Reinforcing Poly(ε-caprolactone) Nanofibers with Cellulose Nanocrystals

Abstract

We studied the use of cellulose nanocrystals (CNXs) obtained after acid hydrolysis of ramie cellulose fibers to reinforce poly(ε-caprolactone) (PCL) nanofibers. Chemical grafting with low-molecular-weight PCL diol onto the CNXs was carried out in an attempt to improve the interfacial adhesion with the fiber matrix. Grafting was confirmed via infrared spectroscopy and thermogravimetric analyses. The polymer matrix consisted of electrospun nanofibers that were collected as nonwoven webs. The morphology as well as thermal and mechanical properties of filled and unfilled nanofibers were elucidated by scanning electron microscopy, differential scanning calorimetry, and dynamic mechanical analysis, respectively. The addition of CNXs into PCL produced minimal changes in the thermal behavior of the electrospun fibers. However, a significant improvement in the mechanical properties of the nanofibers after reinforcement with unmodified CNXs was confirmed. Fiber webs from PCL reinforced with 2.5% unmodified CNXs showed ca. 1.5-fold increase in Young's modulus and the ultimate strength compared to PCL webs. Compared to the case of grafted nanocrystals, the unmodified ones imparted better morphological homogeneity to the nanofibrillar structure. The grafted nanocrystals had a negative effect on the morphology of nonwoven webs in which individual nanofibers became annealed during the electrospinning process and, therefore, could not be compared to neat PCL nonwoven webs. A rationalization for the different effects of grafted and unmodified CNXs in reinforcing PCL nanofibers is provided.

Orientation of cellulose nanocrystals in electrospun polymer fibres

“…Data for single electrospun fibres is scarce in the literature, but one study has reported tensile moduli of *120 MPa for single PCL fibres [30]. A value of 6 MPa for the PCL networks [6] (it is noted that this value is with fillers) is much lower than 1/3 of 120 MPa (40 MPa), and so it is reasonable to assume that Eq. 4 may make some overprediction of the mat modulus.…”

“…Upper and lower limits of g L are considered in the calculations for (i) high aspect ratios nanofibres (g L = 1) and (ii) low aspect ratio nanofibres as g L = 0.1 (an estimate for short fibres [31]). (Table 2) [6,8,17,31]. The aspect ratios of the CNCs used for the studies used in this analysis were *30 for PVA, PAA, PCL; and *100 for PEO fibres.…”

“…CNCs are a potential reinforcement for other polymers due to their high aspect ratio, high elastic modulus (120-150 GPa) and excellent chemical and thermal properties [4]. CNCs have therefore attracted a lot of attention as a reinforcement for thin and functional polymer films [5] and nano and microfibres [6,7].…”

Cellulose Nano Whiskers as a Reinforcing Filler in Polyurethanes

“…Softwood (SW) kraft pulp (Revol et al, 1994;Araki et al, 1998;Araki et al, 1999;Pu et al, 2007), SW sulfite pulp (Beck-Candanedo et al, 2005), hardwood (HW) ECF (elemental chlorine free) pulp (Beck-Candanedo et al, 2005), recycle pulp (Filson et al, 2009), cotton fiber (Revol et al, 1994;Dong et al, 1996;Dong et al, 1998;Araki et al, 2000;Hasani et al, 2008;Cao et al, 2009;Pei et al, 2010;Tang & Weder, 2010;Wang et al, 2010), sisal fiber (de Rodriguez et al, 2006;Tang & Weder, 2010), flax fiber (Cao et al, 2007), ramie fiber (Habibi et al, 2007;Habibi & Dufresne, 2008;Zoppe et al, 2009), wheat straw (Helbert et al, 1996), bamboo residue , bacterial microfibrils (Grunert & Winter, 2002), grass fiber (Pandey et al, 2009), tunicate cellulose (Favier et al, 1995;Angles & Dufresne, 2000;Sturcova et al, 2005;Ljungberg et al, 2006;Habibi et al, 2007;Siqueira et al, 2010;Tang & Weder, 2010), microcrystalline cellulose (MCC) Bondeson et al, 2006;Oksman et al, 2006;Bondeson & Oksman, 2007;Bai et al, 2009;Auad et al, 2010; have all been utilized as cellulose sources for whiskers. The most common preparation method employed is acid hydrolysis, including acid sulfuric and hydrochloric acid.…”

Electrospun chitosan-graft-poly (ε-caprolactone)/poly (ε-caprolactone) nanofibrous scaffolds for retinal tissue engineering

“…Furthermore, it was expected that the grafting modification of CS improved the interfacial adhesion with the PCL fiber matrix. 27 Its properties, such as wettability, surface topography, and porosity of the CS-PCL/PCL scaffolds were characterized. To study the cellular compatibility of the nanofibrous structure for potential applications in retinal tissue engineering, mRPCs were cultured on the scaffolds, and their cell proliferation and differentiation were evaluated.…”