Nonisothermal crystallization kinetic behavior of pure ethylene-Vinyl acetate copolymers and ethylene-Vinyl acetate copolymer/nitrile rubber thermoplastic vulcanizate

Abstract

Thermoplastic vulcanizate (TPV) made from the ethylene-vinyl acetate copolymer (EVA)/nitrile rubber (NBR) blend was fabricated using the dynamic vulcanization method. Differential scanning calorimetry (DSC) was utilized to analyze the nonisothermal crystallization kinetics of both pure EVA and EVA/NBR TPV. The nonisothermal crystallization mechanism was evaluated using the Avrami method modified by Jeziorny, the Ozawa method and the Mo method. The results demonstrate that the nonisothermal crystallization of both pure EVA and EVA/NBR TPV can be adequately described by the Avrami method modified by Jeziorny and the Mo method, while the Ozawa method is not applicable. By elevating the cooling rate, there was a reduction in the crystallization temperature and t_1/2 for both pure EVA and EVA/NBR TPV, while the degree of crystallization increased. At the same cooling rate, the crystallization temperature of the EVA/NBR TPV was found to be higher than that of the pure EVA, suggesting that the presence of NBR facilitated the nucleation of the EVA matrix within the EVA/NBR TPV. Moreover, a steric hindrance effect existed in the NBR phase of EVA/NBR TPV at the same cooling rate, resulting in a larger t_1/2 compared to that of the pure EVA, indicating hindered crystal growth.

Keywords

Ethylene-vinyl acetate copolymer nitrile rubber dynamic vulcanization crystallization differential scanning calorimeter

Introduction

Thermoplastic elastomer (TPE) has a unique combination of properties, including elastomeric behavior at room temperature and the ability to be plasticized at the elevated temperature.^1–4 Typically, TPE consist of two components: a soft segment with rubber-like elasticity and a hard segment with crosslinking points.⁵ The soft and hard segments form a unique two-phase system that is thermodynamically incompatible, resulting in a material with the mechanical elasticity of traditional rubber pre-blend and the reusability of thermoplastics.⁶ A specific TPE is thermoplastic vulcanizate (TPV), which is prepared by mixing rubber with thermoplastic resin under dynamic vulcanization. Usually, the process results in the formation of a dual-phase microstructure, wherein the resin phase is acted as the continuous phase while the rubber phase is dispersed throughout in the continuous phase. TPV is a highly versatile material, exhibiting plasticity at high temperature and high elasticity at room temperature. Moreover, TPV has the advantage of being cost-effectiveness, simple processing and equipment requirements, as well as the ability to adjust the resulting product’s properties across a wide range.^7–9

Ethylene-vinyl acetate copolymer (EVA) is a versatile thermoplastic resin composed of polar vinyl acetate unit and non-polar ethylene unit. Compared with the most thermoplastic resins, EVA has several distinct advantages, firstly, it exhibits the good biocompatibility, which makes it widely used in medical devices, pharmaceutical packaging and other fields related to human health; secondly, it has the excellent oil resistance, making it a popular choice in the manufacturing of automotive and industrial equipment, as well as in the construction industry; additionally, EVA has the low-temperature flexibility, high light transmission and excellent melt processing properties, which make it a widely used material in the manufacture of footwear, packaging materials, solar cells and other fields. The high polarity of EVA also makes it particularly suitable for certain specific applications, such as the manufacture of solar cell back sheets and adhesives.^10–12 Nitrile rubber (NBR) is a polar, unsaturated rubber consisting of butadiene unit and acrylonitrile unit. NBR is renowned for its excellent oil resistance, as well as outstanding properties such as aging resistance, wear resistance and low gas permeability. Therefore, the applications of NBR are diverse, for example, NBR is commonly used for manufacturing fuel system linings and oil seals in the automotive and aerospace industries due to its excellent oil resistance; NBR is frequently used to produce sealing gaskets for oil and natural gas pipelines in the petroleum industry; NBR’s excellent adhesion properties make it an ideal choice for producing printing rollers in the printing industry.^13,14 The blending of EVA with NBR results in the TPV that exhibits both the plasticity of EVA and the high elasticity of NBR. Therefore, it is highly meaningful to combine the advantages of EVA and NBR together to prepare the EVA/NBR TPV with excellent property. Until now, there is no report on the nonisothermal crystallization behavior of EVA/NBR TPV, in spite of the widespread use and popularity of both EVA and NBR. The research in nonisothermal crystallization could potentially provide valuable insight into the behavior of EVA/NBR TPV, enabling the development of new applications and improved product performance.

Crystallization kinetic parameters are crucial for understanding the microstructure and properties of crystalline polymer, as well as optimizing manufacturing process and improving product quality.^15–17 The crystallization behavior of polymer can be categorized into two major classes: isothermal and nonisothermal crystallization.^18,19 Isothermal crystallization occurs when the polymer sample is kept at a constant temperature and its crystallization behavior is controlled by temperature. Conversely, nonisothermal crystallization occurs when the polymer specimen undergoes the different cooling rate. Nonisothermal crystallization methods are widely used in industrial production since nonisothermal conditions are more representative of actual production process. Temperature is the most significant factor influencing the crystallization process of polymer. The crystallization process generally consists of two sections: nucleation and growth. During the nucleation stage, the polymer molecules are arranged around the crystalline core to form microcrystals, which is the beginning of the crystallization process; in the growth phase, the microcrystals continue to expand to form the complete crystals. The kinetic parameters of the nucleation and the growth process determine the crystallization behavior and microstructure formation of the polymer.²⁰ Differential scanning calorimetry (DSC) is a widely employed method for studying the crystallization behavior. By analyzing the crystallization temperature and enthalpy of crystallization of a polymer sample, DSC experiments can simulate the relative or absolute crystallinity of the crystalline polymer, enabling control of the polymer processing. DSC can also be used to research the crystallization behavior of complex polymer, such as TPE. Usually, TPV is typically composed of rubber and thermoplastic resin and the crystallization behavior is also influenced by the rubber. Therefore, an in-depth understanding of the crystallization process is required to optimize TPV production process. Currently, there is extensive research on the kinetics of EVA. Pang et al.²¹ conducted studies on the isothermal kinetics of EVA, demonstrating pure EVA resin exhibits the stable and rapid isothermal crystallization behavior at approximately 74°C. However, most processing methods and applications are conducted under nonisothermal conditions, research on nonisothermal crystallization kinetics holds the more practical value than that of isothermal kinetics. Jin et al.²² conducted research on the nonisothermal kinetics of EVA, elucidating that pure EVA exhibits a homogeneous nucleation mechanism and a three-dimensional spherulitic growth mechanism. There is a considerable amount of literature discussing EVA/NBR TPV both domestically and internationally, including studies conducted by Wang et al.^23,24 on the heat-triggered shape memory of EVA/NBR TPV and Li et al.²⁵ on the influence of chlorinated polyethylene compatibilization on the mechanical performance and morphology of EVA/NBR TPV. However, the level of attention devoted to the nonisothermal crystallization kinetics of the EVA/NBR TPV remains limited. The investigation of nonisothermal crystallization kinetics in EVA/NBR TPV holds significant potential in facilitating the precise control and optimization of the production process.

In this research, the dynamic vulcanization method was employed to prepare the EVA/NBR TPV. The nonisothermal crystallization kinetic behaviors of pure EVA and EVA/NBR TPV were tested by DSC, and in-depth studies were conducted using Avrami, Ozawa and Mo models to systematically examine the effects of the cooling rate and the crystallization mechanism of NBR relative to EVA. This research is important for understanding the crystallization mechanism of pure EVA and EVA/NBR TPV and provides a reference for the crystallization process.

Experimental

Materials

Ethylene-vinyl acetate copolymer (EVA), grade 7470M, vinyl acetate mass fraction 26%, a product of Taiwan Plastics Industry Co Ltd (Taiwan, China). Nitrile rubber (NBR), grade N41, combined with 29% mass fraction of acrylonitrile, a product of PetroChina Lanzhou Petrochemical Co Ltd (Lanzhou, China).

Bis(1-(tert-butylperoxy)-1-methylethyl)-benzene (BIPB), triallyl isocyanurate (TAIC), N-Phenyl-2-naphthylamine (antioxidant D) and other agents are all commonly used industrial grade commercially available products.

Specimen preparation

The peroxide promotion system is utilized in the NBR crosslinking formulation, which consists of the following constituents: 100 phr (per hundred rubber weight, the same as below) NBR, 3.0 TAIC, 1.3 BIPB and 1.0 Antioxidant D.

In order to prepare the EVA/NBR TPV, firstly, the NBR and compounding agent were mixed in an open double roll mill (X[S] K-160, Qun Yi Rubber Machinery Co Ltd, Shanghai, China) at room temperature to obtain NBR pre-blend. EVA particles were then melted and plasticized on an open double roll mill (SY-6215-AL1, Shi Yan Precision Instrument Co, Ltd, Dongguan, China) at 165°C and NBR pre-blend was put into dynamically vulcanize for 8 min to obtain the EVA/NBR compound. The rotor speed of the mixer was maintained at 43 rpm, while the rubber to the plastic ratio of the EVA/NBR TPV was fixed at 70/30. The cooled EVA/NBR compound was placed in a mold, preheated for 6 min on a plate vulcanizing machine (50 T, Qun Yi Rubber Machinery Co Ltd, Shanghai, China) at 165°C, exhausted for 3 times, hot pressed for 8 min and cold pressed for 8 min at a pressure of 10 MPa to obtain EVA/NBR TPV specimen.

Characterization

The nonisothermal crystallization kinetics of pure EVA and EVA/NBR TPV were researched by DSC. The specimen mass was about 5 mg and the testing was conducted under a nitrogen atmosphere. The instrument was set to ramp up from 20°C to 120°C at a rate of 20 °C/min and held at 120°C for 5 min. The cooling temperature range was 120°C–20°C, followed by cooling to 20°C at rates of 5, 10, 15 and 20 °C/min, respectively.

Results and discussion

The exothermic crystallization curves of pure EVA and EVA/NBR TPV at various cooling rates (5, 10, 15 and 20 °C/min) were illustrated in Figure 1. The results showed that all curves were single peaks, the increase of cooling rate led to the increase of curve width. The appearance of crystalline peaks was independent of the heating rate.

Figure 1.

Nonisothermal crystallization DSC curves of specimens at different cooling rates. (a) pure EVA; (b) EVA/NBR TPV (weigh ratio = 70/30).

At slower cooling rates, both the crystallization peaks and curves shifted towards higher temperatures as the chain segments were afforded adequate time to crystallize within a narrower temperature range. With the increase in cooling rate, the rate at which molecular segments entered the crystalline region fell behind the cooling rate, pointing to a reduction in crystallization temperature and hindrance of the crystallization process. However, the faster cooling rate is beneficial to the nucleation reaction, and more chain segments enter the crystal lattice to complete the crystallization, which shows that the crystallization time becomes shorter. From the DSC curves in Figure 1, a series of kinetic parameters can be derived, including initial crystallization temperature (T_o), crystallization termination temperature (T_c), peak crystallization temperature (T_p), half-crystallization time (t_1/2) and crystallization enthalpy change (ΔH_c). Table 1 lists the corresponding values. Although the increase in cooling rate resulted in a shorter crystallization time, the decrease in T_o, T_c, T_p, and ΔH_c indicated that the crystal structure was imperfect. This is related to the relaxation property of chain segment movement, which is generally closely related to temperature, and the movement ability is enhanced with the increasing temperature, facilitating the chain segment adjustment. Compared with the pure EVA, the values of T_o, T_c and ΔH_c of EVA/NBR TPV were higher than that of pure EVA, while T_p and t _1/2 were lower than that of the pure EVA. This is attributed to the fact that TPV is a two-phase structure of the blended material, and due to its excellent interfacial bonding between the two phases, the NBR phase will play a certain role as a nucleating agent, which leads to the T_o and T_c of EVA/NBR TPV being higher than that of pure EVA. Furthermore, due to the spatial site resistance effect, the NBR phase in EVA/NBR TPV will hinder the movement of EVA chain segments, which will affect the crystal growth and decrease the T_p and t_1/2 values.

Table 1.

Crystallization kinetic parameters of nonisothermal crystallization of pure EVA and the EVA/NBR TPV.

		Cooling rates/(°C·min⁻¹)
		5	10	15	20
Pure EVA	T_o (°C)	49.99	45.24	40.99	35.99
	T_p (°C)	55.74	52.49	49.74	47.24
	T_c (°C)	60.99	59.74	57.99	55.99
	t_1/2 (min)	1.050	0.725	0.550	0.463
	ΔH _c	−16.39	−22.15	−23.54	−26.56
	n	2.382	2.453	2.440	2.388
	Zt	0.748	1.780	3.254	4.472
EVA/NBR (70/30) TPV	T_o (°C)	50.25	45.5	41.5	36.75
	T_p (°C)	55.25	52.00	49.25	46.50
	T_c (°C)	61.75	60.25	58.75	57.00
	t_1/2 (min)	1.300	0.825	0.633	0.525
	ΔH _c	−9.04	−10.78	−12.03	−13.26
	n	2.439	2.514	2.529	2.462
	Zt	0.498	1.512	2.930	4.261

Since the presence of NBR phase in EVA/NBR TPV has an impact on the crystallization behavior of EVA, its relative crystallinity needs to be calculated to further investigate its crystallization kinetic behavior. The Jeziorny method enables the calculation of the relative crystallinity (X_t) by calculating the ratio of the area under the crystallization curve from the crystallization onset temperature to a specific crystallization temperature to the total area of the entire crystallization process. The formula is shown below^26,27

X_{t} = \frac{\int_{T_{o}}^{T} (d H / d T) d T}{\int_{T_{o}}^{T_{c}} (d H / d T) d T}

(1)

Where X_t represents the relative crystallinity, T_o denotes the crystallization initial temperature, T_c signifies the crystallization termination temperature and dH/dT is associated with the rate of heat flow.

Figure 2 illustrates the relative crystallinity versus temperature curves for pure EVA and EVA/NBR TPV at cooling rates of 5, 10, 15 and 20 °C/min respectively. The curves in Figures 2(a) and (b) exhibited a typical inverse S-shaped pattern, characterized by rapid initial crystallization in the early stage, followed by slower secondary crystallization in the later stage. The crystallinity curve shifted towards low temperature as the cooling rate increased. This was related to crystal growth and nucleation, and if the cooling rate was relatively fast, nucleation and crystal growth could only be completed at relatively low temperature; furthermore, when the crystallization temperature was the same, an increase in the cooling rate resulted in a decrease in the relative crystallinity of the specimen. This phenomenon can be explained by the fact that with increasing cooling rate, the rate of molecular chain exclusion into the crystal lattice cannot match the cooling rate, resulting in restricted crystallization.²⁸

Figure 2.

Development of relative crystallinity versus temperature during nonisothermal crystallization at four cooling rates. (a) pure EVA; (b) EVA/NBR TPV (weigh ratio = 70/30).

The nonisothermal crystallization process can be described by an equation that expresses the relationship between crystallization temperature (T) and crystallization time (t) in the following manner

t = \frac{(T - T o)}{φ}

(2)

Where T denotes the temperature at t, T_o represents the initial temperature of crystallization and φ represents the constant cooling rate.

Figure 3 displays the relative crystallinity versus crystallization time curves for pure EVA and EVA/NBR TPV at various cooling rates. The curves, depicted in Figures 3(a) and (b), exhibit a typical S-shaped trend with increasing time. Moreover, the results indicated that the slope of the curve becomes larger and the crystallization time becomes shorter with the increasing cooling rate. The crystallization time of EVA/NBR TPV was shorter than that of pure EVA at the same cooling rate and relative crystallinity, where the NBR phase promoted the crystallization of the EVA matrix. A larger t_1/2 was observed for EVA/NBR TPV compared to pure EVA at the same cooling rate, as shown in Figure 3 and Table 1. The slower crystallization rate of EVA/NBR TPV is attributed to the steric hindrance effect generated by the NBR phase.

Figure 3.

Development of relative crystallinity versus time during nonisothermal crystallization at four cooling rates. (a) pure EVA; (b) EVA/NBR TPV (weigh ratio = 70/30).

Avrami equation is generally used to analyze isothermal crystallization process, while most of the actual production takes place under nonisothermal conditions, therefore, the Avrami equation is corrected by Jeziorny method to study the nonisothermal crystallization kinetics, and the equation is expressed as follows^29,30

\ln [- \ln (1 - X_{t})] = n \ln t + \ln Z_{t}

(3)

Where n is the Avrami index and Z_t is the crystallization rate constant. Both n and Z_t are determined by the nucleation and growth mechanism of the crystal. The relative crystallinity of the polymer at different temperature or times is represented by X_t, while the time required for crystallization is represented by t. Since the Avrami equation is only suitable for analyzing isothermal crystallization process and does not consider the effect of cooling rate on the crystallization in nonisothermal crystallization process, Jeziorny et al. corrected for Z_t

\ln Z_{c} = \frac{\ln Z_{t}}{φ}

(4)

Where Z_t is the dynamic crystallization rate constant, Z_c is the Jeziony-corrected dynamic crystallization rate constant and φ is the constant cooling rate, a larger value of Z_c indicates a faster crystallization rate. Compared with the Avrami equation, the Jeziorny method is more widely used.

Figure 4 illustrates the ln[-ln(1-X_t)] versus lnt curves for nonisothermal crystallization of pure EVA and EVA/NBR TPV at cooling rates of 5, 10, 15 and 20 °C/min, respectively. The linear regression the four curves verifies the appropriateness of the Avrami equation for characterizing the nonisothermal crystallization behavior of both pure EVA and EVA/NBR TPV. The Avrami exponent (n), which characterizes the growth mode of crystals during crystallization, is determined from the slope of the linearly fitted curves. On the other hand, the intercept reflects the crystallization rate constant (Z_t) and provides insights into the crystallization rate. Moreover, the curves also provide information on the crystallization half-time (t_1/2), which is defined as the time required for the specimen to reach 50% crystallinity. Table 1 presents the Z_t, n and t_1/2 values obtained from nonisothermal crystallization experiments. Notably, nonisothermal crystallization involves continuous changes in temperature, resulting in temperature-dependent nucleation and crystal growth rates. Consequently, the physical meaning of the Z_t and n parameters in nonisothermal crystallization is distinct from that in isothermal crystallization. Therefore, the Z_t values obtained from the Avrami equation need to be corrected using the Jeziorny method for nonisothermal crystallization. The nearly parallel alignment of the five linear fit lines in Figure 4 suggests that the nucleation properties and crystal geometry of both samples are highly similar. The Avrami exponent n, which falls within the range of 2–3, indicates that the nonisothermal crystallization behavior of the pure EVA and EVA/NBR TPV is primarily influenced by multidimensional heterogeneous nucleation. The Z_t values for both pure EVA and EVA/NBR TPV generally increased, which is consistent with previous studies conducted by Eder and Wlochowicz.^31,32 During nonisothermal crystallization, it is observed that the Z_t values of both pure EVA and EVA/NBR TPV increase with an increase in cooling rate, indicating an enhancement in the crystallization rate. Moreover, the Z_t values of EVA/NBR TPV were lower than that of pure EVA at the same cooling rate. This observation suggested that the volume of NBR phase in TPV is relatively higher, leading to a steric hindrance effect that delays the crystallization of EVA.

Figure 4.

The Avrami plots of ln[-ln(1-X_t)] versus lnt for the nonisothermal crystallization at four cooling rates. (a) pure EVA; (b) EVA/NBR TPV (weigh ratio = 70/30).

Ozawa et al.^33,34 proposed that the nonisothermal crystallization process can be decomposed into a sequence of infinitesimal isothermal crystallization steps, extending the application of the Avrami equation to nonisothermal crystallization conditions

\ln [- \ln (1 - X_{t})] = m \ln φ + \ln K (T)

(5)

The relative crystallinity is represented by X_t, while the cooling rate is denoted by φ and the crystallization rate constant is denoted by K(T). The Ozawa index, m, characterizes the growth and nucleation mechanism of crystals in the specimen.

Figure 5 shows the plot of ln[−ln(1−X_t)] versus lnφ for pure EVA and EVA/NBR TPV at a certain temperature. Upon analysis of the crystallization curve from Figure 5, it is evident that it does not follow a linear trend, which cannot obtain the Ozawa index m and the K(T), suggesting that the Ozawa model is not an appropriate method to characterize the nonisothermal crystallization behavior of pure EVA and EVA/NBR TPV. Therefore, the crystallization process was not applicable to the Ozawa method owing to the presence of non-negligible secondary crystallization for pure EVA and EVA/NBR TPV. In fact, the Ozawa model is also inappropriate to characterize the crystallization behavior of some other polymer. The limitation of the Ozawa model could potentially stem from its failure to account for the effects of secondary crystallization process. Therefore, alternative models should be considered to accurately describe the nonisothermal crystallization behavior of the pure EVA and the EVA/NBR TPV.

Figure 5.

The Ozawa plots of ln[−ln(1−X_t)] versus lnφ for the nonisothermal crystallization. (a) pure EVA; (b) EVA/NBR TPV (weigh ratio = 70/30).

The Mo Zhishen method, which integrates with the Avrami method and the Ozawa method, describes the relationship between cooling rate (φ) and crystallization time (t). The final equation is as follows³⁵

\ln φ = \ln F (T) - α \ln t

(6)

Where F(T) = [K(T)/Z_t]^1/m, α is the ratio of Avrami equation exponent n to Ozawa equation exponent m (i.e., α = n/m), K(T) represents the crystallization rate constant, Z_t is the kinetic crystallization rate constant and m is the Ozawa index. The value of F(T) represents the cooling rate required to achieve the specified crystallinity in unit crystallization time, and the higher the value of F(T), the smaller the crystallization rate.³⁶

Figure 6 displays the lnφ versus lnt curves for nonisothermal crystallization of pure EVA and EVA/NBR TPV at various relative crystallinity. Linear relationships were found to be present for all specimens at various relative crystallinity, suggesting that the Mo method is appropriate for characterizing the nonisothermal crystallization behavior of both pure EVA and EVA/NBR TPV. Table 2 provides the values of F(T) and α, which can be determined from the slope and intercept of the linear relationship between lnφ and lnt. The data presented in Table 2 reveals a positive correlation between the relative crystallinity and F(T), implying that an increase in the cooling rate results in a higher crystallinity achieved per unit time. These results suggest that an increase in the cooling rate can promote polymer crystallization. The α values range from 1.52 to 1.83, all of which are greater than 1, indicating that the Avrami index is marginally larger than the Ozawa index for the nonisothermal crystallization behavior of pure EVA and EVA/NBR TPV. The F(T) value of pure EVA is lower than that of EVA/NBR TPV, as evidenced by the data in Table 2, suggesting that the total crystallization rate of pure EVA is faster than that of EVA/NBR TPV. This conclusion agreed with the result obtained from the Avrami equation.

Figure 6.

The Mo plots of the lnφ versus lnt for the nonisothermal crystallization. (a) pure EVA; (b) EVA/NBR TPV (weigh ratio = 70/30).

Table 2.

The Mo kinetic parameters of nonisothermal crystallized pure EVA and EVA/NBR TPV determined via the DSC method.

Specimens	X_t (%)	F(T)	α
Pure EVA	10	0.33	1.77
	30	1.21	1.71
	50	1.66	1.73
	70	2.05	1.74
	90	2.41	1.83
EVA/NBR (70/30) TPV	10	0.83	1.53
	30	1.51	1.52
	50	1.90	1.54
	70	2.21	1.58
	90	2.54	1.62

In this research, both the Jeziorny method and the Mo method were successful in describing the nonisothermal crystallization behavior of the EVA/NBR TPV, while the Ozawa method failed to describe the nonisothermal crystallization behavior. This result is similar to the findings of our previous research,^28,37 the research further proved the identical perspective.

Conclusion

In this research, the nonisothermal crystallization kinetics of pure EVA and EVA/NBR TPV was employed the Avrami method, the Ozawa method and Mo method. The results revealed that the rate of crystallization in both pure EVA and EVA/NBR TPV was affected by the cooling rate, and the faster cooling rate would lead to the faster crystallization rate. The higher crystallization temperature of EVA/NBR TPV compared with pure EVA proves that the NBR phase plays the role of nucleating agent. Both Avrami analysis modified by Jeziorny and the Mo method were capable of accurately describing the crystallization kinetics of pure EVA and EVA/NBR TPV. Specifically, the Avrami method was employed to determine the key parameters of Z_t and t_1/2, which revealed that the rate of crystallization for all specimens increased with the cooling rate. The n values obtained from the Avrami method indicated that the crystallization process of both pure EVA and EVA/NBR TPV was complex and includes secondary crystallization. The F(T) value of the EVA/NBR TPV was comparatively higher than that of pure EVA, suggesting a lower crystallization rate of the EVA/NBR TPV. The results demonstrated that the presence of NBR phase in EVA/NBR TPV can promote nucleation, while the steric effect of NBR phase in EVA/NBR TPV impedes crystal growth.

Footnotes

Declaration of conflicting interests

The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Funding

The author disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: This work was supported by the Shandong Provincial Natural Science Foundation, China (ZR2021ME028).

ORCID iDs

Yuan Gao

Zhaobo Wang

References

Liu

Zhang

, et al. Strengthening effect of Mullins effect of highdensity polyethylene/ethylene-propylene-diene terpolymer thermoplastic vulcanizates under compression mode. J Thermoplast Compos Mater 2018; 31(10): 1310–1322.

Cao

Huang

, et al. Self-healing natural rubber with tailorable mechanical properties based on ionic supramolecular hybrid network. ACS Appl Mater Interfaces 2017; 9(34): 29363–29373.

Bao

Dou

, et al. Conductive thermoplastic vulcanizates (TPVs) based on polypropylene (PP)/ethylenepropylene-diene rubber (EPDM) blend: from strain sensor to highly stretchable conductor. Composi Sci Technol 2016; 128: 176–184.

Cao

Yuan

, et al. Biobased, self-healable, high strength rubber with tunicate cellulose nanocrystals. Nanoscale 2017; 9: 15696–15706.

Wang

Zhang

, et al. Carbon black reinforced thermoplastic vulcanisates based on ethylene–vinyl acetate copolymer/styrene–butadiene rubber blends. Plast Rubber Compos 2016; 45(10): 415–422.

Fazli

Rodrigue

. Waste rubber recycling: a review on the evolution and properties of thermoplastic elastomers. Mater 2020; 13(3): 782.

Tian

Zhang

, et al. New understanding of microstructure formation of the rubber phase in thermoplastic vulcanizates (TPV). Soft Matter 2014; 10(11): 1816–1822.

Tian

Zhang

, et al. New understanding of morphology evolution of thermoplastic vulcanizate (TPV) during dynamic vulcanization. ACS Sustain Chem Eng 2015; 3(1): 26–32.

Magioli

Sirqueira

Soares

. The effect of dynamic vulcanization on the mechanical, dynamic mechanical and fatigue properties of TPV based on polypropylene and ground tire rubber. Polym Test 2010; 29(7): 840–848.

10.

Salyer

Kenyon

. Structure and property relationships in ethylene–vinyl acetate copolymers. J Polym Sci, Part A-1: Polym Chem 1971; 9(11): 3083–3103.

11.

Kojima

Yanagisawa

. The evaluation of accelerated test for degradation a stacked a-Si solar cell and EVA films. Sol Energy Mater Sol Cells 2004; 81(1): 119–123.

12.

Stark

Jaunich

. Investigation of ethylene/vinyl acetate copolymer (EVA) by thermal analysis DSC and DMA. Polym Test 2011; 30(2): 236–242.

13.

Liu

, et al. Investigation of aging behavior and mechanism of nitrile-butadiene rubber (NBR) in the accelerated thermal aging environment. Polym Test 2016; 54: 59–66.

14.

Wang

, et al. Preparation and tribological properties of graphene oxide/nitrile rubber nanocomposites. J Mater Sci 2012; 47: 730–738.

15.

Jiang

Zhao

Xin

. Influence of a novel β-nucleating agent on the structure, mechanical properties, and crystallization behavior of isotactic polypropylene. J Thermoplast Compos Mater 2013; 28(5): 610–629.

16.

Zhang

Shao

, et al. Thermal properties and crystallization kinetics of a new polypropylene-polyamide 6 composite. J Thermoplast Compos Mater 2015; 29(1): 143–158.

17.

Yang

Wang

, et al. Crystallization and mechanical properties of polyphenylene sulfide/multiwalled carbon nanotube composites. J Thermoplast Compos Mater 2017; 31(11): 1545–1560.

18.

Yang

Sun

, et al. Isothermal and Non-Isothermal Crystallization Kinetics of Poly (ethylene chlorotrifluoroethylene). Polym 2022; 14(13): 2630.

19.

Kelly

Jenkins

. Modeling the crystallization kinetics of polymers displaying high levels of secondary crystallization. Polym J 2022; 54(3): 249–257.

20.

Xue

Yin

Jia

, et al. Enhancing mechanical and thermal properties of styrene-butadiene rubber/carboxylated acrylonitrile butadiene rubber blend by the usage of graphene oxide with diverse oxidation degrees. Appl Surf Sci 2017; 423: 584–591.

21.

Pang

Zhong

Wang

, et al. In-situ synchrotron x-ray scattering study on isothermal crystallization of ethylene-vinyl acetate copolymers containing a high weight fraction of carbon nanotubes and graphene nanosheets. J Polym Res 2012; 19: 1–5.

22.

Jin

Chen

Zhang

. Non-isothermal crystallization kinetics of partially miscible ethylene-vinyl acetate copolymer/low density polyethylene blends. eXPRESS Polym Lett 2010; 4: 141–152.

23.

Wang

Hua

Wang

. Facile design of heat-triggered shape memory ethylene-vinyl acetate copolymer/nitrile-butadiene thermoplastic vulcanizates via zinc dimethacrylate induced interfacial compatibilization. Polym Test 2019; 76: 481–489.

24.

Wang

Xiong

Wang

. A novel heat-triggered shape-memory polymer based on ethylene–vinyl acetate copolymer/nitrile–butadiene rubber thermoplastic vulcanizates. J Thermoplast Compos Mater 2020; 33(9): 1217–1233.

25.

Liu

Wang

, et al. Dynamically vulcanized nitrile butadiene rubber/ethylene-vinyl acetate copolymer blends compatibilized by chlorinated polyethylene. J Macromol Sci Part B 2013; 52(1): 13–21.

26.

Kourtidou

Tarani

Chrysafi

, et al. Non-isothermal crystallization kinetics of graphite-reinforced crosslinked high-density polyethylene composites. J Therm Anal Calorim 2020; 142: 1849–1861.

27.

Jeziorny

. Parameters characterizing the kinetics of the non-isothermal crystallization of poly(ethylene terephthalate) determined by DSC. Polym 1978; 19(10): 1142–1144.

28.

Liu

Shan

Wang

. Nonisothermal crystallization behaviors of ethylene–acrylic acid copolymer and ethylene–acrylic acid copolymer/chloroprene rubber thermoplastic vulcanizate. J Thermoplast Compos Mater 2022; 35(10): 1548–1560.

29.

Zhu

Zhang

Guan

. The nonisothermal crystallization behavior of polyamide-6,6/mobile crystalline material hybrid composites prepared by in situ polymerization. J Thermoplast Compos Mater 2014; 29(5): 638–655.

30.

De Juana

Jauregui

Calahorra

, et al. Nonisothermal crystallization of poly(hydroxy ether of bisphenol-A)/poly(ɛ-caprolactone), PH/PCL blends. Polym 1996; 37(15): 3339–3345.

31.

Eder

Wlochowicz

. Kinetics of non-isothermal crystallization of polyethylene and polypropylene. Polym 1983; 24(12): 1593–1595.

32.

Chen

Zhong

, et al. Nonisothermal crystallization of isotactic polypropylene in carbon nanotube networks: the interplay of heterogeneous nucleation and confinement effect. J Thermoplast Compos Mater 2014; 29(10): 1352–1368.

33.

Di Lorenzo

Silvestre

. Non-isothermal crystallization of polymers. Prog Polym Sci 1999; 24(6): 917–950.

34.

Ozawa

. Kinetics of non-isothermal crystallization. Polym 1971; 12(3): 150–158.

35.

Liu

Wang

, et al. Nonisothermal melt and cold crystallization kinetics of poly(arylether ether ketone ketone). Polym Eng Sci 1997; 37(3): 568–575.

36.

Liu

Wang

, et al. Isothermal melt and cold crystallization kinetics of poly (aryl ether ether ketone ketone)(PEEKK). Eur Polym J 1997; 33(9): 1405–1414.

37.

Wang

Huang

Shan

, et al. Study on Non-isothermal crystallization behavior of high density polyethylene and high density polyethylene/styrene butadiene rubber thermoplastic vulcanizate. Spec Purpose Rubber Prod 2023; 44(1): 39–44. (Chinese).