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Nucleation Role of Basalt Fibers during Crystallization of Poly(#-caprolactone) Composites Qiaolian Lv, Zeren Ying, Defeng Wu, Zhifeng Wang, and Ming Zhang Ind. Eng. Chem. Res., Just Accepted Manuscript • DOI: 10.1021/acs.iecr.6b04510 • Publication Date (Web): 22 Feb 2017 Downloaded from http://pubs.acs.org on February 27, 2017

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Industrial & Engineering Chemistry Research

Nucleation Role of Basalt Fibers during Crystallization of Poly(ε-caprolactone) Composites Qiaolian Lv1 1

2

Defeng Wu1, 2* Zhifeng Wang3

Ming Zhang1, 2

School of Chemistry & Chemical Engineering, Yangzhou University, Jiangsu 225002, China

Provincial Key Laboratories of Environmental Engineering & Materials, Jiangsu 225002, China 3

*

Zeren Ying1

Testing Center, Yangzhou University, Jiangsu 225002, China

Corresponding author, Tel: +86-514-87975230, Fax: +86-514-87975244, E-mail address: [email protected] 1

ACS Paragon Plus Environment


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ABSTRACT The crystallization behavior of the basalt fibers (BF) filled poly(ε-caprolactone) (PCL) composites. Both the pristine BF and treated one have remarkable nucleation effect on the crystallization of PCL, and the latter has higher nucleation activity than the former. However, the PCL chain diffusion is restrained by the physical barrier effect of BF and the increased system viscosities. But nucleation dominates the overall kinetics because composites have far higher crystallization rates than neat PCL. The presence of BF does not alter lamellar structure, but favors the formation of the nuclei with denser fold surface, especially in the treated BF filled composite. The reinforcing effect of BF, together with the increased PCL crystallinity, results in increased mechanical strength of the composite system. This work can provide useful information on the structure and property control of novel PCL/BF composites.

Key words: poly(ε-caprolactone); basalt fibers; composites; nucleation; kinetics.

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1. Introduction Poly(ε-caprolactone) (PCL) is an important biopolymer. It has been studied widely for the tissue engineering and medical applications, as well as the packaging materials.

1-3

Many approaches have been used to tailor its final structure and properties. Introducing rigid chain segments into the backbone of PCL by copolymerization is typical one of chemical methods to control its crystallization and degradation rates. 2 But this chemical approach is complicated and of high costs. Physical methods are far simpler and easy to be employed. For instance, blending PCL with the harder polymers is a good strategy to improve its thermal properties and mechanical strengths. 3 Another effective way is the hybridization with nano- and micro-sized particles such as silicates (layered clay 4, 5 and nano-silica 6) and carbonaceous particles (nanotubes 7-10 and graphene other anisotropic particles such as polysaccharide nanocrystal.

14-16

11-13

), as well as

Besides, unexpected

properties may be obtained through this composite technology, and accordingly, it has been used widely to further extend applications of PCL. 17 Very recently, basalt fiber (BF) reinforced polymer composites have received increasing attention because BF has very high modulus and strength, with natural, eco-friendly and inexpensive characteristics.

18

For instance, its tensile strength and elastic modulus are

higher than glass fiber (GF) by 20-30 %. It also has better impact and abrasion resistance, as well as higher fire resistance than GF.

19

Although BF and GF are both silicates with

similar manufacturing processes, BF does not include secondary materials and hence the preparation route is easy. This is very important because it means that less energy is consumed during production of BF. As a result, the unit cost of BF is lower than that of GF, especially far lower than those of their carbon counterparts such as carbon fiber.

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Thus, BF has attracted much interest as a novel fiber reinforcement for polymer materials increasingly.

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The reported studies revealed that hybridization with BF could improve

friction and wear properties,

20, 21

and fatigue resistance of matrix polymers,

22, 23

with

expectable reinforcing effect. 24-30 Moreover, BF can also be used as the nucleation agent to control the crystallization of matrix polymers.

29, 30

Therefore, incorporation with BF

may be an interesting strategy to control properties of PCL or to fabricate the PCL composites with high performance. There are no reports on the PCL/BF composites in the literatures to our best knowledge, however. Crystallization is one of the most important bulk properties for semicrystalline polymers. PCL is typical one of the semicrystalline biodegradable aliphatic polyesters. Its barrier and mechanical properties, and degradation behavior are closely related with its crystallization histories.

2, 31

For instance, high degree of crystallinity of PCL lowers its

biodegradability and decreases its compatibility with soft tissues. However, low degree of crystallinity of PCL reduces its mechanical strength and barrier property. Thus, control of crystallization is always the hot topic in the research work around PCL based materials. For most of the reported PCL composite systems, the presence of filler particles more or less affects the PCL crystallization, acting as the active filler (nucleation agent), 4-8, 11-14 or the inert one, 9, 15 or even as the antinucleation agent. 10, 16 Does the presence of BF affect the crystallization of PCL? This is not yet clear. In current work, crystallization behavior of the PCL composites with pristine BF and the silicane coupling agent-treated one was studied. The crystallization kinetics and lamellar structure were explored to understand the effect of surface modification of BF on its nucleation ability to PCL. The tensile properties of composites were also studied to establish the structure-property relationship

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of PCL/BF composites, aiming at providing useful guideline on the crystallization control of PCL using BF.

2. Experimental 2.1. Material preparation Poly(ε-caprolactone) (CAPA6400) was purchased from Solvay Co. Ltd., Belgium. Its bulk properties can be found elsewhere.

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Basalt fibers with the average diameters of

7-15 µm and average lengths of 5 mm (the aspect ratio is about 300-520) were purchased from Zhejiang Shijin basalt fiber Co. Ltd., P. R. China. It is a neat fiber material with the elastic modulus of 91-110 GPa and the density of 2.63-2.65 g cm-3. The surface treatment of fibers followed a common method using γ-methacryloxypropyl trimethoxy silane (KH570) as the coupling agent. Detailed route was reported elsewhere. 33 The PCL composites containing 5 wt% pristine or treated basalt fibers were prepared by a Haake Polylab rheometer (Thermo Electron Co., USA) operated at 80 oC and 50 rpm for 5 min. The sheet samples (1 mm thickness) were prepared by compression molding at 80 oC and 10 MPa. The dog-bone specimens (32 mm×4 mm×2 mm) were prepared by the injection molding using a Haake mini-jet (Thermo Scientific Co., USA) with following injection conditions: cylinder temperature 80 oC, injection pressure 600 bar, and holding pressure 500 bar. For better comparison, the neat PCL sample was also processed to keep the same thermal histories. The composite samples with pristine fibers and treated one are hereafter referred as to PCLC and PCLC', respectively. 2.2. Morphology and structure characterizations The dispersion state of basalt fibers in PCL was observed by an S-4800 field-emission scanning electron microscopy (SEM, Hitachi, Japan) at 15 kV accelerating voltage. The

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crystalline morphology was recorded by a DMLP polarized optical microscope (POM, Leika, Germany) equipped with a hot stage. The sheet sample in thickness of about 100 µm was heated to 80 oC at 10 oC min-1 and held for 5 min to eliminate residual thermal histories, and then cooled to the predetermined temperature at 40 oC min-1 (using liquid nitrogen) for the following observation. 2.3. Structure characterizations X-ray diffractometer (XRD, Bruker AXS, D8 ADVANCE, Germany) was used to detect crystalline structure of PCL. The rotating anode generator was operated at 40 kV and 40 mA. The scanning rate was set as 2o min-1 from 2o to 40o. A small-angle X-ray scattering (SAXS) instrument (Bruker AXS GmbH, NanoStar, Germany) was used to characterize the lamellar structure. The testing method was reported elsewhere. 32 2.4. Crystallization characterizations The crystallization process was recorded by a differential scanning calorimeter (DSC, DSC-204F1, NETZSCH, Germany). Route I: the sample (~5 mg) was melted at 80 oC for 5 min and then cooled at 40 oC min-1 (using liquid nitrogen) to the predetermined temperature, annealed for isothermal crystallization. Route II: the samples were cooled with the predetermined rates (2, 4, 6, 8 and 10 oC min-1) to 0 oC, and then heated to 80 oC to record all thermal events. All tests were carried out under nitrogen atmosphere. 2.5. Tensile and viscoelasticity tests The strengths and moduli of samples were measured by an Instron mechanical tester at a crosshead speed of 50 mm min-1 (ASTM D638). The stress-strain traces were recorded. Viscosity tests were performed using a RS600 rotational rheometer (Thermo Electron, USA) using 20 mm parallel plates. The samples were molten for 3 min and experienced

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shear flow sweeps (0.001-10 s-1).

3. Results and discussion 3.1. Nucleation ability of basalt fiber to PCL crystallization Figure 1 gives SEM images of two composite samples. BFs are dispersed as individual fiber and oriented along with injection flow direction (fractured surface is perpendicular to the flow direction). After surface treatment, BF shows higher embedded level by PCL matrix, indicating an improvement of phase adhesion. This improved affinity between two phases affects the crystallization of matrix PCL strongly. Figure 2 shows DSC traces for all samples and the values of thermal parameters are summarized in Table 1. The crystallization temperatures (Tc) of two composite samples increase by about 8-11 oC relative to neat PCL. The degree of crystallinity (Xc) also increases. It indicates that BFs can provide additional nucleation sites and promote PCL crystallization. This nucleation effect can be seen on the composite samples with various loadings of BF (Figure S2 of the Supporting Information). The composite containing 5 wt% BF (PCLC) shows the highest Tc (excessive addition of BF results in saturation of nucleation sites, which may have no contribution to nucleation) and is hence used for the following crystallization study. It is interesting that PCLC' has higher values of Tc and Xc than PCLC, suggesting that the surface treatment of BF further improves its heterogeneous nucleation effect. A simple model developed by Dobreva and Gutzow

35, 36

is used to evaluate the nucleation

activity (Na) of BFs:

log φ = A −

B 2.3∆Tp2

(1)

N a = B* / B 0

(2)

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where φ is cooling rate, ∆Tp the degree of supercooling, and B a parameter related to entropy of melting and specific surface energy. B* is the value of B for filled system and B0 for unfilled one. Their values can be calculated through the slope of the plots of log φ versus 1/ ∆Tp2 shown in Figure 3 (the thermal parameters from the DSC traces with the cooling rates of 2, 4, 6 and 8 oC min-1 are used here, see Figure S2 of the Supporting Information), and the results are summarized in Table 2. The composites have the Na value of about 0.8-0.9, which is indicative of good nucleation activity of BF to the PCL crystallization. 13 This heterogeneous nucleation effect of BF results in evidently reduced spherulite size in the composites, as can be seen in Figure 4. Generally, Na is unity for the inert particles, while approaches zero if the foreign substrate is extremely active. 37, 38 It is notable that PCLC' has lower Na values than PCLC, confirming that the surface treated BF has higher nucleation activity than the pristine one. This is because the surface treatment of BF improves its affinity to matrix PCL. 30 Figure 5a gives the Lorentz-corrected SAXS profiles for all samples. The primary peaks of composites have no evident shift relative to that of neat PCL, indicating that both the pristine BF and treated one do not affect the long period of PCL lamellae. The lamellar structure is further evaluated using the one-dimensional correlation function:

K (z) =

∞

1 2π

2

∫ I ( q)q

2

cos( qz )dq

(3)

0

and the physical meaning of those variables was given by Strobl et al. 39 Figure 5b shows the 1-D correlation function profiles for all samples, in which the calculation ways

40, 41

of the structure parameters, including long period of lamellae (L), and average lamellar thickness ( Lc ) as well as thickness of transition layer (Ltr), are indicated. All samples

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have the identical values of Lc and L in the experimental error ranges. It indicates that both the pristine BF and treated one do not change lamellar thickness and structure of PCL. As a result, the composites show almost the same values of melting point (Tm) with neat PCL (Table 1). In this case, the increased values of degree of crystallinity (Xc%) of composite samples (Table 1) suggests that more crystal grains formed in these systems, with decreased grain size as compared with the neat PCL system. Actually this is already confirmed by the POM observation shown in Figure 4. Besides, hybridization with BF does not alter the crystal structure of PCL, which is confirmed by XRD patterns shown in Figure S3 of the Supporting Information.

3.2. Isothermal crystallization kinetics of PCL-BF composites Figure 6a gives the thermograms of all samples annealed at 42 oC. The DSC traces at other crystallization temperatures are given in Figure S4 of the Supporting Information. The composites have far shorter crystallization time (t) than neat PCL sample at a special temperature (Tc), suggesting that the presence of BF accelerates crystallization process of PCL. The relative degree of crystallinity (Xt) at special t can be calculated by t

Q Xt = t = Q∞

∫ (dH / dt )dt ∫ (dH / dt )dt 0 ∞

(4)

0

where Qt and Q∞ are the heat generated at time (t) and infinite time, respectively, and dH / dt is the rate of heat evolution. The Xt plots for all samples are given in Figure 6b and Figure S5 of the Supporting Information. The values of t1/2 (Table 2) follow the sequence of PCL>PCLC>PCLC' at the same Tc. This indicates that the composite with treated BF has faster crystallization rate than the one with pristine BF. Clearly, the better nucleation activity of treated BF is the key factor accounting for this trend.

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The Xt is dependent of Avrami exponent (n) and crystallization rate constant (k): 42 X t = 1 − exp(kt n )

(5)

Figure 6c and Figure S6 of the Supporting Information show Avrami plots for all samples. The as-obtained n and k values are given in Table 2. The experimental range of Tc (42-45 o

C) in this work is regime II,

43-45

in which both the nucleation and diffusion terms have

contribution to crystallization kinetics. Therefore, both the n and k are closely related to the apparent activation energy ( ∆E ), commonly expressed as the Arrhenius equation:

1 ∆E (ln k t ) = A − n RTc

(6)

Figure 7 gives the Arrhenius plots for all samples. The composite samples have higher ∆E values than neat PCL (Table 2). This means that the presence of BFs interrupts the transport of adjacent chain segments to the growing surface

46

during crystallization of

PCL, acting as the role of physical barrier also. Besides, the increased system viscosities (Figure 8) also reduce chain mobility in the composites (the viscosity of PCLC' doubles relative to that of neat PCL at Newtonian plateau region). But the overall crystallization kinetics is accelerated remarkably by BFs, suggesting that the nucleation role of BFs has far more contribution to PCL crystallization relative to its physical barrier one. In other words, the nucleation, instead of the diffusion, dominates the crystallization kinetics of PCL, especially for the composite containing treated BF. 3.3. Spherulite growth of PCL-BF composites The crystallization kinetics can be further revealed by the secondary nucleation theory: 47, 48

G = G0 exp[ −U * / R (Tc − T∞ )]exp[− K g / Tc ∆Tf )]

10


(7)

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The spherulitic growth rates (G) are obtained from the spherulite growth process (Figure S7 of the Supporting Information), and the results are summarized in Figure 9 and Figure S8 of the Supporting Information. Clearly, the spherulite growth rates follow descending order of PCLC'>PCLC>PCL, which agree well with the kinetic results from isothermal crystallization (Figure 6b). The values of equilibrium melting point ( Tm0 ) can be obtained according to the Hoffman-Weeks procedure, 49 as shown in Figure 10. The plots of ln G + U * / R (Tc − T∞ ) against 1/(Tc ∆Tf ) are given in Figure 11. Kg is a term related with the energy consumed in the formation of nuclei of critical size: 50 nib0σσ eTm0 Kg = ∆H m0 k

(8)

where b is the layer thickness, σ the lateral surface free energy, σe the folding surface free energy, and ∆H m0 the enthalpy of fusion. The ni value is 2 because the Tc range is in regime II. 43-45 Kg and σ e values are listed in Table 2. The reported parameter values of

∆H m0 = 136 J g-3, 34 and b0 = 0.438 nm 51 are used here, and σ = 0.1b0 ∆H m0 . The values of Kg and σe decrease evidently with the addition of BF. This is indicative of the lower barrier for nucleation and less energy consumed by the PCL chain as it is folded to form spherulites in the composite systems. In other words, variation of the enthalpic term overwhelms that of the entropic one during PCL spherulite growth in the presence of BF, resulting in decreased σe values ( σ e =H e − TSe ). PCLC' has lower σe values as compared with PCLC, indicating the formation of denser fold surfaces of PCL lamellae in this system. Therefore, it has a little higher value of Tm than PCLC (Table 1). Clearly, the presence of BF strongly affects the formation of PCL lamellae and spherulite growth, although it nearly has no influence on the final lamellar structure. 11



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3.4. Mechanical behavior of PCL-BF composites Figure 12 gives the tensile curves for all samples. With the addition of 5 wt% pristine BF, the yield strength and Young's modulus increase from 17.8 MPa to 21.9 MPa by 23%, and from 385.3 MPa to 530.7 MPa by 38%, respectively, accompanied by the sharply decreased elongation level because of increased system rigidity. The orientation of BF along with the tensile direction (Figure 1) also has contribution to this evident increase of modulus. This reinforcing effect is close to that reported in polyamide-BF system poly(butylene succinate)-BF one

30

29

and

at the same BF loadings. However, the reinforcing

effect of BF in PCLC is not fully achieved due to poor phase adhesion. Surface treatment can improve this situation evidently. PCLC' has the yield strength and Young's modulus of about 24.2 MPa and 752.5 MPa, increased by 40% and 95%, respectively (compared with PCL). The surface modification of BF, on the one hand, improves adhesion of BF to PCL (Figure 1), and on the other hand, can enhance its heterogeneous nucleation ability. Both have contribution to improved phase adhesion. This favors further improvement of reinforcement role of BF because of improved load transfer level. Besides, the increased degree of crystallinity of PCL also has contribution to the increased strength and rigidity of composites. Thus, the surface treatment of BF is an effective strategy to moderate its influence on the crystallization and mechanical behavior of PCL.

4. Conclusions BF has evident heterogeneous nucleation to PCL crystallization, resulting in increase of crystallization temperatures. Surface treatment of BF can further improve its nucleation activity because of improved affinity between two phases. But the lamellar thickness and structure of PCL are independent of the presence of BF. Besides, BF also plays the role

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of physical barrier to restrain chain diffusion, increasing crystallization activity energy as a result. However, the nucleation rather than physical barrier of BFs is dominant during crystallization of PCL because the composites show accelerated crystallization kinetics. Both the pristine and treated BF have evident reinforcements on PCL. But the latter has stronger reinforcement effect than the former because of improved phase adhesion, and enhanced nucleation ability, as well as increased degree of crystallinity of system. Therefore, surface treatment of BF is a good strategy to tailor final properties of PCL/BF composites.

Acknowledgements Financial support from the National Natural Science Foundation of China (51573156) and the Innovation Program for Undergraduates of Jiangsu Province (201611117020Z) is gratefully acknowledged.

Supporting Information. DSC traces, XRD patterns, POM graphs, plots of relative degrees of crystallinity and spherulite sizes versus time, and Avrami model fittings (PDF)

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(22) Colombo, C.; Vergani, L.; Burman, M. Static and fatigue characterisation of new basalt fibre reinforced composites. Compos. Struct. 2012, 94, 1165-1174. (23) Dorigato, A.; Pegoretti, A. Fatigue resistance of basalt fibers-reinforced laminates. J. Compos. Mater. 2012, 46, 1773-1785. (24) Deák, T.; Czigány, T.; Tamás, P.; Németh, Cs. Enhancement of interfacial properties of basalt fiber reinforced nylon 6 matrix composites with silane coupling agents. eXPRESS Polym. Lett. 2010, 4, 590-598. (25) Lopresto, V.; Leone, C.; De Iorio, I. Mechanical characterisation of basalt fibre reinforced plastic. Compos. Part B-Eng. 2011, 42, 717-723. (26) Meszaros, L.; Gali, I. M.; Czigany, T.; Czvikovszky, T. Effect of nanotube content on mechanical properties of basalt fibre reinforced polyamide 6. Plast. Rubber Compos. 2011, 40, 289-293. (27) Greco, A.; Maffezzoli, A.; Casciaro, G.; Caretto, F. Mechanical properties of basalt fibers and their adhesion to polypropylene matrices. Compos. Part B-Eng. 2014, 67, 233-238. (28) Guo, J.; Mu, S. Y.; Yu, C. F.; Hu, C. N.; Guan, F. C.; Zhang, H.; Gong, Y. M. Mechanical and thermal properties of polypropylene/modified basalt fabric composites. J. Appl. Polym. Sci. 2015, 132, 42504. (29) Song, J. B.; Liu, J. X.; Zhang, Y. H.; Chen, L. H.; Zhong, Y. M.; Yang, W. B. Basalt fibre-reinforced PA1012 composites: Morphology, mechanical properties, crystallization behaviours, structure and water contact angle. J. Compos. Mater. 2015, 49, 415-424. (30) Li, Y.; Sang, L.; Wei, Z. Y.; Ding, C.; Chang, Y.; Chen, G. Y.; Zhang, W. X.; Liang, J. C. Mechanical properties and crystallization behavior of poly(butylene succinate) composites reinforced with basalt fiber. J. Therm. Anal. Calorim. 2015, 122, 261-270. (31) Castillo, R. V.; Müller, A. J. Crystallization and morphology of biodegradable or biostable single and double crystalline block copolymers. Prog. Polym. Sci. 2009, 34, 516-560. (32) Lv, Q. L.; Wu, D. F.; Xie, H.; Peng, S.; Chen, Y.; Xu, C. J. Crystallization of poly(ε-caprolactone) in its immiscible blends with polylactide: insight into the role of annealing histories. RSC Adv. 16


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(44) Chen, H. L.; Li, L. J.; Ou-Yang, W. C.; Hwang, J. C.; Wong, W. Y. Spherulitic crystallization behavior of poly(ε-caprolactone) with a wide range of molecular weight. Macromolecules 1997, 30, 1718-1722. (45) De Juana, R.; CortBzar, M.; Study of the melting and crystallization behavior of binary poly(ε-caprolactone)/poly(hydroxyl ether of bisphenol A) blends. Macromolecules 1993, 26, 1170-1176. (46) Liu, T. X.; Mo, Z. S.; Wang, S.; Zhang, H. F. Isothermal melt and cold crystallization kinetics of poly(aryl ether ether ketone ketone). Eur. Polym. J. 1997, 33, 1405-1414. (47) Hoffman, J. D.; Davis, G. T.; Lauritzen, J. I. In treatise on solid state chemistry. Hannay, HB Ed. Plenum, New York, 1976. (48) Hoffman, J. D.; Miller, R. L.; Marand, H.; Roitman, D. B. Relationships between the lateral surface free energy and chain structure of melt-crystallized polymers. Macromolecules 1992, 25, 2221-2229. (49) Hoffman, J. D.; Weeks, J. J. Melting process and the equilibrium melting temperature of polychlorotrifluoroethylene. J. Res. Natl. Bur. Stand. Sect. 1962, A66, 13-28. (50) Hoffman, J. D.; Miller, R. L. Kinetic of crystallization from the melt and chain folding in polyethylene fractions revisited: theory and experiment. Polymer 1997, 38, 3151-3212. (51) Kuo, S. W.; Chan, S. C.; Chang, F. C. Effect of hydrogen bonding strength on the microstructure and crystallization behavior of crystalline polymer blends. Macromolecules 2003, 36, 6653-6661.

18


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Table 1 calorimetric data a) derived from the cooling and the second heating DSC scan on neat PCL and its composite samples Tc (oC) ∆ Hc (J/g) Tm (oC) ∆ Hm (J/g) Xc (%) PCL 22.4 59.5 57.3 52.2 38.5 PCLC 30.5 62.3 57.6 56.3 41.5 PCLC' 33.2 63.5 58.0 61.9 45.5 a) Tc, crystallization temperature; Tm, the melting point; ∆ Hc, enthalpy of the crystallization process; Samples

∆ Hm, enthalpy of the melting process; Xc, degree of crystallinity ( X c = ∆H m / ∆H m0 , ∆H m0 = 136J/g 34

). The cooling and heating rates are 10 oC min-1.

Table 2 Kinetic parameters of the neat PCL and its composite samples Samples PCL

PCLC

PCLC'

Na -

0.87

0.83

T ( C) 42 43 44 45 42 43 44 45 42 43 44 45 o

t1/2 (min) 11.52 16.15 19.28 24.19 4.39 5.64 8.07 10.92 2.37 3.99 4.72 5.61

n

103k

2.40 2.73 2.38 2.35 2.16 2.51 2.56 2.57 2.78 2.78 2.70 2.67

2.05 0.45 0.80 0.52 35.95 9.15 3.45 1.45 61.76 13.26 11.39 6.62

∆E (kJ mol-1)

105Kg (K2)

σe (erg/cm2)

208.58

1.13

118.52

256.90

0.75

81.15

253.26

0.50

58.38

19



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 CAPTIONS Figure 1 SEM images of (a) PCLC and (b) PCLC' samples (the scale bar is 20 µm). Figure 2 DSC traces of neat PCL and its composite samples recorded from (a) cooling and (b) the second heating scans with the rate of 10 oC min-1.

Figure 3 Dobreva plots of log φ vs. 1/ ∆Tp2 for neat PCL and its composites. Figure 4 POM images of final morphology of (a) PCL, (b) PCLC and (c) PCLC' samples annealed at 42 oC (the scale bar is 20 µm).

Figure 5 (a) SAXS patterns and (b) the curves of one-dimensional correlation function for neat PCL and its composites.

Figure 6 (a) DSC traces and (b) corresponding plots of relative degrees of crystallinity (Xt%) versus time, as well as (c) Avrami plots of log[− ln(1 − X t )] versus log t of the neat PCL and its composite samples annealed at 42 oC.

Figure 7 Arrhenius plots of ln(k 1/ n ) versus 1/Tc for neat PCL and its composites. Figure 8 Steady-state viscosities of neat PCL and its composites (80 oC). Figure 9 Spherulite growth rates for the neat PCL and its composite samples annealed at 42 oC.

Figure 10 Determination of equilibrium melting points for neat PCL and its composites. Figure 11 Lauritzen-Hoffman-Miller plots for neat PCL and its composites. Figure 12 Stress-strain responses for neat PCL and its composites during tensile tests.

20


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Figure 1 (a)

(b)

21



Figure 2 (a)

exo

10 oC/min

Tc PCL PCLC PCLC'

(a) 10

20

30

temperature (oC)

40

50

Figure 2 (b)

PCL PCLC PCLC'

endo

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 22 of 30

Tm

10 oC/min

(b) 30

40

50

temperature ( oC)

60

22


70

Page 23 of 30

Figure 3

PCL PCLC PCLC'

1.0 0.9 0.8

logφ

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


0.7 0.6 0.5 0.4 0.3 0.0008

0.0012

0.0016

0.0020

0.0024

0.0028

1/∆Tp2(K-2)

Figure 4 neat PCL

PCLC

PCLC'

23



Figure 5 (a)

10

log (Intensity)

PCL PCLC PCLC'

1

(a)

0.1 0.00

0.05

0.10

0.15

0.20

-1

q (Å )

Figure 5 (b)

0.8

3 2

PCL PCLC PCLC'

Ltr

0.6

K(Z) (mol.e/cm )

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 24 of 30

0.4

L (nm)

Lc (nm)

13.05 13.19 13.16

5.15 5.30 5.25

0.2 0.0

L

-0.2

Lc

-0.4

Lc

(b)

-0.6 0

10

20

30

40

Z (nm)

24


50

Page 25 of 30

Figure 6 (a)

exo

(a)

PCL PCLC PCLC'

o

42 C 0

5

10

15

20

25

30

time (min)

Figure 6 (b)

100

(b)

80 60

Xt (%)

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


40 20 0

PCL PCLC PCLC'

o

42 C 0

5

10

15

20

time (min)

25


25


Figure 6 (c)

1.0

(c)

0.8

log[-ln(1-Xt)]

0.6 0.4 0.2 0.0

PCL PCLC PCLC'

-0.2

42 oC

-0.4 0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

logt

Figure 7

-0.5 -1.0 -1.5

(1/n)lnk

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 26 of 30

-2.0 -2.5

PCL PCLC PCLC'

-3.0 -3.5 0.003144

0.003152

0.003160

0.003168

1/Tc

26


0.003176

Page 27 of 30

Figure 8

viscosity (Pa s)

1000 900 800 700 600

PCL PCLC PCLC'

500 400 300

200

100 -2 10

-1

0

10

1

10

10

-1

shear rate (s )

Figure 9

30

o

42 C 25

diameter (µm)

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


20 15 10

PCL PCLC PCLC'

5 0 0

50

100

150

200

250

300

time (s)

27


350

400


Figure 10

80

74.9 oC 68.2 oC

70

Tm (oC)

60

65.2 oC

50

PCL PCLC PCLC'

40

30 30

40

50

60

70

Tc (oC)

80

Figure 11

17.2

PCL PCLC PCLC'

17.0

lnG+U /R(Tc-Tinf)

16.8 16.6

*

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 28 of 30

16.4 16.2 16.0 15.8 10

11

12

13

14

5

15 -1

10 (Tc∆Tf )

28


16

17

Page 29 of 30

Figure 12

25

20

stress (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


15

10 samples

modulus (MPa)

strength (MPa)

elongation (%)

PCL

385.3±6.5

17.8±1.1

195.8±30.8

PCLC

530.7±8.2

21.9±2.2

12.2±1.9

PCLC'

752.5±5.8

24.2±1.6

16.1±2.9

5

0 0.0

0.4

0.8

1.2

1.6

strain (100%)

29


2.0


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

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