Effect of poly(ethylene glycol) on the hydrophobic interactions and rheology of proanthocyanidin biopolymers from Pinus radiata

The rheology of solutions of extracts from the bark of Pinus radiata was investigated in the presence of poly(ethylene glycol)s (PEGs) of different molecular weights. PEG with a molecular weight of 4600 (1% w/w) was sufficient to reduce the viscosity of a concentrated (40% w/w) pine tannin extract by one order of magnitude. The reduction of the viscosity was due to the inhibition of molecular association via hydrogen bonding and hydrophobic interactions between tannin and PEG and depended on the molecular weight of PEG. PEG effectively reduced the viscosity of polyphenolic tannins but retained high reactivity toward paraformaldehyde for adhesive formulations. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 1254–1260, 2005     

Evaluation of block shear properties of selected extreme‐pH structural adhesives by short‐term exposure test

Nine structural adhesives with varying pH were selected to examine the effect of adhesive pH on wood–adhesive bond quality. The adhesives evaluated included four highly alkaline phenol–formaldehyde, one intermediate pH phenol–resorcinol–formaldehyde, two acidic melamine–urea–formaldehyde, and two acidic melamine–formaldehyde resins. Block shear specimens were prepared using Douglas‐fir and black spruce wood. The adhesive performance was evaluated by measuring the shear properties (strength and wood failure) of the specimens tested at the dry and vacuum–pressure–redry (VPD) conditions. Adhesive pH, test condition, and wood species showed significant effects on shear properties. The different adhesives performed differently at the dry and VPD conditions. The high‐pH adhesives (phenol–formaldehyde and phenol–resorcinol–formaldehyde) showed similar high wood failures at both test conditions and performed better than the low‐pH adhesives (melamine–formaldehyde and melamine–urea–formaldehyde), especially after the VPD conditioning. The low‐pH adhesives showed high wood failure at the dry condition, but wood failure decreased significantly after VPD conditioning for both species, indicating that the low‐pH adhesives were less durable than the high‐pH adhesives. High‐pH adhesives did not have a negative impact on the strength of the bonded specimens. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Renewable (waste) material based polyesters as plasticizers for adhesives

The aim of the presented work was to replace phthalate based plasticizers with environmentally friendly materials to provide similar properties for poly(vinyl acetate) (PVAc) adhesives.Polyesters synthesized from the liquefied wood (PE-LW) and depolymerized polyethylene terephthalate (PE-PET) were used as renewable raw materials and evaluated as plasticizers used in PVAc dispersion adhesives for flooring applications. As a reference plasticizer, 1,2,3-triacetoxypropane was used.PVAc adhesives were evaluated with respect to solids content, viscosity, glass transition temperature (T_g), tensile shear strength and binding strength.TGA analysis showed significant differences between the thermal stability of added polyesters and the commercial plasticizer. Samples prepared with PE-PET exhibit the best thermal stability even with an increase of 25% PE-PET. The addition of coalescing agents or plasticizers leads to a temporary softening of the PVAc polymer and a decrease in the glass transition temperature.The type and content of plasticizer have great influence on wood–wood binding strength, tensile strength and elongation.The requirements for the mechanical properties of adhesives were fulfilled by the compositions containing 8.8% (w/w) of PE-PET and 20% (w/w) of PE-LW.     

13C-NMR analysis of phenol-urea-formaldehyde prepolymers and phenol-urea-formaldehyde-tannin adhesives

Phenol-urea-formaldehyde-tannin (PUFT) adhesives were prepared by co-polymerization of Pinus pinaster bark tannins with phenol-urea-formaldehyde (PUF) prepolymers at room temperature. A detailed analysis by ¹³C-NMR spectroscopy of the resins together with an evaluation of their properties was performed in order to find suitable preparation conditions for prepolymers prior to their co-polymerization with tannins. ¹³C-NMR spectroscopy allowed identification of the different linkages formed and quantification of the main functional groups in the PUF prepolymers, which were greatly influenced by the preparation conditions. The decrease in the free formaldehyde content in the PUFT adhesives with respect to the original prepolymers was attributed to tannin methylolation at room temperature. The fast increase in the apparent viscosity of the PUFT adhesives after the blending suggested the possibility of a co-polymerization reaction between tannins and the PUF prepolymers; however, the occurrence of this reaction could not be confirmed by ¹³C-NMR.     

Characterization and antioxidative properties of condensed tannins from the mangrove plant Aegiceras corniculatum

Freeze‐dried leaf, stem bark, and root bark powders of Aegiceras corniculatum were extracted with three different types of polar solvents: methanol, ethyl acetate, and water. The methanol extracts had the highest concentrations in total phenolics and extractable condensed tannins, followed by water and ethyl acetate extracts. Analysis by matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry (MALDI‐TOF MS) suggested that condensed tannins from leaf, stem bark, and root bark contained prodelphinidins and procyanidins, with the predominance of prodelphinidins and high level of galloylation. Acid‐catalyzed degradation in the presence of benzyl mercaptan indicated that gallocatechin, epigallocatechin, epigallocatechin‐3‐O‐gallate, and epicatechin‐3‐O‐gallate occurred as the terminal units and (epi)gallocatechin, (epi)gallocatechin‐3‐O‐gallate, (epi)catechin, and (epi)catechin‐3‐O‐gallate occurred as the extension units. The mean degrees of polymerization (mDP) of condensed tannins from leaf, stem bark, and root bark were 13.5, 7.4, and 12.3, respectively. The condensed tannins from leaf and stem bark exhibited a higher DPPH radical scavenging activity and ferric reducing/antioxidant power compared to that of synthetic antioxidant butylated hydroxyanisole (BHA). © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Adhesion and Physicochemical Properties of Soy Protein Modified by Sodium Bisulfite

Soy protein adhesives with a high solid content (28–39 %) were extracted from soy flour slurry modified with sodium bisulfite (NaHSO₃) at different concentrations. 11S‐dominated soy protein fractions (SP 5.4) and 7S‐dominated soy protein fractions (SP 4.5) were precipitated at pH 5.4 and pH 4.5, respectively. The objective of this work was to study the effects of NaHSO₃ on adhesion and physicochemical properties of soy protein. The adhesion performance of NaHSO₃‐modified SP 4.5 was better than SP 5.4; the wet strength of these two fractions was from 2.5 to 3.2 MPa compared with 1.6 MPa of control soy protein isolate. SDS‐PAGE results revealed the reducing effects of NaHSO₃ on soy protein. The isoelectric pH of soy protein decreased as NaHSO₃ increased due to the induced extra negative charges (RS‐SO₃^?) on the protein surface. The rheological properties of soy protein adhesives were improved significantly. Unmodified samples SP 5.4 and SP 4.5 had clay‐like properties and extremely high viscosity, respectively; with 2–8 g/L NaHSO₃ modification, both SP 5.4 and SP 4.5 had a viscous cohesive phase with good flowability. Overall, NaHSO₃‐modified soy protein adhesives in our study have many advantages over the traditional soy protein isolate adhesive such as better adhesion performance, higher solid content but with good flowability and longer shelf life.     

Steam Explosion of Pinus radiata Bark

The steam explosion of Pinus radiata bark has been studied. The effect of time, temperature, and bark moisture content upon water-leachable colour after steam treatment, and upon the extractives, lignin, carbohydrate, inorganic constituents, and the bark matrix have been examined. The process of steam explosion condensed the tannins and flavonoids to form less-extractable species, whilst generating extractable carbohydrate material. The yield of water-insoluble bark matrix after steam explosion remained almost constant (80–82% of original material) over the range of treatment conditions examined.     

CHT and TTT curing diagrams of polyflavonoid tannin resins

TTT and CHT curing diagrams for tannin-based adhesives were built by thermomechanical analysis (TMA) by following the in situ hardening directly in a wood joint, and the curve trends observed were similar to those previously observed for synthetic polycondensation resins on lignocellulosic substrates. Of the parameters that most influence the relative position of vitrification and gel curves on the diagrams (i.e., where the influence has been quantified), chief among them is the reactivity of the tannin with formaldehyde and any factor influencing it: thus, the inherent higher reactivity of the A-ring of the tannin (such as in procyanidins versus prorobinetinidins) and the pH of the tannin solution. The percentage formaldehyde hardener has some influence in CHT diagrams, especially for the slower-reacting tannins, but practically no influence in TTT diagrams within the 4–10% formaldehyde range used. As in the case of synthetic polycondensation adhesive resins, regression equations relating the internal bond strength of a wood particleboard, prepared under controlled conditions, with the inverse of the minimum deflection, obtained by constant heating rate TMA of a wood joint during resin cure, have been obtained for the two types of tannins of lower reactivity (profisetinidins/prorobinetinidins) but not for the faster-reacting procyanidin and prodelphinidin tannins. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 3220–3230, 2001     

Characterization of two maritime pine tannins as wood adhesives

Maritime pine tannins from the two suppliers BIOLANDES and DRT were used in combination with paraformaldehyde (5%), hexamine (6%) and glyoxal (9%) as hardener in the preparation of adhesives for wood-based panels. Both tannins showed similar structures according to the matrix-assisted laser desorption/ionization-time of flight analysis. A high reactivity has been checked by gel time measurements and the viscosity increase. Already the BIOLANDES and the DRT tannin alone registered an internal bond (IB) of 0.4?MPa without any hardener. The BIOLANDES tannin with paraformaldehyde could fulfil the European standard EN 312. In general, DRT tannin obtained the best mechanical results. However, the pH and the moisture content play a fundamental role for the final IB. Thus, DRT tannin with glyoxal as hardener at high pH and moisture content gave an IB of 0.51?MPa. The mechanical resistance differences between BIOLANDES and DRT tannin were confirmed by the ¹³C NMR spectra. DRT tannin presents a lower polymerization de than BIOLANDES, and more reactive sites are available.     

Preparation of liquefied bark‐based resol resin and its application to particle board

Barks of Taiwan acacia (Acacia confusa) and China fir (Cunninghamia lanceolata) were liquefied in the presence of phenol with sulfuric acid (H₂SO₄) and hydrochloric acid (HCl) as catalyst. The properties of resins prepared from liquefied bark and the feasibility of liquefied bark‐based resol resins in particle board manufacturing were investigated. The viscosity and thermosetting property of liquefied bark‐based resol resins were affected by the kind of bark species and the catalyst used. Liquefied bark‐based resol resins using China fir bark as raw material had higher viscosity than the ones using Taiwan acacia bark. In the course of thermosetting, liquefied bark‐based resol resins using Taiwan acacia bark as raw material had a higher maximum temperature of exothermic peak and onset temperature as well as a larger quantity of exothermic heat than those using China fir bark. Resol resins prepared from bark liquefied with H₂SO₄ as catalyst had higher viscosity, while resins with HCl as catalyst had a higher maximum temperature and height of exothermic peak and a larger quantity of exothermic heat at thermosetting. Particle board made with A‐S adhesive that was prepared from liquefied Taiwan acacia bark with H₂SO₄ as catalyst had the best particle board properties than those made with other adhesives. For the particle board made with A‐S adhesive, its static bending strength and internal bonding strength would be increased as the hot‐pressing time extended. The particle board made with hot‐pressing temperature of 150°C and hot‐pressing time of 10 min had the maximum normal and wet static bending strength and internal bonding strength. Its normal static bending strength was 170.8 kgf/cm² and the particle board showed satisfactory wet static bending strength and internal bonding strength. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 87: 1837–1841, 2003     

Alkaline sulfite/anthraquinone pretreatment followed by disk refining of Pinus radiata and Pinus caribaea wood chips for biochemical ethanol production

BACKGROUND: Alkaline sulfite/anthraquinone (ASA) cooking of Pinus radiata and Pinus caribaea wood chips followed by disk refining was used as a pretreatment for the production of low lignified and high fibrillated pulps. The pulps produced with different delignification degrees and refined at different energy inputs (250, 750 and 1600 Wh) were saccharified with cellulases and fermented to ethanol with Saccharomyces cerevisiae using separated hydrolysis and fermentation (SHF) or semi‐simultaneous saccharification and fermentation (SSSF) processes. RESULTS: Delignification of ASA pulps was between 25% and 50%, with low glucans losses. Pulp yield was from 70 to 78% for pulps of P. radiata and 60% for the pulp of P. caribaea. Pulps obtained after refining were evaluated in assays of enzymatic hydrolysis. Glucans‐to‐glucose conversion varied from 20 to 70%, depending on the degree of delignification and fibrillation of the pulps. The best ASA pulp of P. radiata was used in SHF and SSSF experiments of ethanol production. Such experiments produced maximum ethanol concentration of 20 g L^?1, which represented roughly 90% of glucose conversion and an estimated amount of 260 L ethanol ton^?1 wood. P. caribaea pulp also presented good performance in the enzymatic hydrolysis and fermentation but, due to the low amount of cellulose present, only 140 L ethanol would be obtained from each ton of wood. CONCLUSION: ASA cooking followed by disk refining was shown to be an efficient pretreatment process, which generated a low lignified and high‐fibrillated substrate that allowed the production of ethanol from the softwoods with high conversion yields. Copyright © 2012 Society of Chemical Industry     

Bioethanol production from bio‐ organosolv pulps of Pinus radiata and Acacia dealbata

Wood chips from Pinus radiata and Acacia dealbata were pretreated with the white‐rot fungi Ceriporiopsis subvermispora and Ganoderma australe, respectively, for 30 days at 27 °C and 55% relative humidity, followed by an organosolv delignification with 60% ethanol solution at 200 °C for 1 h to produce pulps with high cellulose and low lignin content. Biotreatment for 30 days was chosen based on low weight and cellulose losses (lower than 4%) and lignin degradation higher than 9%. After organosolv delignification, pulp yield for P. radiata and A. dealbata pulps was 45–49% and 31–51%, respectively. P. radiata bio‐pulps showed higher glucan (93%) and lower lignin content (6%) than control pulps (82% glucan and 13% lignin). A. dealbata bio‐pulps also showed higher glucan (95%) and lower lignin content (2%) than control pulps (92% glucan and 4% lignin). Pulp suspensions at 2% consistency were submitted either to separate enzymatic hydrolysis and fermentation (SHF) or simultaneous enzymatic saccharification and fermentation (SSF) for bioethanol production. The yeast Saccharomyces cerevisiae was used for fermentation. Glucan‐to‐glucose conversion in the enzymatic hydrolysis of control and bio‐pulps of P. radiata was 55% and 100%, respectively, and it was 100% for all pulp samples case of A. dealbata. The highest ethanol yield (calculated as percentage of theoretical yield) during SHF of P. radiata control and bio‐pulps was 38% and 55%, respectively, and for A. dealbata control and bio‐pulps 62% and 69%, respectively. The SSF of P. radiata control and bio‐pulps yielded 10% and 65% of ethanol, respectively, and 77% and 82% for A. dealbata control and bio‐pulps, respectively. In wood basis, the maximum conversion obtained (g ethanol per kg wood) in SHF was 37% and 51% (for P. radiata and A. dealbata pulps, respectively) and 44% and 65% in SSF (for P. radiata and A. dealbata pulps, respectively) regarding the theoretical yield. The low wood‐to‐ethanol conversion was associated with low pulp yield (A. dealbata pulps), high residual lignin amount (P. radiata pulps) and the low pulp consistency (2%) used for SHF and SSF. Copyright © 2007 Society of Chemical Industry     

木材加工用耐水性苯酚液化树皮-甲醛胶粘剂的研制

树皮是一种来源丰富可再生的天然高分子材料。本文采用高温苯酚液化的方法,在复合酸存在下将落叶松全树皮液化成为木材胶粘剂的原料。研究了树皮液化产物制备木材胶粘剂的合成工艺,特别是碱用量对苯酚液化落叶松全树皮一甲醛胶粘剂各主要性能的影响。结果表明,增加碱用量会缩短树皮胶的贮存期,但可降低胶中的游离甲醛;通过降低树皮胶合成时的终点黏度,并在合成末期用水稀释,可有效提高树皮胶的适用期,并可确保树皮胶具有很好的胶接强度和耐水性、较快的固化速率以及很低的游离甲醛释放量。     

The chemistry and development of tannin/urea–formaldehyde condensates for exterior wood adhesives

Novolak-like materials were prepared by condensation of urea–formaldehyde resins with resorcinol and/or resorcinolic A-rings of polyflavonoids such as condensed tannins. The copolymers formed were used as thermosetting and cold-setting exterior-grade wood adhesives. Condensation of tannins with small amounts of urea–formaldehyde resins can prevent the water deterioration normally experienced by the latter resins. Conversely, urea–formaldehyde resins improve crosslinking and strength of wood tannin–formaldehyde networks.     

Preparation and characterization of wood polyalcohol‐based isocyanate adhesives

Sugi (Criptmeria Japonica) wood meal was liquefied at 150°C with a mixture of poly(ethylene glycol) 400 and glycerin in the presence of a sulfuric acid catalyst. The resulting liquefaction products were used directly to prepare isocyanate adhesives via mixing with polymeric diphenylmethane diisocyanate without the removal of the residue. The properties of the liquefaction products and the performances of bonded plywood were tested. The results showed that the residue content decreased and the hydroxyl value increased as the reaction time increased. The viscosity and weight‐average molecular weight significantly changed with the reaction time. All the dry test results of the shear strength met the Japanese Agricultural Standard (JAS) criteria for plywood. After a cyclic steaming treatment, however, only the plywood bonding with adhesives from the liquefied wood with a reaction time of 1.5 h satisfied the JAS criteria. The wood failure was very low. The emissions of formaldehyde and acetaldehyde were extremely low. Liquefied‐wood‐based isocyanate adhesives have the potential to become ideal wood adhesives because of their bond durability, safety, and recyclability.     

The effects of zwitterionic and anionic charge densities in polymer chains on the viscosity behavior of a pH‐responsive hydrophobically modified ionic polymer

Sulfur dioxide, N,N‐diallyl‐N‐carboethoxymethylammonium chloride, and the hydrophobic monomer N,N‐diallyl‐N‐octadecylammonium chloride were cyclocopolymerized in dimethyl sulfoxide using azobisisobutyronitrile (AIBN) as the initiator to afford water‐soluble cationic polyelectrolytes (CPE) having a five‐membered cyclic structure on the polymeric backbone. The CPE on acidic hydrolysis of the pendent ester groups gave the corresponding cationic acid salts (CAS), which, on treatment with sodium hydroxide, were converted to polybetaines (PB) and anionic polyelectrolytes (APE), as well as polymers PB/APE containing various proportions of zwitterionic (PB) and anionic fractions (APE) in the polymer chain. The solution properties of the CPE, APE, and PB/APE systems containing varying amounts of the hydrophobic monomers in the range 0–4 mol % were investigated by viscometric techniques. Treating the pH‐responsive CAS polymers 4 with different equivalents of NaOH varied the zwitterionic and anionic charge densities in the polymer chain. It was found that the PB/APE polymer with a ratio of 33 : 67 for the zwitterionic and anionic fractions in the polymer chain, respectively, gave the highest viscosity value. The polymers showed that concentration (C*_HA) of around 1 g/dL was required for the manifestation of significant hydrophobic associations. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 1404–1411, 2005     

Differential scanning calorimetry of hydrolysed mangrove tannin

Mangrove‐bark‐tannin adhesives are potential substitutes for phenol–formaldehyde (PF) wood‐bonding adhesives which are derived from petroleum, a finite natural resource. However, mangrove‐bark‐tannin adhesive exhibits poor adhesive properties, including brittleness, poor wet strength, and poor wood penetration. These shortcomings are due to its high reactivity and structural features. To reduce these shortcomings, the structure of the adhesive was modified by subjecting tannin to (a) caustic hydrolysis and (b) consecutive acetic anhydride and caustic hydrolysis. The effectiveness of these hydrolyses was determined by using differential scanning calorimetry (DSC) to monitor the reaction and cure characteristics of hydrolysed and unhydrolysed tannin with formaldehyde. These hydrolyses resulted in lowering both the activation energy and collision frequency of the cure reaction. Consequently, the initial reactivity of tannin towards paraformaldehyde, which was usually very high, was reduced. The resulting longer reaction time enhanced the extent of reaction, as was evident in the increase in heat of reaction of the hydrolysed tannin. © 2000 Society of Chemical Industry     

Antioxidant activity of pine bark procyanidins in bulk corn oil and corn oil‐in‐water emulsions

In this work, the ability of pine bark procyanidins to hinder oxidation in bulk corn oil and corn oil‐in‐water‐emulsion has been investigated. A preliminary characterisation of the obtained aqueous (AF) and organic (OW) fractions and subfractions suggested a very polar character and showed that both fractions possess remarkable antioxidant activity when minimum concentrations of 2 mg/mL are used. OW fractions and subfractions derived from both pine varieties were able to inhibit oxidation in oils. More specifically, two organic subfractions were the most efficient for retarding the degradation process, with levels of 62% and 50% after 8 days of treatment, respectively. Organic subfractions obtained from both varieties of pine also rendered possible inhibition levels in oil‐in‐water‐emulsions up to 80% after 4 days of oxidation, more than 3 times higher than the levels provided by tocopherol, a well‐known model commercial antioxidant, which confirms the excellent antioxidant potential of procyanidins from pine bark. Practical application: Lipid deterioration leads to losses in quality and nutritional value and to the development of off‐flavours in many foodstuffs. One way to overcome this drawback is by using antioxidants of natural origin, which is a subject of a great scientific and industrial interest, reflected by the growing number of papers and patents published during the last years. Since aqueous and organic fractions obtained from Pinus pinaster and Pinus radiata bark turned out to be an adequate source of procyanidins in previous investigations of our group, their possible antioxidant role in model lipid systems was investigated. This approach entails also another benefit in terms of waste valorisation, since pine bark is a typical residue of agroforestal industries.     

Effects of Pinus pinaster bark extracts content on the cure properties of tannin-modified adhesives and on bonding of exterior grade MDF

Phenol-urea-formaldehyde-tannin (PUFT) adhesives with different degrees of phenol substitution by Pinus pinaster bark tannins were thermally characterized by dynamic mechanical thermal analysis (DMTA) and by differential scanning calorimetry (DSC). They were employed to prepare exterior grade Medium Density Fiberboards (MDF) according to European Standards. DMTA and DSC experiments showed, first, that the tannin-modified adhesives hardened in the low temperature range (30-110°C) and, second, that increasing the tannin content of the adhesives reduced the curing temperature, obtaining at least the same mechanical strength (stiffness) and higher curing enthalpies (ΔH) than the commercial phenolic resin. Although only the MDF boards made using the lowest viscosity tannin-modified adhesive (PUFT-10), with a 44% phenol replacement by tannin, met the outdoor requirements, all the other tannin-modified adhesives boards met the interior grade specifications. Among the board properties evaluated, the low value of thickness swelling after 24-h water immersion of MDF boards prepared using the PUFT-10 (6.6%) is particularly noticeable, which means an improvement of almost 50% compared to that of the commercial PF (12.6%).     

Polyflavonoid Tannins Self-Condensation Adhesives for Wood Particleboard

Work done in the author's laboratory has indicated that polyflavonoid tannins can self-condense to a hardened network without the addition of any hardeners. This allows their use as interior grade adhesives for wood panels. For fast-reacting tannins, such as procyanidins, the catalytic effect exercised solely by the lignocellulosic substrate is enough to give strength performance satisfying relevant standards. For slower-reacting tannins such as prorobinetinidins and profisdetinidins, small amounts of finely divided SiO₂ dissolved in a tannin solution in water at pH of 11–12 is sufficient to catalyse such a self-condensation effect. As there are no added aldehydes, there is little or no detectable formaldehyde.