Preparation And Performance Of Degradable Epoxy Thermosets

Epoxy resin,an engineering material,has been widely used in many fields such as electrician and electronics,aerospace,machinery,architecture and so on.Accordingly,the issue of post-processing or recycling of this materials has received great attention from researchers..In this dissertation,we attempt to prepare degradable epoxy thermosets and explore their structure and properties.（1）The six-armed polycaprolactone（s-PCL）is obtained by ring-opening polymerization（ROP）of monomeric caprolactone using hydroxyl-terminated hexachlorocyclotriphosphazene derivative as initiator and caprolactone as the monomer,which was added to the epoxy precursor and heated to melt,and then cured with a certain stoichiometric amine curing agent,i.e.,ether 4,4’-methylenebis（2-chloroaniline）（MOCA）or 4,4’-diaminodiphenylsulfone（DDS）.From the optical photos and cross-sectional scanning electron microscope image of the cured products,it was observed that the s-PCL was completely miscible with the epoxy matrix cured with MOCA,without discernable macroscopic phase separation.For the counterpart,the cross section of DDS-cured epoxy thermosets appeared a clear phase separation structure,indicating these samples developed macroscopic phase separation;Furthermore,from the curves of XRD,s-PCL existed as amorphous state in MOCA-cured resin,while,for the DDS-curing system,partial crystalline form of s-PCL could be detected when the content of s-PCL was 40 wt%;DMA results showed that for MOCA cured products,as the content of s-PCL increased,theα-transition temperature of the material dropped slowly.When the hardener was DDS,the situation was slightly complicated due to the effect of s-PCL confined crystallization;Moreover,the samples,degraded in the alkaline solution（10%NaOH aqueous solution）for 30 days,were also observed by Scanning Electron Microscope（SEM）,which showed that their surfaces were rough.Large and irregular holes or grooves could be found distinctly,indicating that the materials can be gradually degraded in the alkaline solution.（2）Vinyl polysilazane（PSN1）,with different stoichiometric ratios,was added to the epoxy precursor as the curing agent,and then the epoxy thermosets were obtained through the curing reaction.Uniform cross-sectional surfaces of the samples were observed with the results of SEM images.suggesting that no macroscopic phase separation happened in these materials.The three-point bending results showed that as the content of PSN1 increased,the value of the flexural strength,flexural modulus,and K_ICof the products dropped;the DMA curve showed that No.5 sample had the lowestα-transition temperature of 103.3 ^oC.In addition,the storage modulus andα-transition temperature of the materials were greatly affected by the content of PSN1.After degradation in alkaline environment,SEM images demonstrated that the surfaces of the sample were uneven and rough with small grooves and holes after being degraded by alkaline solution（10%NaOH aqueous solution）for a period of time.（3）Employing ethylene glycol as the initiator,a series of dihydroxyl-terminated polycaprolactones（PCL）with different molecular weights were synthesized by ROP.The epoxy groups of ethylene glycol diglycidyl ether were ring-opened by the hydroxyl groups of PCL under the role of a catalyst to prepare the epoxy thermosets.The XRD results showed that the crystallization behavior of PCL in epoxy thermosets may be affected by its molecular weight.When the molecular weight of the PCL exceeded a critical value,its XRD curves appeared a sharp diffraction peak.When the molecular weight of the polycaprolactone in the crosslinked structure was low（less than about 1660）,it was amorphous in the crosslinked network.When the molecular weight rose to 2110,a weak crystalline diffraction peak of polycaprolactone appeared in the XRD curve.When the molecular weight increased further,sharp crystalline diffraction peaks appeared in the curve.In addition,the epoxy thermosets were found to be degraded in alkaline solution,and the weight of epoxy thermosets decreased significantly at a short time after immersing in 10%NaOH aqueous solution.