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1 – 10 of 17Lijun Qiao, Allan J. Easteal, Clive J. Bolt, Philip K. Coveny and Robert A. Franich
Four different approaches were taken to improve the water resistance of poly(vinyl acetate) (PVAc) emulsion adhesives. The improved wood adhesives were tested according to the ISO…
Abstract
Four different approaches were taken to improve the water resistance of poly(vinyl acetate) (PVAc) emulsion adhesives. The improved wood adhesives were tested according to the ISO 9020 standard. Tensile storage modulus (E’) and glass transition temperature of the polymer films were measured using dynamic mechanical thermal analysis to quantify the influence of different approaches on those variables. Gel fraction and swelling ratio of the polymer film were measured to evaluate internal crosslink density. The experimental results showed that blending melamine/urea/formaldehyde (MUF) resin with PVAc emulsions modified the water resistance considerably and the film had a high E’ since an interpenetrating network‐type structure was formed in the polymer. The advantages and limitations of each modification were assessed on the basis of comparison of the results.
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Lijun Qiao, Allan J. Easteal, Clive J. Bolt, Philip K. Coveny and Robert A. Franich
Fillers with different chemical properties were used to study their effects on poly(vinyl acetate) (PVAc) emulsion wood adhesives. The elastoplastic behaviour of the filler…
Abstract
Fillers with different chemical properties were used to study their effects on poly(vinyl acetate) (PVAc) emulsion wood adhesives. The elastoplastic behaviour of the filler treated PVAc emulsions was studied using differential scanning calorimetry and dynamic mechanical thermal analysis. The results show that the glass transition temperature (Tg) of the polymer is not changed significantly by the addition of the fillers, while the tensile modulus is changed together with the hardness and stiffness. The viscosity of the emulsions and their performance on wood surfaces are greatly affected by fillers. Fillers with high oil‐absorption capacity increase viscosity to a greater extent. The acidity of the fillers influences the setting time for bonding of the emulsions to wood, and the water resistance, since some chemical reactions can take place during curing.
Lijun Qiao, Phil K. Coveny and Allan J. Easteal
Modifications of poly(vinyl alcohol) (PVA) can improve the properties and performance of poly(vinyl acetate) (PVAc) emulsions stabilized with these modified colloids. Water…
Abstract
Modifications of poly(vinyl alcohol) (PVA) can improve the properties and performance of poly(vinyl acetate) (PVAc) emulsions stabilized with these modified colloids. Water resistance and toughness of the emulsions as wood adhesives can be achieved through chemical reactions of the hydroxy groups of the colloid with various modifiers. The chemical changes can be carried out either in the preparation of PVA through hydrolysis of copolymers of vinyl acetate and other monomers, or by the reaction of modifiers with PVA aqueous solutions. The modified PVAc emulsions show better properties than those of the conventional emulsions in performance tests and applications. The modified colloids are becoming increasingly used in the manufacture of PVAc emulsions in the adhesive industry, because of their advantages over emulsions made using conventional (unmodified) PVA. The trend of current research is to introduce more functionality into the colloid, so that the traditional protective colloids can be modified to function as crosslinkers and chain transfer agents.
Lijun Qiao and Allan J. Easteal
Various modifications of polyvinyl acetate emulsion wood adhesive were made and their performance evaluated in standard tests. The results are interpreted in the context of…
Abstract
Various modifications of polyvinyl acetate emulsion wood adhesive were made and their performance evaluated in standard tests. The results are interpreted in the context of adhesion theories and the chemical structures of the polymers and wood. The adhesion of the polymers to wood and the cohesive strength of the polymers are the two predominant factors determining the performance of the adhesives. Adhesive strength in thermosetting resins is enhanced by irreversible chemical reactions that create extensive networks within the adhesive layer and strong bonds to the wood substrate, leading to strong and durable joints that passed all of the performance evaluation tests. Most of the PVAc emulsions exhibited good adhesive performance in the dry state, but failed in water soak and boiling water immersion tests since their adhesion and cohesion are mainly based on weaker physical interactions. Emulsions with (hard) core‐(soft) shell morphology and correspondingly high glass transition temperatures gave poor performance under all conditions.
Lijun Qiao, Allan J. Easteal, Clive J. Bolt, Philip K. Coveny and Robert A. Franich
Poly (vinyl acetate)‐based emulsion polymer/isocyanates (EPI) structural wood adhesives were prepared and their performance benchmark tested according to the specifications of the…
Abstract
Poly (vinyl acetate)‐based emulsion polymer/isocyanates (EPI) structural wood adhesives were prepared and their performance benchmark tested according to the specifications of the Japanese JAS‐111 standard. The changes of the glass transition temperature of the cured emulsions relative to unmodified poly(vinyl acetate) emulsion, measured using differential scanning calorimetry, indicated the chemical structure changes resulting from modification of poly(vinyl acetate) emulsion. The EPI adhesives showed excellent water resistance and near‐colourless gluelines in wood joints, ease of application and additional significant advantages over other types of wood adhesives. The performance test results are interpreted on the basis of the viscoelastic behaviour of free‐standing adhesive films. Other types of crosslinkers were used in the study to compare with the isocyanate hardeners.
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Lijun Wan, Jiaqi Qiao and Quansheng Sun
The application of reinforcing old bridges by adding external prestressed steel bundles is becoming more and more widespread. However, the long-term safety performance test of the…
Abstract
Purpose
The application of reinforcing old bridges by adding external prestressed steel bundles is becoming more and more widespread. However, the long-term safety performance test of the strengthening method is rarely carried out. In this paper, the bearing capacity of a 420 m prestressed concrete (PC) continuous girder bridge after five years of strengthening is analyzed.
Design/methodology/approach
The bridge model of the bridge structure and strengthening scheme is established by the finite element software of the bridge. The theoretical load-bearing capacity of the bridge under the latest standard load grade is obtained by finite element analysis. The actual bearing capacity of the bridge is obtained by field test. Through the comparative analysis of theory and practice, the health state of the bridge after five years of reinforced operation is judged. The damage to the overall stiffness and external prestressing of the bridge is also analyzed.
Findings
The results of deflection and strain show that the stiffness and strength of the secondary side span and the middle span decrease slightly, and the maximum reduction of bearing capacity is 4.5%. The static stiffness of the whole bridge decreases as a result of cracks, and the maximum decrease is 21%. In the past five years, the relaxation loss of the external prestressing of the bridge is 3.31–3.97%, which is the main reason for the decrease in bearing capacity.
Originality/value
Through the joint analysis of the bridge stiffness and the loss of external prestressing, the strengthening condition of the bridge after five years of operation is effectively analyzed. The strengthening effect of the external prestressed steel beam strengthening method is analyzed, which can provide a reference for similar bridge strengthening.
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Yan Zhang, Lijun Guan and Shaosheng Jin
This study aims to explore the degree of Chinese consumers' trust and confidence in the Chinese dairy products supply chain and the relationships between trust and overall…
Abstract
Purpose
This study aims to explore the degree of Chinese consumers' trust and confidence in the Chinese dairy products supply chain and the relationships between trust and overall confidence in dairy products safety and quality.
Design/methodology/approach
This study collected data from 1,278 respondents by field survey from five provinces of China. The data were analyzed using ordered logit model.
Findings
This study shows the following results: (1) Chinese consumer confidence in domestic dairy products and trust in actors of the dairy chain are at a moderate-to-low level. (2) Government regulators are considered to take the most responsibility, with both an optimism-enhancing and a pessimism-reducing effect (the former effect is greater), while perceived trust in dairy farmers and retailers has little effect. (3) Perceived care has both an optimism-enhancing and a pessimism-reducing effect, and the former effect is stronger. Competence and openness have an optimism-enhancing effect and a pessimism-reducing effect, respectively. (4) The importance of the three dimensions of trust related to optimism-increasing and pessimism-reduction is limited, except in the case of government regulators.
Originality/value
This study contributes to a better understanding of consumer trust in food safety and also help demonstrate to the actors and institutions involved in the dairy supply chain the best way to improve the performance of their duties to meet the consumers' needs for safe and quality dairy products.
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Lijun (Gillian) Lei, Yutao Li and Yan Luo
The emergence of social media as a corporate disclosure channel has caused significant changes in the production and dissemination of corporate information. This review identifies…
Abstract
The emergence of social media as a corporate disclosure channel has caused significant changes in the production and dissemination of corporate information. This review identifies important themes in recent research on the impact of social media on the corporate information environment and provides suggestions for further explorations of this new but fast-growing area of research. Specifically, we first review the evolution of Internet-based corporate disclosure and related regulations, and then focus on three recent streams of research: 1) companies’ use of social media; 2) information produced by non-corporate users and its impact on capital markets; and 3) the credibility of corporate information on social media platforms.
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Sipeng Fang, Zheqing Gong and Lijun Chen
The purpose of this paper is that the long fluorocarbon monomer is used to modify the latex. The film of the resultant latex has the C-F bond with high bond energy and low surface…
Abstract
Purpose
The purpose of this paper is that the long fluorocarbon monomer is used to modify the latex. The film of the resultant latex has the C-F bond with high bond energy and low surface energy, which can effectively improve the heat resistance and water resistance of the resultant film. In addition, a mixture of CO-436 and dibutyl maleate (DBM) as surfactants is used as the emulsifier, which brings the new application of the above surfactants.
Design/methodology/approach
The modified Vac-VeoVa10 copolymer nanometre latex modified VAc-VeoVa10 latex has been successfully synthesized via the semi-continuous seeded emulsion polymerization, which VAc and VeoVa10 is used as the main monomers and long fluorocarbon monomer was used as the functional monomer. Potassium persulphate (KPS) and the mixture of CO-436 and DBM were used as the initiator and emulsifier, respectively. The structure of resultant latex film was characterized by Fourier transform infrared spectroscopy (FTIR). The latex films were tested by thermogravimetric analysis, differential scanning calorimetry and contact angle. The particle size and its distribution of the latex were measured by the nano particle size analyzer.
Findings
Detailed investigation was conducted on the factors influencing the properties of the latex and film. The stability of the resultant latex is good. The average particles of the latex and its distribution are small and uniform, respectively. In comparison with the conventional latex film, the thermal stability and hydrophobicity of the resultant latex film are improved obviously.
Originality/value
The modification of p (VAc-VeoVa10) using a new emulsifier and long fluorocarbon monomer has not been widely reported. In this study, the modified Vac-VeoVa10 copolymer nanometre latex modified VAc-VeoVa10 latex has been successfully synthesized via the semi-continuous seeded emulsion polymerization, which VAc and VeoVa10 is used as the main monomers and long fluorocarbon monomer was used as the functional monomer. KPS and the mixture of CO-436 and DBM were used as the initiator and emulsifier, respectively.
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