Research On The Of Corn Stalk/hectorite Composite Superabsorbents

Super absorbent polymer?SAP?also known as water retention agent is a new type of non-poisonous,harmless,polution-free functional polymer.As SAP contains a lot of carboxyl,oxhydryl that belong to lydrophilic grouping and three-dimensional net structure,it can quickly absorb hunderds of thousands of times of water relative to their own in a short time and hold the water in it for a long time.So far SAP has many types and wide application,such as the field of medicine and health,forestry and horticulture industry,construction business,industry and so on.There are lots of corn stalks increased more than seven billion tons one year in China.With the developing of agriculture of our country and growth in the living standard of peasant farmers,the quantity of corn stalks increase more and more fast,now the corn stalks have became one of the three major agriculture waste.More and more attention are paid to the researches of corn stalks these days,and there are more and more using of corn stalks in many fields,such as agricultural use,feeds use,cellulose use,culture medium use,industry use and so on.Among all of these fields we must emphasize the cellulose use.Not only because cellulose is part of corn stalk,but also it is natural polymer containing a lot of hydrophilic groupings.So after the graft copolymerization of corn stalk and SAP,we can get the products which has better water absorption and better salt tolerance.Laponite consisting of silicon and magnesium is the artificial synthesis of colloidal material,which has stratiform structure consisted of octahedron and trihedron.Because of its special microcosmic structure it has many useful properties,such as thixotropy,dispersity,suspension property,thickening and so on.After a little of laponite being put into the water,it quickly swell and finally beconme the high viscosity gelatum,which consists of network structure and contains large amount of water.Considering the micromedhanism structure and performance porperty of laponite,we put it into the synthetic resin in order to improve the property of the SAP,such as water absorption,the water retention rate,and the salt tolerance etc.Following the trend of SAP development this study attempt to put the modified corn stalk and laponite into the synthesisof resin.Acrylic acid modified-corn stalk/hectorite composite superabsorbents were prepared by graft copolymerization of acrylamide?AM?and acrylic acid?AA?with acrylic acid-modified corn stalk in an aqueous solution by way of water solution polymerization.Factors affecting water absorption,water retention,fertilizer solution absorption and gel strength of the modified corn stalk/hectorite composite superabsorbents,such as amount of acrylic acid modified-corn stalks,AA/AM mass ratio,AA neutralization degree,crosslinker amount,hectorite amount and initiator amount,etc,were investigated.Morphologies,structure and thermal properties of the modified corn stalk/hectorite composite superabsorbents were characterized by FTIR,XRD,SEM and TGA.Acrylic acid modified-corn stalk/hectorite composite superabsorbents,having rapid water absorption rate,high water absorbency and water retention,rapid fertilizer absorption rate and high fertilizer solution absorbency,high gel strength and good heat-resistance,have been synthesized.The main research findings are as follows.1.The corn stalk/hectoirte had rapid water absorption rate and fertilizer absorption rate,with about 50min for reaching absorption equilibrium for water and urea solution,respectively,and 30min for reaching absorption equilibrium for KCl and NH₄H₂PO₄ solution,respectively.The sequence of absorption capacities of water and fertilizer solution for the corn stalk/hectorite composite superabsorbents is as follows:water absorbency>urea solution absorbency>KCl solution absorbency>NH₄H₂PO₄ solution absorbency.2.When the acrylic acid-modified-corn stalk amount was 15%,the ammonium persulfate amount was 1.6%,the crosslinker amount was 0.1%,the acrylic acid neutralization degree was 70%,the acrylic acid/acrylamide mass ratio was 60:40,the hectorite amount was 1%water absorbency and fertilizer solution absorbency of the corn stalk/hectorite composite superabsorbents reached the maxima.3.When the acrylic acid-modified-corn stalk amount was 35%,the ammonium persulfate amount was 1.6%,the crosslinker amount was 0.5%,the acrylic acid neutralization degree was 70%,the acrylic acid/acrylamide mass ratio was 60:40,the hectorite amount was 9%water retention and gel strength of the corn stalk/hectorite composite superabsorbents reached the maxima.4.With the increase of acrylic acid-modified-corn stalk amount,water absorbency and fertilizer solution absorbency of the corn stalk/hectorite composite superabsorbents increased firstly and then decreased secondly,while water retention and gel strength of the corn stalk/hectorite composite superabsorbents increased gradually.With the increasing amount of initiator ammonium persulfate,water absorbency,fertilizer solution absorbency,water retention and gel strength of the corn stalk/hectorite composite superabsorbents increased firstly and then decreased secondly.With the increase of crosslinker amount,water absorbency and fertilizer solution absorbency of the corn stalk/hectorite composite superabsorbents decreased steadily,while water retention and gel strength of the corn stalk/hectorite composite superabsorbents increased gradually.With the increasing of acrylic acid neutralization degree,water absorbency,fertilizer solution absorbency,water retention and gel strength of the corn stalk/hectorite composite superabsorbents increased firstly and then decreased secondly.With the increase of acrylic acid/acrylamide mass ratio,water absorbency,fertilizer solution absorbency,water retention and gel strength of the corn stalk/hectorite composite superabsorbents increased firstly and then decreased secondly.With the increase of hectorite amount,water absorbency and fertilizer solution absorbency of the corn stalk/hectorite composite superabsorbents decreased steadily,while water retention and gel strength of the corn stalk/hectorite composite superabsorbents increased gradually.5.SEM showed that the surface of the hectorite was uneven with severe aggregation and clear sheet or rod-like structure.The surface of unmodified corn stalks was smooth and dense,showing a discontinuous fiber sheet structure.After acrylic acid modification,the modified corn stalk was rough,porous with irregular fragments.The corn stalk/hectorite composite superabsorbents had rough and wrinkled like surface with a gully and porous structure.XRD data showed the amorphous structure of the corn stalk/hectorite composite superabsorbents.The original sharp diffraction peaks attributed to crystalline structure of hectorite and corn stalk disappeared.FTIR spectra showed the charcteristics of absorption peaks assigned to the modified corn stalk unit,hectorite unit,AA unit and AM unit in the corn stalk/hectorite composite superabsorbents,confirming the target structure of the corn stalk/hectoritecompositesuperabsorbents.TGAdatashowedthatthe thermogravimetric curve of the corn stalk/hectorite composite superabsorbents could be divided into four stage.Hectorite could obviously enhance heat resistance of the corn stalk/hectorite composite superabsorbents.