Decreasing the formaldehyde emission in urea‐formaldehyde using modified starch by strongly acid process

The incorporation of the modified starch (MS) in urea‐formaldehyde resins at different stage of the synthesis was studied in this article. The synthesized resins were characterized by Fourier transform infrared spectroscopy, indicating that the ester bond can be introduced into the UF structure after the addition of MS. The curing reactions were examined with differential scanning calorimetry and it reveals that curing temperature of UF resin are slightly shifted to higher temperatures. To study the bonding strength and formaldehyde emission of the bonded plywood, the addition method and amount of MS are systematically investigated. The performance of the UF resins is remarkably improved by the addition of MS around 15% (weight percentage of the total resin) in the second stage. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40202.     

Catechol-containing waterborne polyurethane adhesive inspired by mussel proteins

A series of waterborne polyurethane (PDMAPU) containing catechol group were prepared by double-bond random copolymerization of terminated double bond polyurethane prepolymer with modified acrylamido dopamine under thermal initiation. This kind of mussel-like waterborne polyurethane adhesive is inspired by marine mussel, as well as it is environment-friendly and used in bonding of leather. FTIR and ¹H NMR proved the successful introduction of catechol group into polyurethane matrix. Oxidative cross-linking between catechol unit and molecular chain in PDMAPU structure, the thermal stability and crystallization ability of PDMAPU was significantly improved. The increase of the particle size of PDMAPU emulsion showed that the introduction of catechol group changed the microstructure of polyurethane and enhanced the cross-linking degree. The water resistance of polyurethane emulsion was further improved. Compared with PU without catechol group, the peel strength of leather substrate adhered by PDMAPU emulsion increased from 0.42 to 1.93 MPa, which indicated that PDMAPU has better bonding properties with leather. The bidentate hydrogen bond formed with catechol group as the reaction sites is considered to be the key reason for the adhesion of mussel-like polyurethane adhesive to hydrophilic substrates. This work provides an alternative to prepare environment-friendly high performance adhesive for hydrophilic substrates.     

Perfecting a polyurethane-type structural adhesive

A structural adhesive made from a woven glass material precoated with two-component polyurethane has been perfected. After the coating of the glass fabric, the adhesive is obtained by reacting a premix (dihydroxylated polymer) and a harder (free and blocked diisocyanates) in the presence of a tin catalysts. Values obtained for the strength of the assemblies (3 MPa on shearing) and for the working temperature (as low as 80°C) andt he allowed storage temperature (20°C) and time 91 year) of the adhesive are far better than those initially expected.     

Recycling of rigid polyurethane foam: Micro-milled powder used as active filler in polyurethane adhesives

Rigid polyurethane (PUR) foams are widely used as heat insulation material in construction industry or for electronic appliances manufacturing. After finishing their life-time, it is necessary to eliminate foam wastes. The aim of this study was to prepare a pair of industrial PUR adhesives of medium viscosity containing recycled rigid PUR foam. Three methods of milling were tested: knife-milling, two-roll milling, and ball-milling. Only two-roll milling gives the PUR micro-powder usable for following adhesives modification. The micro-powder was used as passive filler in PUR adhesives and potential reactivity for polyol pack replacement was studied. Hydroxyl and amine numbers were determined in mixture with virgin polyol. One-component PUR prepolymer adhesive was prepared using various dosages of the micro powder and the tensile strength of bound wood was measured. As additional parameters, also free film adhesive mechanical parameters were tested and particle size distribution of the micro powder was analyzed. Two adhesive formulations were prepared for independent evaluation of the micro powder reactivity. The results showed growing of the mechanical strength of wood bonding with growing dosage of the micro powder.     

Synthesis and characterization of waterborne polyurethane adhesive from MDI and HDI

A series of waterborne polyurethane adhesives (WPUAs) were prepared from diphenylmethane‐4,4′‐diisocyanate (MDI), 1,6‐hexamethylene diisocyanate (HDI), poly(1,4‐butanediol adipate) diol (PBA), 1,4‐butanediol (BDO), and internal‐emulsifying agents by the prepolymer mixing method. The viscosity, mechanical properties, thermal properties, and adhesion strength of the samples were measured. The structure–property relationship was discussed primarily. The results indicated that the MDI/HDI and PBA/BDO molar ratio influenced these properties. The WPUA exhibited excellent T‐peel strength and mechanical properties at a suitable MDI/HDI (or PBA/BDO) molar ratio. Moreover, higher MDI/HDI (or PBA/BDO) molar ratio resulted in higher thermal stability. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Synthesis of acrylate polymers by a novel emulsion polymerization for adhesive applications

Pressure‐sensitive adhesives (PSAs) are viscoelastic–elastomeric materials that can adhere strongly to solid surfaces with light contact pressure and a short contact time. Polyacrylates produced by solution polymerization are used widely because of their good adhesive properties. A novel emulsion polymerization was established to improve the low physical properties of PSA on the basis of conventional poly(n‐butyl acrylate) (PBA) by emulsion polymerization. PBA latex was synthesized by the emulsion polymerization of 50 wt % n‐butyl acrylate mixed with 15 wt % ethyl acetate (EA) with Emal‐10P and Emulgen‐920 as anionic and nonionic surfactants, respectively, at 70°C. Potassium persulfate (KPS) or a combination of KPS and dicumyl peroxide (DCP) was used as the initiator. The KPS/DCP system gave a very high‐molecular‐weight PBA of a narrow molecular weight distribution with a weight‐average molecular weight/number‐average molecular weight value of 1.01–1.03 in 15 min. The PSA tape was prepared by the casting of the PSA latex onto a corona poly(ethylene terephthalate) film as an adherent to obtain a 50‐μm‐dry‐thickness film. The PSA tape produced from PBA by the novel emulsion polymerization showed better adhesive properties, such as 180° peel adhesion, shear holding power, and rolling ball tack tests according to JIS and ASTM standards, than PSA tape produced from solution polymerization. The occlusion of a small amount of EA in emulsion particles before polymerization was found to give higher properties than those of PBA prepared by the addition of EA to the PBA latex after polymerization. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100:413–421, 2006     

Linear segmented polyurethanes. III. Mathematical model for a two-steps polymerization

In the first article of this sequel (J. Appl. Polym. Sci., 2018, 135, 45747), an experimental and theoretical investigation was developed on the two-steps synthesis of linear segmented thermoplastic polyurethanes. The reactions were carried out at 60°C, with methylene diphenyl diisocyanate (MDI), two poly(tetramethylene oxide) macrodiols, and 1,4-butanediol (BD) as chain extender. In our second article (J. Appl. Polym. Sci., 2019, 136, 46946), a mathematical model for the prepolymerization was developed, that involved integrating a differential equation for each generated polymer species. The present article extends such model, and predicts the molecular structure along the finishing stage. In each stage, the new model first solves the molar balances at polymer topologies level (i.e.,: Disregarding the molar mass distribution [MMD] of the reacted macrodiol chains), and then calculates the MMD of the evolving polymer and its main subsets through an algebraic convolution procedure. The model reproduces the prepolymerization predictions of our previous article, but is three orders of magnitude faster. In the finishing stage, up to 156,000 polymer topologies and 4.53 × 10⁸ polymer species were calculated; and the rate constant was readjusted to (k₂ = 0.00129 L mol⁻¹ s⁻¹), in order to fit the measured MMDs.     

Recycling of polymers from plastic packaging materials using the dissolution–reprecipitation technique

In this work, results are presented on the application of the dissolution/reprecipitation technique in the recycling of polymers from waste plastic packaging materials used in food, pharmaceuticals and detergents. Initially, the type of polymer in each packaging was identified using FT-IR. Furthermore, experimental conditions of the recycling process (including type of solvent/non-solvent, initial polymer concentration and dissolution temperature) were optimized using model polymers. The dissolution/reprecipitation technique was applied in the recycling of a number of plastic materials based on polyethylene (LDPE and HDPE), polypropylene, polystyrene, poly(ethylene terephthalate) and poly(vinyl chloride). The recovery of the polymer was measured and possible structural changes during the recycling procedure were assessed by FT-IR spectroscopy. Potential recycling-based degradation of the polymer was further investigated by measuring the thermal properties (melting point, crystallinity and glass transition temperature), of the polymer before and after recycling, using DSC, their molecular properties (average molecular weight) using viscosimetry, as well as their mechanical tensile properties. High recoveries were recorded in most samples with the properties of the recycled grades not substantially different from the original materials. However, a slight degradation was observed in a few samples. It seems that this method could be beneficial in waste packaging recycling program.     

Experimental study of the Mode I adhesive fracture energy in DCB specimens bonded with a polyurethane adhesive

The Mode I fracture energy of a polyurethane adhesive with low Young’s modulus was investigated. Metal adherends in standardized double cantilever beam (DCB) tests are typically too stiff for soft adhesives, making it difficult to measure the fracture energy accurately. However, soft adhesives, such as a single-component polyurethane adhesive tested in this paper, are in high demand in the automobile industry. Thus, accurate measurement techniques must be established. Flexible substrates composed of spring steel were used for the DCB tests to accommodate the deformation of the adhesive layer. First, the applicability of the flexible substrates was discussed using specimens bonded with an epoxy adhesive. For soft adhesives, however, the deformation of the adhesive layer must be considered in the calculation methods of the fracture energy. Although the deformation effect on the DCB tests has been discussed with Winkler’s elastic foundation, the crack length must be measured along with the load and displacement. To overcome the difficulty of measuring the crack length, a calculation method based on Winkler’s elastic foundation was introduced applying the compliance-based beam method (CBBM). Finally, the fracture energy of the polyurethane adhesive was discussed by comparing the calculation methods with and without measuring the crack length.     

新型光敏封装胶的研制

介绍了一种光敏封装胶的制备方法，分析了影响光敏封装胶性能的主要因素。试验表明，该胶具有光学性能好、粘接力强、光固化速度快、收缩率低等优点。可用于耦合器等光纤通讯器件的粘接封装。     

Depolymerization of renewable resources—lignin by sodium hydroxide as a catalyst and its applications to epoxy resin

Alkali lignin was successfully depolymerized into polyols with high hydroxyl number via direct hydrolysis using sodium hydroxide (NaOH) as a catalyst, without any organic solvent agent. Hydrolysis of lignin can produce a multitude of high‐value products via alkali‐catalyzed cleavage. This process usually gives good results with respect to the yield of phenols. Through this method, the numbers of the hydroxymethyl and phenolic hydroxyl groups of lignin had been dramatically increased, reaching 2.11%, nearly four times higher than that in the original one. Meanwhile, we added the same amounts (20 wt %) of different depolymerization of lignin (DL) into epoxy resin (EP), and the results showed that DL could not only increase the decomposition temperature of EP, but also remarkably improve its mechanical properties. The optimum reaction time was 1.5 h, the reaction temperature was 250°C, and the optimum sodium hydroxide concentration was 15 wt % for depolymerizing lignin. The mechanical and thermal properties of cured lignin‐based epoxy resin (LEP) were compared with cured neat EP. The cured DL‐based epoxy resin (DLEP) showed the highest adhesive shear strength up to 2.66 MPa, which displayed 122% of the adhesive shear strength of EP. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42176.     

单组分聚氨酯反应型热熔胶的研制

以异氰酸酯和多元醇为主要原料合成了系列单组分反应型湿固化聚氨酯热熔胶(PUR),考察了不同的软段结构、-NCO含量、固化时间、催化剂和增粘树脂等对其性能的影响。研究结果表明,采用自制的多元醇,设定w(-NCO)≈3.5%,当w(催化剂)=0.1%、w(增粘树脂)=20%时,所得PUR的综合性能较好,开放时间为7min,固化时间为24h,拉伸强度达到9.3MPa,初粘强度达到0.44MPa,剪切强度达到7.9MPa。     

Synchronous curable deoxidizing capability of epoxy–anhydride adhesive: Deoxidation quantification via spectroscopic analysis

Thermoset resins have been extensively utilized as an adhesive for electronic devices. In particular, semiconductor packaging materials between chips/substrates require electrical interconnections by using deoxidizing agents along with thermoset adhesives. In this study, a facile combination of hydroxyl‐functionalized epoxy and cyclohexane‐structured cyclic anhydrides produced curable acidic moieties, thereby allowing synchronous deoxidizing and curing without the use of a deoxidizing agent. By contrast, unitary cyclic anhydrides rarely presented acidic moieties, probably due to their rapid networkable reactivity caused by structural flexibility once opened, which was detected and quantified by spectroscopic analyses. This binary system in the absence of additional deoxidizing agents achieved the complete wetting of common Sn‐based solders via chip bonding systems due to the generated acidic moieties. The binary mixture also showed an increased glass transition temperature of 110 °C and enhanced Young's modulus of 1.6 GPa, relative to the ternary mixture (85 °C and 0.8 GPa) comprising a deoxidizing agent. This discovery is beneficial in terms of the simplification of composition design and mechanical robustness of solderable adhesives. Quantification via spectroscopic studies can also help anticipate the deoxidizing capability of binary and ternary systems at different temperatures for various bondable and solderable applications. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46639.     

Cellulose nanofibrils in biobased multilayer films for food packaging

The aim of this study was to evaluate a thin, TEMPO‐oxidized (2,2,6,6‐tetramethylpiperidine‐1‐oxyl–mediated oxidation) cellulose nanofibril (CNF) coating as a barrier layer in multilayer packaging films together with biobased polyethylenes. The purpose was also to explore the possible interactions between food products and the biobased films, and to evaluate the feasibility of these films for packaging of dry foods. CNF provided the biobased multilayer films with an oxygen barrier suitable for both demanding food products and modified atmosphere packaging (MAP). The MAP pouches made of these multilayer films retained their atmosphere and shape and protected ground hazelnuts from further oxidation for the storage time used in this study. However, irradiation used to sterilize packed foods and aroma compounds from clove in particular impaired the oxygen barrier property of the CNF layer, while the water vapor barrier property of the multilayer films remained unaffected. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44830.     

Mechanical recycling of nanocellulose containing multilayer packaging films

The aim of this study was to demonstrate mechanical recycling of low density polyethylene (LDPE) films coated with a thin layer of cellulose nanofibrils (CNFs). CNF acts as an effective barrier against oxygen and mineral oil residues. Two different CNF grades were tested, and both were applied onto plasma activated LDPE film using a pilot coating line. The coated films were shredded with the help of liquid nitrogen, compacted and compounded with virgin LDPE and compatibilizer, and processed into cast films and injection molded test specimens. The CNF coatings were completely blent as microscale agglomerates in the LDPE matrix. The effect of these agglomerates on the barrier and heat sealing properties was statistically insignificant compared to recycled uncoated LDPE. The mechanical properties were only moderately changed. CNF‐coated LDPE films can therefore be recycled back into films without sacrificing the characteristic properties of the base polymer. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46237.     

Synthesis of polyurethane acrylates by hydrogenated castor oil and dimer‐based polyester diol and study on pressure‐sensitive adhesive

Synthesis of polyurethane acrylate (PUA) and preparation of the UV‐cured pressure‐sensitive adhesives (PSA) are reported. Molecular weight (M_w) (by gel permeation chromatography) and viscosity (η*) of PUA were measured. Characterization of PUA and PSA before and after UV‐curing was made by FTIR. Increase of the hydroxyls from hydrogenated castor oil/hydroxyls from dimer‐based polyester diol (OH_HCO/OH_Diol) ratio decreased the M_w and η* value of PUA. Dynamic viscoelastic properties (by dynamic rheological spectrometer) and performance of the UV‐cured PSA were also studied. Increase of the OH_HCO/OH_Diol ratio increased the storage modulus (G′), the loss modulus (G″), and complex viscosity (Eta*) of the UV‐cured PSA, which, in turn, enhanced holding power and shear adhesion failure temperature (SAFT) and yet decreased peeling strength. Substitution of OB for DBTDL depressed the M_w and η* value of PUA, while the G″ and Eta* values of the UV‐cured PSA were elevated, which, in turn, increased the holding power and SAFT and yet depressed the peeling strength. Elevation of the tackifying resin content depressed the G′, G″, and Eta* values of the cured PSA and yet increased glass transition temperatures (T_g) of PSA, measured by differential scanning calorimetry. Peeling strength of PSA elevated as increasing the tackifying resin, while the holding power and SAFT fell. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 1814–1821, 2005     

聚氨酯粘合剂的研究

采用双预聚工艺,用多组分乙烯基单体共聚,在主链结构上引入含不同极性基团的单体,通过聚合合成多种类型的聚氨酯粘合剂。探讨了聚氨酯合成的条件,反应温度70~100℃、反应时间4~5 h,使用配比(质量比A∶B)为1∶2,25℃固化10~15 m in,聚氨酯的熔点明显提高,从而达到提高聚氨酯的耐高温性和粘接强度。     

Promotion effect of bifunctional five‐membered cyclic dithiocarbonate on curing of one‐component epoxy resin by imines as latent initiator

This article deals with curing of a one‐component epoxy resin containing a bifunctional five‐membered cyclic dithiocarbonate 1 with an imine 2 as a latent initiator. When 1 was added to a mixture of epoxy resin and 2 , the curing rate and initial adhesive strength increased higher than that without 1 . It was supposed that the reaction of 1 and an amine released from 2 was much faster than the amine–epoxide reaction, and a thiol group formed by the reaction of 1 with the amine accelerated the amine–epoxide reaction. The adhesive strength of the one‐component epoxy resin containing 10 mol % of 1 exhibited the highest value. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 961–964, 2004     

Synthesis and performance characteristics of a water‐based polyacrylate microemulsion for UHMWPE fiber adhesive coating

The water‐based polyacrylate microemulsion for ultrahigh molecular weight polyethylene (UHMWPE) fibers adhesive coating was synthesized by the emulsion polymerization of methyl methacrylate (MMA), butyl acrylate (BA), acrylic acid (AA), and hydroxyethyl acrylate (HEA) in the presence of a composite of sodium lauryl sulfate (SLS), OP‐10, and n‐octyl alcohol (NOA) as the emulsifier. The effects of the mass fraction of emulsifier and the reaction time on the properties of emulsion and its membrane were investigated. When m(BA) : m(MMA) : m(AA) : m(HEA) was 50 : 50 : 3 : 10 (wt ratio) and the mass fraction of emulsifier was 13 wt % and the reaction time was 3 h at 80°C, the latex particle diameter was 30 nm tested by transmission electron microscope (TEM). The Fourier transform infrared (FTIR) spectrometer and differential scanning calorimeter (DSC) were used to characterize the chemical structure and the glass transition temperature (T_g) of microemulsion membrane. The application results showed that this microemulsion was an ideal adhesive coating for UHMWPE fibers. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci, 2006     

Cure‐on‐demand wood adhesive based on the frontal polymerization of acrylates

We demonstrated for the first time a cure‐on‐demand wood adhesive using thermal frontal polymerization with Southern Pine wood. Monomer structure, initiator loading, and filler loading all had an impact on the strength of the adhesive and the cure‐on‐demand ability. More flexible, ethoxylated monomers produced stronger adhesives; though, the ethoxylate groups reduce the ability of the system to be polymerized frontally. Addition of a highly reactive comonomer (acrylic acid) to increase molecular weight between crosslinks along with the ethoxylated triacrylate increased the propensity for frontal polymerization and made a tougher polymer. Increasing initiator loading could help ensure front propagation, but a maximum initiator loading was reached where the gaseous byproducts of the peroxide initiator made the network highly porous and thus lacking strength. Fillers such as kaolin and sawdust helped overcome decreases in strength at high initiator loadings. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 44064.