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Polyurethane foams from renewable and sustainable polyols Noemi Finez Acero noemi.fi[email protected] Instituto Superior T´ ecnico, Lisboa, Portugal July 2014 Abstract The aim of this thesis is the production of polyurethane foams with polyols from liquefied wood. The objective is to find the best combination of appropriate properties to polyurethane foams with maximum content of polyols from wood liquefaction to decrease the price and make the foam envi- ronmentally friendlier. First of all, experimental work began with the optimizing of wood liquefaction reaction. This part was performed with different type of catalysts in order to find the best yield results and the cheapest catalyst at industrial level. Next was carried the extraction of the polyols in order to eliminate the sugar molecules present in liquefied wood, as consequence of the breaking of bonds in cellulose, lignin and hemicellulose through depolymerization. The polyols were characterized with the determination valor OH and acid value and the spectroscopic technique ATR-FTIR. In the second part of this thesis was obtained the foams which presented good results when compared with commercial foams and include polyols from of fossil fuels. The formulation of the foams should be improve, but the results show that is possible the use polyols from liquefied wood for produce industrial foams with lower cost. Keywords: liquefaction, liquefied wood, extraction, polyols, catalyst, polyurethane foams. 1. Introduction Biomass is naturally occurring organic material that can be used as a renewable feedstock for the production of chemicals and fuels. The most abundant biomass is lignocellulosic, which is the major component of cell walls of plants and can be used as an alternative to fossil fuels. (Green Chem.[2013]) Nowadays some products made from fossil fuels are an emergent problem, as consequence of their nature and lower biodegradability. Con- version technologies refer to a wide array of state- of-the-art technologies capable of converting unre- cyclable solid waste into useful products, such as green fuels and renewable energy, in an environ- mentally beneficial way. The aim of this thesis is utilizing liquefaction conversion technology to liq- uefied wood. This method gives the possibility for the obtention of a product which can be used to produce materials and fuels.([8]) The most familiar and accessible biomass lignocellulosic feedstocks are wood, algae, municipal solid waste, sewage sludge and scraps from paper.([15]) With the polyols obtained from the liquefied wood were produced polyurethane foams for iso- lation uses. These polyols are an environmen- tally conscious alternative to the depleting fossil resources and the catalytic transformation of the constituents of lignocellulose to this value added chemical has attracted a lot of attention because it is presented as an environmentally attractive and energy efficient process compared to the currently used high temperature and energy consuming in gasification or pyrolysis technologies. Also the use of these polyols decreases the price of the foam and makes it more biodegradable. But it is necessary to take into account that the polyols have to satisfy some structural requirements in order to compete with petrochemical polyols, such as the right func- tionality and molecular weight. 2. Conversion technologies Conversion technologies refer to a wide array of bi- ological, chemical, thermal (excluding incineration) and mechanical technologies capable of converting different kinds of biomass into useful products and chemicals, green fuels such as hydrogen, natural gas, ethanol and biodiesel, and clean, renewable en- ergy such as electricity. Utilization of conversion technologies can be used to transform solid waste which can reduce greenhouse gas emissions, reduce dependence of imported fossil fuels and enhance re- cycling efforts.([9]) 2.1. Thermochemical conversion Thermochemical biomass conversion includes a number of possible methods, such as, pyrolysis, gasification, and liquefaction, to produce fuels and 1

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  • Polyurethane foams from renewable and sustainable polyols

    Noemi Finez [email protected]

    Instituto Superior Técnico, Lisboa, Portugal

    July 2014

    Abstract

    The aim of this thesis is the production of polyurethane foams with polyols from liquefied wood.The objective is to find the best combination of appropriate properties to polyurethane foams withmaximum content of polyols from wood liquefaction to decrease the price and make the foam envi-ronmentally friendlier. First of all, experimental work began with the optimizing of wood liquefactionreaction. This part was performed with different type of catalysts in order to find the best yield resultsand the cheapest catalyst at industrial level. Next was carried the extraction of the polyols in order toeliminate the sugar molecules present in liquefied wood, as consequence of the breaking of bonds incellulose, lignin and hemicellulose through depolymerization. The polyols were characterized with thedetermination valor OH and acid value and the spectroscopic technique ATR-FTIR. In the second partof this thesis was obtained the foams which presented good results when compared with commercialfoams and include polyols from of fossil fuels. The formulation of the foams should be improve, butthe results show that is possible the use polyols from liquefied wood for produce industrial foams withlower cost.Keywords: liquefaction, liquefied wood, extraction, polyols, catalyst, polyurethane foams.

    1. Introduction

    Biomass is naturally occurring organic materialthat can be used as a renewable feedstock forthe production of chemicals and fuels. The mostabundant biomass is lignocellulosic, which is themajor component of cell walls of plants and canbe used as an alternative to fossil fuels. (GreenChem.[2013]) Nowadays some products made fromfossil fuels are an emergent problem, as consequenceof their nature and lower biodegradability. Con-version technologies refer to a wide array of state-of-the-art technologies capable of converting unre-cyclable solid waste into useful products, such asgreen fuels and renewable energy, in an environ-mentally beneficial way. The aim of this thesis isutilizing liquefaction conversion technology to liq-uefied wood. This method gives the possibility forthe obtention of a product which can be used toproduce materials and fuels.([8]) The most familiarand accessible biomass lignocellulosic feedstocks arewood, algae, municipal solid waste, sewage sludgeand scraps from paper.([15])

    With the polyols obtained from the liquefiedwood were produced polyurethane foams for iso-lation uses. These polyols are an environmen-tally conscious alternative to the depleting fossilresources and the catalytic transformation of theconstituents of lignocellulose to this value added

    chemical has attracted a lot of attention becauseit is presented as an environmentally attractive andenergy efficient process compared to the currentlyused high temperature and energy consuming ingasification or pyrolysis technologies. Also the useof these polyols decreases the price of the foam andmakes it more biodegradable. But it is necessaryto take into account that the polyols have to satisfysome structural requirements in order to competewith petrochemical polyols, such as the right func-tionality and molecular weight.

    2. Conversion technologies

    Conversion technologies refer to a wide array of bi-ological, chemical, thermal (excluding incineration)and mechanical technologies capable of convertingdifferent kinds of biomass into useful products andchemicals, green fuels such as hydrogen, naturalgas, ethanol and biodiesel, and clean, renewable en-ergy such as electricity. Utilization of conversiontechnologies can be used to transform solid wastewhich can reduce greenhouse gas emissions, reducedependence of imported fossil fuels and enhance re-cycling efforts.([9])

    2.1. Thermochemical conversion

    Thermochemical biomass conversion includes anumber of possible methods, such as, pyrolysis,gasification, and liquefaction, to produce fuels and

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  • chemicals.

    2.1.1 Gasification

    Gasification converts biomass through partial ox-idation into a gaseous mixture of syngas consist-ing of hydrogen H2, carbon monoxide CO, methaneCH4 and carbon dioxide CO2. The oxidant can besteam, CO2 or their mixtures, with a small amountof air, and it is the main parameter affecting thesyngas composition. Air is the most used gasify-ing agent, due to the great availability and no cost,but the large amount of nitrogen requires higherpower on blowers and bigger equipment and espe-cially lowers the heating value of the syngas pro-duced. Pure O2, avoiding the nitrogen content, in-creases the syngas heating value but also the oper-ating costs due to the O2 production. Steam, dueto the great availability and about zero cost of wa-ter, increases the heating value and H2 content ofsyngas, and can be produced using the excess ofheat of the power plant. The syngas can be used inturbines and boilers or as feed gas for the produc-tion of liquid alkanes by FischerTropsch Synthesis.([10])Gasifiers can be divided into two main fami-lies, fixed bed (from which are derived the movingbed) and fluidized bed. Within the fixed bed gasi-fiers it is possible to distinguish updraft configura-tion when biomass move from the top and the gasi-fying agent from the bottom; downdraft configura-tion (concurrent), when the biomass and the gasify-ing agent move together from the top to the bottomof the reactor; crosscurrent when the biomass movesdown and the agent is fed at right angles.([12])

    2.1.2 Pyrolysis

    Pyrolysis is a thermal decomposition process thatoccurs in the absence of oxygen or when signifi-cantly less oxygen is present than required for com-plete combustion. The rate of thermal decomposi-tion depends on biomass particle size and type, aswell as, the heating rate, final temperature, reactorconfiguration and presence of impurities.Pyrolysisof biomass is a promising route for the productionof solid (char), liquid (tar), and gaseous productsas possible alternative sources of energy and chem-icals. The yield of these products can be changedby selecting appropriate heating rates and pyrol-ysis temperatures.Production of liquid products ismaximum at temperatures between 352C and 452C.Low temperatures and high residence times favorthe production of char, while the higher temper-atures and short residence times lead to high liq-uid production. Depending on the operating con-ditions, the pyrolysis process can be divided intothree subclasses: conventional pyrolysis, fast py-rolysis and flash pyrolysis. In the conventional

    pyrolysis the biomass is heated slowly to producechar as a major product. At present, the preferredtechnology is fast or flash pyrolysis at high tem-peratures with very short residence times. In fastpyrolysis, biomass is heated rapidly in the absenceof oxygen, and it decomposes as vapours, aerosols,gases and char. Fast pyrolysis (more accuratelydefined as thermolysis) is a process in which thebiomass is rapidly heated to high temperatures inthe absence of air. If the aim is the production ofmainly liquid and/or gaseous products a fast py-rolysis is recommended. Fast pyrolysis processesproduce 6075 wt.% of liquid bio-oil, 1525 wt.% ofsolid char, and 1020 wt.% of noncondensable gases,depending on the feedstock used. If the purposewere to maximize the yield of liquid products re-sulting from biomass pyrolysis, a low temperature,high heating rate, short gas residence time processwould be required. If the purpose were to maxi-mize the yield of fuel gas resulting from biomass py-rolysis, a high temperature, low heating rate, longgas residence time process would be preferred.([11])The liquid bio-oil produced by fast pyrolysis has theconsiderable advantage of being storable and trans-portable, as well as the potential to supply a num-ber of valuable chemicals that offer the attraction ofmuch higher added value than fuels. The vapoursand aerosols can be quickly condensed to liquidcalled bio-oil. The flash pyrolysis of biomass isa promising route with regard to the production ofsolid, liquid (bio-oil or bio-crude-oil) and gaseousproducts as possible alternate energy sources. Up-grading by lowering the oxygen content and remov-ing alkalis by means of hydrogenation and catalyticcracking of the oil may be required for certain ap-plications . Major problem of the present reactorsfor flash pyrolysis are the quality and the stabilityof the produced oil, strongly affected by char/ashcontent of bio-oil. Besides the known problems con-cerning solid particles in the bio-oil, char fines willcatalyze repolymerization reactions inside the oil re-sulting in a higher viscosity. The flash pyrolysis ofbiomass inherently results in the production of py-rolytic water, which is one of the major drawbacksof the bio-oil produced. ([14])

    2.1.3 Liquefaction

    Lignocellulose is a complex, macromolecular poly-mer composed through the cross-linking of CO andCC bonds in its three primary constituents: cel-lulose, hemicellulose, and lignin. Through lique-faction, lignocellulosic components are brought tolow molecular weight compounds with high reactiv-ity that can be used in many useful potential ap-plications. To separate the primary constituentsand keep their respective structural units intact,cracking lignocellulose macromolecules can be per-

    2

  • Figure 1: Products from pyrolysis. Source: Energyproduction from biomass (part 2): conversion tech-nologies.Peter McKendry

    formed. ([8]) Liquefaction technique can be done inthe presence of organic solvents (phenols or polyhy-dric alcohols) using acidic or alkaline catalyst (or-ganic or inorganic) at temperatures ranging from120 to 180C, or without catalyst at higher tempera-tures ranging from 180 to 250C. Recently, also othersolvents, such as cyclic carbonates,lower alcoholsand dioxane were examined and used successfullyfor the liquefaction of woody biomass.([4]) Catalyticliquefaction has attracted a lot of attention due toits simple operation, high production level and highenergy conversion and because it is presented as anenvironmentally attractive and energy efficient pro-cess compared to the currently used high tempera-ture and energy consuming gasification or pyrolysistechnologies. That is the reason why in this projectthe conversion of the lignocellulosic biomass (wood)is produced by catalytic liquefaction.Depending of the final use of the liquefied woodis chose the kind of liquefaction reaction, and thereagents. Is important to bear in mind that phenolis damaged to the environment. Also is importantto make sure that the selected temperature of thereaction is compatible with the boiling point of thesolvents. It is necessary to choose the time and thetemperature of the reaction carefully, to obtain thebiggest yield of liquefaction possible. As larger thetime and temperature of the reaction are as largerthe percentage of liquefaction is. But if the temper-ature is too high the spending of energy is biggerand part of the components from the liquefactionvolatilize. Also if the temperature is too high startsa reaction of condensation of the liquefaction prod-ucts. Both situations reduce the percentage of liq-uefaction. The residue from liquefaction products isthe major factor in the evaluation of the efficiency

    of lignocellulosic liquefaction. ([13])

    2.1.4 Uses of liquefied wood

    In this moment there are a lot of interest in theproduction of liquefied wood because it can be usein different fields. The first one in be investigatedwas the use of the liquefied lignocellulosic biomassto obtain adhesives and other polymers, after thatthe efforts starting to focus to produce fuel. But itis even possible get products for the alimentary in-dustry (sugars). The hydroxyl groups from liquefiedwood components can be used as polyols to producepolyurethane foams, polyurethane resin precursors,phenolic resin and adhesives among the more im-portant uses.The obtaining of the polyols from liq-uefied wood can be reproduced in the industry withlow cost, then it means that they are an interest-ing substitute for polyols from petroleum, but thewood’s polyols have to satisfy some structural re-quirements in order to compete with petrochemicalpolyols, such as the right functionality and molecu-lar weight. ([5])In this case the polyols obtained from liquefiedwood were used to produce polyurethane foam.

    3. Wood: chemical characteristicsWood biomass is comprised of C, H, O and N,and also little quantities of Ca, K and Mg. Thecomponents of lignocellulosic biomass include cel-lulose, hemicellulose, lignin, extractives, lipids, pro-teins, simple sugars, starches, water, hydrocarbons,ash, and other compounds. Cellulose is the ma-jor chemical in wood, it is a linear polymer com-posed of repeating anhydroglucose units. Celluloseis a remarkably pure organic polymer, consistingof units of anhydroglucose held together in a giantstraight chain molecule.These anhydroglucose unitsare bound together by beta-(1,4)-glycosidic link-ages. By forming intramolecular and intermolecu-lar hydrogen bonds between OH groups within thesame cellulose chain and the surrounding cellulosechains, the chains tend to be arranged parallel andform a crystalline supermolecular structure. Then,bundles of linear cellulose chains form a microfibrilwhich is oriented in the cell wall structure. Cel-lulose is insoluble in most solvents and has a lowaccessibility to acid and enzymatic hydrolysis. Dueits crystallinity is the less susceptible to the lique-faction. ([2])

    Hemicellulose is the second major chemicalspecies in wood. They are amorphous polysaccha-rides, such as xylans, galactoglucomannans, ara-binogalactans, glucans, and galactans. The hemi-celluloses, unlike cellulose, not only contain glu-cose units, but they are also composed of a num-ber of different pentose and hexose monosaccha-rides. Hemicelluloses tend to be much shorter in

    3

  • Figure 2: Schematic illustration of building units ofcellulose.

    length than cellulose, and the molecular structureis slightly branched. Because of the amorphousmorphology, hemicelluloses are partially soluble orswellable in water. Hemicellulose act as the cementmaterial holding together the cellulose micelles andfiber. Among the most important sugar of thehemicelluloses component is xylose. In hardwoodxylan, the backbone chain consists of xylose unitswhich are linked by beta-(1,4)-glycosidic bonds andbranched by alpha-(1,2)-glycosidic bonds with 4-Omethylglucuronic acid groups. For softwood xy-lan, the acetyl groups are fewer in the backbonechain. ([2])Lignin is a chemical compound that is most com-

    Figure 3: Schematic example of one possible xylanstructure (xylan are a group of hemicelluloses).

    monly derived from wood and is an integral part ofthe cell walls of plants. Lignin is a complex, highmolecular weight (in excess of 10.000 amu) polymerbuilt of hydroxyphenylpropane units. It is a com-pletely different polymeric material, being highlycross linked and having phenolic like structures asthe monomeric base. The molecule consists of var-ious types of substructures that appear to repeatin random manner. The polysaccharide compo-nents of plant cell walls are highly hydrophilic andthus permeable to water, whereas lignin is more hy-drophobic. The crosslinking of polysaccharides bylignin is an obstacle for water absorption to the cellwall Lignins are polymers of aromatic compounds.Lignin is covalently linked with xylans in the caseof hardwoods and with galactoglucomannans in thecase of softwoods. ([2])

    4. Polyurethane

    Polyurethanes (PUs) are a very large family ofmaterials. The reaction between isocyanate andhydroxyl compounds was identified in the 19 thcentury, the foundations of polyurethanes industry

    Figure 4: Schematic illustration of building units oflignin.

    Figure 5: Structure of lignocellulose. Source: Ge-nomics of cellulosic biofuels. Nature 454, 841845(2008).

    were laid in the en of the 30’s; Otto Bayer and hiscoworkers at I.G. Farben in Leverkusen, Germany,first made polyurethanes in 1937.

    4.1. Polyurethane’s marketThe request for polyurethane is mainly generatedby increasing demand from construction industrydominated by Asia. The product value chain startswith feed stock material until the end-use. Thepolyurethane market is segmented based on producttypes such as flexible foam, rigid foam, coatings, ad-hesives and sealants and elastomers; based on end-use as furniture and interiors, construction, auto-motive, electronics and appliances, footwear, pack-aging; and based on geography into Europe, NorthAmerica, Asia Pacific and Rest of the World.([3])

    4.2. Polyurethane’s chemistryPUs come from the reaction between polyol (alco-hol containing multiple OH groups) and isocyanate(NCO functional group). The result is a polymerwith a multiple urethane groups (-NH-COO-). Theprinciple of the polymer chemistry of the PU reac-tion is the extension of to di and polyfunctional iso-cyanates and hydroxyl compounds resulting in theformation of linear, branched or cross linked poly-

    4

  • mers. The isocyanate reacts also with water (2:1),this is responsible of the foaming of urethane poly-mers in the production of foams by the liberationof carbon dioxide and the simultaneous formationof urea groups (during cure process).

    4.3. Polyurethane foams

    Flexible foams are the largest market segmentpolyurethanes and can be obtained in block ormolded. They can be produced with different den-sities and applied mainly in the production of mat-tresses and car seats. Rigid foams are the secondmost important market polyurethanes. They areused as thermal insulation in household appliancesand in the building construction. Polyurethanesare a large family of polymers with very than theyhave in common the presence of repeating urethanegroups in their molecular structure. They are pre-pared from the polyol component and isocyanates.Currently, for this application, only the productionof polyol from renewable resources is reported. Al-though aliphatic di-isocyanates from dimerizationof fatty acids are commercial, they do not have suf-ficient reactivity for application in foams, but theycould be used for coatings and other applications.Thus, isocyanate for foams must be aromatic. But,polyols from different kinds of biomass, for examplefrom wood, have an excellent chance for competingwith petrochemical polyols in quality and especiallyin price of production. ([16])

    4.3.1 Types of production

    There are two different ways to prepare thepolyurethanes: one shot method and prepolymermethod. The first one consists in the reaction ofthe isocyanate with the other components. In theprepolimer method, the isocyanate reacts at firstwith the polyol to make the prepolymer. After thatthe prepolimer reacts with the other components toobtain the final polymer. ([1])

    5. Experimetal5.1. Reagents

    Wood chips and sawdust from pine wood were usedas a raw material. DEG, 2-Ethylhexanol from thechemical company Sigma Aldrich were used as areagents.In the reaction of PU foams B8871, DMDEE,TCPP, TEP, Safron 6605, DP45, DME, Voranol1010L, MPG, GA13 VTA, TDI TX, Propane andIsobutane were used as a reagents.

    5.2. Pretreatment

    At least 12 hours before of doing the reaction isnecessary to impregnate the wood spraying solventsor liquefied wood.

    5.3. Liquefaction reactionThe liquefaction was carried in a wide-necked reac-tion flask, equipped with a multiple socket lid andstarring head and proper stirring shaft, thermopar,a Dean-Stark separator/condenser and a solid drop-ping funnel; the wood/solvent mixture and the cat-alyst were placed in the reaction flask. The flaskwas put on a heating mantle and preheated at 160C.The liquefaction was conducted under constant stir-ring and reflux until it finished. After the reaction,the product was leave to cool until 80C. The result-ing reaction mixture filtered in a kitasato apparatusuntil colourless filtrate was obtained. The liquefiedresidue collected, was dried in oven at 120C to untilconstant weight was verified, for the determinationof the liquefaction yield (α) in mass terms.

    α = (100 − WfWi

    ) ∗ 100 (1)

    In the expression Wf is the final weight, after driedthe residue and Wi is the initial weigh of the wood.

    5.4. ExtractionTo produce polyurethane foams the sugars from theliquefied wood were extracted. This procedure al-lows to improve the reaction with the isocyanate toproduce polyurethane. The extraction was carriedout in a decanter flask where the liquefied woodwith more or less the same quantity of water wasmixed and stirred.

    5.5. One component foam technologyThe one component foams foaming process has gen-erally 4 stages as shown in figure 6. Three different

    Figure 6: Schematic diagram of foaming process.

    compositions of foams were done.

    5.6. CharacterizationIn order to do the characterization of the liquefiedwood and its polyols, the following experimentaltest were realized: Acid value, hydroxyl number,ATR-FTIR, and SEM.

    5.6.1 Acid and OH values

    The experimental method used to obtain acid andOH values is not explained because it is confidential.

    VAcid =vKOH 5, 61

    mSample(2)

    VOH =(blank − vKOH) 0, 5 56, 1

    mSample+ VAcid (3)

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  • 5.6.2 SEM

    Scanning electron microscopy (SEM) observationsof wood powder and liquefaction residue andpolyurethane foam, were micrographed on a HitachiS-2400 equipment, with a 15 kV beam. Sampleswere sputter coated with a thin layer of gold toavoid electrostatic charging during scanning.

    5.6.3 Attenuated total reflectance-Fourier trans-form infrared (ATR-FTIR)

    FTIR spectra were recorded on a Nexus-ThermoNicolet spectrometer (64 scans and resolution of 4cm-1 ) in the 4000400 cm-1 range.

    5.6.4 Quick tests

    The three different compositions were evaluatedby the research center of the company Greenseal.The properties of a foam can be analysed throughthe Quick tests. The foam samples were obtainedthrough two different dispensing procedures: Foambead on paper and on mould. The rating is givenvisually. The tests are doing in two different tem-perature conditions: 23C and 5C.

    6. Results and discussionIn this section are showed the results from thecharacterization of the obtained liquefied wood andpolyurethane foams.

    6.1. Characterization of polyols from liquefied woodIn order to do the characterization of the polyolsobtained from the liquefied wood, the following ex-perimental test were realized: Acid value, hydroxylnumber, ATR-FTIR.

    6.1.1 Acid and OH value

    The acid value and the hydroxyl number are ob-tained to calculate the average molecular weight.The hydroxil number is also important to know thenecessary amount of isocyanate. Higher OH num-bers usually increase the cost of the formulation dueto higher isocyanate consumption.

    ¯PM =f 56100

    VOH + VAcid(4)

    In the expression f is the funcionality, VOH is thehydroxyl value and VAcid is the acid value. Thefuncionality is consider 2,5 as a medium valuebetween 2 (lineal structure of the molecules) and 3(branched structure).

    Results found in literature ([17],[18],[6]): the re-sults for polyols from liquefied wood suggest biggerhydroxyl value 10931323 mg KOH/g and acid valuedeterminate was 7.38.0 mg KOH/g. In this thesisthe hydroxyl value is much more low because the

    Table 1: Average molecular weight calculated fromVOH and V acid

    PM f VOH Vacid3605.769 2.5 34.408 4.488

    extraction of the sugars was done. It is importantto note that the molecules in biopolyols have plentyof primary hygroxyl groups, including sugar, whichindicate these products should have good reactivitywith isocyanate, however to much hydroxyl groupsconfer more rigidness to polyurethane foam. Thephysical and chemical properties of polyols furtherto extraction suggest that they have great poten-tial for further reaction with isocyanate to producefoam applications.

    6.2. ATR-FTIR, Attenuated total reflectanceFourier transform infrared spectroscopy

    Figure 7: ATR-FTIR analysis of mixture of sol-vents, pine wood sawdust, liquefied wood from liq-uefaction, polyols and sugars from extraction of liq-uefied product.

    The ATR-FTIR analysis of mixture of solvents,pine wood sawdust, liquefied wood from liquefac-tion, polyols and sugars from extraction of lique-fied product. The figure 7 shows the results fromthe ATR-FTIR. In all the samples appear the prin-cipal peaks at 1050 cm−1 attributed to the −COstretching vibrations, around 2900 cm−1 typical of−CH stretching vibrations and around 3300 cm−1which is the typical band arising from the −OH.All these functional groups are present in the liq-uefactions solvents (DEG and 2-Ethylhexanol) andproducts but the peak at 2900 cm−1 does not ap-pear in wood. The reason why they do not appearin wood is because most of atoms of carbon are

    6

  • bonded between them in the macromolecules thatconstituted wood (lignin, cellulose and hemicellu-lose), and a lot of the oxygen atoms are bondedwith double bonds to the chain, and when thembreak a hidrogen atom join to the oxygen becoming−OH group. The absorption band at 1710 cm−1is attributed to the stretching vibration of −C = Ocommon for all soluble components of wood depoly-merization. These esters were probably producedby a dehydration reaction between carboxyl groupsof wood components in presence of the acid. Car-boxyl groups are ordinarily present in hemicelluloseand are also formed by oxidation of carbohydratesand lignin. Also, the spectra show some absorptionbands which are characteristic for cellulose such asCH2 group absorption bands at 1450 cm

    −1. It isremarkable that the sample from the wood sugarshas bigger peaks at 3300cm−1 (-OH) and especiallyat 1050 cm−1 (-CO), because when the wood com-ponents bonds are broken a lot of this groups ap-pear, specially when the cellulose breaks in sugarslike glucose.

    6.3. Study of different catalysts for the liquefaction

    To optimize the liquefaction reaction, the reactionwas carried out with 5 different catalysts and thekinetic of the reactions were compared.

    The conversion results were obtained with lowquantities of trichloroisocyanuric acid and alu-minium chloride. They are the cheapest catalysts.Is very interesting for the industrial application tocarry out the reaction with the lowest content ofcatalyst to get the liquefied wood as cheaper aspossible, because the catalyst is the most expensivereagent.

    In the figure 8 is showed the reaction yield versusthe time of the two best catalysts, 2 and 3, studiedwith concentrations of 0,1% and 0,5%. The cat-alytic performance of catalyst 3 is correlated withthe acidity of the reaction system due to it is stronglewis acid, and it form basic salts, resulting in thepH value of the solution becoming quite acidic. Andthis catalyst promoted the cleavage of lignin. ([7])Is to bear in mind that if the time of the reactionis too much, the recondensation of a solid polymerstarts, because repolymerization reactions of the in-termediate products formed by the decompositionof lignin.

    6.4. SEM applied to liquefaction of wood

    The wood particles that remained after liquefactionwere analized using SEM and compared them tothe starting material in order to gain more infor-mation about the process. Figure 9 shows the SEMmicrographs of extracted pine wood prior to thereaction and of the residue after the reaction. In

    Figure 8: Conversion results of catalysts 2 and 3.

    Figure 9: SEM pictures of residues from reactionswith catalysts 2 and 3 compared with row wood.

    the SEM images is showed the row wood and theresidue from reaction with catalysts 2 and 3 withx100, x500 and x1500 augment. The micrographsreveal a substantial difference in wood particle com-position and size. The starting material consistedin pine wood sawdust constituted by a mix of smallparticles, torn fibres, and intact wood parts. Theresidue appears to contain only irregular, powderyparticles of wood fragments, perhaps mixed withsome of the products of the polycondensation pro-cess that occur towards the end of the liquefactionprocesses.During the reaction the smallest particlesand damaged fibres would undergo dissolution first,leaving behind only the most resistant undamagedparts of wood. There is a big difference betweenthe different concentrations of the catalysts. In the

    7

  • images with x100 augment is possible to appreci-ate that the particles are really much smaller aftercarry out the reaction with a 0,5 % concentrationof catalyst than with 0,1%. With more augmentit is possible see that the particles are much moredegraded also with 0,5% of concentration. The de-gree of depolymerization with 0,5% of catalyst wassubstantially higher than with 0,1%.

    6.5. Characterization of polyurethane foams

    During and after the obtaining of the foams, theywere studied and characterized.

    6.6. Quick tests

    The foam tested properties were evaluated accord-ing to a scale from -5 to 5 (being -5 the worst re-sults and 5 the best). The rating is given visuallyand during the froth spray, during curing processand after cure foam. The tests were done in twodifferent temperature conditions: 23C and 5C (thetemperature is the same inside the can and in theenvironment). The tests are done in two differenttemperature conditions to see the effect of the tem-perature in the reaction, room temperature (23C)and a low temperature (5C). The results of thequick test are showed in the figure 10. The proper-ties of the three formulations are quite similar. Butthe formulation C has the best properties, probablybecause has more kinds of additives and more quan-tity of them in its formulation. It has more quantityof surfactant (B8871) and also contents plasticizer(DP45); they reduce the defects related with thebubble coalescence. Almost all the evaluations ofthe properties of this foam’s formulation are 3 ormore. For one of the purpose of this project, toobtain foams with maximum as possible of alterna-tive green reagents, the formulations B and C arethe more interesting, because their percentage ofpolyol from wood is bigger and the properties ofthis first attempt were satisfactory. In the figure10 is possible to see that the best results were ob-tained for cell collapse and the curing streaks in allthe foams formulations, this properties are relatedwith the velocity of curing of the froth. The worstresults were obtained in base holes, specially for theformulation of foam B. It happens in contact withpaper (porous surface) because the blowing agentsare captured and remain between the paper’s sur-face and the foam. Comparing the results betweenthe properties of the foams on paper and on mould,the properties on paper are much better because inthe mould there are less contact with air and a ge-ometry restriction. In the pictures of the figure 11appear the different foams, produced at two differ-ent temperatures (5 and 23C). In them is possiblesee that the more appreciable defect are the baseholes, specially in the foams produced at 23C. Thisproblem are bigger in foams B and C. The foams

    produced at 5C present less defects.

    Figure 10: Benchmarking performed between for-mulations.

    Figure 11: Pictures of the different foams.

    6.6.1 Output test

    Figure 12: Output results at 5C.

    The purpose of this test is to determine theoutput rate of the foam in mass/time. It consistsof dispensing the foam through the applicator fromthe aerosol. Two different values are measured:the mass difference of the can before and afterdispensing (released liquid) and also the mass offoam dispensed (released foam). The output ratedepends strongly on the viscosity. The higherthe viscosity of the prepolymer of polyurethaneproducts, the lower the will be the output rate. A

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  • viscous product has a lower rate of expansion. Theviscosity depends on the canister temperature andthe shelf life of the can. A cold and aged canisterdecrease the output rate. From the 3 foamsformulations, as showed at figure 12,formulation Chas the lowest output rate (is the most viscous)due to its composition with more additives of highmolecular weight.

    6.6.2 Foam structure (SEM)

    SEM images of polyurethane foam samples areshown in figure 13. It can be seen that the bio-polyols gave acceptable quality for preparation ofpolyurethane foams. In the SEM images of thecross sec-tion of the different polyurethane foamsis showed how the obtained cells are. The pore sur-face was mostly regular and smooth, but with dif-ferent size of cells (particularly in foam B). The sizedistribution is approximately 200-500 micrometresin diameter. The ideal structure is composed byhomogeneous network of dodecahedra cells (honey-comb structure), where gas grows inside during thefoam formation. This structure is the thermody-namically more stable. The quality of properties ofthe foams can be related with their microscopicalcell structure. It is well known that the cell size ofthe rigid foam has an important effect on mechan-ical properties. The excellent honeycomb structureobtained during foam formation made it possiblefor a considerable amount of still air to be trapped,thus, leading to an increased passive insulation. Ac-cording to figure 10 the best properties were showedby foam with formulation C. This formulation hasthe maximum score in most of the properties eval-uated (specially on paper). In the SEM images ispossible to appreciate that its cells are smaller andmore homogeneous, and that means that there ismore surface well distributed (it opposes more im-pediment as isolating).

    7. Conclusions

    It was shown that it is possible to convert woodinto liquefied wood via acid liquefaction, at atmo-spheric pressure and moderate temperatures, in thepresence of DEG and 2-Ethylhexanol as solventsand with different type of catalysts. After studyingthe liquefaction reaction with different catalysts itwas found that the best options are trichloroisocya-nuric acid and aluminium chloride, both of themwith good yield of reaction and cheaper than oth-ers known in literature. Also was confirmed that ispossible to carry out the liquefaction reaction withonly 0,1% of catalysts, important fact because thecatalyst is the most expensive reagent. Once thenecessary amount of polyols were obtained, threedifferent polyurethane foams were produced by the

    (a) Foam C x 35 (b) Foam B x35

    (c) Foam A x 35

    Figure 13: SEM images of Foams.

    company Greenseal. The resultant foams have goodproperties, specially that related with cell collapseand the curing streaks. And they are more respect-ful with the environment.

    7.1. AchievementsThe principal achievementwas to find the way andformulation to produce polyurethane foams for iso-lation uses with the maximum contents of polyolsfrom liquefied wood. These polyols are an alterna-tive to the depleting fossil resources and the cat-alytic transformation of the constituents of ligno-cellulose to this value added chemical because itis presented as an environmentally attractive andenergy efficient process compared to the currentlyused high temperature and energy consuming gasi-fication or pyrolysis technologies. Also the use ofthese polyols decreases the price of the foam andmakes it more biodegradable. Another achievementof the present work were founding a good catalystto improve the liquefaction reaction and make itcheaper.

    7.2. Future WorkThe results of the obtained foams show that is pos-sible the use of the polyols from wood for producethe foams in industrial way from green sources,biodegradable and with lower cost that the onesproduced with petrochemical reagents. But it isnecessary to take into account that the polyols haveto satisfy some structural requirements in order tocompete with petrochemical polyols, such as theright functionality and molecular weight. Then theformulation of the polyurethane foams should beimprove to satisfy more this requirements and en-hance their properties, especially those that havethe worst results like the presence of base holes (pro-duced for the encapsulation of the blowing agents).Also the biodegradability should be studied the evo-lution of the foams during a long period of time to

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  • make sure that is not an inconvenient to the finaluse of the foams.

    AcknowledgementsI would like to express my thanks to Professor Dr.Jãao Carlos Moura Bordado to give me the oppor-tunity to develop my dissertation in his departmentin the IST. I would like also to express my grat-itude to my advisor Dr. Maria Margarida Piresdos Santos Mateus for encouraging my research. Iam also grateful to the workers of Greenseal Re-search Center, who helped and advise me duringthe polyurethane foams production.

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