Elsevier

Carbohydrate Polymers

Volume 90, Issue 4, 6 November 2012, Pages 1732-1738
Carbohydrate Polymers

Rheological properties of suspensions containing cross-linked starch nanoparticles prepared by spray and vacuum freeze drying methods

https://doi.org/10.1016/j.carbpol.2012.07.059Get rights and content

Abstract

The rheological behavior of suspensions containing vacuum freeze dried and spray dried starch nanoparticles was investigated to explore the effect of these two drying methods in producing starch nanoparticles which were synthesized using high pressure homogenization and mini-emulsion cross-linking technique. Suspensions containing 10% (w/w) spray dried and vacuum freeze dried nanoparticles were prepared. The continuous shear viscosity tests, temperature sweep tests, the frequency sweep and creep-recovery tests were carried out, respectively. The suspensions containing vacuum freeze dried nanoparticles showed higher apparent viscosity within shear rate range (0.1–100 s−1) and temperature range (25–90 °C). The suspensions containing vacuum freeze dried nanoparticles were found to have more shear thinning and less thixotropic behavior compared to those containing spray dried nanoparticles. In addition, the suspensions containing vacuum freeze dried particles had stronger elastic structure. However, the suspensions containing spray dried nanoparticles had more stiffness and greater tendency to recover from the deformation.

Highlights

► Starch nanoparticles were produced through spray drying and vacuum freeze drying. ► Rheological behavior of suspensions containing these two types StNPs was investigated. ► Suspensions contain spray dried StNPs showed lower viscosity within shear range tested. ► Suspensions contain freeze dried StNPs showed stronger shear thinning and thixotropic. ► Suspensions containing freeze dried starch StNPs showed stronger elastic structure.

Introduction

Starch nanoparticles (particle size 1–1000 nm) comprising starch molecules and various cross-linkers are new class of biomaterials (Rodrigues and Emeje, 2012, Simi and Emilia Abraham, 2007). They have excellent mechanical and inherent functional properties such as low/non toxicity, low immunogenicity and good biocompatibility. Because of this reason, these starch nanoparticles have drawn considerable attention in food (Arora & Padua, 2010), medicine (Santander-Ortega et al., 2010), textile (Vigneshwaran et al., 2006), and biotechnology fields (Xiao et al., 2005). These starch nanoparticles have been regarded as highly valuable for their potential application as drug carrier materials in pharmaceutical industry (Jain et al., 2008, Kumari and Rani, 2011, Malam et al., 2011, Mohanraj and Chen, 2006).

Physical methods such as precipitation (Ma, Jian, Chang, & Yu, 2008) and microfluidization (Liu, Wu, Chen, & Chang, 2009) can produce these starch nanoparticles. Similarly chemical methods such as emulsion polymerization (Wang, Liu, & Pope, 2003) and emulsion cross-linking (Jain et al., 2008) can be used to produce these nanoparticles. Among these methods, emulsion cross-linking has been applied more commonly to manufacture various starch nanoparticles (Agnihotri et al., 2004, Bodnar et al., 2006). The emulsion cross-linking method has become the method of choice because it is easy to carry out and the yield of the nanoparticles is fairly high. When high pressure homogenizer is applied to produce the emulsions, this method is capable of reducing amount of surfactants used, lowering the particle size with ease, and increasing the productivity (Liu et al., 2009, Mcclements et al., 2007).

When the nanoparticles are produced, it is necessary to remove the solvent, especially water by drying. The drying step is necessary to extend the storage life of the starch nanoparticles and to reduce the volume/weight of the final product. So far, spray drying and vacuum freeze drying are the two most commonly used methods for removing the water in the production of nanoparticles (Jain et al., 2008, Patil et al., 2010). The particle temperature (during drying) and the rate of water removal are quite different in these two drying systems. Because of these reasons, the final particles produced by using these two drying systems are quite different, especially in appearance, particle size, degree of crystallization, and re-dispersibility. Among these properties, re-dispersibility of particles can have remarkable influence or impact on their application (Kho & Hadinoto, 2010). The rheological properties can be excellent indicators of the re-dispersing behavior of suspensions containing these starch nanoparticles (Kimura et al., 2011).

The rheological properties, which include the continuous shear viscosity and storage or loss modulus, vary with shear rate, temperature, frequency and time. The rheological properties of suspensions containing nanoparticles are investigated and reported. For example, the rheological features of suspensions containing chitosan–sodium tripolyphosphate nanoparticles (Li & Huang, 2012), iron nanoparticles (Borin, Zubarev, Chirikov, Müller, & Odenbach, 2011), cell-wall particle (Day, Xu, Øiseth, Lundin, & Hemar, 2010) and silica nanoparticles (Triebel & Münstedt, 2011) have been reported. However, to the best of our knowledge, there are no publications reporting the effect of drying methods (used to produce nanoparticles) on the rheological properties of suspension containing starch nanoparticles. Therefore, the objective of this study was to investigate the effect of two drying methods (vacuum freeze drying and spray drying) on the rheological properties of suspensions containing these starch nanoparticles. The continuous shear viscosity tests are carried out to determine the effect of shear rate and temperature on apparent viscosity of the suspensions. The dynamic rheological tests are carried out to investigate the effect of frequency on the elastic and loss modulus and phase angle. The creep recovery test is carried out to determine the extent of recovery (from deformation) of the suspensions from applied stress. The Cross model is used to represent the shear dependent viscosity while the Power Law type equations are used to represent the frequency dependence of storage and loss modulus. The creep-recovery data are modeled using Burger's model which contains Maxwell and Kelvin models in series.

Section snippets

Materials

Soluble starch was purchased from Beijing Aoboxing Biological Technique Company (Beijing, China). Sodium chloride, sodium hydroxide, cyclohexane, acetone and acetic acid were provided by Beijing Chemical Company (Beijing, China). Tween-80 and Span-80 were purchased from Tianjing Fuchen Chemical Company (Tianjing, China). Sodium trimetaphosphate (STMP) was obtained from Tianjing Dengfeng Chemical Company (Tianjing, China). All of these reagents were of analytical grade and used without further

Continuous shear viscosity properties

In order to describe the variation in the flow properties of suspension containing cross-linked starch nanoparticles (obtained by spray and freeze drying as described in Section 2.3) under continuous shear, the Cross model (Eq. (1)) is used (Susan-Resiga, Bica, & Vékás, 2010).η=η+η0η1+(Cγ˙)mHere η is the apparent viscosity (Pa s), η is the viscosity at infinite shear rate (Pa s), η0 is the viscosity at zero shear rate, c is the consistency (s), γ˙ is the shear rate (s−1), and m is the flow

Conclusions

The rheological characteristics of suspensions containing vacuum freeze dried and spray dried starch nanoparticles was investigated. The suspensions containing vacuum freeze dried nanoparticles showed higher apparent viscosity compared to the suspensions containing spray dried nanoparticles within 0.1–100 s−1 shear rate and 25–90 °C temperature range. The suspensions containing vacuum freeze dried particles had greater propensity to undergo shear thinning compared to the suspensions containing

Acknowledgments

This research was supported by National Natural Science Foundation of China (31000813), Chinese Universities Scientific Fund (2012QJ009), High Technology Research and Development Program of China (2011AA100802), and Commonweal Guild Agricultural Scientific Research Project of China (201003077).

References (33)

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These authors contributed equally to this work.

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