Patent Application: US-201414768137-A

Abstract:
the present describes wood adhesives reinforced with cellulose nanocrystals , in liquid and powder forms in which resin system are a phenol - formaldehyde polymer and / or lignin - phenol - formaldehyde polymer and polymeric methylene diphenyl diisocyanate , and a method of making this polymer in liquid and powder from and the composite products that can be produced therefrom .

Description:
for easier understanding , a number of terms used herein are described below in more details : “ lignin ” generally refers to a group of phenolic polymers that give strength and rigidity to plant materials . lignins are complex polymers , and tend to be referred to in generic terms . lignins may include , for example , industrial lignin preparations , such as kraft lignin , lignosulfonates , and organosolv lignin from by - products of bio - ethanol process , and analytical lignin preparation , such as dioxane acidolysis lignin , milled wood lignin , klason lignin , cellulolytic enzyme lignin , and etc . “ lignin component ” represents any lignin - containing materials . lignin component can be derived from industrial lignin preparation , analytical lignin preparation , and etc , which are from renewable resources , especially from lignocelluloses . the lignin component can be a material or compositions , which is modified or treated or purified portion of lignin . “ lignocelluloses materials ” include all plant materials . for example , materials include wood materials ( such as wood strands , wood fibers or wood chips or wood particles ), grass materials ( such as hemp or flax ), grain materials ( such as the straw of rice , wheat , corn ), and etc . a “ phenolic compound ” is defined as a compound of general formula aroh , where ar is phenyl ( phenol ), substituted phenyl or other aryl groups ( e . g . tannins ) and a lignin and combinations thereof . the phenolic compound may be selected from the group consisting of phenol , a lignin and combinations thereof . in a preferred embodiment the phenolic compound is phenol . in another preferred embodiment the phenolic compound is a combination of phenol and a lignin . starting materials are understood as all compounds and products added to produce the adhesive polymer disclosed herein . a formaldehyde compound may be selected from the group consisting of formaldehyde and paraformaldehyde and combinations thereof . the paraformaldehyde has the formula hoch2 ( och2 ) nch2oh , in which n is an integer of 1 to 100 , typically 6 to 10 . paraformaldehyde will be decomposed to formaldehyde before it methylolation reaction with phenol or lignin . “ cellulose nanocrystals ( cnc )” includes all cellulose nanocrystals made from different resources , such as wood ( softwoods and hardwoods ), plants ( for example , cotton , ramie , sisal , flax , wheat straw , potato tubers , sugar beet pulp , soybean stock , banana rachis etc ), tunicates , algae ( different species : green , gray , red , yellow - green , etc . ), bacterials [ common studied species of bacteria that produces cellulose is generally called gluconacetobacter xylinus ( reclassified from acetobacter xylinum )], and etc . cnc may also be defined as nanocrystalline cellulose ( ncc ). one such cellulose nanocrystals ( cnc ) are a cellulosic rod - like shaped nanomaterial and are extracted from a variety of naturally occurring cellulose sources such as wood pulp , cotton , some animals , algae and bacteria . nccs or cncs can be obtained by various processes but the most common extraction technique relies on a chemical hydrolysis of the cellulose source under harsh acidic conditions , which releases the rigid crystalline parts of the microfibrils . typical dimensions for cncs are generally from 3 to 20 nanometers in cross section and from several tens of nanometers up to several microns in length . cnc is characterized by a high degree of crystallinity with an axial ratio ranging generally between few tens up to several hundreds . the scope of the claims should not be limited by the preferred embodiments set forth in the examples , but should be given the broadest interpretation consistent with the description as a whole . phenol - formaldehyde ( pf ) resins are known to be prepared from two main chemicals that are reacted at elevated temperatures through methylolation and condensation to form a phenolic polymer . the polymer formation is strongly related to the molar ratio of phenol to formaldehyde , and the ph at which the reaction is carried out . the phenolic resin is called novolac resin when the molar ratio of formaldehyde to phenol is less than 1 and at low ph . the phenolic resin is called resol type when the molar ratio of formaldehyde to phenol is higher than 1 , and the ph is higher than 7 . resol type phenolic resins will crosslink , usually at elevated temperatures . the basic purposes of the present invention is 1 ) to incorporate cnc into phenol - formaldehyde resin system or lignin - phenol - formaldehyde resin system in liquid form or powder form , 2 ) to improve the bonding properties and mechanical properties of wood composites made with such formulations either in liquid form or powder form , and 3 ) to improve mechanical and thermal properties of cnc - phenol - formaldehyde molded products and / or cnc - lignin - phenol - formaldehyde molded products made with such formulations in powder form . more specifically , the collective purposes of the present invention are 1 ) to incorporate cnc into phenolic resin with low viscosity in liquid form and make cnc - phenolic resin in powder form through spray drying process , 2 ) to provide a process for preparing thermoset resin in powder form wherein a cnc is well distributed into lignin - phenol - formaldehyde resin and / or phenol - formaldehyde resin which cnc has strong intimate contact with lignin - phenol - formaldehyde resin and / or phenol - formaldehyde resin , which can be used as powder resin for wood composites and for molded components , 3 ) to incorporate cnc into phenolic resin ( either lignin - phenol - formaldehyde resin or straight phenol - formaldehyde resin ) in liquid form , which can be used for wood composites , and 4 ) to incorporate cnc into isocyanate and make cnc - isocyanate binder ( adhesive ) in liquid form for wood composites . below we described the general chemistry associated with forming the final resin mixtures . the first step of the process according to the invention consists of mixing lignin if applicable , with phenol , formaldehyde ( or paraformaldehyde ), and a base and letting the so obtained mixture react at elevated temperatures . the order of addition of the above starting compounds is not important , but it is preferred to load phenol first , then water , later on lignin , after that , formaldehyde in the form of para - formaldehyde , and then raise the temperature to 50 - 60 ° c ., and then load sodium hydroxide in the form of a solution containing 50 % by weight of sodium hydroxide . the so prepared mixture is heated to temperatures ranging between 60 - 75 ° c ., preferably ˜ 70 ° c ., for a period of 1 to 2 hours , for example . in this step , the methylolation reaction takes place in which formaldehyde reacts on the ortho position of the phenol and with available sites on the lignin . the second step of process according to the invention consists of loading more sodium hydroxide in the form of a solution containing 50 % by weight of sodium hydroxide in the system , and the temperature is maintained same as the first step . the period of time is , for example , 10 minutes to 1 hour . the methylolation reaction continues . such a two - stage processing is actually important . indeed , the same process could be made in only one stage at different temperatures , such as 80 - 95 ° c ., such processing may not produce the same resin , and the resin obtained in one stage may not have the same quality as the resin produced in two steps . the third step of process according to the invention consists of raising the temperature to 75 - 95 ° c . for condensation reaction of methylolated lignin with methylolated phenol , preferably 80 - 85 ° c . for a certain period of time . at this stage , controlling the reaction temperature is important . otherwise , a proper viscosity may not be achieved . the viscosity is varied for different applications , such as around 70 - 80 cps for spray drying to make powder resin , around 100 - 200 cps for osb with solids content around 45 - 50 %, around 250 - 3000 cps or over for plywood making . in applications , the amounts of raw materials added at each stage , the temperature at which the addition is carried out and / or the molar ratios of formaldehyde to phenol may vary depending on the needs . in practices , the molar ratio of formaldehyde to phenol preferably ranges from 1 . 8 : 1 to 3 . 0 : 1 . more preferably , the molar ratio ranges from 2 . 2 : 1 to 2 . 8 : 1 to achieve better results ; the weight ratio of base ( sodium hydroxide and / or potassium hydroxide ) to phenol or lignin ( if applicable ) ranges from 0 . 03 : 1 . 00 to 0 . 30 : 1 . 00 . more preferably , the weight ratio ranges from 0 . 08 : 1 . 00 to 0 . 15 : 1 . 00 to achieve better results . the fourth step of process according to invention consists of a ) preparing the cnc aqueous dispersion through soaking the required amount of cnc in water for a few hours to make sure the cnc is well dispersed in water ( it could become gel - like liquid if the cnc concentration reaches to ≧ 3 - 5 % wt ) with different methods , such as sonication , high shear mixing etc . ; b ) transferring pre - prepared cnc dispersion into phenol - formaldehyde resin ( pf ) or lignin - phenol - formaldehyde ( lpf ) resins and adjusting the solids content to 25 - 30 % wt through the addition of water if necessary ; c ) mixing the mixture of cnc - phenolic resin ( cnc - pf and / or cnc - lpf ) with a high shear mixer under 2000 rpm or higher for 10 min or sufficient time to obtain uniform cnc - pf ( post blending ) or cnc - lpf ( powdered cnc - pf and / or cnc - lignin - pf ) system . the fifth step of the process according to invention consists of converting the liquid cnc - lpf and / or cnc - pf system into a powder form with a certain feed rate ( depending on the capacity of the spray - dryer ). the outlet temperature was set at 85 - 95 ° c . through a pulverization spray dryer . it is also possible to add part of cnc dispersion in the first step of the process of mixing lignin if possible , with phenol , formaldehyde ( or paraformaldehyde ), and a base and letting the so obtained mixture react at elevated temperature , and continue with second , third steps of process . in this case , the cnc is incorporated with phenolic resin system via in - situ polymerization . it also can combine fourth step and fifth step of the process to convert the liquid cnc - lpf and / or cnc - pf system into powder form . the steps of the process according to the invention consist of similar first three steps as cnc - phenolic resin formulation in powder form described in previous section above except cnc was added in the first step in powder form . below we list some specific examples of the general chemistry just described . preparation of phenol - formaldehyde adhesive in liquid form for making powder resin in this example , all materials are counted by weight parts to prepare a formulation of phenol ( 98 %): 750 parts by weight , paraformaldehyde ( 91 %): 645 parts by weight , sodium hydroxide ( 50 wt %): 195 parts by weight , and water : 1550 parts by weight . the “ n ” value for formaldehyde is 1 to 100 , and preferably 6 to 10 . in a 4 - l reaction vessel , phenol , paraformaldehyde , and part of water ( 850 parts ) were added to make a medium having a solids content around 50 wt %. the system was heated to around 50 ° c ., and the first part of sodium hydroxide ( 75 parts ) was added . the system was heated to approximately 70 ° c . and was kept at this temperature for one and a half hours . subsequently , the second part of sodium hydroxide ( 60 parts ) and water ( 300 parts ) were added , with the temperature maintained at approximately 70 ° c . for another half an hour . afterwards , the temperature was increased to 80 - 90 ° c ., and the viscosity was monitored . when the viscosity of the resin system reached to 20 - 30 cps , ph was monitored and around 20 parts of sodium hydroxide ( 50 % wt ) were added to bring ph to over 10 . when the viscosity reached to 70 - 100 cps and ph around 10 . 4 , the reaction was terminated by cooling the reactor to approximately 30 ° c . the contents were transferred to a container and stored in a cold room for later use . the adhesive was coded pf . the viscosity of pf was 100 cps and the ph of the pf was 10 . 45 . preparation of lignin - phenol - formaldehyde adhesive in liquid form for making powder resin in this example , all materials are counted by weight parts to prepare a formulation of phenol ( 98 %): 660 parts by weight , kraft softwood lignin from black liquor ( prepared by pulp & amp ; paper division of fpinnovations ) ( partially oxidized kraft lignin obtained from the lignoforce system ™”) ( 90 %): 350 parts by weight , paraformaldehyde ( 91 %): 565 parts by weight , sodium hydroxide ( 50 wt %): 400 parts by weight , and water : 1730 parts by weight . in a 4 - l reaction vessel , phenol , kraft softwood lignin , paraformaldehyde , some of the sodium hydroxide ( 80 parts ), and some of the water ( 1400 parts ) were added to make a medium having a solids content around 50 wt %. the system was heated to approximately 70 ° c . and was kept at this temperature for one and a half hours . subsequently , the second portion of sodium hydroxide ( 100 parts ) and remaining water were added , with the temperature maintained at approximately 70 ° c . for another half an hour . afterward , the temperature was increased to 80 - 90 ° c ., and the viscosity was monitored . when the viscosity of the resin system reached to around 50 cps , some sodium hydroxide was loaded to being up the ph to over 10 . viscosity of resin was checked every 20 minutes . when the viscosity reached to 70 - 100 cps , the reaction was terminated by cooling the reactor to approximately 30 ° c . the contents were transferred to a container and stored in a cold room for later use . the adhesive was coded lpf . the viscosity of lpf was 97 cps and the ph of the lpf was 10 . 26 . another batch was synthesized under the same condition and two batches were mixed together . [ phenol ( 660 parts ), kraft softwood lignin ( 360 parts ), paraformaldehyde ( 565 parts ) mentioned in previous paragraph were loaded in except part of sodium hydroxide and part of water ]. the pf made in example 1 and lpf made in example 2 were used to prepare nano - crystalline cellulose - phenol - formaldehyde ( cnc - pf ) and cellulose nanocrystals - lignin - phenol - formaldehyde ( cnc - lpf ) adhesives through post - blending with cnc dispersion in phenolic resin and drying through a spray dryer . the lpf ( and / or pf ) was divided into several portions , in which one was used as a control , and other portions for adding different levels of cnc . the procedure is described as follows : 1 ) soaking and dispersing the required amount of cnc in water overnight ; 2 ) transferring cnc water dispersion into phenolic resin and adding water to solids content about 28 % ( detailed in table 1 ); 3 ) mixing the mixture of cnc - lpf in liquid form and / or cnc - pf in liquid form at a speed of 2000 rpm for 10 minutes with a high shear mixer to obtain uniformly distributed cnc - lpf or cnc - pf resin formulations ; 4 ) drying the uniformly distributed cnc - lpf and / or cnc - pf formulations with a pulverization spray dryer ( model : be - 1037 , series : bowen ) from incotech inc . ( bennières , quebec , canada ) ( outlet temperature of 88 - 91 ° c . and feed rate of 48 gram per minute ). ( please see table 1 for detailed information of cnc - lpf and cnc - pf powder ) three - layer osb panels were made with cnc - phenolic resins prepared in example 3 . these resins were only used in surface layers and 100 % commercial phenolic powder resin was used in the core layer , under the pressing conditions listed in table 2 . detailed information about the resins in surface and core layers is listed in table 3 . the physical and mechanical properties of osb panels , including 24 - h thickness swelling ( ts ), 24 - h water absorption ( wa ), internal bond ( ib ) strength , modulus of elasticity ( moe ) and modulus of rupture ( mor ) were measured according to csa o437 . 1 - 93 standard and the results are illustrated in tables 4 , 5 , and 6 . 1 average of 4 specimens per panel , in which two specimens were tested under top face up , and two specimens were tested under top face down , 1 average of 4 specimens per panel , in which two specimens were tested under top face up , and two specimens were tested under top face down . specimens were soaked in water at 20 ° c . for 24 hrs before testing . from table 4 , it can be seen that the addition of cnc into lignin phenolic resins could reduce the thickness swelling from 19 . 5 % for the osb made with pnclpf0 ( without cnc ) to 17 . 7 % for the osb made with pnclpf4 ( cnc : 3 . 90 %). the water absorption ( wa ) and internal bond ( ib ) strength were basically the same for the osb made with and without cnc . addition of cnc into phenolic resin did not significantly improve the moe and mor for the osb panels at dry conditions ( table 5 ); however , it improved the wet bending strength of the osb made with lignin phenolic resins from average values of 1528 mpa ( moe of osb made with pnclpf0 ) and 8 . 1 mpa ( mor of osb made with pnclpf0 ) to average values of 2172 mpa ( moe of osb made with pnclpf4 ) and 12 . 5 mpa ( mor of osb made with pnclpf4 ). cnc was formulated with phenol ( 99 wt %) 150 parts by weight ; formaldehyde ( 40 % wt %) 240 parts by weight ; sodium hydroxide ( 50 wt %) 55 parts , cnc ( powder ) 2 . 6 parts , and water 120 parts . in a 1 - l reactor vessel , phenol , one third of the caustic , two thirds of the water , and cnc were added and the system was heated to around 60 ° c . subsequently , one half of the formaldehyde solution was added over 30 minutes and another one fourth of water was added . at this point , the system temperature was raised to 65 - 70 ° c . and kept constant for 30 minutes . the temperature was then raised to 80 - 85 ° c ., kept at this level for one hour , and then decreased to 65 - 70 ° c . at this point , the remaining formaldehyde was added over 30 minutes as well as the remaining water . the system was kept at 65 - 70 ° c . for another 30 minutes . subsequently , the remaining sodium hydroxide was added and the temperature was kept at 80 - 85 ° c . until the required viscosity ( 350 cps ) was reached . the reaction was terminated by cooling the system with cooling water to around 30 ° c . the resulting products were transferred to a container and stored in a cold room ( 4 ° c .) before use . the adhesive was coded as cnc - pf . the cnc content was 1 wt % based on the solids content of the polymer adhesive . yellow birch veneer strips ( 1 . 5 mm thick × 120 mm wide × 240 mm long ) were cut from the veneer purchased from a local mill ( with the long direction being parallel to the wood grains ), and stored at − 30 ° c . for certain time , then conditioned at 20 ° c . and 20 % relative humidity ( rh ) for two weeks . the adhesive polymer formulations prepared above were applied to one side of each face layer ( the manufacturing condition for 3 - ply plywood panel making is given in table 7 ). after manufacturing , the panels were conditioned at 20 ° c . and 20 % rh until reaching consistent moisture content . these three - ply plywood samples were then cut into testing specimen sizes ( 25 mm wide × 80 mm long ) for a plywood shear test . at least thirty specimens were cut from each plywood panel . half of the specimens was tested in the pulled open mode while the other half of the specimens was tested in the pulled closed mode . the cross - section of the test samples was 25 mm by 25 mm . specimens were tested wet after 48 hours of soaking in 20 ° c . running water . it can be seen that the cnc - pf resin improved the bonding strength of 3 - ply plywood after 48 hours soaking , in which the average value of bonding strength increased by about 37 % comparing with the lab - synthesized pf resin ; cnc - pf resin also improved the bonding strength after boiling - drying - boiling treatment . the lignin based phenol - formaldehyde resin was synthesized under the condition similar to example 2 . however , the ph of the resin was about 11 . 4 . the cnc was post - blended with such resin as shown in table 9 . for all formulations , a high shear mixer was applied and all formulations were mixed at 2000 rpm for 15 minutes . cnclpf0 was the sample without cnc . cnclpf1 was prepared by : 1 ) dispersing cnc in water to make high concentration dispersion , and 2 ) adding the required lignin - phenol - formaldehyde resin in the cnc dispersion and 3 ) mixing them with a high shear mixer . cnclpf2 and cnclpf3 were prepared in the same way except cnc content : 1 ) directly adding the cnc in the resin , 2 ) using glass rod to mix cnc in resin , and 3 ) using a high shear mixer to obtain uniform formulation . the 2 - ply plywood samples with such formulations were made with cross - section of 10 mm by 20 mm . the temperature was 150 ° c . and the press time was 3 minutes . the detailed information on the panel making is listed in table 10 . after samples were made , and they were stored in a conditioning chamber for one week and then 5 specimens for each formulation were tested after 48 hour soaking in water ( around 20 ° c . ), and tested wet at a 10 mm / min speed using an mts testing machine . the testing results are shown in table 11 . from table 11 , it can be seen that adding cnc in lignin - pf resins through post - blending can improve the wet shear strength , in which the average value increased by about 13 . 6 % with 1 . 94 % cnc in the resin ( no . 3 in table 11 ), and 18 . 1 % with 3 . 5 % cnc in the resin comparing with control ( no . 1 in table 11 ). the cnc - pf powders in table 1 coded ppf0 , ppf1 and ppf3 were used . the electric press with dimension of 12 inches by 12 inches was used to make the molded products under 150 ° c . for 3 . 5 minutes with aluminum mold of 6 - 7 mm in width , 50 mm in length , and 1 mm in thickness . the thermo - mechanical properties were evaluated by dynamic mechanical analyzer ( dma q 800 from ta instruments ) with following conditions : in dynamic mold , frequency of 1 hz , strain of 0 . 1 %, and heating rate of 10 ° c ./ min from 25 ° c . to 250 ° c . the storage moduli of these materials are illustrated in fig1 . from fig1 , it can be seen that with addition of small amount of cnc could significantly improve the storage modulus , in which 0 . 5 % wt cnc increased the modulus by 25 %- 30 % in different temperatures ( from 30 ° c . to 210 ° c . ), and 2 . 0 % wt cnc increased the modulus by 48 %- 51 % in different temperatures ( from 30 ° c . to 210 ° c .) the first step of process according to invention consists of a ) preparing the cnc aqueous dispersion through soaking the required amount of cnc in water for a few hours to make sure the cnc is well dispersed in water ( it could become gel - like liquid if the cnc concentration reaches to ≧ 3 - 5 % wt ) with different methods , such as sonication , high shear mixing etc . ; b ) transferring pre - prepared cnc dispersion into polymeric mdi via mechanical mixing to form stable uniform cnc - pmdi emulsion system and adjusting the active component content to 40 - 70 % wt through the addition of water if necessary . the spray - dried ncc powder was dispersed in water at different concentrations ( 0 . 5 %- 1 . 5 %) by magnetic mixing , followed by mechanical mixing and ultrasonic mixing at room temperature . the resulting ncc suspensions were characterized as follows : 1 ) viscosity measured by a viscometer ( brookfield — lvt ), 2 ) turbidity measured with a micro 1000 ir turbidimeter ( scientific inc . company ), and 3 ) birefringence ( a specific property of non - aggregated ncc ) checked under polarized light . cnc suspension was mixed with emulsifiable pmdi , i - bond ® mdf em 4330 from huntsman ( here after e - mdi ) with different ratio of cnc aqueous dispersion to e - mdi based on actual weight via mechanical means . the mixture of cnc - e - mdi emulsion is stable for certain period time . an automated bond evaluation system ( abes ) was used to evaluate the bond strength development of ncc / e - mdi resin as a function of time at 120 ° c . measured by abes . the test conditions with abes are given as : a . veneer : 117 × 20 × 0 . 7 mm aspen b . bonding area : 5 mm × 20 mm c . cnc dosage in glue : 2 % cnc based on e - mdi d . assembly time : no e . pressing : 120 ° c . for 30 - 90 seconds f . replicate : 5 at each bonding condition the sodium forms of cnc , spray - dried cnc ( code sd cnc ), and freeze - dried cnc ( code fd cnc ), were dispersed in water first and then incorporated with e - mdi at loading level of 0 . 5 - 1 . 0 % wt . based on e - mdi weight ( same as example 8 ). the resulting adhesives ( or binders ) are used to manufacture strand boards . the panel manufacturing conditions are listed as follow : target mat moisture : 6 . 5 - 7 . 5 % in face layer and 5 - 7 % in core layers slack wax content : 1 . 0 % ( on a dry wood basis ) in face and core layers resin content in face : 2 . 5 % e - mdi with / without cnc ( on a dry wood weight ) resin content in core : 2 . 5 % regular polymeric mdi ( on a dry wood weight ) target board density : 624 ± 24 kg / m 3 ( 39 ± 0 . 5 lb / ft 3 ) ( oven dry basis ) all strand board were conditioned in a chamber at 65 % rh and 20 c until they reached the equilibrium moisture contents prior test . the internal bond ( ib ) strength , thickness swelling ( ts ) and water absorption ( wa ) of 24 hour soaking in running water at 20 ° c ., dry modulus of rupture ( mor ) and modulus of elasticity ( moe ), and wet mor and moe after 24 hour running water soaking according cas o437 - 93 standard . the mechanical properties of strand board made with e - mdi with / without cnc is illustrated as below : it can be seen that addition of cnc into polymeric mdi can improve wet flexural strength ( mor ) and also moe . addition of cnc could also reduce the thickness swelling ( ts ) and water absorption ( wa ). araki j ., wada m ., kuga s ., and t . okano ( 1998 ). low properties of microcrystalline cellulose suspension prepared by acid treatment of native cellulose . colloids surf . a , 142 : 75 - 82 auad , m . l ., v . s . contos , et al . 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