Solid-Phase Grafting Method Through Selective Heating And Its Application In Functionalization Of Polypropylene

Polyolefins,mainly including two polymer materials,polyethylene(PE)and polypropylene(PP),are widely used in all aspects of the national economy.They are the most consumed polymer materials,with annual global consumption of 200 million tons,accounting for more than 50%of the total consumption of the three major polymer synthetic materials.China is the world's largest producer and consumer of polyolefins.Its consumption in 2018 was nearly 60 million tons,accounting for more than 60%of the total consumption of synthetic resins.However,after years of rapid development,the polyolefin industry has shown a clear excess trend,and China has experienced a structural excess problem,that is,overcapacity of general products and large-scale imports of high-performance products.High performance is not only the most important development direction of polyolefins,but also the only way to solve China's structural excess problem.Graft modification is an important method to achieve high performance of polyolefins.Graft modification with polar monomers is the most important research direction of polyolefin graft modification.Polyolefins are hydrophobic and chemically inert,ungraft-modified polyolefins are often limited in their applications in bonding,painting,coloring,blending,and reinforcement modification.For this reason,the research on graft modification of polyolefins has been one of the most important research hotspots for polyolefin high performance.Nowadays,polymer grafting methods mainly include melt grafting method,solution grafting method and solid phase grafting method.The most commonly used method is the melt grafting method,which requires the use of peroxide as graft initiator,causing polymer cross-linking or degradation.In addition,the peroxide residue and the ungrafted monomer together cause the grafted product to be colored and odorous.The solid phase grafting method can partially overcome the shortcomings of the melt grafting method.Residual peroxides and ungrafted monomers can be removed after the grafting reaction,but the grafting reaction must be performed below the melting point of the polymer,resulting a very low grafting efficiency.Academia and industry are always looking for an efficient solid phase grafting method.In this thesis,a systematic study on the polymer solid-phase grafting method was conducted,and a new solid phase grafting method was invented.This method is a solid phase grafting reaction at a temperature higher than the melting point of the polymer.Using this method,we successfully modified polypropylene resin and its products.The main research contents and innovative contributions are as follows:1.A new solid phase grafting method at temperature higher than the melting point of the polymer was proposed:selective heating grafting method.Using polypropylene powder as the graft polymer,maleic anhydride(MAH),vinylsilane and vinyl silicone oil as the graft monomers,a high-performance functional polypropylene resin was prepared by microwave irradiation.The grafting mechanism was studied,and the effects of the amount of grafted monomers and microwave irradiation time on the grafting ratio,the changes in mechanical properties,crystallization behavior of polypropylene resin before and after grafting were discussed.The results show that the selective heating grafting method is a new solid phase grafting method that does not require an initiator and the grafting temperature is higher than the melting point of the polymer.Using this method,a maleic acid(MA)grafted polypropylene with high melt strength was first prepared.Since the grafting reaction occurred on the surface and the voids of the polypropylene powder,the remaining MAH that did not undergo the grafting reaction could be washed with water after reaction.The maleic acid grafted polypropylene prepared by the new method contains a large amount of ? crystals,and the grafted polypropylene also has the characteristics of high toughness.Therefore,MA grafted polypropylene is a kind of high-performance polar polypropylene resin,which has the characteristics of no odor,excellent rigidity and heat resistance.Further research has found that adding a trace amount of partially reduced GO to MAH can increase the grafting reaction temperature and the graft ratio of MAH under microwaves,and the performance is further improved.The obtained MA grafted polypropylene can continue to react with sodium hydroxide to prepare sodium maleate(NaMA)grafted polypropylene.The NaMA grafted onto the polypropylene molecular chain affects the polypropylene crystallization behavior and makes polypropylene resin The rigidity and heat resistance are further improved.The obtained high melt strength polar NaMA grafted polypropylene is colorless and odorless,and has similar mechanical and thermal properties as the nucleating agent NA11 modified polypropylene.Further research found that a small amount of sodium chloride can also graft unsaturated silanes that are not easily absorbing microwaves to polypropylene molecular chains,indicating that this new grafting method has broad applicability.2.Preparation and application of Janus polypropylene film.A new grafting method was used to prepare the NaMA grafted polypropylene resin as the raw material.The solvent method was used to induce the self-assembly of the resin to prepare a Janus film that was one side superhydrophilic and another side hydrophobic,the film could be used for water collection and reducing water evaporation.The reasons for the film's superhydrophilic properties were studied,the excellent properties of the film in collecting water and preventing water evaporation were discovered,and the possibility of application of the film in reservoirs and agricultural water-saving irrigation was discussed.3.Design and preparation of superwetting polypropylene surface.A superhydrophilic,superlipophilic,and superamphiphilic polypropylene surface was prepared by using the new solid phase grafting method,and polypropylene sheets with microporous surfaces were used as raw materials.The effects of graft modification on surface morphology and chemical composition,as well as the effect of micro-nano structure on the surface of polypropylene on surface wettability were studied,and the formation mechanism of superwetting was analyzed.The results show that the properties of the graft monomer,the capillary action of the microporous surface,and the micro-nano structures in the capillaries together give superwetting properties to the surface of polypropylene.By grafting a hydrophilic monomer(NaMA)or a lipophilic monomer(unsaturated silicone oil)onto a polypropylene sheet having a microporous surface,polypropylene surfaces with superhydrophilic and superlipophilic properties can be obtained.Polypropylene surface with superamphiphilic properties can also be prepared by grafting hydrophilic and lipophilic monomers simultaneously.The experiment also obtained surprising results.The surface of the prepared superhydrophilic polypropylene can be bonded with water-based adhesive(PVA solution),and the bonding strength can reache to 8Kpa.It shows that this new method for preparing superwetting surfaces may have important application prospects in the fields of coatings,printing and adhesion.4.Design and preparation of high flux PP ultrafiltration(UF)membrane.PP flat membrane and PP hollow fiber membrane were used as raw materials,flat ultrafiltration membranes with ultra-high water/oil flux under normal pressure and hollow fiber membranes with ultra-high water flux under pressure condition were prepared.The stability of the modified ultrafiltration membrane,the effect of the microporous structure in the membrane on the wettability of the membrane,and the effects of grafting monomers and microwave irradiation time on the properties of grafting ratio,water/oil flux,etc.The results show that grafting hydrophilic monomers(NaMA),lipophilic monomers(unsaturated silicone oil),and grafting the above two monomers on polypropylene flat UF membranes can obtain PP UF membranes with ultrahigh water flux,ultrahigh oil flux or ultrahigh water and oil flux..These three ultrafiltration membranes can significantly increase the flux of water or different oils.Using the new grafting method to graft NaMA onto polypropylene hollow fiber membrane can increase the membrane's water flux by 12 times.This is a simple and efficient method for preparing high flux polypropylene UF membranes.