Publication: Preparation and characterization of bacterial cellulose and polyethylene oxide blend films
Abstract
Bu çalışmada, çözelti döküm yöntemi ile 4 farklı bileşimde bakteriyel selüloz (BC) (Gluconacetobacter xylinus'un mikrobiyal fermantasyonu ile üretilmiş), polietilen oksit (PEO) ve kitosan (CH) karışım filmleri hazırlanmıştır. Karışımların hazırlanmasında sabit oranda CH-PEO (%85-%15) ve farklı miktarlarda BC (%0, %2, %4, %6) kullanılmıştır. Hazırlanan filmlerin detaylı termal, mekanik, spektroskopik, morfolojik ve yüzey karakterizasyonu çalışmaları yapılmıştır. BC’un asit hidrolizi için sülfürik asit kullanılmış, taramalı ve geçirimli elektron mikroskopu (SEM&TEM) analizleri BC’un kristalin ve oldukça gözenekli bir yapıya sahip olduğunu ortaya çıkarmıştır. Atomik kuvvet mikroskopu (AFM) ile filmlerin yüzey pürüzlülüğü belirlenmiş ve, BC miktarı arttıkça karışımların yüzey pürüzlülüğünün de arttığı gözlenmiştir. Hazırlanan filmlerin mekanik mukavemeti, stres-gerinim testleri ile belirlenmiş olup, sonuçlar artan BC miktarının gerilme değerinde ve kopma uzamasında artışa neden olduğunu göstermiştir. Dinamik mekanik analiz (DMA) ile karışım filmlerin camsı geçiş sıcaklıkları (Tg) ve zincirlerin dolaşma yoğunluğu (N) değerleri hesaplanmıştır. Sonuçlar, BC oranı arttıkça karışımların hem Tg hem de N değerinin arttığını göstermektedir. Karışımların termal analizi için diferansiyel taramalı kalorimetri (DSC) ve termal gravimetrik analiz (TGA) teknikleri kullanılmıştır. BC ilavesi PEO'nun kristalinitesini bir ölçüde bastırmış ve karışım filmlerinin termal stabilitesini etkilemiştir. CH ve BC herhangi bir erime noktası göstermediğinden ve tüm karışımlarda CH– PEO oranı sabit olduğundan, PEO'nun erime noktasındaki düşüş BC ilavesinden kaynaklanmaktadır. BC partiküllerinin gözenekli yapısı sayesinde zincirler arasındaki etkileşimi artırarak PEO’nun morfolojik yapısını bozduğu düşünülmektedir. BC partiküllerinin PEO zincirleri arasına girerek PEO’nun C-O-C eter oksijeni ile hidrojen bağı yapması kristal yapıyı etkilemiştir. Bu sonuçlar literatür bilgileri ile de desteklenmektedir. Bildiğimiz kadarıyla CH ve PEO'nun karışımları üzerine literatürde birçok çalışma olmasına rağmen, umut verici yeni bir aktif gıda ambalaj malzemesi olabilecek BC dolgulu PEO-CH karışımların karakterizasyonu hakkında bir rapor bulunmamaktadır.
In this study, 4 different compositions of bacterial cellulose (BC) (produced by microbial fermentation of Gluconacetobacter xylinus), polyethylene oxide (PEO), and chitosan (CH) blend films were prepared by solution casting method. A fixed ratio of CH-PEO (%85-%15) and different amounts of BC (%0, %2, %4, %6) were used. The detailed thermal, mechanical, spectroscopic, morphological and surface characterizations of the blend films were performed. Acid hydrolysis was applied for the hydrolysis of BC and, scanning and transmission electron microscope (SEM&TEM) analyses revealed that obtained BC has a highly porous structure. AFM determined the surface morphology of the blend films and the surface roughness of blends increased upon the increased amount of BC, which may be attributed to BC enrichment on the blend film surface. Stress-strain tests determined the mechanical properties of the blends, and an increased amount of BC resulted in a slight increase in the stress value and elongation at break. Glass transition temperatures (Tg) and degree of entanglement density (N) of the blend films were calculated by dynamic mechanical analysis (DMA), and both were increased with the amount of BC. The increase in Tg values was due to the filler effect of BC, which was placed between PEO and CH chains, preventing segmental movements to some extent. Differential scanning calorimetry (DSC) and thermal gravimetric analysis (TGA) were used for the thermal analysis of the blend films. The BC addition suppressed the crystallinity of PEO, and the thermal stability of blends was slightly affected by BC. CH and BC do not display any melting points and the ratio of BC to PEO is fixed in all blends. The decrease in melting point of PEO in blend composition was due to the interaction between BC and PEO chains. It is notable that the BC hindered the PEO crystallinity to some extent. This result was confirmed by Fourier transform infrared spectroscopy (FT-IR) results. Although many studies on CH and PEO blends has been found in the literature, to the best of our knowledge, there is no report on the detailed characterization of the BC filled PEO-CH blends which may be a novel promising active food packaging material.
In this study, 4 different compositions of bacterial cellulose (BC) (produced by microbial fermentation of Gluconacetobacter xylinus), polyethylene oxide (PEO), and chitosan (CH) blend films were prepared by solution casting method. A fixed ratio of CH-PEO (%85-%15) and different amounts of BC (%0, %2, %4, %6) were used. The detailed thermal, mechanical, spectroscopic, morphological and surface characterizations of the blend films were performed. Acid hydrolysis was applied for the hydrolysis of BC and, scanning and transmission electron microscope (SEM&TEM) analyses revealed that obtained BC has a highly porous structure. AFM determined the surface morphology of the blend films and the surface roughness of blends increased upon the increased amount of BC, which may be attributed to BC enrichment on the blend film surface. Stress-strain tests determined the mechanical properties of the blends, and an increased amount of BC resulted in a slight increase in the stress value and elongation at break. Glass transition temperatures (Tg) and degree of entanglement density (N) of the blend films were calculated by dynamic mechanical analysis (DMA), and both were increased with the amount of BC. The increase in Tg values was due to the filler effect of BC, which was placed between PEO and CH chains, preventing segmental movements to some extent. Differential scanning calorimetry (DSC) and thermal gravimetric analysis (TGA) were used for the thermal analysis of the blend films. The BC addition suppressed the crystallinity of PEO, and the thermal stability of blends was slightly affected by BC. CH and BC do not display any melting points and the ratio of BC to PEO is fixed in all blends. The decrease in melting point of PEO in blend composition was due to the interaction between BC and PEO chains. It is notable that the BC hindered the PEO crystallinity to some extent. This result was confirmed by Fourier transform infrared spectroscopy (FT-IR) results. Although many studies on CH and PEO blends has been found in the literature, to the best of our knowledge, there is no report on the detailed characterization of the BC filled PEO-CH blends which may be a novel promising active food packaging material.