| The research of biodegradable polyester is an important direction of the reduction of environmental pollution and the usage of petrochemical resources. The polymer foaming materials are essential part in the materials field. Wherein, poly(butylene succinate)(PBS) have drawn much attention due to its good thermal stability, outstanding processability and excellent mechanical properties. However, the low-melt strength of PBS limits its wide application in foam industry because of its low molecular weight and linear structure. Moreover, due to the low density, renewable, biodegradable and excellent mechanical properties, cellulose nanocrystals(CNC) are widely acted as the reinforcement nanofillers. However, because of the hydrophilic nature and high special surface area of CNC, as well as the intermolecular hydrogen bonding cause self-aggregation of CNC, and it has inefficient compounding with most nonpolar thermoplastics polyester so that limits its application of being used as nanofillers. Therefore, to expand the application of CNC as filler in polymeric matrix, the surface properties should be changed by chemical modification. In this work, the acetylated cellulose nanocrystals(ACNC) will be used as nanofillers to reinforce the PBS matrix and then to prepare the PBS foaming materials.The CNC are obtained by sulfuric acid hydrolysis from cotton liner, and then react with acetic anhydride to gain the ACNC. The successful acetylation was confirmed by the appearance of a new peak in the carbonyl area around 1746 cm-1 and a new absorption band at 1240 cm-1 in the FTIR spectroscopy. And according to the results of element analysis, it can be calculated the DSsurface acetyl of ACNC was 71.1%. In addition, it is confirmed the ACNC preserve the rod-like morphology and the original crystalline structure of the nanocrystals via the results of TEM and XRD.For the PBS foam materials, when the content of chemical blowing agents azodicarbonamide(AC) reached 5 wt%, the foams had optimal the cell density and cell size, were 1.25?105 cell/cm3 and 203.7 ?m, respectively. Furthermore, the addition of ACNC could further improve the cell morphology of PBS foams. For example, the cell density and cell size of PBS/AC(5)/ACNC-2 foam sample was increased from 1.25×105 cell/cm3 to 1.53×105 cell/cm3 and decreased from 203.7 ?m to 190.5 ?m respectively, in comparison with PBS/AC(5)/ACNC-0 sample. At same time, the content of ACNC would also have effect on cell morphology and performance of PBS foams under the 5 wt% AC content. When the addition of ACNC reached 5 wt%, the PBS/AC(5)/ACNC-5 sample gained the maximum value of cell density and the minimum value of cell size, reached 1.95?105 cell/cm3 and 178.8 ?m, respectively. And compared with PBS/AC(5)/ACNC-0 sample, the bending strength and bending modulus were increased by 50.0% and 34.1%, respectively. Meanwhile, for the PBS/AC(5)/ACNC-5 foam sample, the glass transition temperature(Tg) and degree of crystallinity within the PBS fraction(?c) of the foams was increased to-32.4 oC and 39.8%, respectively. These results of the improvement were attributed to the moderate ACNC possess well disperse in PBS matrix and the strong interaction between nanofillers and matrix, the well-dispersed ACNC could provide much of cell nucleation sites and improved the crystallization nucleation of PBS component. However, when the superfluous ACNC was added into PBS matrix(like 7 and 10 wt%), the redundant nanocrystals may cause self-aggregation and then damage the continuous structure of PBS resulted in the microphase separation, these would be adverse affected the cell morphology and thermal mechanical properties of final PBS foam materials. |
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