Effects Of Fatty Acids And Plasticizers On Theproperties Of Starch-based Straws

With the progress of technology and the improvement of living standards,people pay more and more attention to environmental protection,traditional plastic straws took a long time to degrade and were difficult to recycle,which brought great pressure on environmental protection.Up to now,after the promulgation of the "plastic ban",the main share of disposable plastic straws in the market has been replaced by paper straws and PLA straws,but paper straws were easy to become sticky and soft,and PLA straws were expensive,which brings consumers a bad consumer experience.Therefore,there was a need for a new environmentally friendly straw in the market.Among them,starch-based materials were outstanding for their total degradation,non-toxicity,low cost and easy availability of raw materials.However,the development of starch-based straws is limited by the high degree of soaking and swelling and the tendency of retrogradation to cause cracking of the starch-based straws.In order to improve the above shortcomings,this thesis used corn starch as the main material,added fatty acids to inhibit the recovery of starch-based straws,used plasticizer to improve the physicochemical properties of starch-based straws,and further determined the optimal proportion of plasticizer for the extrusion of starch-based straws.Finally,on this basis,the effect of retrogradation on the performance of starch-based straws was studied.The main contents and research conclusions were as follows:(1)The effect of fatty acids on the properties of starch-based straws was investigated.All the extruded samples showed characteristic diffraction peaks of V-type crystallization.The relative crystallinity of the samples increased from 5.76%(control)to 15.63%(lauric acid)and the short-range order degree increased from0.1482(control)to 0.1560(stearic acid)after extruded with fatty acids.This indicated that the formation of starch-fatty acid complexes facilitated the generation of crystalline structures and the ordering of short-range structures within the starch.With the shortening of fatty acid chain length and the increase of saturation,the relative crystallinity and short-range ordered structure of the samples gradually increased.Therefore,the starch-based straws with stearic acid addition presented the lowest relative crystallinity and degree of order among all samples with fatty acid extrusion.Compared to the control,the peak viscosity of the starch-based straw samples added with stearic acid decreased from 1626 c P to 585 c P,and the setback value decreased from 937 c P to 86 c P.The decrease in setback value indicated that the retrogradation of the samples was inhibited.In addition,the samples added with stearic acid presented the lowest water uptake among all fatty acid starch-based straws,with low swelling and upright non-bending after 30 min immersion at 25 ℃.(2)The effects of different plasticizers on the properties of starch-based straws were investigated.Some water molecules(3%,w/w)were replaced by different environmental plasticizers for compound plasticizing to improve the performance of starch-based straws.The addition of different plasticizers did not change the crystalline type of the samples.The addition of hydrophilic plasticizers facilitated the generation of V-type crystalline structures during starch extrusion,while hydrophobic plasticizers reduced the relative crystallinity of the samples.The addition of other plasticizers weakened the hydrogen bonding within the samples and presented a lower Tg’,and the plasticization of the starch-based straws was enhanced.Smaller volume plasticizer molecules(e.g.glycerol),with strong hydrogen bonding,achieved better plasticization of starch-based straws,and starch-based straws plasticized with glycerol had higher toughness,lower water absorption,paste viscosity and swelling.(3)The effect of compound plasticizing systems with different ratios of water(W)and glycerol(G)on the properties of fatty acid(SA)-starch-based straws was investigated.17.5%G+2.5%W+SA had the highest crystallinity of starch-based straws.This was because the complex formation exists not only between starch and fatty acid but also between starch and glycerol.The results of FTIR spectroscopy showed that the binding site of the plasticizer to the starch molecule changed as the ratio of moisture and glycerol changed.10%G+10%W+SA possessed the highest moisture content(26.43)and fatty acid content of the complex(1.66%).Glycerol at low concentrations acted as an anti-plasticizer,and a high concentration of glycerol will form glycerol rich areas outside starch molecules,limiting the movement of plasticizer molecules,as evidenced by the results of DSC and H NMR.In addition,starch-based straws extruded with different ratios of water and glycerol showed different pasting characteristics and thermal stability.5%G+15%W+SA had the lowest water absorption(22%)and showed the lowest swelling in simulated immersion tests of starch-based straws.(4)The effect of retrogradation on the properties of starch-based straws was investigated.There was a strong correlation between the orderliness,mechanical strength,water absorption and retrogradation time of each of the starch-based straws.The retrogradation peaks of the samples which possessed high moisture content were became more intense and sharper with the increase of retrogradation time.The order of the starch-based straws was proportional to the retrogradation time,with the 20%W+SA order increasing at the fastest rate of 75%.The retrograded starch-based straws showed a stiffer texture,in which the maximum bending force of 20%W+SA straws increased the most from 601.2 g to 4209.5 g.The maximum bending force of17.5%G+2.5%W+SA straws increased the least from 4276.1 g to 6249.3 g.After retrogradation,the water absorption rate of starch-based straw decreased,the swelling degree decreased after 30 min immersion in water,and the water resistance increased.