Subscriber access provided by Columbia University Libraries
Article
Crystallization Temperature as the Probe to Detect Polymer-Filler Compatibility in the Poly(#-Caprolactone) Composites With Acetylated Cellulose Nanocrystal Chunjiang Xu, Defeng Wu, Qiaolian Lv, and Lili Yan J. Phys. Chem. C, Just Accepted Manuscript • DOI: 10.1021/acs.jpcc.7b05055 • Publication Date (Web): 08 Aug 2017 Downloaded from http://pubs.acs.org on August 13, 2017
Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a free service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are accessible to all readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.
The Journal of Physical Chemistry C is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.
Page 1 of 33
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
The Journal of Physical Chemistry
Crystallization Temperature as the Probe to Detect Polymer-Filler Compatibility in the Poly(ε-caprolactone) Composites with Acetylated Cellulose Nanocrystal Chunjiang Xu1 1
2
*
1
Defeng Wu1, 2* Qiaolian Lv1
Lili Yan1
School of Chemistry & Chemical Engineering, Yangzhou University, Jiangsu 225002, China
Provincial Key Laboratories of Environmental Engineering & Materials, Jiangsu 225002, China
Corresponding author, Tel: +86-514-87975230, Fax: +86-514-87975244, E-mail address:
[email protected] ACS Paragon Plus Environment
The Journal of Physical Chemistry
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
ABSTRACT Poly(ε-caprolactone) composites containing the acetylated cellulose nanocrystal (aCNC) with various degrees of substitution (DS) were prepared for the phase compatibility study. An interesting phenomenon around the alteration of crystallization temperature (Tc) was reported here. Tc of PCL increases evidently in the presence of pristine CNC (DS=0) due to its nucleation effect. But for the composites with aCNCs, Tc decreases monotonously with increasing DSs of aCNCs, and is even lower than that of the neat PCL at higher DSs. This is attributed to the improved compatibility between the matrix and particles, which is further evaluated by the Flory-Huggins parameters. Therefore, the alteration of Tc can be used as the probe to detect the compatibility between two phases in aliphatic polyester composites with chemically modified CNCs. From another perspective, crystallization of aliphatic polyesters can be controlled using aCNCs with different DSs.
2
ACS Paragon Plus Environment
Page 2 of 33
Page 3 of 33
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
The Journal of Physical Chemistry
1. Introduction In recent years, cellulose nanocrystal (CNC) has attracted a great deal of interest in the polymer nanocomposite field due to its appealing intrinsic properties such as nanoscaled dimensions, high surface area, low density and good mechanical strength. 1 In addition, it is readily available, renewable, and biodegradable, and hence has been incorporated into a wide range of polymer matrices,
2, 3
especially with biodegradable aliphatic polyesters
to prepare green composites with fully degradable characteristics. 3, 4 However, CNCs are hydrophilic, and not compatible with the hydrophobic polymers. Accordingly, they tend to agglomerate among themselves in polymer matrix. The formation of hydrophobic surfaces is necessary in this case to achieve better dispersion of CNCs. CNCs are easily to be modified chemically because of an abundance of hydroxyl groups on their surface. Different chemical modifications have so far been attempted, including esterification, etherification, oxidation, acetylation, silylation and polymer grafting, etc. 1, 5
It has been confirmed that chemical modifications are the effective strategies to tune the
surface energy characteristics of CNCs to improve their compatibility with polymers. The morphological characterizations such as transmission electron microscopy (TEM) and atom force microscopy (AFM) are used to evidence improved dispersion of CNCs, which is commonly regarded as an indirect indicator of improved compatibility between CNCs and matrices. However, there are no simple or semi-quantitative methods reported up to now to directly reveal the compatibility between these two phases. In the previous work, 6, 7 it was found that pristine CNC plays the role of heterogeneous nucleation agent to the crystallization of aliphatic polyesters such as poly(ε-caprolactone) (PCL) and poly(β-hydroxybutyrate) (PHB); while it acts as the anti-nucleation one after
3
ACS Paragon Plus Environment
The Journal of Physical Chemistry
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
surface acetylation or polymer grafting despite improved two-phase compatibility. For instance, the presence of pristine CNC particles increases crystallization temperature and spherulite growth rate of aliphatic polyesters evidently, while the presence of acetylated CNC or polylactide-grafted one could reduce crystallization temperature and kinetics. 6, 7 This suggests that some thermal parameters may be used as the probe to indicate altered compatibility in the polymer/CNC systems. In this work, therefore, acetylated CNCs with various degrees of substitution were used to be incorporated with PCL for the miscibility study. The crystallization and melting behavior of composites were then explored with the aim of establishing relations between thermal parameters of matrix and alteration of system compatibility caused by the altered degrees of substitution of CNCs. The main objective is to propose a simple and facile method to evaluate the compatibility between two phases in the aliphatic polyester composites with chemically modified CNCs. 2. Experimental 2.1. Material preparation Poly(ε-caprolactone) (CAPA6400) is a commercial product purchased from Solvay Co. Ltd., Belgium, with -OH values lower than 2 mg KOH g-1. Its number average molecular weight (Mn) and density are about 37,000 g mol-1 and 1.15 g cm-3, respectively. The microcrystalline cellulose (MCC) used for the preparation of CNC is also a commercial product purchased from Sinopharm Chemical Reagent Co. Ltd., P. R. China. It is a white powder, with the average length and diameter of 60 and 20 µm, respectively. Its degree of polymerization (DP) is 210~240. CNC suspension was prepared by the way of acidic hydrolysis of MCC reported in the previous work. 8 The 1D rod-like nanostructure of as-prepared CNC particles was already
4
ACS Paragon Plus Environment
Page 4 of 33
Page 5 of 33
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
The Journal of Physical Chemistry
studied in detail.
9, 10
Acetylation of CNC and the following preparation of PCL/CNC
composites followed a continuous way developed in the previous work, 11 without freeze drying step. In short, an organic solvent-assisted centrifugation route was firstly used to remove the residual water of CNC suspension and then, the obtained CNC pulp was mixed with acetic acid for the swelling process at room temperature using small amount of H2SO4 as the catalyst, followed by the acetylation at predetermined temperatures, with continuous stirring. The as-obtained acetylated CNC (aCNC) pulp was then washed by ethanol, and mixed with the PCL solution (using chloroform as the solvent). Finally, the composite film was prepared by solution casting, followed by vacuum-drying to constant mass weight. The degree of substitution (DS) of acetylated CNC (aCNC) was calculated according to an approach developed by Xin et al.
12
through nuclear magnetic resonance
spectroscopy. Six kinds of aCNCs with different DSs (0.71, 0.94, 1.45, 1.85, 2.36 and 2.71) were obtained and used for the composite preparation. The composite with pristine CNC was also prepared by the solution mixing and casting for the property and structure comparison. The neat PCL sample also experienced the same routes to keep the same solution and thermal histories with the composite ones. Hereafter the composite samples are referred as to PCLCs, where s denotes the weight fraction of filler particles. For the most cases, the samples with 3 wt% particle contents (PCLC3) were studied, except for the determination of equilibrium melting points (the samples with a series of particle contents were used in this case). 2.2. Structure and property characterizations The DSs of aCNC particles were characterized by nuclear magnetic resonance (NMR) spectroscopy. 1H NMR was conducted by a Bruker Advance 600 spectrometry (Germany)
5
ACS Paragon Plus Environment
The Journal of Physical Chemistry
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
at 600 MHz. CDCl3 was used as the solvent for the measurements. Detailed calculation way of DS can be found elsewhere.
11
The chemical structure on the surface of aCNC
particles was characterized by the Fourier transformed infrared spectrophotometer (FT-IR, Bruker IFS66/S, Germany). Infrared absorption spectra were recorded in the wavelength region of 4000-500 cm-1 with the reflection mode. All the FT-IR spectra were obtained by coadding 64 scans at room temperature with the resolution of 2 cm-1. The interactions between PCL chain and aCNC particles were characterized using an X-ray photoelectron spectroscopy (XPS), which was performed with an ESCALAB 250Xi system (Thermo Scientific Co., USA) equipped with an Al anode XR50 source operated at 200 W. The overview spectra were recorded with pass energy of 20 eV at 0.05 eV steps at a pressure
