Preparation and characterization of poly(l-lactic acid)/TiO2 nanoparticle nanocomposite films with high transparency and efficient photodegradability

https://doi.org/10.1016/j.polymdegradstab.2007.03.026Get rights and content

Abstract

Poly(l-lactic acid)–TiO2 nanoparticle nanocomposite films were prepared by incorporating surface modified TiO2 nanoparticles into polymer matrices. In the process of preparing the nanocomposite films, severe aggregation of TiO2 nanoparticles could be reduced by surface modification by using carboxylic acid and long-chain alkyl amine. As a result, the nanocomposite films with high transparency, similar to pure PLA films, were obtained without depending on the amount of added TiO2 nanoparticles. A TEM micrograph of the nanocomposite films suggests that the TiO2 nanoparticles of 3–6 nm in diameter were uniformly dispersed in polymer matrices. Photodegradation of PLA–TiO2 nanoparticle nanocomposite films was also investigated. The results showed that nanocomposite films could be efficiently photodegraded by UV irradiation in comparison with pure PLA.

Introduction

Poly(l-lactic acid) (PLA) is a biodegradable polymer derived from l-lactic acid. It is a highly versatile material and is made from 100% renewable resources like corn, sugar beets, wheat and other starch-rich products. PLA is a versatile polymer that has many potential uses, including many applications in the textile and medical industries as well as in the packaging industry. Therefore, as for the PLA, a number of basic studies concerning thermal properties, crystallization [1], [2], [3], [4], [5], [6], [7], [8], and applied studies concerning improvement of thermal and mechanical properties and applications for tissue engineering and so on [9], [10], [11], [12], [13], [14], [15], [16], [17], have been reported. Although biodegradation of a polymer like PLA is advanced in the ground where moisture and bacteria exist, 2–3 months is needed generally speaking for the decomposition [18], and biodegradation does not advance in the air. As a solution, by adding photodegradability to a biodegradation polymer, degradability can be efficiently promoted under any conditions [19], [20], [21], [22], [23], [24]. Titanium dioxide (TiO2) nanoparticles have been investigated in recent years because of their photocatalytic effects that decompose various organic chemicals such as aldehyde, toluene and polymers such as PE [25], [26], PP [27], PVC [28] and PS [29]. The photocatalysis reaction is well known to active oxygen species, e.g. O2, HO2 radicals, HO radicals, from H2O or O2 by oxidative or reductive reductions under UV conditions. These active oxygen species lead to a degradation reaction by attacking polymer chains and accelerating chain cleavage.

Thus, if TiO2 nanoparticles are introduced into PLA matrices, the above-mentioned disadvantages can be improved. Previous studies have revealed that the polymer–TiO2 composite could potentially be used as a photodegradable product. However, there still remain unresolved problems related to the uniform dispersion of photocatalyst in polymer matrices. The direct mixing of the nanoparticles with PLA often lead to their aggregation within PLA matrices. The micrometer-sized severe aggregation of TiO2 nanoparticles can significantly reduce the efficiency of photodegradation by the decrease of interfacial areas between TiO2 and the polymer chain.

In this paper, we synthesized TiO2 nanoparticles and modified the surface of TiO2 using propionic acid and n-hexylamine to disperse them into the PLA matrices without aggregation, and investigated the optical, mechanical and thermal characterizations of nanocomposite films. Finally, the photodegradation properties of nanocomposite films were then studied.

Section snippets

Materials

Titanium oxychloride (TiOCl2·xHCl·H2O (HCl: 38–42%, Ti: 15%)) was purchased from Fluka. Propionic acid and n-hexylamine were purchased as analytical grade reagents from Wako Pure Chemical Ind., Ltd, and used without further purification. Other chemical reagents were obtained as analytical grade and used without further purification. Poly(l-lactic acid) was supplied by Mitsui Chemicals Co., Japan (LACEA H-100 grade: l-lactic acid repeat units >98%, d-lactic acid repeat units <2%) and used

Characterization of TiO2 nanoparticles modified by propionic acid and n-hexylamine

The XRD of bare TiO2 nanoparticles is shown in Fig. 1.

These TiO2 nanoparticles were formed to be anatase phase and average crystallite size was calculated as 3.3 nm from the peak of (101) reflection using Sherrer's equation.Sherrer's equation is as follows:D=0.9λβcosθwhere D is the crystallite size, λ is wavelength of the radiation, θ is the Bragg's angle and β is the full width at half maximum.

IR spectrum of bare TiO2 nanoparticles is represented in Fig. 2(a). The peak at ∼1620 cm−1 is

Conclusion

By effective surface modification of TiO2 nanoparticles using carboxylic acid and long-chain alkyl amine, the TiO2 nanoparticles were uniformly dispersed into the PLA matrices without aggregation. As a result, photodegradability of nanocomposites can be efficiently promoted. The photodegradation rate of nanocomposites can be controlled by TiO2 nanoparticles content. The development of PLA–TiO2 nanoparticle nanocomposites can lead to an eco-friendly disposal of polymer waste.

Acknowledgements

This work was carried out under the research and development activity of Mitsui Chemicals, Inc., Japan.

References (31)

  • H. Tsuji et al.

    Polymer

    (1995)
  • H. Yamane et al.

    Polymer

    (2003)
  • H. Tsuji

    Polymer

    (2002)
  • H. Tsuji et al.

    Polymer

    (2006)
  • H. Urayama et al.

    Polymer

    (2003)
  • E. Olewnik et al.

    Polym Degrad Stab

    (2007)
  • W. Sakai et al.

    Polymer

    (2002)
  • J.-H. Chang et al.

    Polymer

    (2003)
  • M.-A. Paul et al.

    Polymer

    (2003)
  • A.R. Boccaccini et al.

    Composites Part A

    (2005)
  • F.G. Torres et al.

    Compos Sci Technol

    (2007)
  • R.L. Shogren et al.

    J Polym Degrad Stab

    (2003)
  • H. Tsuji et al.

    Polym Degrad Stab

    (2006)
  • A. Copinet et al.

    Chemosphere

    (2004)
  • B. Ohtani et al.

    Polym Degrad Stab

    (1992)
  • Cited by (0)

    View full text