Prepration And Properties Of Poly(Ethylene Adipate) Composites

With the implementation of the sustainable development strategy in recent years and people's growing awareness of environmental protection,more attention has been paid to the biodegradable polymer materials.Poly?ethylene adipate??PEA?is a biodegradable aliphatic polyester,which has been widely used in packaging,plastic film and other fields.In addition,it has been often used to synthesize polyurethane.However,the molding period of PEA is very long and the mechanical strength of the product is low because of the poor crystallization performance of PEA,which greatly has limited its application greatly.In order to solve the above problems,in these paper carbon nanotubes,silk fibers and oriented poly?vinylidene fluoride?were added into PEA matrix.The effects of these fillers on the crystal structure and crystallization thermo-dynamics and dynamics of PEA were studied in detail.In addition,this dissertation also studied the preparation of PVDF?crystals,which provides theoretical guidance for the further preparation of multi-functional PEA composites.The main findings are as follows:?1?In the PEA/MWCNTs-OH composites prepared by ultrasonic dispersion method,MWCNTs-OH can be effectively distributed in PEA after ultrasonic treatment.With increasing the content of MWCNTs-OH,the crystal size of PEA decreases,while the nucleation density and crystallization temperatures increase significantly.The results clearly showed that MWCNTs-OH has a strong heterogeneous nucleation effect on PEA.In addition,the isothermal crystallization kinetics of pure PEA and its composite system were studied by Avrami Equation.It was shown that under the same conditions,the crystallization rate of PEA in its composites was obviously higher than that of pure PEA,but the crystal structure of PEA did not change.?2?After the introduction of the silk fibers?SF?into the supercooled PEA melt,the columnar crystals of PEA formed around the silk fibers.But the crystal structure of columnar crystals was not affected by the crystallization temperature.Further thermodynamic results of PEA/silk fiber composites revealed that the addition of silk fibers hinders the crystallization of PEA during the non-isothermal crystallization stage.The surface of the silk has porous structure,which will hinder the stretching and orderly arrangement of the PEA polymer segments.As a result,the PEA molecules did not have sufficient time for orderly arrangement during on-isothermal crystallization,and eventually led to a decrease in the degree of perfection of the PEA crystal.In the isothermal crystallization process,there was sufficient time for the crystallization of PEA in the composite,so more thermodynamically stable crystals were formed.The thermal stability of the composites was further investigated.It was found that at100°C-350°C,the thermal stability of the composites is better than pure silk but weaker than pure PEA.Between 250°C and 500°C,due to the rapid degradation of PEA,the decomposition rate of composite materials is accelerated.Finally,the intermolecular interactions of the composites were investigated.It was found that there is a strong hydrogen-bonding intermolecular force between silk and PEA resin,which greatly affects the silk-induced crystallization of PEA.The crystalline properties of PEA/silk fiber composites are excellent,so the mechanical properties and toughness are improved.At the same time,the decomposition rate of the composites is also accelerated,and its environmental performance is improved.?3?Oriented PVDF film was prepared by melt drawing method,and its influence on the crystallization behavior of PEA was studied.The results showed that the oriented PVDF membrane has a strong heterogeneous nucleation effect on the PEA,characteristic of a columnarcrystal at the interface between the PVDF and PEA.The columarcrystal size increased with the crystallization temperature.The crystallization ability of PEA grown on the oriented PVDF film substrate was significantly strengthed.When PEA was isothermally crystallized at 50°C,its melting exothermic peak shifted to high temperatures with increasing time,indicating that the PEA chains has begun to align on the surface of the oriented PVDF film within a certain period of time.In addition,it was also found that adding MgCl₂ can promote the production of?-PVDF crystals at 155°C.During annealing the samples,the?crystals can induce the phase formation of?crystals.Further study showed that MgCl₂ has a strong heterogeneous nucleation effect on PVDF,which increases the crystallization rate of both?-form and?-form crystals.