Study On The Preparation And Properties Of Environmentally Friendly Polymers Based On Polylactic Acid

The water-soluble temporary plugging agent usually selects easily degradable water-swellable polymer materials.The volume of the temporary plugging agent becomes larger after absorbing water,so as to play a water shutoff effect,and further hydrolyze into oligomers and small molecules to realize plugging removal.Ordinary polymer materials cannot be completely degraded,so biodegradable materials are needed.Since polylactic acid has good biodegradability and processability,it is an environmentally friendly thermoplastic polymer,so this article uses it as a raw material for oilfield temporary plugging agent.However,because polylactic acid has high brittleness,poor hydrophilicity,and slow degradation rate,it needs to be modified by physical and chemical methods to improve its mechanical properties and degradation properties.In this paper,the bulk polymerization method is used to copolymerize polyethylene glycol(PEG),glycolide(GA)and lactide(LA)into a PLGA-PEG-PLGA copolymer.The samples were characterized by FT-IR,~1H-NMR,GPC and contact angle tests.FT-IR and ~1H-NMR tests confirmed the successful synthesis of the copolymer and the triblock structure of the copolymer.The GPC test investigated the effect of the addition of PEG,the reaction temperature,the reaction time and the addition of the catalyst Sn(Oct)2 on the molecular weight of the copolymer;the contact angle test analyzed the effect of the addition of PEG on the hydrophilicity of the copolymer.The experimental results show that when the mass ratio of the raw materials LA,GA,PEG is 5:1:1.5,140°C,18 h,and the addition amount of Sn(Oct)2 is 0.5 wt%,the molecular weight of the product can reach 6038 g/mol,the contact angle is 26.25°,and the compressive strength is 2.2 MPa.At this time,the hydrophilicity of the prepolymer is good,but the mechanical strength is too low when used directly as a temporary plugging agent in oilfields,and further modification is required.Toluene 2,4-diisocyanate(TDI)was used as the chain extender to extend the chain of the PLGA-PEG-PLGA prepolymer to obtain the PLGA-PEG-PLGA high polymer.The success of the chain extension reaction was confirmed by FT-IR,and the influence of reaction temperature,reaction time and TDI addition amount on the molecular weight of PLGA-PEG-PLGA polymer was investigated by GPC test.Under the optimal reaction conditions of 140°C,30 min,the molar ratio of TDI to prepolymer is 1.2:1,the molecular weight of the product is 36339 g/mol and the contact angle is 37.44°,indicating that the synthesized PLGA-PEG-PLGA polymer still has good hydrophilicity.Then,the PLGA-PEG-PLGA high polymer was composite modified with nano-Si O2 to prepare inorganic/polymer composite materials.Use silane coupling agent KH570 to chemically modify the surface of nano-Si O2 to obtain KH570-Si O2.Then,5 wt%KH570-Si O2 and PLGA-PEG-PLGA high polymer were melt blended and extruded to obtain a particle size of Composite material particles between 0.2-5 mm.The microscopic cross-sectional structure of the composite material was observed by SEM,and it was found that the KH570-Si O2 particles were uniformly dispersed in the polymer matrix.DSC and TG tests show that the addition of KH570-Si O2 improves the thermal stability of the polymer.Compression test results show that the composite material has a modulus of elasticity of 218.0 MPa,a yield stress of 12.6 MPa,and good stiffness,strength and impact resistance.The composite material particles are used as a temporary plugging agent.The temporary plugging agent swells and then dissolves in the simulated formation water.The breakthrough pressure of the plugging is 26.6 MPa,and the plugging rate can reach 99%.After the temporary plugging agent plays the role of temporarily blocking water,it can be degraded within 7 days to achieve complete plugging removal.