# The Effect of Boron Nitride on the Thermal and Mechanical Properties of Poly(3-hydroxybutyrate-co-3-hydroxyvalerate)

^{1}

^{2}

^{*}

## Abstract

**:**

## 1. Introduction

## 2. Materials and Methods

#### 2.1. Materials

^{3}, surface area 20 m

^{2}/g); the other BN (FBN), commercial grade (PHPP325B) (2.2 g/cm

^{3}, surface area 60 m

^{2}/g), from Saint-Gobain Ceramics, France. Octyltriethoxysilane (OTES) was purchased from Sigma-Aldrich, Steinheim, Germany.

#### 2.2. Surface Modification of Boron Nitride

#### 2.3. Preparation of Nanobiocomposites

#### 2.4. Characterization of BN Nanoparticles and Composites

^{−1}region. Scanning Electron Microscopy (SEM) was carried out by using the instrument FEI-Philips XL 30 ESEM-FEG (Amsterdam, The Netherlands) in order to investigate the morphologies of samples and the dispersion of BN particles in composites. Particle sizes were found using ImageJ software.

#### 2.5. Thermal Properties of PHBV/BN Nanobiocomposites

_{m}and T

_{c}) as well as the melting and the crystallization enthalpies (ΔH

_{m}and ΔH

_{c}) were determined. The crystallinity was calculated from the formula below [34]:

#### 2.6. Mechanical Properties of PHBV Nanobiocomposites

## 3. Results and Discussion

#### 3.1. Morphological Characterization of BN Particles by SEM

#### 3.2. SEM of Nanocomposites

#### 3.3. Characterization by XRD and FTIR

_{3}asymmetrical stretching at 3015–2960 cm

^{−1}, CH

_{2}asymmetrical stretching at 2945–2925 cm

^{−1}, CH

_{3}symmetrical stretching at 2885–2865 cm

^{−1}, C=O stretching at 1723–1740 cm

^{−1}, CH

_{2}wagging at 1320–1159 cm

^{−1}[40], asymmetrical –C–O–C– stretching, symmetrical –C–O–C– stretching at 800–975 cm

^{−1}[41], CH

_{2}scissoring at 1453–1459 cm

^{−1}, C–O stretching at 1065–1030 cm

^{−1}and C–C stretching at 979–980 cm

^{−1}[42]. BN exhibited characteristic peaks as B–N at 1300–1400 cm

^{−1}and B–N–B at 775–820 cm

^{−1}[43,44]. OTES exhibited Si–O stretching at 1053–1114 cm

^{−1}and CH

_{n}(C–H) stretching at 2850–3000 cm

^{−1}[45,46]. The silane peaks were not observed in FTIR spectrum of composites because of overlapping of silane peaks with PHBV peaks in the same region. Figure 6 shows a comparison between the infrared spectrum of silanized and nonsilanized BN particles. After both BN particles were treated with silane, the spectrum showed new bands in addition to the characteristic peaks of BN. In the spectrum of OSBN and OSFBN, the bands at 2850–3000 cm

^{−1}regions were attributed to the CH

_{2}asymmetric and symmetric stretching vibration, respectively, which originated from the silane-containing molecule. The band at 1053 cm

^{−1}is assigned to the in-plane Si–O stretching and that at 1114 cm

^{−1}is assigned to the perpendicular Si–O stretching.

#### 3.4. Thermal Stability of Nanocomposites

_{10}), at 50% weight loss (T

_{50}), the initial decomposition temperature (T

_{i}), and the maximum rate of degradation temperature (T

_{max}) are presented in Table 3. As shown in Table 3, T

_{i}, T

_{10}, T

_{50}and T

_{max}values increased in the composites. When the initial weight loss is taken as a point of comparison, the onset degradation temperature (T

_{i}) for neat PHBV is 234.45 °C and increases to 252.70 °C and 251.10 °C for PHBV/1OSBN and PHBV/1OSFBN composites. The surface treatment by silane results in improved initial thermal stability in comparison to untreated BN. Another important thermal property is the temperature corresponding to the maximum rate of weight loss (T

_{max}). T

_{max}shifted to higher temperatures as the BN content increased, from 275.08 °C to 295.50 °C. This result showed that the thermal stability of the composites improved with the addition of the BN to the polymer matrix. One of the most important property of boron nitride is its high-temperature resistance. As a result of this property, inclusion of the BN within a polymeric matrix results in increasing of the thermal stability of the composite. The fabrication of gelatin-BN nanocomposites was investigated by Biscarat et al. [33]. An increase of gelatin degradation temperature was observed by using DSC. It was concluded that gelatin chains that intercalate into BN are restricted by the nanosheets, and the movement of segments is restrained. An electrostatic interaction or a hydrogen bond between the charged groups of gelatin chains and BN acts as physical crosslinking and reduces the activity of the gelatin [33].

#### 3.5. Thermal Properties of Composites

_{m1}and T

_{m2}. The double melting endotherms have been reported by several groups [51,52,53]. The double melting peak in polymers may be due to several reasons. The origin for the double melting behavior of PHBV is still being researched. It was generally accepted that the double melting peaks were caused by melting–recrystallization–melting behavior during heating scans [52]. The first melting peak values are in the range of 166–171 °C for composites as opposite to 170 °C for neat PHBV. The degree of crystallinity (Xc) from the first heating scan was computed and presented in Table 4. The BN addition does not influence crystallinity of the matrix for silanized samples up to 3 wt% loadings. The addition of the surface treated BN to the polymer matrix (PHBV/1OSBN) slightly increased the crystallinity of PHBV from 57% to 60%.

_{c1}) and the heat of crystallization (ΔH

_{c}) were determined from the DSC cooling runs of samples. These are shown in Table 4 for composites with different BN contents. From Table 4, cold crystallization temperature nanocomposites did not much change with the change in nanoparticle concentration. The heat of crystallization of 1 wt.% PHBV/1OSBN and PHBV/1OSFBN composites was higher than the neat PHBV, while it decreased with the increase in nanoparticle loading. This behavior can be explained by agglomeration of BN particles at higher loadings.

#### 3.6. Mechanical Analysis Results

^{2}/g), which can promote a better intercalation of BN nanosheets between PHBV chains in comparison to OSBN (26.89 m

^{2}/g) and can influence the polymer chain organization. Studies concerning surface area have shown that reinforcement is related to nanoparticle surface area [61]. The larger surface area of OSFBN leading to the stronger interactions between the BN and PHBV. In this work, the partial exfoliation of the OSFBN allows for maximum surface area exposure between the filler and PHBV; (3) the flake-like nanoparticles showed higher tensile strength than disk type particles.

#### 3.7. Mechanical Modelling

_{c}, E

_{m}and E

_{f}symbolize the Young’s modulus of nanocomposite, matrix and filler respectively. E

_{m}value was taken from directly Admajoris as 2.95 GPa. E

_{f}, the Young’s modulus of hexagonal boron nitride was taken from literature as 40 GPa [24]. The factors ${\mathsf{\eta}}_{\mathrm{L}}$ and ${\mathsf{\eta}}_{\mathrm{T}}$ are given by equations in Table 5 as a function of E

_{f}(the modulus of the filler) and E

_{m}(modulus of the matrix). Φ

_{f}symbolizes the volume fraction of nanoparticle in composite, it is defined as:

_{c}/E

_{m}of nanocomposites for different mechanical models is given in Table 6. Model predictions were in good agreement with experimental results.

## 4. Conclusions

^{2}/g) and aspect ratio (18.9) displayed by OSFBN can promote a better intercalation of BN nanosheets between PHBV chains and influence the mechanical properties. Theoretical modeling can be used to predict the potential modulus improvements of adding a filler to a matrix. In our research, The Halpin–Tsai and Hui–Shia models were used to evaluate the effect of reinforcement by BN particles on the elastic modulus of the resulting composites. Both model equations predict values close to the experimental results.

## Author Contributions

## Funding

## Conflicts of Interest

## References

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**Figure 1.**Scanning Electron Microscopy (SEM) micrograph of particles after 60 min ultrasonication (

**a**) silanized BN (

**b**) silanized FBN.

**Figure 10.**Tensile stress and elongation at break values of (

**a**) PHBV/BN and (

**b**) PHBV/FBN nanocomposites.

**Figure 11.**Young’s modulus variation with (020)/(110) relative intensity ratio of (

**a**) PHBV/OSBN and (

**b**) PHBV/OSFBN composites

**Figure 12.**Comparison of mechanical models with experimental data for (

**a**) PHBV/OSBN and (

**b**) PHBV/OSFBN nanocomposites.

Sample | Boron Nitride Content (wt.%) |
---|---|

PHBV | - |

BORTEK | |

PHBV/0.5OSBN | 0.5 |

PHBV/1BN | 1 |

PHBV/1OSBN | 1 |

PHBV/2OSBN | 2 |

PHBV/3OSBN | 3 |

SAINT GOBAIN (PHPP325B) | |

PHBV/0.5OSFBN | 0.5 |

PHBV/1FBN | 1 |

PHBV/1OSFBN | 1 |

PHBV/2OSFBN | 2 |

PHBV/3OSFBN | 3 |

(020)/(110) | |
---|---|

PHBV | 1.42 |

PHBV/0.5OSBN | 3.17 |

PHBV/1OSBN | 3.40 |

PHBV/2OSBN | 4.58 |

PHBV/3OSBN | 2.56 |

PHBV/0.5OSFBN | 4.98 |

PHBV/1OSFBN | 6.72 |

PHBV/2OSFBN | 4.70 |

PHBV/3OSFBN | 3.76 |

Sample | T_{i} (°C) | T_{10} (°C) | T_{50} (°C) | T_{max} (°C) | Char (%) |
---|---|---|---|---|---|

PHBV | 234.45 | 243.50 | 256.04 | 275.08 | 1.81 |

PHBV/0.5OSBN | 251.90 | 271.35 | 283.39 | 293.90 | 1.82 |

PHBV/1BN | 250.30 | 271.97 | 282.97 | 292.30 | 2.03 |

PHBV/1OSBN | 252.70 | 270.67 | 282.10 | 294.70 | 2.23 |

PHBV/2OSBN | 253.50 | 271.53 | 282.73 | 295.50 | 2.88 |

PHBV/3OSBN | 254.30 | 271.06 | 282.30 | 295.50 | 3.97 |

PHBV/0.5OSFBN | 248.92 | 269.00 | 279.45 | 289.44 | 2.17 |

PHBV/1FBN | 247.09 | 268.18 | 278.92 | 289.54 | 2.53 |

PHBV/1OSFBN | 251.10 | 267.82 | 278.37 | 289.90 | 2.62 |

PHBV/2OSFBN | 251.90 | 269.40 | 279.50 | 291.06 | 3.06 |

PHBV/3OSFBN | 253.45 | 270.17 | 280.11 | 294.17 | 3.75 |

Sample | First Heating | Cooling | Second Heating | ||||||
---|---|---|---|---|---|---|---|---|---|

T_{m1} (°C) | T_{m2} (°C) | ΔH_{m1} (j/g) | X_{c} (%) | T_{c1} (°C) | ΔH_{c} (j/g) | T_{m1} (°C) | ΔH_{m2} (j/g) | X_{c} (%) | |

PHBV | 170 | 173 | 88 | 60 | 122 | 86 | 171 | 100 | 68 |

PHBV/0.5OSBN | 169 | 174 | 87 | 60 | 122 | 88 | 170 | 98 | 67 |

PHBV/1BN | 171 | - | 81 | 57 | 124 | 84 | 172 | 95 | 65 |

PHBV/1OSBN | 166 | 173 | 86 | 60 | 121 | 91 | 168 | 100 | 69 |

PHBV/2OSBN | 171 | - | 86 | 60 | 122 | 87 | 170 | 100 | 70 |

PHBV/3OSBN | 168 | 175 | 83 | 56 | 123 | 81 | 164 | 90 | 64 |

PHBV/0.5OSFBN | 170 | 175 | 87 | 60 | 123 | 89 | 171 | 99 | 68 |

PHBV/1FBN | 171 | - | 87 | 60 | 125 | 89 | 171 | 100 | 69 |

PHBV/1OSFBN | 169 | 173 | 89 | 61 | 122 | 90 | 169 | 102 | 71 |

PHBV/2OSFBN | 170 | - | 85 | 59 | 124 | 84 | 172 | 95 | 67 |

PHBV/3OSFBN | 171 | - | 82 | 58 | 124 | 81 | 172 | 91 | 65 |

Model | Array Type | Formula |
---|---|---|

Halpin–Tsai Model | Random array | $\begin{array}{c}\frac{{E}_{c}}{{E}_{m}}=\frac{3}{8}\left(\frac{1+\xi {\eta}_{L}{\varphi}_{f}}{1-{\eta}_{L}{\varphi}_{f}}\right)+\frac{5}{8}\left(\frac{1+2{\eta}_{T}{\varphi}_{f}}{1-{\eta}_{T}{\varphi}_{f}}\right)\\ {\eta}_{L}=\frac{\left(\frac{{E}_{f}}{{E}_{m}}\right)-1}{\left(\frac{{E}_{f}}{{E}_{m}}\right)+\xi}\\ {\eta}_{T}=\frac{\left(\frac{{E}_{f}}{{E}_{m}}\right)-1}{\left(\frac{{E}_{f}}{{E}_{m}}\right)+2}\end{array}$ |

Hui–Shia Model | Regular array | $\begin{array}{c}\frac{{E}_{c}}{{E}_{m}}=\frac{1}{1-\frac{{\varphi}_{f}}{4}\left(\frac{1}{\xi}+\frac{3}{\xi +\Lambda}\right)}\\ \xi ={\varphi}_{f}+\frac{{E}_{m}}{{E}_{f}-{E}_{m}}+3\left(-{\varphi}_{f}\right)(\frac{\left(1-g\right){\alpha}^{2}-\frac{g}{2}}{{\alpha}^{2}-1})\\ g=\frac{\pi}{2}\alpha \\ \Lambda =\left(1-{\varphi}_{f}\right)(\frac{3\left({\alpha}^{2}+0,25\right)g-2{\alpha}^{2}}{{\alpha}^{2}-1})\end{array}$ |

Sample | Halpin–Tsai Deviation (%) | Hui–Shia Deviation (%) |
---|---|---|

PHBV/0.5OSBN | 2.480 | 1.743 |

PHBV/1OSBN | 3.447 | 4.829 |

PHBV/2OSBN | 3.575 | 6.306 |

PHBV/3OSBN | 9.353 | 4.757 |

PHBV/0.5OSFBN | 5.578 | 6.730 |

PHBV/1OSFBN | 13.473 | 15.560 |

PHBV/2OSFBN | 6.133 | 1.123 |

PHBV/3OSFBN | 7.460 | 0.011 |

© 2018 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).

## Share and Cite

**MDPI and ACS Style**

Öner, M.; Kızıl, G.; Keskin, G.; Pochat-Bohatier, C.; Bechelany, M.
The Effect of Boron Nitride on the Thermal and Mechanical Properties of Poly(3-hydroxybutyrate-co-3-hydroxyvalerate). *Nanomaterials* **2018**, *8*, 940.
https://doi.org/10.3390/nano8110940

**AMA Style**

Öner M, Kızıl G, Keskin G, Pochat-Bohatier C, Bechelany M.
The Effect of Boron Nitride on the Thermal and Mechanical Properties of Poly(3-hydroxybutyrate-co-3-hydroxyvalerate). *Nanomaterials*. 2018; 8(11):940.
https://doi.org/10.3390/nano8110940

**Chicago/Turabian Style**

Öner, Mualla, Gülnur Kızıl, Gülşah Keskin, Celine Pochat-Bohatier, and Mikhael Bechelany.
2018. "The Effect of Boron Nitride on the Thermal and Mechanical Properties of Poly(3-hydroxybutyrate-co-3-hydroxyvalerate)" *Nanomaterials* 8, no. 11: 940.
https://doi.org/10.3390/nano8110940