Preparation And Performance Study Of Room Temperature Curing Polyurethane Repair Adhesive For Conveyor Belts

Rubber conveyor belts are widely used in industries such as mining.However,they are often susceptible to wear and tear.Although polyurethane adhesives are frequently utilized as repair adhesives for rapid on-site repairs of rubber wear due to their superior performances,the bond strength and other properties of existing polyurethane repair adhesives for rubber fall short of the actual needs.Moreover,the research on the relationship between the structural composition of polyurethane materials and adhesion and other properties is still incomplete,making it challenging to macroscopically regulate the comprehensive performance of polyurethane repair adhesives.To address these practical issues,this project successfully developed a high-adhesion polyurethane repair adhesive that can cure at room temperature,enabling the rapid repair of rubber conveyer belts through surface modification.Additionally,the study also provided a comprehensive investigation of the adhesive properties and other characteristics of polyurethane repair adhesive,including soft segment structure,soft segment molecular weight,etc.The study provides theoretical support for the preparation and performance control of polyurethane repair adhesive,which is of significant practical importance for the efficient repair of rubber conveyor belts at room or low temperatures.The main research of this paper is as follows:（1）In the second chapter of this thesis,the problem of weakly polar SBR rubber substrate being difficult to bond effectively was addressed by using trichloroisocyanuric acid（TCCA）as a modifier for surface treatment.The chemical modification mechanism of TCCA on SBR rubber was investigated,and the concentration of TCCA was optimized while analyzing the destructive properties of TCCA surface modification.The results indicated that TCCA reacts with the SBR rubber substrate by chlorination and oxidation to achieve surface modification,increasing the surface energy of SBR rubber to 12.35 m J·m^-2after modification.Furthermore,cracks appeared on the surface of SBR rubber after modification,thereby increasing the roughness,and the density of cracks increased with the increase of TCCA modifier concentration.A chlorinated layer was produced on the surface of modified SBR rubber substrate,with a depth of approximately 10μm.Low concentrations of TCCA modifier（1～4 wt%）will not damage the main body of SBR rubber,and the best concentration of TCCA modifier is 3 wt%.The highest bond strength of polyurethane repair adhesive to SBR after modification can be increased from 0.51 N/mm to 6.92 N/mm.（2）In chapter 3 of the thesis,the poor adhesive performance of polyurethane repair adhesive to SBR rubber was addressed.Polytetrahydrofuran diol（PTMG-1000）with a regular molecular structure was selected as the soft segment and reacted with diphenylmethane diisocyanate（MDI）to prepare prepolymer,and 3,3’-dichloro-4,4’-diaminodiphenylmethane（MOCA）was used as the chain extender.The effect of the content of soft and hard segments on the room temperature curing performance,bonding performance and other properties of PTMG-MDI polyurethane repair adhesives was investigated.The results showed that as the hard segment content increased,the degree of microphase separation between soft and hard segments,carbonyl hydrogen bonding,surface energy,curing rate at room temperature,hardness,and bonding performance with modified SBR rubber all increased significantly for the PTMG-MDI polyurethane repair adhesive.Bounding strength reached up to 11.73 N/mm,and the tensile strength increased and then decreased,reaching up to 20.8 MPa.The peak loss,elongation at break,and wear resistance decreased significantly.The viscosity was adjusted by changing the solvent addition,and the influence mechanism of adhesive viscosity on the bonding performance was also analyzed.The results showed that the adhesion depth of PTMG-MDI polyurethane repair adhesive on the surface of SBR rubber substrate increased as the viscosity decreased,with the bonding performance between the two phases increasing and then decreasing.（3）In Chapter 4 of this thesis,a solution is proposed to address the issue of low strength and poor wettability of the PTMG-MDI system’s polyurethane repair adhesive.Oligomeric diols such as polycaprolactone diol（PCL,2000 molecular weight）,polytetrahydrofuran diol（PTMG）,polypropylene glycol（PPG）and terminal hydroxy polybutadiene（HTPB）with different types and molecular structures were selected,along with MDI,to synthesize four types of MDI system polyurethane repair adhesives with different soft segments:CPU-PCL,CPU-PTMG,CPU-PPG and CPU-HTPB.The effects of soft segment type and structure on the room temperature curing performance,adhesive performance and other properties of MDI system polyurethane repair adhesives were investigated.The results show that CPU-PCL possesses the best surface energy,curing rate,tensile strength,hardness and bonding performance to modified SBR rubber due to the presence of strong polar ester groups in its molecular structure.The elongation and abrasion resistance are also the best,while the wear resistance is the poorest.CPU-PPG,on the other hand,has the worst curing rate at room temperature,tensile property and bonding property to modified SBR rubber due to the side methyl group in the molecular structure,which negatively impacts structural regularly and molecular chain interactions,thereby failing to meet practical application requirements.Two groups of MDI-based polyurethane repair adhesives with different soft segment lengths were synthesized using 600,1000,and 2000 molecular weight PCL and PTMG as oligomeric diols,MDI as diisocyanate,and MOCA as a chain extender.The effects of the soft segment length i.e.,soft segment molecular weight,on the room temperature curing performance,adhesive performance and other properties were investigated.The results indicate that as the molecular weight of the soft segment phase increases,the flexibility of the molecular chain increases,but the molecular cohesion is affected,resulting in a significant decrease in the curing rate,adhesive strength,tensile strength,and hardness,and a significant increase in the elongation at break and wear resistance of the MDI-based polyurethane repair adhesives.