Struture And Performance Of Poly (Butylenes Ssuccinate) Based Nanocomposites Reinforced With Cellulose Nanocrystals

The development of biodegradable polymers has been a subject of great interestin materials science for the protection of environment. Poly (butylenes succinate)(PBS) is a biodegradable polyester material, with various advantages of odorless,tasteless, non-toxic, good processability. PBS possessed excellent mechanic propertyapproaching those of polyolefins, polyethylene, and polypropylene, good heatresistance with a softening temperature close to100oC. These advantages make PBSmaterial become a promising material in the packaging field. In this study, cellulosenanocrystal (CNs) can be obtained from cotton linters though sulfuric hydrolysismethod, and then incorporated into PBS material though melt blending process. Withthe increasing of the CN content, the blending strength and blending modulus of thePBS/CNs nanocomposite increased to15.2MPa and728MPa gradually, up to15wt%,1.65and1.83times as pure PBS material respectively. The results showed that CNscan improve the blending property of PBS by its inherent rigidity. When the contentof CNs is higher than the percolation threshold (VRC), the flexural modulus ofPBS/CNs nanocomposite can be greatly improved.With the increasing of CN content, the tensile strength of PBS/CNsnanocomposites increased firstly and then decreased. When the content of CNs is3wt%, the tensile strength reaches the maximum, namely27.36MPa, a14.3%increase over the pure PBS material. Due to the fact that CNs is easily to beaggregated in the PBS matrix, especially for the PBS/CNs nanocomposite with highCN loading level, which may lead to the formation of stress defects. The mechanicproperty of film material is much more sensitive to the stress defects than platematerial. Besides, In order to improve the compatibility between the CNs fillers andPBS matrix, the surface of cellulose nanocrystals was chemically modified by aceticanhydride to provide acetylated cellulose nanocrystals (ACN). The surfacemodification also decreases the hydrogen-bond interaction of hydroxyl group, whichis in favor of the dispersibility of CNs in the PBS matrix. With the increasing of CNcontent up to7wt%, the tensile strength and Young’s modulus increased gradually, and the maximum value is38.6MPa and398.3MPa respectly. As for the PBS/CNsnanocomposites, when the CNs content is7wt%, the value of blending strength andthe Young’s modulus is21.3MPa and402.6MPa, respectively. The reason is that ACNhave better dispersibility than the CNs in the PBS matrix. Therefore, ACN has thepotential to further increase the tensile strength of PBS film material with highloading level.Azodicarbonamide(AC) has been widely used as chemical foaming agent.The PBS/CNs foaming nanocomposites can be obtained by the introduction ofAC/ZnO foaming system. During the foaming process, CNs plays an important roleas the nucleating agent in the polymer melt though the heterophase bubble nucleationmechanism. With the increasing of CNs content, the cell size decerease firstly andthen increase, On the contrary, the cell density increase firstly and then decrease. Thereason is that the gaseous phase has weting effect on the CN surface, the bubble startsat the surface of CNs and form the gas core. However, the CNs with high loadinglevel is easy to be aggregated, and lead to the uneven distribution of cell size and themerge of cell. The formation of three-dimension percolation phenomenon can damagethe intact and continuous structure of the original PBS matrix and the cell wall iseasily to be ruptured. Likewise, with the increasing of CNs content, the blendingstrength of PBS/CNs nanocomposite increased firstly and then decrease, when theCN content is5wt%, the blending strength reaches the maximum value, namely6.3MPa. The reason is that CNs can improve the blending strength of PBS/CNsnanoconposite by its inherent rigidity and the nucleation effect of CNs makes theaverage cell size of PBS/CNs foam material decrease, leading to the uniformdistribution of cell size. When the CNs content is higher than5wt%, the merge orrupture of cell pore may cause the stress defects. Therefore, the blending strengthdecreases with the increase of CNs content. It is worth noted that all the PBS/ACNnanocomposites exhibited increased blending modulus values in the range of0wt%～15wt%of CNs content, which may be ascribed to the formation ofthree-dimension percolation network and the improvement of the rigidity of PBS/CNsnanocomposites.