Reinforced polystyrene through host-guest interactions using cyclodextrin as an additive

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Highlights

  • We demonstrate a process using cyclodextrin (CD) as an additive.

  • Addition of the CD enhanced mechanical properties of polystyrene (PS).

  • Acetylated βCD increased the fracture energy keeping constant Young’s modulus.

  • Acetylated γCD increased the fracture energy not only Young’s modulus.

  • Acetylated CD formed sea-island phase separation in PS.

Abstract

Polystyrene (PS) is one of the most widely used polymeric materials. However, PS is too brittle to utilize for various applications. Additives are typically added into PS to create stronger PS. PS was successfully strengthened by adding cyclodextrin (CD), which could form inclusion complexes with benzene rings. Acetylated CD (AcCD) and PS were dissolved in toluene to obtain casting film with different contents of AcCD. Interestingly, 3–4 wt% of AcCD increased the fracture energy up to four times. In particular, AcγCD showed better molecular recognition than AcβCD, increasing the Young’s modulus by approximately 160%. Since CD has mainly been used to reinforce soft materials, this report expands the understanding host-guest chemistry of CD and suggests new application.

Introduction

Polystyrene (PS) and its composites are widely used in our daily life. PS is used in containers, insulators, buffer materials, etc. However, PS itself is too brittle to apply to various applications. To overcome this issue, many researchers have investigated additives for PS to improve its mechanical properties. Mainly soft components, nanoclay, fiber, inorganic additives have been reported [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] as well as incorporation of interaction between PS chains [1], [2], [3], [4]. The use of soft components, e.g., rubber, is the oldest and most investigated approach [5], [6], [7], [8], [9], [10], [11]. Soft components form a sea-island phase separation structure [7], [8], [9], [11], [12], and the soft phase in the sea-island structure changes its shape during deformation. The transformation of the soft phase releases stress in the materials. Adding nanoclay increases the modulus of PS [13], [14], [15], [16] because interactions between PS and inorganic additives, such as nanoclay, form additional cross-links. Additional cross-links enhance the mechanical properties of PS. Similarly, the addition of fibers to PS also increases the modulus of the materials in the same way [17], [18], [19], [20], [21], [22], [23]. These enhancements were achieved by the interaction between the PS matrix and additives. However, with high loading levels, the mechanical properties decreased. This happened due to the agglomeration of inorganic additives [24], [25], [26]. According to previous reports, the interactions between additives and PS seem to be important for enhancing the mechanical properties of PS. Herein, we choose a host-guest interaction for the reinforcement of PS.

Cyclodextrin (CD) is a well-known macrocyclic molecule that shows host-guest interactions. The host-guest interaction of CD has exhibited functions such as self-healing, stimuli responsiveness, and toughening properties [27], [28], [29], [30], [31], [32], [33], [34], [35], [36], [37], [38], [39], [40], [41], [42], [43], [44], [45], [46], [47], [48], [49], [50]. Furthermore Methylated CD toughened poly(lactic acid) acting as a plasticizer with decreased Young’s moduli and increased fracture energy [51].

In this report, we will demonstrate the toughening effect of host-guest interactions in PS. Acetylated CD (AcCD) was added to the PS matrix without chemical bonds (Fig. 1). Adding acetylated γCD (AcγCD) increased the fracture energy of PS with an increased Young’s modulus, whereas acetylated βCD (AcβCD) increased the energy while the Young’s modulus remained constant. The PS mixtures in this report exhibited a Young’s modulus of approximately 1 GPa and 15% elongation at break. This result increases the potential and understanding of the host-guest chemistry of CD.

Section snippets

Preparation of film of polystyrene with AcCD (PS/AcCD)

Commercially available PS and AcγCD were added to 50 mL glass vial. Toluene was added to prepare 5 wt% of solution. After stirring for 1.5 h at room temperature, the solution was casted on Teflon petri-dish. Films were obtained by standing still the Teflon-dish at room temperature at 1 atm more than 15 h. Obtained films were dried to remove residual toluene at 60 °C for 15 h. Amounts of PS, AcβCD, and AcγCD are summarized in Tables S2 and S3.

Preparation of film of PMMA with AcCD (PMMA/AcCD)

Commercially available PMMA and AcCD were added to

Mechanical properties of polymer mixtures

Pure PS has a fracture energy of 0.6 MJ m−3. Adding AcCD changed the fracture energy of PS/AcβCD and PS/AcγCD (Fig. 2a). Less than 4 wt% of AcβCD increased the fracture energy of PS/AcβCD. Adding more AcβCD decreased the fracture energy. In particular, 15 wt% or more of AcβCD resulted in PS/AcβCD having a lower fracture energy than pure PS.

PS/AcγCD showed a similar tendency. PS/AcγCD had a peak fracture energy with 3 wt% of AcγCD. PS/AcγCD with more than 3 wt% AcγCD had a smaller fracture

Conclusion

Herein, we have shown that host-guest interactions are also present in very hard polymeric materials such as PS. In tensile tests, AcCD proved that host-guest interactions exist. With a proper amount (approximately 3–4 wt%) of AcCD, the elongation at break increased along with the fracture energy. Specifically, PS/AcγCD showed a linear relation for the Young’s modulus and the fracture energy. When the Young’s modulus of PS/AcγCD increased, the fracture energy also increased. However, PS/AcβCD

CRediT authorship contribution statement

Junsu Park: Conceptualization, Formal analysis, Investigation, Data curation, Writing - original draft. Shunsuke Murayama: Formal analysis. Motofumi Osaki: Writing - review & editing. Hiroyasu Yamaguchi: Writing - review & editing. Akira Harada: Writing - review & editing, Supervision. Go Matsuba: Formal analysis, Writing - review & editing, Supervision. Yoshinori Takashima: Conceptualization, Validation, Writing - original draft, Project administration, Funding acquisition.

Acknowledgement

This research was funded by a Grant-in-Aid for Scientific Research (B) (No. JP26288062 & JP18H02035) from MEXT and Scientific Research on Innovative Area Grant Number JP19H05721 from JSPS of Japan, JST-Mirai Program Grant Number JPMJMI18E3 and the Ogasawara Foundation for the Promotion of Science & Engineering.

The authors would like to thank Dr. Noboru Ohta (SPring-8, JASRI) for the synchrotron radiation scattering measurements. The synchrotron radiation experiments were performed at the BL40B2

References (53)

  • Y.M. Zhang et al.

    Cyclodextrin-based multistimuli-responsive supramolecular assemblies and their biological functions

    Adv. Mater.

    (2020)
  • M. Nakahata et al.

    Self-healing materials formed by cross-linked polyrotaxanes with reversible bonds

    Chem.

    (2016)
  • M.W. Fowler et al.

    Rubber toughening of polystyrene through reactive blending

    Polym. Eng. Sci.

    (1988)
  • W. Wang et al.

    Improvement of mechanical properties of anisotropic glassy polystyrene by introducing heat-labile reversible bonds

    Macromolecules

    (2019)
  • S.G. Turley

    A dynamic mechanical study of rubber-modified polystyrenes

    J. Polym. Sci. Part C Polym. Symp.

    (1963)
  • S.L. Aggarwal et al.

    Structure and properties of microcomposites and macrocomposites from block polymers

    Rubber Chem. Technol.

    (1978)
  • M. Schneider et al.

    Toughening of polystyrene by natural rubber-based composite particles: Part I Impact reinforcement by PMMA and PS grafted core-shell particles

    J. Mater. Sci.

    (1997)
  • H. Jinnai et al.

    Direct observation of three-dimensional bicontinuous structure developed via spinodal decomposition

    Macromolecules

    (1995)
  • B. Hoffmann et al.

    Morphology and rheology of polystyrene nanocomposites based upon organoclay

    Macromol. Rapid Commun.

    (2000)
  • A. Arora et al.

    Effect of clay content and clay/surfactant on the mechanical, thermal and barrier properties of polystyrene/organoclay nanocomposites

    J. Polym. Res.

    (2011)
  • N. Greesh et al.

    Role of nanoclay shape and surface characteristics on the morphology and thermal properties of polystyrene nanocomposites synthesized via emulsion polymerization

    Ind. Eng. Chem. Res.

    (2013)
  • D. Maldas et al.

    Influence of coupling agents and treatments on the mechanical properties of cellulose fiber–polystyrene composites

    J. Appl. Polym. Sci.

    (1989)
  • D. Qian et al.

    Load transfer and deformation mechanisms in carbon nanotube-polystyrene composites

    Appl. Phys. Lett.

    (2000)
  • B. Lin et al.

    Electrical, rheological, and mechanical properties of polystyrene/copper nanowire nanocomposites

    Ind. Eng. Chem. Res.

    (2007)
  • M.R. Barzegari et al.

    Mechanical and rheological behavior of highly filled polystyrene with lignin

    Polym. Compos.

    (2012)
  • S. Fujisawa et al.

    Superior reinforcement effect of TEMPO-oxidized cellulose nanofibrils in polystyrene matrix: optical, thermal, and mechanical studies

    Biomacromolecules

    (2012)
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