W.; Chiu, R.; Kalogeras, I. M.; Vassilikou-Dova, A. Prediction of glass transition temperatures: binary blends and copolymers. Mater. Lett. 2008, 62, 3152−3155.

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