Preparation and characterization on the eco-friendly corn starch based adhesive of with salient water resistance, mildew resistance

Starch adhesive is a commonly used bonding glue that is sustainable, formaldehyde-free and biodegradable. However, there are obviously some problems related to its high viscosity, poor water and mildew resistance. Hence, exploring a starch-based adhesive with good properties that satisfies the requirements of wood processing presents the context of the current research. Thus, corn starch was used as raw material to form oxidized starch (OCS) via oxidation using sodium periodate, it was reacted with a synthesis polyurea compound that prepared from hexanediamine-urea (HU) obtained by deamination to yield a oxidized starch-hexanediamine-urea adhesive (denoted hereafter as OCSHU). The oxidation process was optimized in terms of oxidant concentration, reaction time and temperature. Furthermore, the impact of HU addition on the mechanical properties of the adhesive was explored. Results indicate adhesive exhibited outstanding shear strength, when 13 % of NaIO4 was used as an oxidant to treat starch at 55 °C for 24 h, and involved in a subsequent reaction with 40 % of HU. The dry shear strength, 24 h cold water strength, 3 h hot water strength and 3 h boiling water strength are 1.84, 1.50, 1.32, and 1.31 MPa. Meantime, OCSHU adhesive solution revealed good storage stability whereas cured resin exhibited mildew resistance. The developed adhesive is a simple and green biomass wood adhesive.

Preparation of a high-strength, hydrophobic performance starch-based adhesive with oxidative cross-linking via Fenton's reagent

Starch is a highly attractive carbohydrate in the production for the preparation of adhesives in recent years, due to its widespread availability, renewability, and abundance of reactive hydroxyl groups. However, the mechanical properties, hydrophobicity, self-adhesion, and particularly high energy efficiency are generally unsatisfactory for current starch-based adhesives. On this premise, starch was oxidized using Fenton's reagent in a ""one-pot cooking" process. The prepared oxidized starch was chain expanded by polyvinyl alcohol (PVA) and then cross-linked with a 10 % isocyanate (PM-200) to fabricate a starch-based adhesive (SFA) with a network crosslinked structure. SF12A35%/2.5-55 adhesive shows significantly higher wet shear strength (1.18 MPa), a remarkable 94 % increase compared to SF0A35%/2.5-55. The adhesive film also demonstrates both hydrophobicity (99° contact angle) and exceptional energy efficiency, with a DSC test revealing a notable 10 % elevation in energy efficiency. In addition, the crosslinked structure increases its molecular weight, thereby increasing its self-adhesion (Fig. S1). This study opens up new possibilities for the design and manufacture of multifunctional starch-based adhesives.

A fully bio-based soy protein wood adhesive modified by citric acid with high water tolerance

Despite the widespread application prospect of soybean meal flour (SF) as a non-toxic and renewable wood adhesive, the practical application is limited by its poor mechanical properties and water resistance. In this work, a novel SF-based wood adhesive (CSP) was developed using citric acid (CA) as a modifier, which was further designated to produce plywood on a laboratory scale. Moreover, the effects of the mass ratio of CA/SF, hot-pressing temperature, and hot-pressing time on the bonding properties and water resistance of the resulting plywood were investigated in detail. As a result, under the optimal hot-pressing conditions (180 °C, 5 min), high-performance plywood bonded by CSP (CA/SF = 15/100) adhesive was fabricated, whose dry shear strength, cold-water wet shear strength (20 °C for 24 h), and hot-water wet shear strength (63 °C for 3 h) reached 1.65 MPa, 1.99 MPa, and 1.58 MPa, respectively. Due to the easy preparation process, sustainability, and favorable properties, the proposed fully bio-based CSP wood adhesive has great potential for the large-scale fabrication of eco-friendly wood panels in industry.

Eco-friendly bio-based adhesive for plywood from natural rubber latex (NRL)-blended isocyanate cross-linked starch

Synthetic adhesives used in the production of plywood are a matter of concern because of the emission of carcinogenic gas formaldehyde, increased environmental pollution, and the depletion of fossil fuels. In this study, a bioadhesive composed of natural rubber latex (NRL) and rice starch was developed. However, rice starch has low moisture resistance, resulting in low adhesion. Thus, to enhance the effectiveness of NRL-blended rice starch-based bioadhesive, rice starch was cross-linked with polymeric 4,4″-diphenylmethane diisocyanate (pMDI) resin, which is an environment-friendly, formaldehyde free, and moisture resistant that is highly compatible with starch. The chemical interaction, viscosity, solid content, and gel time of the developed NRL-isocyanate cross-linked rice starch-based bioadhesive was investigated. The efficacy of the formulated bioadhesive was demonstrated by the fabrication of plywood. The presence of isocyanate and urethane capabilities in the bioadhesive formulations was confirmed by Fourier transform infrared spectroscopy (FTIR). The bioadhesive type Iso-A was discovered to have the highest viscosity of 8270 mPa.s, whereas Iso-B has the shortest gel time of 3.46 min and the highest solid content of 44%; the higher solid content accelerates the gel time. In terms of physical and mechanical properties of plywood, Iso-B has the lowest thickness swelling (TS) value of 13%, lowest water absorption (WA) value of 52% and shear strength value of 1.92 MPa, which corresponds to the ISO 12466-2-2007 standard requirements. Based on the results, NRL-blended isocyanate starch-based bioadhesive could be a good potential raw material for eco-friendly plywood industries with adequate accuracy.

Preparation and characterization of the bonding performance of a starch-based water resistance adhesive by Schiff base reaction

Starch is one of the important raw materials for the preparation of biomass adhesives for its good viscosity and low-cost properties. However, the drawbacks of poor water resistance and bonding performance seriously restrict its application in the wood industry. To resolve those problems, an environment-friendly renewable, and high water resistance starch-based adhesive (OSTH) was prepared with oxidized starch and hexanediamine by Schiff base reaction. In order to optimize the adhesive preparation process, the effect of different oxidation times and oxidant addition on the mechanical performance of plywood were investigated. In addition, the curing behavior characteristics, thermomechanical properties, and thermal stability of the OSTH adhesives were analyzed by differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), and thermogravimetric analysis (TG). Fourier-transform infrared (FTIR) spectrometry and Liquid Chromatography-Mass Spectrometry (LC-MS) were used to explain the reaction mechanisms involved. The results show this adhesive has an excellent bonding performance at the oxidation time of 12 h with 11 % (w/w, dry starch basis) NaIO4 as an oxidant. The dry shear strength, 24-hour cold water, and 3-hour hot water (63 °C) soaking shear strength of the plywood bonded with this resin were respectively 1.87 MPa, 0.96 MPa, and 0.91 MPa, which satisfied the standard requirement of GB/T 9846-2015 (≥0.7 MPa). Thus, this study provided a potential strategy to prepare starch-based wood adhesives with good bonding performance and water resistance.

[Research progress of occupational hazards in plywood manufacturing]

Occupational disease hazards in plywood manufacturing mainly include wood dust, formaldehyde, phenol, ammonia, noise, terpene, microorganisms, etc. The exposure is complex with multiple factors accompanied or coexisted. In the production process, these factors are exceeded, and mass occupational disease hazard events occurred among workers. Exposure to wood dust, formaldehyde, terpene, etc., put workers at increased risk of cancer. This article provides a review of this issue in order to provide a scientific basis for the prevention and control of occupational disease hazards in plywood manufacturing.

Insights on the physico-chemical properties of alkali lignins from different agro-industrial residues and their use in phenol-formaldehyde wood adhesive formulation

The current study investigates for the first time the physico-chemical performances of lignins from cactus waste seeds (CWS) and spent coffee (SC) in comparison to previously isolated lignins from sugar byproducts (bagasse (SCB) and beet pulp (SBP)). In this work, lignin-phenol formaldehyde (LPF) resins were formulated using various lignin loadings (5-30 wt%), characterized and applied in the manufacturing of plywood panels. Several characterization techniques were applied to identify the chemical and morphological properties, thermal stability, and phenolic content of the extracted lignins, as well as the bonding strength and wood failure of the formulated resins. Results showed that the CWS and SC could be considered as an important source for lignin recovery with a considerable yield of 15.46 % and 27.08 % and an important hydroxyl phenolic content of 1.26 mmol/g and 1.36 mmol/g for CWS and SC, respectively. Interestingly, 20 wt% of extracted lignins in PF adhesives were the optimal formulation showing an improved modulus of elasticity (MOE) of about 3505, 3536 and 3515 N/mm², and a higher modulus of rupture (MOR) of about 55, 55 and 56 N/mm² for panels containing CWS, SC and SCB-lignins, respectively, over the reference panels (MOE = 3198 N/mm² and MOR = 48 N/mm²). Additionally, formaldehyde emission from plywood remarkably decreases by up to 20 % when lignin was incorporated into the PF matrix. Herein, the treatment of the CWS and SC for the extraction of alkali lignin and its application showed a new route to produce high added-value products from underused residues.

Preparation of a high bonding performance soybean protein-based adhesive with low crosslinker addition via microwave chemistry

Human health and environmental protection demand wood-based panel industry for innovative soy-based adhesives with high production efficiency, straightforward synthesis processes, non-toxicity, and high bonding performance. A simple and efficient microwave pretreatment process and low addition of bio-derived crosslinking agent was used in this study to prepare a non-toxic and high-bonding performance soybean protein-based adhesive. After 4 min of microwave pretreatment time, the complex quaternary structure of soybean protein molecule unfolds, the soybean protein disperses evenly and stably, and active groups of soybean protein molecules are exposed. After adding 3.85% crosslinking agent, the moisture absorption rate of the soybean protein-based adhesive decreases by 41.77%, the residual rate increases by 3.68%, and the wet shear strength of the resultant plywood increases to 1.12 MPa, which satisfies requirement of interior use plywood. Compared with previously reported soy-based adhesives, this adhesive is dependent on fewer chemical reagents, but has good bonding performance. The 204.41% of relative cell viability indicates the resultant adhesive was non-toxic. The proposed high-efficiency, high-performance, non-toxic biomass adhesive has great prospects for the industrial application.

Strategic hazard mitigation of waste furniture boards via pyrolysis: Pyrolysis behavior, mechanisms, and value-added products

Waste furniture boards (WFBs) contain hazardous formaldehyde and volatile organic compounds when left unmanaged or improperly disposed through landfilling and open burning. In this study, pyrolysis was examined as a disposal and recovery approach to convert three types of WFBs (i.e., particleboard, plywood, and fiberboard) into value-added chemicals using thermogravimetric analysis coupled with Fourier-transform infrared spectrometry (TG-FTIR) and pyrolysis coupled with gas chromatography/mass spectrometry (Py-GC/MS). TG-FTIR analysis shows that pyrolysis performed at an optimum temperature of 250-550 °C produced volatile products mainly consisting of carbon dioxide, carbon monoxide, and light hydrocarbons, such as methane. Py-GC/MS shows that pyrolysis at different final temperatures and heating rates recovered mainly phenols (25.9-54.7%) for potential use as additives in gasoline, colorants, and food. The calorific value of WFBs ranged from 16 to 18 MJ/kg but the WFBs showed high H/C (1.7-1.8) and O/C (0.8-1.0) ratios that provide low chemical energy during combustion. This result indicates that WFBs are not recommended to be burned directly as fuel, however, they can be pyrolyzed and converted into solid pyrolytic products such as biochar with improved properties for fuel application. Hazardous components, such as cyclopropylmethanol, were removed and converted into value-added compounds, such as 1,4:3,6-dianhydro-d-glucopyranose, for use in pharmaceuticals. These results show that the pyrolysis of WFBs at high temperature and low heating rate is a promising feature to produce value-added chemicals and reduce the formation of harmful chemical species. Thus, the release of hazardous formaldehyde and greenhouse gases into the environment is redirected.

Preparation of glycidyl methacrylate grafted starch adhesive to apply in high-performance and environment-friendly plywood

In this paper, cassava starch was used as the main raw material to prepare high performance and environment-friendly starch-based adhesive. Starch was grafted with glycidyl methacrylate (GMA), and then cross-linked with sodium trimetaphosphate (STMP). Before preparation of plywood, polyaryl polymethylene isocyanate (PAPI) was mixed as chain extension agent. Prepared starch adhesives are used in wood-based panel applications. From the Fourier transform infrared (FTIR) analysis, it was found that GMA was successfully grafted to the starch adhesives which improved the hydrophobicity and shear strength of the adhesive. The plywood using modified starch adhesive at pH 4.50-5.50 showed the highest wet shear strength, 1.00 MPa, which was 163% higher than that using unmodified starch adhesive. The Scanning electron microscopy (SEM) results showed that the original morphology of starch particles were destroyed and became smaller during GMA grafting, which made the modified starch-based adhesive easier to penetrate into the bonding interface of plywood. The characterization results of the adhesive film also showed that the mechanical properties of the adhesive were better when the grafting reaction pH was 4.50-5.50. Graft copolymerization modification of starch improves the hydrophobic properties of starch binders.

Formaldehyde and VOC emissions from plywood panels bonded with bio-oil phenolic resins

Pyrolysis bio-oil was used to partially substitute for phenol in reacting with formaldehyde for the production of bio-oil phenol formaldehyde plywood (BPFP) panels, with the phenol substitution ratio being 20%, 40%, or 60%. Emissions of formaldehyde and volatile organic compounds (VOCs) from the BPFP panels were studied using solid-phase micro-extraction (SPME) followed by headspace gas chromatography/mass spectrometry (GC/MS), and were compared to those from the phenol formaldehyde plywood (PFP) panels. The sources for VOCs were analyzed, and the health risks associated with the BPFP were examined. Results showed that at 80 °C: (1) Formaldehyde emissions from the BPFP panels were increased to about 4 times that of PFP; (2) VOCs emissions were significantly reduced by up to 84.9% mainly due to the greatly reduced phenol emissions, although the total number of VOCs was increased from 20 to 35; (3) BPFP presents greatly increased carcinogenic and non-carcinogenic health risks because of its much stronger emissions of formaldehyde, N,N-dimethylformamide, benzofuran, furfural, and many chemicals from the bio-oil. It is highly advisable that the health risks are properly taken care of before the wide application of BPFP, or similar bio-oil based engineered wood products.

The possibilities to identify combusted fuel based on an analysis of ash from local heating

Combustion of undesirable components with a high calorific value (waste: plastics, rubber, chipboard, plywood etc.) contribute to an increased emissions of PM particles. The possibility of identification of non-desirable fuels was verified by analysis of unburned carbon from bottom ash by means of pyrolysis-GC/MS. Compounds derived from thermal conversion of main wood components in the unburned carbon are formed by aldehydes, ketones, alkanes, alkenes, alkanoates, polycyclic aromatic hydrocarbons, compounds containing benzene, compounds containing phenol and nitrogen. Unburned carbon from plywood/chipboard contains compounds with nitrogen (heterocyclic and aliphatic) in increased concentrations (33-51 ng/mg) compared with unburned carbon from pure wood (7-12 ng/mg). The concentrations increased almost two times were proved for compounds containing phenols in unburned carbon from wood composite. Total amount of determined organic compounds is also almost two times higher than that contained in unburned carbon from wood. The indication of waste wood combustion from unburned carbon is possible using the ratio: phenol/(2-methylphenol+4-methylphenol).

A novel application of silicone-based flame-retardant adhesive in plywood

A silicone-based elastomer filled with vinyl-silane treated aluminum hydroxide was used to replace conventional polyurethane-based adhesive to provide a flame-retardant adhesive for plywood. The shear strength and fire performance of such a silicone-based (SI) adhesive glued plywood (SI/plywood) were investigated and compared to those of the polyurethane-based (PU) adhesive glued plywood (PU/plywood). The shear strength of the SI/plywood [(0.92 ± 0.09) MPa] was about 63% lower than that of the PU/plywood at room temperature, but it was less sensitive to water (62% reduction for the PU/plywood and 30% reduction for the SI/plywood after hot-water immersion at 63 °C for 3 h). The fire performance of plywood was assessed by a simulated match-flame ignition test (Mydrin test), lateral ignition and flame spread test, cone calorimetry, and thermocouple measurements. With a higher burn-though resistance and thermal barrier efficiency, and lower flame spread and heat release rate, the SI/plywood exhibited a superior fire-resistance and reaction-to-fire performance and improved fire-resistance as compared to the PU/plywood. The SI adhesive generated an inorganic protective layer on the sample surface that visibly suppressed glowing and smoldering of the plywood during combustion. The SI adhesive was also combined and reinforced with cellulosic fabric (CF) or glass fabric (GF) to prepare composite plywood (SI/CF/plywood and SI/GF/plywood) with improved fire performance. The cone calorimetry and thermocouple measurements indicated that the use of CF or GF in SI/CF/plywood and SI/GF/plywood, respectively, suppressed the delamination and cracking of the composite plywood and promoted the formation of an effective thermal barrier during smoldering and flaming combustion. Particularly, the SI/GF/plywood exhibited the most effective fire barrier with no crack formation, and the lowest heat release rate among the plywood types investigated in this study.

Potentially harmful secondary metabolites produced by indoor Chaetomium species on artificially and naturally contaminated building materials

The presence of the fungal genus Chaetomium and its secondary metabolites in indoor environments is suspected to have a negative impact on human health and well-being. About 200 metabolites have been currently described from Chaetomium spp., but only the bioactive compound group, chaetoglobosins, have been screened for and thus detected in buildings. In this study, we used a liquid chromatography high-resolution mass spectrometry approach to screen both artificially and naturally infected building materials for all the Chaetomium metabolites described in the literature. Pure agar cultures were also investigated to establish differences between metabolite production in vitro and on building materials as well as in comparison with non-indoor reference strains. On building materials, six different chaetoglobosins were detected in total concentrations of up to 950 mg/m² from Chaetomium globosum along with three different chaetoviridins/chaetomugilins in concentrations up to 200 mg/m² . Indoor Chaetomium spp. preferred wood-based materials over gypsum, both in terms of growth rate and metabolite production. Cochliodones were detected for the first time on all building materials infected by both C. globosum and Chaetomium elatum and are thus candidates as Chaetomium biomarkers. No sterigmatocystin was produced by Chaetomium spp. from indoor environment.

Visualization of the structural changes in plywood and gypsum board during the growth of Chaetomium globosum and Stachybotrys chartarum

Fungal growth in indoor environments is associated with many negative health effects. Many studies focus on brown- and white-rot fungi and their effect on wood, but there is none that reveals the influence of soft-rot fungi, such as Stachybotrys spp. and Chaetomium spp., on the structure of building materials such as plywood and gypsum wallboard. This study focuses on using micro-computed tomography (microCT) to investigate changes of the structure of plywood and gypsum wallboard during fungal degradation by S. chartarum and C. globosum. Changes in the materials as a result of dampness and fungal growth were determined by measuring porosity and pore shape via microCT. The results show that the composition of the building material influenced the level of penetration by fungi as shown by scanning electron microscopy (SEM). Plywood appeared to be the most affected, with the penetration of moisture and fungi throughout the whole thickness of the sample. Conversely, fungi grew only on the top cardboard in the gypsum wallboard and they did not have significant influence on the gypsum wallboard structure. The majority of the observed changes in gypsum wallboard occurred due to moisture. This paper suggests that the mycelium distribution within building materials and the structural changes, caused by dampness and fungal growth, depend on the type of the material.

The microcapsule-type formaldehyde scavenger: the preparation and the application in urea-formaldehyde adhesives

The limitation and regulation of formaldehyde emissions (FE) now shows great importance in wood-based materials such as plywood and particle board manufactured for building and furnishing materials. The widely used formaldehyde-based adhesives are one of the main sources of FE from the wood products. In this work, a new kind of long-term effective formaldehyde scavenger in the microcapsule form was prepared by using an intra-liquid desiccation method. The characterizations of the capsule (UC) were performed including the morphologies, the yields, the loading efficiency as well as its sustained-release of urea in aqueous conditions. The prepared UC could be integrated in urea-formaldehyde resins by simply physical blending, and the mixtures were available to be applied as the adhesives for the manufacture of plywood. The bonding strength (BS) and the FE of the bonded plywood in both short (3h) and long (12 week) period were evaluated in detail. It was found that the FE profile of the plywood behaved following a duple exponential law within 12 week. The addition of UC in the adhesive can effectively depress the FE of the plywood not only in a short period after preparation but also in a long-term period during its practical application. The slow released urea would continuously suppress the emission of toxic formaldehyde in a sustained manner without obviously deteriorating on the BS of the adhesives.

Analysis and evaluation of a fruit bin for apples

A fruit bin is an essential part of apple harvesting, storage, and transport. The lateral pressure distribution on the bin walls by apples in the bin are not well understood, thus making it harder to predict the behavior of the vertical walls of the bin. In this study, a bin was loaded with apples and deflections of the base and a vertical wall were experimentally measured and then modeled using finite element methods to understand typical static load distribution. One of the factors determining the accuracy of an analytical model is accurate representation of load distribution on the structure. A mathematical model was used to validate the lateral pressure distribution applied by the apples on the vertical walls and the bottom plate of the bin. The effect of unit weight of an apple and the angle of repose of apples on load distribution in the bin has been analyzed. Angle of repose is found to be a significant parameter for the lateral pressure distribution on the bin walls. A nonlinear lateral pressure distribution was observed along the depth from top to bottom of the bin. The resulting finite element model allows for comparison of deformation behavior of fruit bins constructed with a variety of materials, such as plywood, wood plastic composites, or a thermoplastic polymer. Although this study dealt with bins for apples, the sensitivity analyses for a range of unit weights and angles of repose for apples makes the analysis results versatile for use with other kinds of fruits and vegetables that fall within the reported range of unit weight and angle of repose.