The Effect Of Pullulan On Condensed Matter Structure Evolution Of Starch

Starch derives from a wealth of sources,which is eco-friendly and the main energy source of human activities.Starch,as a slurry,has excellent adhesion and biocompatibility,the desizing process of which is convenient and efficient without secondary contamination.Therefore,starch is suitable for sizing polyester and cotton yarns,and has high commercial value in the food industry and textile engineering.However,the industrial application of starch-based materials is limited due to the problem of starch retrogradation and poor flexibility.Previous researches have indicated that the hydrophilic colloid is able to simultaneously delay the retrogradation of starch and improve the physical properties of starch film.As a result,the combination of hydrophilic colloid and starch has a good research prospect for the optimization of starch properties.In this paper,in order to provide a novel research idea for exploring the interaction between starch and hydrophilic colloid,potato starch(Potato starch,PS)and pullulan(Pullulan,PUL)were blended to form a research model.The main research contents were as follows:(1)Exploring the effect of PUL on the condensed matter structure evolution of PS;(2)Explaining the mechanism of PUL delaying PS retrogradation from the perspective t of molecular motion;(3)Analyzing the mechanism of PUL affecting physical properties of PS serosa.Firstly,a series of PS and PS-PUL retrogradation solutions with different concentration gradients were prepared by iso-volumetric dilution method.Then,the influence of PUL on PS condensed and entangled matter were investigated by ubbelohde viscometer,small angle X-ray scattering(SAXS)of synchrotron radiation from Shanghai light source,and dynamic laser light scattering(DLS).The results showed that the entanglement concentration increased by 45.45% after adding PUL into PS,and the molecular conformation was delayed from spherical to ellipsoidal to rod-shaped.Based on the theoretical analysis of polymer condensed matter,these results indicated that PUL was able to slow down the kinematic velocity of molecular chain,decrease the degree of molecular entanglement when PS was fully regenerated,and increase the flexibility of PS molecular chains.The molecular motion state of starch from gelatinization to retrogradation was similar to the molecular structure change in the evolution process of condensed matter.Therefore,different concentrations of condensed matter retrogradation solutions were stored at low temperature for different periods to simulate the starch retrogradation process.The results of SAXS and DLS showed that the addition of PUL restricted the molecular conformation evolution speed of the complex system,and reduced the radius of gyration and values of shape factor.Therefore,these phenomena revealed that PUL could delay the process of PS retrogradation by restricting PS chains expansion,making clusters structure of PS chain more compact,and decreasing the stability of three dimensional network structure by complete regeneration of PS.It is well known that starch retrogradation is bound to occur in the process of starch film formation.However,the condensed matter theory holds that cluster structure of molecular chain in the concentrated solution state is in a relatively stable state without considering the molecular aggregation.Therefore,a concentrated solution in a condensed state(1 g/dL,w/v)was used to simulate the film forming solutions(6 g/dL,w/v),which were stored in constant temperature and humidity for a certain period to imitate the film formation.The mechanism of PUL effecting physical properties of PS film were analyzed by the changes of molecular conformation,sizes of chain cluster,and rigidity of molecular chain.The experimental results displayed that addition of PUL decreased the moisture adsorption performance by 18.61%,the reason was that PUL was able to delay the speed of PS chain motion during film formation and reduce the degree of PS chain expansion,resulting in denser and more uniform porosity of PS-PUL film than PS film.In addition,as PUL was able to reduce the ordered arrangement of PS molecular chains and the formation of hydrogen bonding,the breaking strength of PS-PUL film decreased by 20.34%.Furthermore,the elongation at break of PS-PUL film was increased by 23.45% because PUL could improve the flexibility of the molecular chains,leading to the occurrence preferentially of the molecular chain stretching process of PS-PUL film.Lastly,the buckling resistance of PS-PUL film increased by 49.51%,which further proved the correctness of the mechanism that PUL could improve the flexibility of the molecular chain.