Doctor of Philosophy / Department of Grain Science and Industry / X. Susan Sun / The ecological and public health liabilities related with consuming petroleum resources have inspired the development of sustainable and environmental friendly materials. Plant protein, as a byproduct of oil extraction, has been identified as an economical biomaterial source and has previously demonstrated excellent potential for commercial use. Due to the intrinsic structure, protein-based materials are vulnerable to water and present relatively low wet mechanical properties. The purpose of this study focuses on increasing protein surface hydrophobicity through chemical modifications in order to improve wet mechanical strength. However, most of the water sensitive groups (WSG), such as amine, carboxyl, and hydroxyl groups, are also attributed to adhesion. Therefore, the goal of this research is to reduce water sensitive groups to an optimum level that the modified soy protein presents good wet adhesion and wet mechanical strength. In this research, we proposed two major approaches to reduce WSG: 1). By grafting hydrophobic chemicals onto the WSGs on protein surface; 2). By interacting hydrophobic chemicals with the WSGs. For grafting, undecylenic acid (UA), a castor oil derivative with 11-carbon chain with a carboxyl group at one end and naturally hydrophobic, was used. Carboxyl groups from UA reacted with amine groups from protein and converted amines into ester with hydrophobic chains grafting on protein surface. The successful grafting of UA onto soy protein isolate (SPI) was proved by both Infrared spectroscopy (IR) and ninhydrin test. Wood adhesive made from UA modified soy protein had reached the highest wet strength of 3.30 ± 0.24 MPa with fiber pulled out, which was 65% improvement than control soy protein. Grafting fatty acid chain was verified to improve soy protein water resistance. For interaction approach, soy oil with three fatty acid chains was used to modify soy protein. Soy oil was first modified into waterborne polyurethanes (WPU) to improve its compatibility and reactivity with aqueous protein. The main forces between WPU and protein were hydrogen bonding, hydrophobic interactions, and physical entanglement. Our results showed that WPU not only increased protein surface hydrophobicity with its fatty acid chains but also enhanced the three-dimensional network structure in WPU-SPI adhesives. WPU modification had increased wet adhesion strength up to 3.81 ± 0.34 MPa with fiber pulled out compared with 2.01 ± 0.46 MPa of SPI. Based on IR and thermal behavior changes observed by DSC, it was inferred that a new crosslinking network formed between WPU and SPI. To exam if the UA and WPU technologies developed using soy protein are suitable for other plant proteins, we selected camelina protein because camelina oil has superior functional properties for jet fuels and polymers. Like soy protein, camelina protein is also highly water sensitive. However, simply applied UA and WPU to camelina protein following the same methods used for soy proteins, we did not obtain the same good adhesion results compared to what we achieved with soy protein. After protein structure analysis, we realized that camelina protein is more compact in structure compared to soy protein that made it weak in both dry and wet adhesion strength. Therefore, for camelina protein, we unfolded its compact structure with Polymericamine epichlorohydrine (PAE) first to improve flexible chains with more adhesion groups for future reaction with UA or WPU. PAE with charged groups interacted camelina protein through electrostatic interaction and promoted protein unfolding to increase reactivity within protein subunits and between protein and wood cells. Therefore, the wet adhesion strength of camelina protein was improved from zero to 1.30 ± 0.23 MPa, which met the industrial standard for plywood adhesives in terms of adhesion strength. Then the wet adhesion strength of camelina protein was further improved after applying UA and WPU into the PAE modified camelina protein. In addition, we also found PAE unfolding significantly improved the dry adhesion strength of camelina protein from 2.39 ± 0.52 to 5.39 ± 0.50 MPa with 100% wood failure on two-layer wood test. Camelina meal which is even more economical than camelina protein was studied as wood adhesive. Through a combination of PAE and laccase modification method, the wet adhesion strength of camelina meal was improved as high as 1.04 ± 0.19MPa, which also met industrial standards for plywood adhesives. The results of this study had proven successful modification of oilseed protein to increase water resistance and wet mechanical strength. We have gained in-depth understanding of the relationship between protein structure and wet adhesion strength. The successful modification of plant proteins meeting the industrial needs for bio-adhesives will promote the development of eco-friendly and sustainable materials.

Different native starches, modified starches and plant proteins were evaluated as wood adhesives. They were combined with different synthetic polymers in order to achieve improved adhesive properties. The study was divided into two parts: development of starch based adhesive formulations and evaluation of an existing protein based adhesive.  Eight different starches and two different plant proteins were used in the first part. Starch 1 and starch 2 as well as protein 1 and protein 2 were some of the used materials. These materials were dispersed in synthetic polymers such as poly (vinyl acetate) (PVAc), styrene-butadiene rubber (SBR), poly (vinyl alcohol) (PVA), poly (acrylic acid) (PAA) and poly (ethylene-co-vinyl acetate) (EVA). Five different cross-linking agents were also tested. In the second part of the study, protein 2 was used as a renewable material. It was dispersed in dispersing media 2 and filler 1 was used. In an effort to increase the amount of renewable material in the adhesive composition, six different renewable fillers were examined. Lower pressing temperatures as well as lower amounts of cross-linking agent 1 were evaluated in order to observe their influence on the adhesive properties of the protein based adhesive. All formulations were characterized by measurement of viscosity, solid content and pH. The adhesive properties of some of the formulations in both parts of the study were characterized according to SS-EN 204:2001 and EN 14257 (WATT 91). The best results, of the starch based formulations, were obtained when starch 1 and protein 2 were dispersed in dispersing media 2 or dispersing media 7. These formulations in combination with cross-linking agents were classified as D2 and passed the criteria for heat resistance (WATT 91). However, the results were comparable with the reference sample. It was possible to replace filler 1, totally or partly, in the protein based adhesive with renewable fillers. Protein based adhesive formulations with filler 2 and filler 4, amongst others, showed improvement of the adhesive properties. These formulations passed D3 and D4 – wet criteria and almost passed D4 – boiling criteria. The amount of renewable material in the protein based adhesive was increased from ~32 % to ~56 % in the formulations that obtained the best adhesive properties. The amount of non-petrochemical material was ~67 % in all new formulations as well as in the reference sample.  By decreasing the pressing temperature from 110 °C to 90 °C or by decreasing the amount of cross-linking agent 1 from 15 % to 5 %, a protein based system that passes D3 criteria can be obtained.

This project addresses two main subjects of moisture-cure polyurethane (PUR) wood adhesives: wood/PUR interactions and structure-property behavior emphasizing on weather durability. For these purposes, one simplified model PUR (MPUR) and three more commercially significant PURs (CPURs) with different hard segment contents were prepared. Separately, an early side project involved the synthesis of a 13C and 15N double-labeled polymeric methylenebis(phenylisocyanate) (pMDI) resin; this was used for the solid-state NMR characterization of isocyanate cure chemistry in wood bondline. MPUR and a CPUR were employed to investigate whether wood/adhesive interactions influence PUR properties. Wood interactions significantly altered PUR hard/soft domain size distribution (atomic force microscopy, AFM), thermal transition temperatures (dynamic mechanical analyses, DMA), and urethane/urea hydrogen bonds (Fourier transform infrared spectroscopy, FTIR). The effects of hard segment content on properties of PUR prepolymers, and cured PURs (films and wood composites) were studied. Hard segment content largely influenced the PURs’ molecular weights, viscosity, penetration, thermal transitions, and hard segment hydrogen bonds, but only slightly altered the dry (unweathered) bondline toughness. Three accelerated weathering procedures were developed to evaluate CPUR bondline weather durability through mode-I fracture testing. Both hard segment content and weathering conditions were found to significantly influence the bondline weather durability. Among these weathering procedures, only one (VPSS) was able to effectively distinguish weather durability of PUR adhesives, and therefore it was selected for detailed structure-weather durability studies. PUR weather durability was found to correlate with its moisture sensitivity and hard segment softening temperature; both were provided by water-submersion DMA. Much attention was directed to the investigation of weather-induced PUR molecular changes. FTIR studies provided evidences of post-cure, hydrolytic degradation, and variation of urethane/urea hydrogen bonds. DMA presented weathering effects on PUR thermal properties. Special efforts have been made to correlate these analytical results with PUR weather durability. A 13C and 15N double-labeled pMDI resin was synthesized and used for solid-state NMR characterization of isocyanate cure chemistry in wood bondline, particularly to detect the evidence of urethane formation. Rotational echo double resonance (REDOR) NMR clearly revealed the formation of urethane linkages, but largely overestimated their content. / Ph. D.

This work addresses the morphology of the wood/ Phenol-Formaldehyde (PF) adhesive interphase using yellow-poplar. In this case, morphology refers to the scale or dimension of adhesive penetration into wood. The objective is to develop methods for revealing ever smaller levels of wood/resin morphology. Dynamic techniques that are commonly utilized in polymer blend studies are investigated as potential methods for probing the wood/ adhesive interphase morphology. These are Dynamic Mechanical Analysis (DMA) and solid state NMR using CP/MAS. PF resin molecular weight is manipulated to promote or inhibit resin penetration in wood, using a very low or a very high molecular weight PF resin. With DMA, the influence of PF resin on wood softening is investigated. It is first demonstrated that the cooperativity analysis according to the Ngai coupling model of relaxation successfully applies to the in-situ lignin glass transition of yellow-poplar and spruce woods. No significant difference in intermolecular coupling is detected between the two woods. It is then demonstrated that combining simple DMA measurements with the cooperativity analysis yields ample sensitivity to the interphase morphology. From simple DMA temperature scans, a low molecular weight PF (PF-Low) does not influence lignin glass transition temperature. However, the Ngai coupling model of relaxation indicates that intermolecular coupling is enhanced with the low molecular weight PF. This behavior is ascribed to the low molecular weight PF penetrating lignin on a nanometer scale and polymerizing in-situ. On the other hand, a high molecular weight resin with a broad distribution of olecular weights (PF-High) lowers lignin glass transition temperature dramatically. This plasticizing effect is ascribed to a small fraction of the PF resin being low enough in molecular weight to penetrate lignin on a nanoscale, but being too dispersed for forming a crosslinked network. With CP/MAS NMR, intermolecular cross-polarization experiments are found unsuitable to probe the angstrom scale morphology of the wood adhesive interphase. However, observing the influence of the PF resins on the spin lattice relaxation time in the rotating frame, HT1r, and the cross-polarization time (TCH) is useful for probing the interphase morphology. None of the resins significantly affects the cross-polarization time, suggesting that angstrom scale penetration does not occur with a low nor a high molecular weight PF resin. However, the low molecular weight PF substantially modifies wood polymer HT1r, indicating that the nanometer scale environment of wood polymers is altered. On the other hand, the high molecular weight PF resin has no effect on wood HT1r. On average, the high molecular weight PF does not penetrate wood on a nanometer scale. Interestingly, the low molecular weight PF resin disrupts the spin coupling that is typical among wood components. Spin coupling between wood components is insensitive to the high molecular weight PF. Finally, it is noteworthy that the two PF resins have significantly different T1r 's in-situ. The low molecular weight resin T1r lies within the range of wood relaxations, suggesting some degree of spin coupling. On the other hand, the T1r of the high molecular weight PF appears outside the range of wood relaxations. Spin coupling between the high molecular weight resin and wood components is therefore inefficient. The CP/MAS NMR and DMA studies converge to identify nanometer scale penetration of the low molecular weight PF in wood. On the other hand, the high molecular weight PF resin forms separate domains from wood, although a very small fraction of the PF-High is able to penetrate wood polymers on a nanoscale. / Ph. D.

The performance of connections and full-scale shear walls constructed with acrylic foam pressure sensitive adhesive (PSA) tape is the focus of this thesis. The objectives of this study were first to investigate the bonding characteristics of adhesive tape to wood substrates and then to expand this investigation to cover adhesive-based shear walls subjected to high wind and seismic loadings. A total of 287 monotonic connection tests and 23 reversed cyclic wall tests were performed to achieve these objectives. Connection tests were performed in accordance with ASTM D 1761-88 (2000), and walls were tested using the CUREE (Consortium of Universities for Earthquake Engineering) general displacement-based protocol. Variables investigated within the main study were the following: the use of OSB versus plywood sheathing, the effect of priming and surface sanding on adhesion, and the comparison of connections involving mechanical fasteners with those that utilized only adhesive tape or a combination of the two. It was found that an application pressure of 207 kPa (30 psi) or greater was needed to form a sound bond between the acrylic foam adhesive tape and a wood substrate. Properly bonded OSB and plywood connections provided fairly ductile failure modes. Full-scale walls constructed with adhesive tape performed similarly to traditional wall configurations, while walls constructed with a combination of adhesive tape and mechanical fasteners provided significant gains in strength and toughness. The results of this study serve to provide a foundation for expanding the engineering uses of acrylic foam adhesive tape for structural applications. / Master of Science

The increasing environmental concern has reawakened an interest in materials based on renewable resources as replacement for petroleum-based materials. The main objective of this thesis was to explore plant proteins, more specifically wheat gluten, as a binder in wood adhesives intended for typical solid wood applications such as furniture and flooring. Alkaline and acidic dispersions of wheat gluten were used as wood adhesives to bond together beech wood substrates. Soy protein isolate was used as a reference. The tensile shear strengths of the substrates were measured for comparison of bond strength and resistance to cold water. AFM in colloidal probe mode was used to investigate nanoscale adhesion between cellulose and protein films. Wheat gluten was divided into the two protein classes; glutenins and gliadins, and their adhesive performance was compared with that of wheat gluten. Heat treatment and mild hydrolysis were investigated as means for improving bonding performance of wheat gluten. The treated wheat gluten samples were analysed by SE-HPLC and 13C-NMR to correlate molecular size distribution and structural changes with bonding performance. Soy protein isolate is superior to wheat gluten, especially in regards to water resistance. However, the bond strength of wheat gluten is improved when starved bond lines are avoided. The AFM analysis reveals higher interfacial adhesion between soy protein isolate and cellulose than between wheat gluten and cellulose. These results partly explain some of the differences in bonding performance between the plant proteins. Soy protein isolate contains more polar amino acid residues than wheat gluten and possibly interacts more strongly with cellulose. Furthermore, the bond performances of wheat gluten and glutenin are similar, while that of gliadin is inferior to the others, especially regarding water resistance. The extent of penetration of the dispersions into the wood material has a large impact on the results. The bonding performance of gliadin is similar to the others when over-penetration of the dispersion into the wood material is avoided. Moreover, the bond strength of the wheat gluten samples heated at 90°C was in general improved compared to that of wheat gluten. A small improvement was also obtained for some of the hydrolyzed wheat gluten samples (degree of hydrolysis: 0-0.6 %). The improvements in bonding performance for the heat treated samples are due to polymerization, while the improvements for the hydrolyzed samples are due to denaturation. The 13C-NMR analysis of the treated samples confirms some degree of denaturation. / QC 20120514

Adhesives used for wood composites such as particleboard are conventionally of petrochemical nature with formaldehyde as a base substance and represent a pain point in the industry due their toxic emissions. Consequently, adhesives are subject to an agenda to develop more benign, low-impact alternatives. On the one hand, the issue has been addressed by means of optimisation of composition and amounts, and on the other hand, development of biobased adhesives from different renewable feedstock has been taking place over the past decades. Yet, these bio-adhesives remain a niche segment as renewability or lower toxicity alone is widely not enough despite increasingly strict regulations on formaldehyde emissions. Emphasis on a more comprehensive set of beneficial properties of ‘green’ adhesives is needed for successful adoption in the market. In this context, this study investigates the holistic sustainability potential of a yet untapped bio- adhesive feedstock: macroalgae. Current research on an algae-based adhesive from cultivated biomass in Sweden suggests suitable adhesive properties for particleboard manufacture. Complementing these promising findings on material properties, this study assesses sustainability of using an algae-based adhesive in a particleboard production system as opposed to conventional formaldehyde-based resins. A comparative cradle-to-gate life cycle assessment of different scenarios was conducted, with the specific aim to explore changes in toxicity, climate change impacts and eutrophication due to the known benefits of cultivated macroalgae in these areas. A considerably better performance for algae-based adhesives was found across impact categories (CML baseline method) compared to formaldehyde-based scenarios, as well as a similar pattern with respect to cumulative energy demand. Particularly under a low-impact preservation method for the algal biomass, relative impacts were substantially lower without exception. Furthermore, a potential for carbon sequestration and replacing of fossil with biogenic carbon flows was identified, as well as bioremediation of location eutrophication through nutrient uptake of the biomass during cultivation. Despite the early stage and the need for further research, the results point to a promising potential for macroalgae as a feedstock for biobased wood adhesives which go beyond renewability. / Lim som vanligtvis används för träkomponenter som exempelvis spånskivor är konventionellt från petrokemiska källor med formaldehyd som basämne, och anses vara en utmaning för branschen på grund av dess giftiga utsläpp. Därav är det av intresse för branschen att utveckla bättre alternativ med mindre miljöpåverkan. Utvecklingen har dels skett genom optimering av sammansättning och proportioner, men under det senaste decennierna har även utveckling av biobaserade lim från olika förnyelsebara råvaror tagit fart. Dessa biobaserade lim är dock fortfarande ett nischat område, att enbart arbeta med förnybara råvaror som ger lägre toxicitet verkar inte vara tillräckligt, trots allt striktare bestämmelser om formaldehydutsläpp. Därför krävs det tydliga bevis av miljövinsterna med lim av förnyelsebara råvaror för att denna metod ska bli mer framgångsrik på marknaden. I detta sammanhang undersöker denna uppsats, genom ett holistiskt perspektiv, potentialen med lim gjort på det ännu outnyttjade förnyelsebara materialet makroalger. Aktuell forskning på algbaserat lim från odlad biomassa i Sverige har uppvisat lämpliga limegenskaper för användning inom spånskivetillverkning. Som ett komplement för dessa potentiella fördelaktiga egenskaper, bedömer denna uppsats miljönyttan med användandet av ett algbaserat lim i produktionssystem av spånskivor, i relation till det konventionella formaldehydbaserade limmet. Därmed görs en jämförande livscykelanalys från vaggan till grinden av olika scenarier, med syftet att undersöka förändringar i toxicitet, klimatpåverkan och övergödning, i och med att dessa tre påverkanskategorier redan har visat på kända miljöfördelar. Resultatet visade att det algbaserade limmet hade betydligt bättre miljöprestanda i alla påverkanskategorier undersökt med metoden CML baseline i jämförelse med det formaldehydbaserade limmet, vilket även visades för kategorin kumulativt energibehov. När en konserveringsmetod används för att processa algbiomassan, är skillnaden i miljöpåverkan av dom två limmen lägre inom alla påverkanskategorier. Slutligen identifierades potential för kolbindning och utbyte av biogena och fossila kolflöden, även bioremediering av lokal övergödning genom att biomassan upptog näringsämnen under odling. Trots det tidiga stadiet och behovet av fortsatt forskning så visar dessa resultat en fortsatt potential för makroalger som ett råmaterial för biobaserade trälim som tar förbybarhet ett steg längre.

Abstract The wood industries to this day use almost exclusively petroleum derived adhesives that are based mainly on the reaction of formaldehyde with urea, melamine or phenol. These adhesives have low cost and good adjustable properties which makes it hard for bio-based alternatives to compete. Phenol formaldehyde (PF), as an example of a synthetic adhesive, has been in use for over 100 years. In some parts of the world, legislation around formaldehyde is changing, and there is an increasingly voluntary awareness about the toxicity and unsustainability of formaldehyde. Industries realize that raw materials from oil is unstainable. The latter is currently a driving factor behind research on alternatives to amino based adhesives. Also, consumer interest in healthy and sustainable products, such as emitting less formaldehyde indoors, increases the need for bio based adhesives. Cellulose contained in plant cell walls is a renewable, abundant and nontoxic resource. During the last decades, many innovations have been achieved around cellulose and this trend does not seem to be slowing down. Cellulose shows excellent mechanical properties, high strength, high elastic modulus as well as having a low density. Research about cellulose reinforced adhesives has been increased the last years. This thesis studied the enhancement of phenol formaldehyde adhesive with Crystalline Nano Cellulose (CNC) at 5wt% and 10wt% loading levels for producing plywood boards. Indecisive results when using CNC higher than 3wt%, especially with PF resin, have been reported by other authors. In this thesis, European standards were applied. EN 314 was applied to test the panels shear strength. Three (3) treatment classes were selected, indoor room condition as well as pre-treatments 5.1.1 and 5.1.3. Other properties measured were modulus of elasticity, thickness swelling, formaldehyde emissions. Results showed a shear strength increase for all pre-treatment classes. 10wt% CNC mixture with phenol formaldehyde in water bath, pre-treatment (5.1.1) for 24h showed the highest increase in shear strength (+73,9%). The 10 wt% CNC mixture panels also showed the highest wood fibre failure of all panel types produced. A decrease in MOE has been observed with 10 wt% CNC compared to the 5 wt% CNC panels. Formaldehyde emissions tests were inconclusive, but since less PF was used, there was a general reduction in emissions. The 5 wt% CNC panels were superior in terms of modulus of elasticity and swelling and also showed improved shear strength.