تاثیر نانوپرکننده های دی اکسیدتیتانیم و مونت موریلونیت بر ویژگی های توپوگرافی، حرارتی و نوری فیلم های زیست نانوکامپوزیت بر پایه نشاسته

در این پژوهش، فیلم های زیست نانو کامپوزیت نشاسته‌ی نرم شده (ps) حاوی نانولایه های دو بعدی سدیم مونت موریلونیت (mmt) و نانوذرات سه بُعدی دی اکسید تیتانیم (tio2) به روش قالب ریزی تهیه شدند. توپوگرافی سطح و ساختار شیمیایی فیلم ها توسط میکروسکوپ نیروی اتمی (afm) و طیف سنجی فروسرخ (ftir) مطالعه گردید. در آمیزه‌ی دوجزئی psmmt، لایه های ورقه ای شده‌ی نانورس، به طور یکنواخت در ماتریس پلیمری پخش شده اند. تصاویر سه بعدی میکروسکوپ نیروی اتمی (afm) توزیع یکنواخت تر نانورس و tio2، زبری کمتر و سطح صاف تر ماتریس ps3% mmttio2 نسبت به فیلم های دوجزئی ps3%mm را نشان داد. وجود پیوندهای هیدروژنی و برهمکنش های الکترواستاتیک بین نانورس و tio2 با یکدیگر و با زنجیرهای نشاسته توسط پیک های مربوط به پیوند coh در 1 cm1142 و1cm 990 و افزایش پهنای باند و شدت جذب در ناحیۀ 1cm800500 در طیف سنجی فروسرخ (ftir) تایید گردید. نتایج آزمون گرماسنج پویشی تفاضلی (dsc) نشان داد، افزایش غلظت tio2 فیلم های ps3%mmt باعث افزایش دمای ذوب و دمای انتقال شیشه ای (tg) به ترتیب از 1/295 تا 3/306 درجه سانتی‌گراد و از 1/199 تا 6/207 درجه سانتی‌گراد گردیده است. افزایش غلظت نانورس تاثیر معنی داری بر پارامترهای رنگی فیلم نداشت، اما با افزایش 1% محتوی tio2 در فیلم حاوی 3% نانورس، اختلاف رنگ کلی (δe) و اندیس سفیدی (wi) فیلم ها به ترتیب %6/86 و 76% افزایش یافته و از میزان سرخی وزردی آنها کاسته شد. به منظور بررسی کدورت و رفتار جذب پرتوهای نوری از اسپکتروفتومتری uvvis در دامنه طول موج nm 200800 استفاده شد. نتایج نشان داد که می توان فیلم نانوکامپوزیتی حاصل را به عنوان ماده بسته بندی جهت حفاظت از محتویات در برابر پرتوهای نور uv و مرئی بکار برد.

The Effects of TiO2 and MontmorilloniteNanofillers on Structural, Thermal and Optical Properties of Starch based Nanobiocomposite Films

Introduction: Biodegradable films for food packaging applications have attracted an increasing amount of consideration over the last two decades, predominantly due to environmental pollution and the realization that our petroleum resources are not infinite. Starch, which is one of the natural biopolymers, has been considered as one of the best candidates primarily because of its processbility, availability and price. The main disadvantages of starch films are their pronounced hydrophilic character therefore; they are permeable to water vapor and have usually poor mechanical properties. However, these features can be significantly improved by blending with nanodimension materials such as Montmorillonite (MMT) and Titanium dioxide (TiO2). The main reason for this improvement in comparison with conventional composites is the large surface area which results in high interactions between the nanofillers and polymer when these nanomaterials are well dispersed. The behavior of nanocomposite films has been depended to the dispersion of the nanoparticles in the polymer matrix. MMT as a onedimensional (1D) material is the most commonly used layered silicates. TiO2 as threedimensional (3D) nanoparticle has been investigated most widely because it is inert, inexpensive and, has a high refractive index with UV shielding potential. The study on films with different dimensions of nanofillers simultaneously is rarely reported. MMT and TiO2 as two inorganic nanofillers have different shapes and structures, so the combination of TiO2 and MMT apparently had a synergistic effect on the starch film properties. The aim of this study was to control particle agglomeration and investigate the synergistic effect of combination of TiO2 nanoparticles and MMT layers and on the surface topography, color, and thermal properties of plasticized starchMMTTiO2 nanocomposites. Materials and methods:.First, 100 ml of potato starch solution with a concentration of 4% (w/v) was prepared by dispersion of the starch in distilled water and was gelatinized at 80ºC for 15 min. Different levels of MMT (3 and 5% w/w starch) and TiO2 (0.5, 1 and 2% w/w starch) were dissolved in distilled water and were added to the gelatinized starch after treatment with ultrasound for 30 min. Glycerol, as a plasticizer, with concentrations of 50% (w/w starch) were added to the filmogenic solution. The plasticized starch (PS) based filmogenic solutions were dried in an oven at 45 °C for 15 hours. The surface roughness and topography and thermal properties of the films were determined through atomic force microscopy (AFM) and differential scanning calorimetry (DSC) analysis, respectively. Fourier transforms infrared (FTIR) spectroscopy in the range of 4000 to 400 cm1. UVVis spectroscopy was employed to evaluate the absorbance and opacity behavior of the PSMMTTiO2 nanocomposite films in the wavelength range of 200800 nm. The color parameters of films were measured by a portable colorimeter. Statistical analysis was performed on a completely randomized design with the analysis of variance (ANOVA) and Duncan’s multiple range tests was used to detect differences among the mean values of the films properties Results and discussion: Atomic force microscopy’s images demonstrated an obviously uniform dispersion of MMT and TiO2 nanomaterials in the PS3%MMTTiO2matrix with smoother surfaces and a lower roughness parameters than that for the corresponding binary PSMMT nanocomposites with the MMT filler content (3 wt%). Surface roughness of starch films was changed depending on the MMT and TiO2 content. The results of the roughness parameters and topographic images were confirmed by the high frequency distribution curves. In the PS3 and 5% MMT films, most parts have height of about 400 and 600 nm, respectively; While the height of the PSMMT1% TiO2 bionanocomposites film were 200 and 800 nm. FTIR revealed the hydrogen bonds and electrostatic interactions between nanofillers with starch and themselves by the peaks associated with bond COH at 1142 cm1 and 990 cm1 and wide and high intensity IR absorption in the 500800 cm1.Evanescence of 3626 and 3452 cm1 peaks assigned to OH groups of MMT in the PS3MMT spectrum affirmed the interaction between starch and MMT.Shift in melting temperature and glass transition (Tg) towards higher temperature respectively from 295.1C to 306.3 C and from 199.1 C to 207.6 C were illustrated by DSCresults due to addition of TiO2 in the PS3%MMT matrix.Improvement of thermal stability might be attributed much jammed and conjugated 3D MMTTiO2 network combined together, or powerful interaction between PS and nanofillers could also slowdown the polymer chains motion and melting point during heating. These results showed a significant effect of combination of 1D MMT layers and 3D TiO2 nanoparticles on the thermal properties of PS nanobiocomposite starch based films. Montmorillonite did not affect color of nanocomposite. The transparency of a nanobiocomposite film is not significantly varied when the clay layers with about one nm thick are excellent dispersed through the polymer matrix, since such MMT platelets are less than the of visible light wavelength and do not block lights transmission. Transmittance, redness and yellowness of new ternary films decreased when TiO2 was added to PS3%MMT matrix at 1%. In this case, color difference (ΔE) and whiteness index (WI) are increased 86.6% and 76% respectively.Starch and PSMMT films were colorless. The presence of TiO2 imparted whiteness to the nanocomposites due to its inherent whiteness. This phenomenon can be enucleated as the large specific surface area and high refractive index of nanosized TiO2 particles were accounted or diffuse reflection of light from the interface of the materials, and consequently, transparency loss of the composite films. UVVis spectroscopy was employed to evaluate the absorbance and opacity behavior of the PSMMTTiO2 nanocomposite films in the wavelength range of 200800 nm. Incorporation of TiO2 nanoparticles into the starch film solution caused a significant decrease of transmittance in visible, UVA (360 nm), UVB (300 nm), and UVC (240 nm) regions. The results of UVVis spectroscopy showed that this type of films could be used as a packaging material to shield against UV and visible light.