Cellulose nanofiber reinforced poly(vinyl alcohol) composite film with high visible light transmittance

doi:10.1016/j.compositesa.2008.07.005

Composites Part A: Applied Science and Manufacturing

Volume 39, Issue 10, October 2008, Pages 1638-1643

https://doi.org/10.1016/j.compositesa.2008.07.005 Get rights and content

Abstract

In this paper, we presented the fabrication and characterization of poly(vinyl alcohol) (PVA) composite film reinforced with high volume of electrospun cellulose nanofibrous mat (CNM). Its visible light transmittance and mechanical properties were examined in relation to fiber content in the composite. Optimal CNM content in the composite was found to be 40 wt% in terms of its overall properties. This composite film exhibited visible light transmittance of 75%, and its mechanical strength and Young’s modulus were increased by 50% and 600%, respectively, as compared to neat PVA film.

Introduction

Fiber reinforced plastic (FRP) composites exhibit excellent flexural strength and elastic modulus [1]. FRPs with high transmittance of visible light are of great interest in the manufacture of transparent or translucent structural panel for applications as bendable displays, airplane canopies/windows, and light transmitting electromagnetic wave shielding material [2], [3]. Factors such as fiber content, size, and refractive index (RI) of reinforcement fibers play significant roles in the light transmittance of composite materials. For example, lowering fiber content in composite may improve light transmittance; utilization of bigger fiber while fiber content is kept constant reduces the frequencies of reflection/refraction at fiber/resin interfaces, hence imparting composite good light transmittance; the close RI matching of fiber and polymer matrix to a third decimal place may prevent light scattering at the fiber/resin interfaces, resulting in high quality light transmittance of such composites [4]. However, this matching at certain temperature becomes mismatch because RI of resin matrix varies with temperature. As a result, the initial transparent composite turns into opaque as environmental temperature changes [5]. Additionally, it has been demonstrated that the mismatching of RI is enhanced with the increasing of fiber content in the composite [1]. Therefore, the manufacture of a transparent or translucent FRP with high content of reinforcement fiber has become a challenge.

It has been reported that the application of nanofibers as reinforcement in the composite is highly effective in the preparation of optical transparent FRP. Bacterial cellulose nanofibers (10 nm thick and 50 nm wide) reinforced resin with fiber content as high as 70% are highly transparent with light transmittance of over 80% in the wavelength of 500–800 nm. Moreover, its light transmittance is insensitive to temperature variation. Additionally, its mechanical strength reaches up to 325 MPa, and Young’s modulus to 20–21 GPa, which is more than five times that of engineered plastics [6]. Thus this type of FRP is a very promising optically functional material.

As far as we know, bacterial and plant cellulose is the only nature-made nanofiber applicable for FRPs [3], [7]. Its manufacturing process is complex, time- and energy-consuming. Up to now, electrospinning is reported to be the only available simple but versatile technique in producing sufficient amount of nanofibers for application [8]. Several tens of various organic/inorganic polymer nanofibers have been obtained so far [9], [10]. In electrospinning, the polymer jet is drawn up to 100,000 times in less than one-tenth of a second. This extremely high draw ratio can closely align polymer molecular chains along the fiber axis and make the electrospun nanofibers mechanically strong [11], [12]. Although it has been found applications in various areas [9], electrospun nanofiber reinforced plastic with enhanced mechanical properties and good transparency has been rarely reported. Bergshoef et al. studied the fabrication of transparent epoxy resin reinforced with ultrathin electrospun nylon 4,6 fiber, whose content in the composite film was reported to be ca. 3.9% only [11].

In view of the mechanical properties of transparent FRPs are highly correlated with the content of reinforcement fiber in the composites, in this study we try to make a FRP by impregnating as much as 60 wt% electrospun nanofiber into a transparent polymer matrix, and then to characterize its light transmittance and mechanical properties over a broad range of fiber content. For this purpose, cellulose nanofiber and poly(vinyl alcohol) (PVA) were used as reinforcement and polymer matrix, respectively. The large amount of hydroxyl groups on these two components assures satisfying fiber/resin interfacial interactions through hydrogen bonding, leading to desirable adhesion at the fiber/PVA interfaces. Consequently, the as-obtained composite may possible show high percent light transmittance even at high fiber content, and improved mechanical properties.

Section snippets

Materials

Cellulose acetate (CA) (M_w = 3.0 × 10⁴, acetyl content 39.8 wt%) was purchased from Eastman. Poly(vinyl alcohol) (DP = 1750 ± 50, 99 + % hydrolyzed) was from commercial market in China.

Preparation of cellulose nanofibrous films

2:1 (v/v) acetone/N,N-dimethylacetamide(DMAc) mixture solvent was used as the spinning solvent for cellulose acetate as reported in our previous work [13]. The concentration of CA was 20 wt% in the solution. The CA spinning solution was placed in a syringe with a stainless needle of gauge 18. A negative electrode was clamped

Results and discussion

Due to the high acetyl content of 39.8%, cellulose acetate nanofiber has characteristic hydrophobic surface [13]. This normally would lead to poor interfacial interaction with hydrophilic PVA matrix. In order to enhance the compatibility at the interface between the filler fiber and PVA matrix, acetyl groups of cellulose acetate nanofiber were hydrolyzed to regenerate hydroxyl groups and turn it into cellulose nanofiber. Fully hydrolysis was confirmed by the disappearance of absorption peak at

Conclusion

The impregnation of non-transparent CNM into PVA film may manufacture composite film with high visible light transmittance of as much as 75% even the fiber content in the composite is 40 wt%, largely due to the intimate contact and strong interfacial adhesion between ultrafine dimension of cellulose nanofiber and PVA matrix. The CNM/PVA composite film is non-transparent because the transmitted light is scattered. High fiber content (⩾40 wt%) in the composite increased its mechanical strength by

Acknowledgements

The authors thank the financial support from the Initiative Fund for the Returned Overseas Chinese Scholar administered by the State Education Ministry, and the Key Project of Natural Science Foundation of Fujian Province (Grant No. E0620001).

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Cellulose nanofiber reinforced poly(vinyl alcohol) composite film with high visible light transmittance

Abstract

Introduction

Section snippets

Materials

Preparation of cellulose nanofibrous films

Results and discussion

Conclusion

Acknowledgements

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Light transmitting electromagnetic wave shielding composite materials using electromagnetic wave polarizing effect

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Optically transparent polymethyl methacrylate composites made with glass fibers of varying refractive index

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