Preparation,Structure And Properties Of PBS Copolymer And Layered Silicate Composite

As a potential material research field,polymer/layered silicate nanocomposites have broad application prospects.It is widely concerned because its composite with biodegradable material can improve material performance,reduce the cost of production and minimize environmental pollution.Poly(butylene succinate)(PBS)is an environmentally friendly aliphatic polyester with excellent biodegradability,melt processability and heat resistance.At present,compared with common engineering plastics,PBS has poor mechanical strength due to its high crystallinity and high production cost.How to improve the mechanical and thermal properties of PBS through low-cost methods to expand the potential of PBS in various applications is one of the focuses of research.The blending modification method is adopted to improve the performance of PBS material by blending with layered silicate,which avoids the high requirement of synthesis conditions and reduces the production cost.However,the compatibility of blending composite directly determines the performance and application of blending composite.The conventional way to solve the compatibility problem is to modify layered silicates first and then blend them with polyester to increase the compatibility between blended composites.However,the study on PBS is still limited,and the intermolecular interaction between composites is relatively complex,and the influence relationship on the macroscopic properties of composites is not completely clear.In this study,The main chain structure of PBS was modified by changing the sequence of polymer materials and layered silicate blends to change the internal structure of blends.Modified layered silicate modifiers,such as the cationic modifier of montmorillonite,were introduced into the main chain structure of PBS to prepare PBS based modifiers with different structure polarity,and then mixed with layered silicate to prepare composite materials.In this process,the modification of PBS can also make it have certain functions,thus expanding its application range.The main contents and conclusions are as follows:Salicylic acid(SA)was introduced into the main chain of PBS by melt copolymerization,and cationic modifier quaternary ammonium salt(GTA)was reacted with the end group of the chain of PBS under the condition of heated reflux.Three modifiers,including PBSA,high-crystalline PBSGTA and low-crystalline PBSnGTA,were prepared.The results showed that PBSA had better mechanical properties and thermal stability after being modified by 0.5%SA.After the addition of SA,PBSA showed spherulite morphology.The introduction of phenyl groups in SA changed the regular spiral chain structure of PBS,and the melting point of PBSA remained unchanged and the crystallinity decreased.Because the free binding energy containing SA segment is low,the presence of SA can improve the degradation rate of PBS based modifiers and promote the growth of green plants.After modification by GTA,the initial thermal decomposition temperatures of PBSGTA and PBSnGTA were increased by 30? and 28? respectively.The modified material has good thermal stability and has no relation with the crystallinity of PBS.With the increase of GTA,the crystallinity of PBSGTA increased,while the crystallinity of PBSnGTA decreased.PBSGTA modifiers all showed spherulite morphology,and the spherulite size increased gradually,but the crystalline shape of the modifiers is the same as PBS.The spherulite size of PBSnGTA decreased gradually,resulting in higher nucleation density.When 5%GTA is added,the mechanical properties of PBSGTA and PBSnGTA are best.They have antibacterial properties against escherichia coli,and the antibacterial properties have nothing to do with the crystallinity of the modifiers.The blending composites of modified PBS and layered silicates were prepared by melting and blending with three kinds of layered silicates,montmorillonite(MMT),organic montmorillonite(OMMT)and Kaolin.After MMT was added,MMT particles could be uniformLy dispersed in the PBS substance,showing a detached and dispersed granular structure in PBSGTA,and existing in an enveloped state in the amorphous phase of PBSnGTA.The thermal stability of PBSGTA was improved by adding MMT,but the thermal stability of PBSnGTA was decreased.The influence of crystallinity on the thermal stability of composites is great.Because PBSnGTA blends with MMT in an amorphous phase,its interaction force becomes weak and its compatibility is poor.After OMMT was added,OMMT existed in PBSGTA as partial intercalation with good compatibility.In PBSnGTA,a poor compatibility sheet structure is formed.The addition of OMMT increased the glass transition temperature Tg of PBSGTA,but had little effect on the melting point Tm and crystallization temperature Tc,and the initial thermal decomposition temperature reached 322?.When 3wt%MMT and 3wt%OMMT were added respectively,the blends had good mechanical properties.The mechanical properties of the blended composite become worse after Kaolin is added.The compatibility order of layered silicates in PBSGTA matrix is OMMT>MMT>Kaolin.The order of compatibility with PBSnGTA matrix is MMT>OMMT.The addition of OMMT can improve the toughness of PBS A composites,but its strength decreases.OMMT and Kaolin have poor compatibility with PBSA matrix,and Kaolin has a certain degree of agglomeration when it is distributed in PBSA matrix,and it is not good for the material to be widely used for forming.The combustion heat of PBSGTA and PBSA at 298.15 K was measured by Bomb Calorimeter.The standard molar enthalpy of formation of PBSGTA and PBSA was calculated as ?fHm?=-1.51×106±380.23 kJ·mol-1 and ?fHm?=-1.33×106±1211.14 kJ·mol-1,respectively,and the molar heat capacities of the two modifications were linearly related to the temperature within the range of 293?346 K.The kinetic parameters of PBSGTA samples during thermal decomposition were measured,and the apparent activation energy and pre-exponential factors of the samples under different methods and mechanism equations were obtained.The kinetic equation of the thermal decomposition stage of the sample is as follows:Dynamic mechanical properties such as modulus,stress relaxation and creep of modified materials and their blends with layered silicates were analyzed by DMA.It was found that the strong interaction between cationic groups in GTA and the modified substrate enhanced the resilience of the composite materials,and the energy storage modulus of the modified materials was increased,and the energy storage modulus of PBSGTA changed three times as much as that of PBSnGTA.The addition of GTA reduced the thermal motion ability of PBSGTA chain more than PBSnGTA,resulting in the decrease of Tg of PBSGTA.From 10? to-50?,the change in stress relaxation of PBSnGTA is about 1%,while the change in stress relaxation of PBSGTA is about 30%,indicating that the crystalline phase of polymer is the main factor affecting the stress relaxation of materials.When 5%GTA was added,the change of stress and elongation of the materials were the smallest,independent of temperature.When MMT content is greater than 3%,the interaction force between MMT and PBSGTA matrix will be weakened.As a result,the motion ability of the molecular chain segment of the composite will be relatively increased,and Tg will transfer to the low-temperature zone.When MMT is added,the resilience and viscosity of the blended composite material increase simultaneously,making both the energy storage modulus and loss modulus increase,while the loss factor of the material remains basically unchanged.OMMT has a great effect on the dynamic mechanical properties of PBSGTA composites,but has no effect on the viscosity of PBSnGTA.The loss modulus of PBSnGTA is basically unchanged.Because OMMT increases the resilience of composites,the loss factor is reduced.Kaolin increases the viscosity and loss modulus of the blended composite.Stress relaxation and creep show that the addition of 3%OMMT has the least effect on the stress of the composite material,and is independent of temperature.The rheometer was used to analyze the mechanical behavior of GTA modified PBS and GTA modified PBSn.The results show that the linear viscoelastic range of GTA modified PBS modifier is wider than PBSn modifier.However,when the temperature is 200?,PBS and its modified materials show the mechanical behavior of Newtonian fluid.When OMMT is added,the mechanical properties of blended composites are affected by the crystallinity of materials.The energy storage modulus of PBSGTA increases while that of PBSnGTA decreases.The different crystallinity of blending materials makes the degree of interaction between OMMT and groups within the modified materials,such as cations in GTA,and-OH and-COOH of unmodified PBS,and the change of energy storage modulus is opposite.