Bonding Mechanism And Properties Of Modified Aluminum Phosphate/wood-based Materials

This study prepares a modified aluminum phosphate adhesive,which was made of Al₂(OH)₃ and H₃PO₄ as the main raw materials,H₃BO₃ as curing,phenol-added polyvinyl formal polymer(PFPVA)as an auxiliary agent,to cope with the more strict limitation applied to the formaldehyde emission of the wood-based board.To prepare this adhesive,the following four aspects were studied in this thesis.Part 1:Preparation and evaluation of the performance of aluminum phosphate(ALPO)made of different P/Al molar ratios.The discussion of the bonding mechanism and performance of ALPO/wood-based board.Part 2:H₃BO₃(BA),as curing,can be used for preparing boric modified aluminum phosphate(BALPO).The effects of H₃BO₃on adhesive characters,bonding mechanism,and wood-based board performance are discussed.Part 3:Polyvinyl alcohol(PVA),as an auxiliary agent,can be used for preparing PVA-added BALPO(PVA-BALPO).The effects of PVA on adhesive characters,bonding mechanism,and wood-based board performance are discussed.Part4:Preparation of phenol-added polyvinyl formal polymer(PFPVA)by PF resin and acetalized PVA.PFPVA,as an auxiliary agent,can be used for preparing PFPVA-added BALPO(PFPVA-BALPO).The influence of PFPVA characters on the bonding mechanism and wood-based board properties is analyzed.The main conclusions are as follows:1)ALPO with better performance was prepared while the P/Al molar ratio,temperature,and reaction time were 2.6:1.0,110-120?,and 30 minutes,respectively.The plywood was obtained while the temperature,time,pressure,and resin content were 160?,1.0 min/mm,1.2 MPa,and 200 g/m²(double-sided),respectively.Its bonding strength meets the demands of Type III plywood in the national standards GB/T 9846-2015.IB of particleboard meet the demands of Type P1 particleboard of the national standards GB/T 4897-2015,except for MOR.2)BALPO with better performance was prepared while an H₃BO₃ content of 4g/100 ml ALPO(60?63%solid content)was added to the 1)ALPO formula.The bonding strength of plywood meets the demands of Type III plywood in standards GB/T9846-2015.MOR and IB of particleboard meet the demands of Type P1 particleboard of the national standards GB/T 4897-2015.3)PVA-BALPO with better performance was prepared while a 20%PVA content(percentage of total resin content)was added to the 2)BALPO formula.The bonding strength of plywood meets the demands of Type III plywood in standards GB/T 9846-2015.MOE,MOR,IB,and TS₂ of particleboard meet the demands of Type P2particleboard of the national standards GB/T 4897-2015.4)PFPVA-BALPO with better performance was prepared while a 20%PFPVA content(percentage of total resin content,PF content accounts for 8%)was added to the 2)BALPO formula.The bonding strength of plywood meets the demands of Type II plywood in standards GB/T 9846-2015.MOE,MOR,IB,and TS₂ of particleboard meet the demands of Type P2 particleboard of the national standards GB/T 4897-2015.The formaldehyde emission of particleboard meets the demands of E₁ level of the national standards GB/T 18580-2017.5)Modified aluminum phosphate:The main components of ALPO adhesive include ALPO4,Al(H₂PO₄)₃,ALPO-36(include crystal water),and P₂O₅,its crystal becomes 95.0%;H₃BO₃ connected with ALPO in the form of[BO4]tetrahedrons and generated BPO4,a tiny amount of un-reacted H₃BO₃ exists as B₂O₃.This also resulted in a decrease of Al(H₂PO₄)₃,ALPO-36,P₂O₅ content with a lower crystallinity of BALPO.PVA was combined with BALPO by hydrogen bond and C-O-P bond,which limited the crystal growth of BALPO structure,thus resulting in a significant decrease of crystallinity of PVA-BALPO structure.A PFPVA-BALPO based interpenetrating polymer network(IPN)was prepared via in-situ copolymerization of mixed PFPVA with BALPO,which significantly reduces the crystallinity of the PFPVA-BALPO composite structure.6)Bonding mechanism:ALPO was combined with cellulose or hemicellulose mainly by a hydrogen bond.More specifically,there was an esterification reaction between the adhesive and cellulose/hemicellulose,and part of lignin was degraded and then combined with ALPO by C-O-P bond.The reduction in the degradation of lignin was attributable to fewer unreacted phosphate from BALPO structure because of the reaction of BA and ALPO.The esterification reaction of PVA and BALPO could further reduce the number of unreacted phosphates.A PFPVA-BALPO based IPN structure was prepared by the moisture-resistant PFPVA and BALPO,which minimize the hydrolysis of phosphoric,to avoid the degradation of lignin.Thus,PFPVA-BALPO could connect with wood in the manner of a"glue nail".7)Combustion performance of particleboard:ALPO showed a good flame-retardancy and smoke suppression performance,which can promote the rapid dehydration and carbonization of the surface parts of wooden substrate,and form a composite carbon layer with it,thus effectively reducing heat transfer and smoke production efficiency and hinder the sustained combustion of the wooden unit.