Preparation Of Unfilled Xnbr With High Strength And Toughness

Carboxylic nitrile rubber（XNBR）is fabricated by introducing organic acids such as acrylic acid or methacrylic acid into nitrile rubber chain.The introduction of carboxyls would improve the mechanical properties of XNBR slightly.However,in order to obtain good application value,XNBR still needs to be strengthened and toughened.In rubber industry,rubbers are usually to be reinforced and toughened by incorporating various fillers.Although the mechanical strength can be effectively improved,the incorporation of fillers also brings other problems,such as filler dispersion,interface regulation and processing difficulties.Weak interactions,such as hydrogen bonds and coordination bonds,can undergo reversible breakage and recombination events.In this thesis,we have introduced weak bonds into sulfur bonds crosslinked XNBR.Once the rubber material being stretched,the weak bonds would break prior to the covalent bonds to dissipate energy,which would protect the material to be destroyed by early stress concentration.As a result,the rubber material would be strengthened and toughed.The main contents are as follows:（1）Based on the“click”reaction between 4-Phenyl-3H-1,2,4-triazolin-3,5-dione（TAD）and double bonds of the XNBR,the TAD was grafted onto rubber chains by immersing the sulfur crosslinked XNBR into TAD solution in THF.The urazole moieties in TAD structure wouid form hydrogen bonds,which can improve the strength and toughness of XNBR.The results showed that the tensile strength,modulus and toughness of the sulfur crosslinked XNBR increased significantly with the increase of TAD grafting ratio.When the grafting ratio of TAD was 4.96%,the tensile strength and modulus of the sulfur crosslinked XNBR were 3 and 2.7-fold higher than those of the unmodified XNBR,respectively.（2）We designed a XNBR with high strength and toughness based on the coordination interaction between carboxyl of XNBR and Zr⁴⁺.Typically,the XNBR was compounded with Zr OCl₂·H₂O,sulfur and other curing agents followed by hot-pressing,during which the Zr⁴⁺-COOH coordination bonds and covalent crosslinking bonds were formed in XNBR networks.The results show that the strength,modulus and toughness of XNBR were improved simultaneously with the increase of Zr OCl₂·H₂O loading.In detail,the tensile strength,modulus,and fracture energy of XNBR-1/8 are 2.5,4,2.5-folder higher than those of unmodified XNBR.（3）A series of supramolecular polymers based on hydrogen bonds with different structures were synthesized through the reaction between 1,12-diaminododecane（DDA）and acrylic acid（AA）,which were compounded with XNBR and other processing agents.After the sample being vulcanized,supramolecular polymers were formed in situ in the rubber matrix,thus sulfur crosslinked XNBR was prepared with high strength and toughness.The results showed that the tensile strength,modulus and toughness of the materials were improved by incorporating different supramolecular polymers.Specially,when the ratio of DDA to AA is 1:3,the tensile strength and fracture energy of the supramolecular polymer incorporated XNBR were 2.1 and 2.7 times higher than those of the blank sample,respectively.