Figure 1 - uploaded by Jignesh Shukla
Content may be subject to copyright.
Source publication
Polyurethane adhesives made from synthetic chemicals are non-biodegradable, costly and difficult to find raw materials from local market. To avoid solid pollution problem, cost effectiveness and easy availability of raw materials, biomaterials based polyurethane adhesives are used in current industrial interest. Direct use of castor oil in polyuret...
Contexts in source publication
Context 1
... hydroxyl value of polyol was determined by acetic anhydride- pyridine method 34 . The structure and characterization data of the polyols presented in Figure 1 and Table 2 respectively. ...
Context 2
... shear strength of different polyurethanes on wood-wood and metal-metal substrate (10 pcs.) analysed under the effects of chain length of polyols, cross linking density, types of polyols and Isocyanate adducts shown in Figure 10, 11 and 12. ...
Context 3
... effects of cross-linking density on thermal stability of castor oil based polyurethane adhesives were studied. Thermo grams indicate that the negligible weight loss up to 240 °C i.e. the polyurethanes are stable up to 240 °C with irrespective of cross- linking density (NCO/OH ratio) which shown in Figure 13. ...
Citations
... Excessive amounts of isocyanate embrittle the adhesives, lowering the lap shear strength. Furthermore, increased rigidity may impede the orientation possibility required for optimal substrate-adhesive interaction [301]. Palm oil-based adhesives frequently perform poorly due to their high saturated fatty acid content. ...
Over the last 50 years, the use of wood adhesives in the manufacturing of wood-based panel goods has increased the efficiency of wood resources. Wood adhesives are becoming more popular as the need for wood-based panels grows. By 2028, the global market for wood adhesives is expected to reach 21.8 billion dollars. Even though urea-formaldehyde (UF), phenol-formaldehyde (PF), melamine-formaldehyde (MF), phenol-resorcinol-formaldehyde (PRF), and resorcinol-formaldehyde (RF) resins are excellent in terms of bonding performance, workability, quality, and economy, they consist of harmful or toxic chemical agents derived from fossil resources, which make their application severely limited. This review aims to go through the most significant ‘green’ wood adhesives for manufacturing high-performance wood-based panels, such as lignin, tannin, protein, natural rubber, emulsion polymer isocyanate (EPI), 1C PUR polyurethane (for glue-laminated wood and cross-laminated timber), PMDI (for particleboards, medium-density and low-density fiberboards), carboxylic acid, and vegetable oil. The physical and mechanical characteristics of bio-based wood adhesives, as well as the development of sustainable, greener, and high-performance bio-based wood adhesives, are discussed in this work. Original research papers and review articles are among the most important sources since they provide complete information on the most recent developments in sustainable, eco-friendly, and high-performance bio-based wood adhesives.
... Palm oil has been reportedly used by researchers for the production of PU adhesives, which shows higher hydrolytic stability and hydrophobicity. Patel et al. studied the ringopening reaction of epoxidized palm olefin with phthalic acid, which is utilized to generate PU adhesives with, which contain palm oil-based polyester [41]. Khoon et al. studied polyurethane wood adhesive derived from palm oil-based polyester polyol, where glycerol was used as a crosslinker and DBTL as a catalyst [18]. ...
Among numerous synthetic macromolecules, polyurethane in its different forms has proven its sheer dominance and established a reputation as a reliable and trusted material due to its proficiency in terms of superior properties, which include: high mechanical strength and abrasion resistance, good durability, good adhesion, good thermal stability, excellent chemical and weathering resistance. Synthetic polyurethane materials are non-biodegradable, poisonous, and use petrochemical-based raw materials, which are now depleting, leading to a surge in polyurethane production costs. Bio-based polyurethanes (PU) have been synthesized by researchers in recent decades and have mostly overtaken petrochemical-based PU in terms of challenges such as solid pollution, economic effectiveness, and availability of raw materials. Enormous kinds of available bio-renewable sources as predecessors for the production of polyols and isocyanates have been explored for the development of “greener” PU materials; these bio-based polyurethanes have significant potential to be used as future PU products, with a partial or total replacement of petroleum-based polyurethanes, due to increasing concern about the environment, their relatively low cost and biodegradability. This critical review concentrates on the possibilities of renewable sources to be used for polyurethane production and gives a clear perspective on the journey, utilization, and recent advancements in the field of different bio-based polyurethane polymers that have arisen over the last decade.
... Moghadam et al. [5] in their research reported a simple procedure in line with the fundamentals of green chemistry to synthesize wood adhesive PUs from modified castor oil, whose lap shear strengths appeared to surpass the analogous benchmark. Patel et al. [28] proposed the modification of castor oil to develop natural polyols as feedstock for polyurethane with adhesive applications on wood and metal substrates. Bio-sourced PUs obtained by Sahoo et al. [14], when evaluating the influence of the NCO:OH molar ratio, exhibited adhesion strength values almost fourfold greater than the commercial benchmark. ...
... Thus, even though the adhesion strengths under shear deformation are not statistically different when conducting the biosourced adhesive synthesis via the proposed single-step process, the failure becomes mainly substrate-based, so that the adhesion performance is clearly enhanced. Moreover, the values of the lap shear strength provided by the ASTM D906 test obtained with the synthesized PUs, particularly noticeable on oak wood, seem to meet the requirements for being considered as wood adhesives, since they appear to be fairly competitive with the values previously reported by Silva et al. [60], Ang et al. [61] and Sahoo et al. [14], even exceeding those resulting from the investigations of Somani et al. [62], Patel et al. [28] or Wang et al. [63], thus encompassing a wide range of polyurethane adhesives, most of them based on castor oil and both aromatic and aliphatic diisocyanates. ...
During the last decades, the replacement of the traditionally petro-based raw materials by eco-friendly substances in polyurethane production has become a great challenge. The synthesis of polyurethanes is mainly conducted by means of a selective reaction between active isocyanate and hydroxyl groups, yielding a characteristic segmented chemical structure. In this study, the traditional solvent-based polycondensation reaction for the synthesis of bio-based polyurethane adhesives, involving first cellulose acetate modification with 1,6-hexamethylene diisocyanate and subsequent crosslinking with castor oil, was evaluated and compared with a simpler solvent-free single-step protocol. The impact of the preparation procedure and reagent proportions, on the chemical structure, thermo-rheological behaviour and ultimate adhesion performance were evaluated. The rheological response and adhesion performance of these bio-inspired polyurethanes were also compared to those found in some commercial adhesives. This research highlights the reinforcing and stabilizing effect of cellulose acetate on bio-polyurethane performance. Particularly, the inclusion of cellulose acetate into the adhesive manufacture allowed a reduction in the maximum curing time under room conditions to almost one week, while yielding a higher thermal stability and a fourfold increase in elastic modulus in comparison to the cellulose acetate-free counterpart. Moreover, the proposed solvent-free synthetic route enhanced the microphase mixing of the ensuing bio-based polyurethanes, exhibiting an adhesion performance comparable to the considered commercial benchmarks, but with failure occurring primarily within the substrate material – the preferred locus of failure.
... PU adhesives have been widely applied to bond different substrates, such as wood, glass, plastic, and ceramics, due to their good wetability on the surfaces of substrates, strong adhesion strength, and good chemical resistance [1,3]. These adhesives are generally prepared from petroleum-based and non-biodegradable synthetic prepolymers [4]. With increasing concerns about global climate change and shortage of fossil fuel resources, polymers derived from renewable resources are ideal sustainable alternatives for providing green polymeric materials, which can degrade after their service life [5]. ...
Polyurethane (PU) adhesives were prepared with bio-polyols obtained via acid-catalyzed polyhydric alcohol liquefaction of wood sawdust and polymeric diphenylmethane diisocyanate (pMDI). Two polyols, i.e., crude and purified liquefied wood (CLW and PLW), were obtained from the liquefaction process with a high yield of 99.7%. PU adhesives, namely CLWPU and PLWPU, were then prepared by reaction of CLW or PLW with pMDI at various isocyanate to hydroxyl group (NCO:OH) molar ratios of 0.5:1, 1:1, 1.5:1, and 2:1. The chemical structure and thermal behavior of the bio-polyols and the cured PU adhesives were analyzed by Fourier transform infrared spectroscopy (FTIR) and thermogravimetric analysis (TGA). Performance of the adhesives was evaluated by single-lap joint shear tests according to EN 302-1:2003, and by adhesive penetration. The highest shear strength was found at the NCO:OH molar ratio of 1.5:1 as 4.82 ± 1.01 N/mm2 and 4.80 ± 0.49 N/mm2 for CLWPU and PLWPU, respectively. The chemical structure and thermal properties of the cured CLWPLW and PLWPU adhesives were considerably influenced by the NCO:OH molar ratio.
... Generally, O-H and N-H groups in the polymeric backbone are important for the coating to have good adhesion with the metallic substrate, and one may use the polyol and chain extender having similar properties to have better adhesion. 61 Furthermore, the flexibility of the coatings was also not impressive as there were many cracks on the coatings. A similar case was with the pencil hardness and the impact test. ...
The current study presents an attempt to develop two molecules, namely sulfonated aromatic diol (SAD) and sulfonated aromatic diamine (SADAM), to induce flame retardancy, thermal stability, and dispersion ability for water-based polyurethane dispersions (WPUDs). The previously reported itaconic acid-based polyester polyol was used for prepolymer synthesis as well as for chain extension. Pre- and post-sulfonated compounds were subjected to characterization tests such as FTIR, 13C-NMR, 1H-NMR, and CHNS for confirmation of their structures. The standard dispersant used for the basis of comparison was commercially available dimethyl propionic acid (DMPA). WPUDs were synthesized in different molar concentrations of DMPA, SAD, and SADAM, and the covalent incorporation of all three molecules in the polymer backbone was confirmed by FTIR. The WPUD films were subjected to various thermal tests like TGA and DSC as well as mechanical tests like flexibility and pencil hardness. WPUD films obtained from SADAM showed a remarkable increase in Tg as well as char content. The THRI values for SAD- and SADAM-based films were better than DMPA-based films. SAD- and SADAM-based WPUD films also showed an increase in LOI value and UL-94 ratings with the maximum LOI value of 26. Dispersions based on DMPA showed better stability as compared to dispersions based on SAD and SADAM.
... Another novel approach to synthesize bio-based PU adhesive is to modify the active sites of castor oil for wood-to-wood and metal-to-metal bonding and the adhesive was synthesized using polyester polyols, epoxy based polyester polyols and castor oil based polyester polyols. The lap shear test has been conducted to evaluate adhesive strength and castor oil polyester polyols based PU adhesive proved to be best candidate among all the considered adhesives (Patel et al., 2009). Some of the polymer adhesives synthesized from biomaterials used in wood industries are depicted in Fig. 4. Despite numerous advantages of one-or two-part PU adhesives, shelf life of these adhesives is not enough. ...
The global market of polymer adhesives has been majorly contributed by large scale industries such as aerospace, automobile, construction, electronics, and healthcare industries. The phenol formaldehyde resins, elastomers and thermoplastic resins have laid the foundation for polymers in adhesive applications. The adhesion mechanisms of polymer adhesives such as mechanical interlocking, chemical bonding and thermodynamic adhesion plays an important role in deciding the mode of application. Among a plethora of properties, polymer adhesives provide excellent surface wettability with high adhesion property and product flexibility compared to other adhesives readily available in the market. These properties make them worth exploring in numerous applications ranging from aerospace to medical industry. In this article, different important polymers used in adhesive applications such as polyesters, polyurethanes, polyacrylates, silicone and epoxy-based adhesives are discussed in the light of above mentioned points. The synthesis of these polymers along with their properties and specific applications are discussed in detail. We describe commercially available polymer adhesives synthetically derived from petrochemical sources, and also some of the bio-sourced polymer adhesives with their area of application are discussed. This detailed book article would help researchers to gain a broader understanding of different available adhesives and help them choose the right one according to the specific application and properties needed, and thereby contribute to the growth of polymer adhesives globally.
... From the results presented in Fig. 1, it can be seen that the adhesives present normalized FTIR spectra with very similar profiles. The bands in the 3450 cm −1 region are attributed to the symmetric and asymmetric stretching vibrations of the N-H of the urethane groups, while the bands between 2950 and 2850 cm −1 correspond to the C-H stretching vibrations [6,30]. The peaks around 1710 and 1220 cm −1 , correspond to the stretching vibrations of the C]O and to the asymmetric stretching vibrations of the C-O linkages of the urethane group, respectively [6,30]. ...
... The bands in the 3450 cm −1 region are attributed to the symmetric and asymmetric stretching vibrations of the N-H of the urethane groups, while the bands between 2950 and 2850 cm −1 correspond to the C-H stretching vibrations [6,30]. The peaks around 1710 and 1220 cm −1 , correspond to the stretching vibrations of the C]O and to the asymmetric stretching vibrations of the C-O linkages of the urethane group, respectively [6,30]. The peaks at 1550 cm −1 are attributed to the inplane bending vibration of N-H moieties, while the peaks at 1400 cm −1 are attributed to the bending vibration of C-H linkages. ...
... They can cause irritation of the eyes, risks of cancer, skin irritation and bronchial health impacts. Some of these adhesives are very sensitive to hydrolysis, and stress scission [14], consequently the formaldehyde-based particleboard are susceptible to have a low water resistance. These compounds also cause serious environmental damage and contribute to the global supply shortage of petrochemical products [15]. ...
... The wide range of industrial applications of castor oil has led to a steady increase in demand for this material in the world market. This oil is very flexible in its applications such as in wood adhesives [14,18]. A wide range of variables that affect the performance of a wood adhesive which are related to the environment such as the level and rate of a change in both temperature and relative humidity [19]. ...
Particleboard is one of the composite panels fabricated from wood particles blended and bonded together with a synthetic or natural resin under hot pressure. These panels are widely used in the production of furniture and house building such as cabinets, stair treads, table tops, sliding doors, and other applications. Many factors contribute to the quality and properties of the panels. The adhesive is one of the considerations that should be measured in the production process of panels which is directly interrelated to the conditions of product, costs, and use. The demands of formaldehyde-free particleboard are continuously rising nowadays due to its low environmental impact and it is not harmful to human health. The natural oil based polyurethane resin is one of the alternatives to formaldehyde-based resins.
... The use of polyurethane adhesives in many industrial fields is becoming increasingly common. Their range of application includes not only the construction, automotive, and wood processing industries, but also the manufacturing of wind turbines and aircrafts (Desai et al. 2003b;Patel et al. 2009;Clerc et al. 2017;Najib et al. 2017). Because polyurethane adhesives cure without the need to add a curing agent, they are characterised by an easier reticulation method than epoxy adhesives, leading to reduced production costs. ...
... For many years, research has endeavoured to develop properties of polyurethane adhesives for various application areas by combining different modifications (Deka and Karak 2009;Patel et al. 2009). The physical and chemical properties of adhesives can be adjusted by changing the components comprising the adhesive mixture, which are added during prepolymer synthesis (Desai et al. 2003a;Deka and Karak 2009;Volkova et al. 2013). ...
Fillers can greatly affect the properties of adhesives, and this research aimed at enhancing the performance of adhesives by using different concentrations of fillers. This paper describes the influence of using recycled polyurethane particles (powder of particle size from 10 µm to 50 µm) as a filler on some properties of polyurethane adhesives for the gluing of wood. Two kinds of one-component, moisture-curing polyurethane adhesives were used. The observed properties were the contact angle between the wood and adhesive droplet, and the strength of bonded joints (shear strength). From the results, it was concluded that the contact angle increased with an increase in filler (in the entire observed range from 0% to 15% filler). The content of filler also affected the strength of bonded joints and their thermal stability. The strength of bonded joints decreased with an increase in filler content when samples were conditioned in cold water. However, the strength of bonded joints increased with an increase in filler content when samples were boiled in water.
... This may be attributed to CO structure, which is the main constituent of the soft segments in HPUs. CO thermally degrades in three stages; the first from about 300 to 350°C is related to degradation of ester groups while the other two stages in the temperature ranges of 350 to 425°C is attributed to decomposition of triacylglycerides with the formation of 10 undecanoic acid and heptenal [20,33]. The thermal degradation in NCO-PU polymeric chains start with the urethane bonds [34] followed by the main decomposition of the ester and aromatic rings at -310°C [35]. ...
In the present study, the effects of architecture and structural building blocks of the polyurethane chains on their properties were studied. New linear and hyperbranched polyurethanes (LPU and HPU) were prepared via A2 + B2 and A2 + B3 methodologies, respectively. Polyethylene glycol (PEG-1000) and castor oil (CO) were used as bi- and trifunctional monomers (B2 and B3), respectively. However, A2 monomers were synthesized by the reaction between ethylene glycol (EG) with terephthaloyl chloride (TPC) and reacting the product with excess toluene diisocyanate (TDI) to produce isocyanate-terminated PU (NCO-PU). NCO-PU was reacted with PEG to synthesize LPU; however, its reaction with CO synthesized HPU. NCO-PU, LPU and HPU were characterized by FTIR, H-NMR, GPC, TEM, TGA, DSC and XRD. The prepared PUs were applied as coatings and their physical, chemical and mechanical properties were investigated. The results showed that the degree of branching of HPU was 79%. No phase separation was observed in NCO-PU as indicated by its DSC curve. However, two phases are detected in HPU and LPU that represent to the hard and soft segments. NCO-PU displayed the highest crystallinity index (CrI = 89.26%). However, the high degree of branching in HPU led to lower CrI than LPU. The lack of entanglements in HPU led to its slightly lower solution viscosity than LPU. TEM images showed spherical PU nano-particles. The surface of HPU coating showed the highest gloss which is due to its low degree of crystallinity. HPU and LPU exhibited excellent chemical resistivity.
