Dynamic Mechanical Properties and Adhesive Joint Strengths of Emulsion Polymers Produced by Power Feed Technique. III. Adhesive Joint Strengths of Grafted Power Feed Copolymer

Power feed copolymers were synthesized using styrene and n-butyl acrylate through non-uniform feeding emulsion polymerization. Poly(vinyl alcohol) (PVA) was used as a protective colloid, onto which vinyl monomers were grafted. Power feed copolymer had a very broad glass transition temperature compared with random copolymer, even if grafting and/or crosslinking were introduced to the system. This tendency was almost the same as the non-grafted power feed copolymer where only low molecular weight surfactant was used.

Adhesive joint strengths of power feed copolymers were evaluated compared with random copolymers. In the case of usual linear power feed copolymer, the adhesive joint strengths were not higher than those of random copolymer, which was considered to be due to the lower film strengths of the power feed copolymer. Power feed copolymer having grafting showed slightly higher adhesive joint strengths over a wide range of temperatures than random copolymer. When crosslinking was introduced to the system, power feed copolymer showed much higher adhesive joint strengths over a wide temperature range.     

Dynamic Mechanical Properties and Adhesive Strengths of Emulsion Polymer by Power Feed Technique, I

Dynamic mechanical properties and adhesive strengths of power feed copolymer and random copolymer synthesized using styrene or methyl methacrylate and n-butyl acrylate were investigated. Although the two systems were synthesized from the same raw materials, power feed copolymer had a very broad transition compared with random copolymer. This fact was explained by the fact that the system synthesized through power feed method was an alloy of copolymers which are a continuous series from monomer A rich copolymers to monomer B rich copolymers. The dynamic mechanical behavior of film cast from solution was almost the same as that of emulsion film, which indicated more extensive application of power feed copolymer. In the P(nBA/St) system, power feed copolymer maintained its adhesive strengths over a wide temperature range compared with random copolymer. The absolute value, however, was not so high. This was due to the low cohesive strengths of the films.     

Dynamic Mechanical Properties and Adhesive Joint Strengths of Emulsion Polymers Produced by Power Feed Technique. II. Chemical Structure of Grafted Power Feed Polymer

Power feed copolymers were synthesized using styrene and n-butyl acrylate through a non-uniform feeding emulsion polymerization. Poly(vinyl alcohol) (PVA) was used as a protective colloid, onto which vinyl monomers were grafted. With the increase of PVA, grafting was also increased. Feeding method did not affect grafting nor grafting efficiency to a great extent. However, the amount of initiator had a negative correlation against grafting or grafting efficiency. From NMR spectroscopy, it was known that n-butyl acrylate monomer grafted onto PVA rather than copolymerized with styrene monomer. In order to increase the cohesive strengths of each phase, grafting was introduced to the power feed polymerization. In these cases, the chemical structure of grafted power feed polymer was investigated.     

Dynamic Mechanical Properties and Adhesive Joint Strengths of Emulsion Polymers Produced by Power Feed Technique. II. Chemical Structure of Grafted Power Feed Polymer

Power feed copolymers were synthesized using styrene and n-butyl acrylate through a non-uniform feeding emulsion polymerization. Poly(vinyl alcohol) (PVA) was used as a protective colloid, onto which vinyl monomers were grafted. With the increase of PVA, grafting was also increased. Feeding method did not affect grafting nor grafting efficiency to a great extent. However, the amount of initiator had a negative correlation against grafting or grafting efficiency. From NMR spectroscopy, it was known that n-butyl acrylate monomer grafted onto PVA rather than copolymerized with styrene monomer. In order to increase the cohesive strengths of each phase, grafting was introduced to the power feed polymerization. In these cases, the chemical structure of grafted power feed polymer was investigated.     

Kinetics of silane grafting and moisture crosslinking of polyethylene and ethylene propylene rubber

Peroxide initiated graft copolymerization of vinyl trimethoxy silane (VTMO) and vinyl triethoxy silane (VTEO) onto polyethylene (PE) and ethylene propylene copolymer (EPR) was studied. The kinetics of grafting, studied by differential scanning calorimetry, are the same for all the systems and the activation energy for VTMO is 170 ± 4 KJ/mol. Activation energy for VTEO is 185 ± 5 KJ/mol. The VTMO and VTEO graft copolymers of PE and EPR were prepared by reactive processing in a Brabender extruder in the temperature range of 150–200°C. Moisture catalyzed crosslinking of the silane grafted copolymer was also studied. The influence of the structure of the catalyst, its concentration, moisture concentration, temperature, and time on degree and rate of crosslinking has been evaluated. Crosslinking reactions follow first order kinetics with respect to both catalyst and moisture concentration. Activation energy (E_a) of the crosslinking reaction has been determined as 65 KJ mol^?1. The mechanism of grafting and crosslinking is discussed.     

淀粉基木材胶黏剂的制备与性能

以玉米淀粉为接枝骨架,过硫酸铵为引发剂,与接枝单体乙酸乙烯酯-丙烯酸丁酯进行接枝共聚反应,制取淀粉基木材胶黏剂。对得到的淀粉接枝共聚物进行了表征分析及性能研究。IR谱图表明,样品除了保持淀粉的特征吸收峰外,在1730—1740cm。之间出现了羰基特征吸收峰。X-粉末衍射图表明,样品多为弥散峰,证明淀粉接枝共聚物基本为少量结晶态与无定形态共存的结构。TG、DTA曲线证实了接枝共聚反应的发生,且淀粉接枝共聚物的热稳定性优于纯玉米淀粉。性能测试结果表明,制备的胶黏剂具有较好的高温稳定性、粘接性,各项指标已达到了国家标准HG／T2727—95中聚乙酸乙烯酯木材胶黏剂的性能指标,特别是压缩剪切干强度远远超过了国家标准。     

Adhesion and Failure Mechanisms of a Model Hot Melt Adhesive Bonded to Polypropylene

A model hot melt adhesive (HMA) based on an ethylene/vinyl acetate copolymer (EVA), an Escorez® hydrocarbon tackifier, and a wax has been used to bond together polypropylene (PP) films to give equilibrium bonding. Peel strengths were determined over a broad range of peel rates and test temperatures. Contrary to the peel behavior of joints with simple rubbery adhesives [1], peel strengths with this semi-crystalline adhesive are not rate-temperature superposable, and multiple transitions in failure locus occur. The semi-crystalline structure of the HMA also prevents rate-temperature superposition of its dynamic moduli.

At different test temperatures, the dependence of peel strength on peel rate shows some resemblance to the dependence of the loss tangent of the bulk adhesive on frequency. This is consistent with a previous result [2] that the HMA debonding term. D, varies with the loss tangent of a HMA at the T-peel debonding frequency.

This model HMA, similar to block copolymer/tackifier blends [3], consists of two phases: an EVA-rich and a tackifier-rich phase, in its amorphous region. At a low peel rate of 8.33 × 10^-5 m/s, the peel strength shows a maximum at a temperature that corresponds to the transition temperature of the tackifier-rich phase (T₁). At a higher peel rate of 8.33 × 10^-3 m/s, the peel strength rises with increasing test temperature, but becomes essentially constant at temperature T₁'. It is believed that, to optimize the peel strength of a HMA at ambient temperature, it is advantageous to formulate the EVA polymer (or other semi-crystalline polyolefins) with a compatible tackifier that yields a tackifier-rich phase with a transition temperature (T₁') in the vicinity of room temperature.     

硅烷交联聚氯乙烯的制备和性能

对由悬浮共聚合成的氯乙烯／乙烯基三乙氧基硅烷共聚树脂的水解交联行为和交联聚氯乙烯的性能进行了研究。结果发现，通过聚合过程添加pH调节剂可得到凝胶含量很低的氯乙烯／乙烯基三乙氧基硅烷共聚树脂；该类共聚树脂加工后有一定程度交联发生，凝胶含量随共聚树脂中乙烯基三乙氧基硅烷含量增加而增加；当加工样品在水中浸渍后凝胶含量又有较大幅度提高，说明水解交联的发生；交联后PVC高温力学性能和耐热变形性提高。     

Studies of crosslinked styrene–alkyl acrylate copolymers for oil absorbency application. I. Synthesis and characterization

The prepolymers for a novel oil absorbent were synthesized by copolymerizing styrene with 2‐ethylhexyl acrylate (EHA), lauryl acrylate (LA), lauryl methacrylate (LMA), and stearyl acrylate (SA). Suspension polymerization was carried out using benzoyl peroxide (BPO) as an initiator with a varying monomer feed ratio, and the copolymers were characterized by FTIR, ¹H‐NMR, DSC, and a solubility test. The copolymers were random copolymers with a single phase, and their compositions were similar to those in the monomer feed. The T_g of the copolymer could be controlled by varying the styrene/acrylate ratio. Acrylates introduced the crosslinking to linear polymers as a side reaction. Crosslinked copolymers were synthesized by adding divinylbenzene (DVB) as a crosslinking agent. At a low degree of crosslinking (0.5 wt % DVB), the T_g of the crosslinked copolymers was lower than or similar to that of the uncrosslinked ones. At a high degree of crosslinking, the T_g increased with increasing crosslinking density. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 903–913, 2000     

J-103石油管道热熔胶的研究

本文研究了以中低分子量热塑性弹性体SBS及乙烯基共聚物改性EVA的热熔胶配方体系。剥离强度PE－PE86．6N／cm，－30℃下柔性好。DSC分析显示：熔融温度范围较窄（ΔT＝23℃），软化峰值温度97℃。     

木材用交联型醋丙胶粘剂的研制

研制一种由醋酸乙烯、丙烯酸丁酯、特种单体共聚而成的水性交联型环保胶粘剂以替代目前广泛使用的氨基树脂,适应绿色环保要求。     

Miscibility and adhesive properties of ethylene vinyl acetate copolymer (EVA)‐based hot‐melt adhesives. I. Adhesive tensile strength

A series of ethylene vinyl acetate copolymers (EVA) were blended with some tackifier resins that are made from wood extracts, and possible relations between their miscibility and properties as hot‐melt adhesives (HMA) were investigated. From our previous report on miscibility of various EVA‐based HMAs, we chose some blends that represent some of typical miscibility types and measured their adhesive tensile strengths. When the blends were miscible at testing temperatures, the temperature at which the maximum value of adhesive tensile strength was recorded tended to move toward higher temperature as tackifier content of blends increased. This result corresponds to the glass transition temperature (T_g) of the blends that became higher as tackifier content of blends increased when blend components were miscible. In terms of HMA performances, we suggest that factors other than miscibility affect absolute values of adhesive tensile strength more directly than miscibility; this idea has to be investigated further in a future study. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 719–725, 2002     

Phase separation in random copolymers from high conversion free radical copolymerization, 3

The effect of phase separation in chemically heterogeneous copolymers on the dynamic-mechanical data, i. e. the dynamic shear modulus and mechanical damping, was studied over a wide temperature range for the binary copolymer systems AN/MA, AN/VA, CHMA/MA and S/BA (AN: acrylonitrile, VA: vinyl acetate, CHMA: cyclohexyl methacrylate, MA: methyl acrylate, S: styrene, BA: n-butyl acrylate). Dynamic-mechanical tests are very sensitive to detect two coexisting phases within the chemically heterogeneous copolymers. Additionally, the morphology of the two-phase copolymers was investigated by transmission electron microscopy. Without exception, the studied copolymers show domain-matrix structures of dispersed rubber-like phases in the thermoplastic matrix. The domain sizes depend on the monomer reactivity ratios and the copolymer miscibility.     

SBS改性胶粘剂的合成及其性能研究

在交联单体丙烯酸（AA）存在下,研究了SBS／MMA－BA四元接枝共聚合及其产物的性能。讨论了AA用量、混合单体用量、SBS起始浓度、混合单体配比及反应温度对接枝共聚物性能的影响。获得适宜的合成工艺条件。通过大量测试表明,用SBS改性的接枝共聚物配制的胶粘剂,具有粘结力大、剥离强度高、使用方便等特点。     

Physical properties of some vinyl tetrahydroabietate and vinyl maleopimarate acid anhydride copolymers

The stress–strain and torsional characteristics of some experimental copolymers of vinyl tetrahydroabietate and vinyl maleopimarate acid anhydride with vinyl chloride and vinyl acetate have been determined. Similar studies were also undertaken on peroxide-cured compositions of a vinyl chloride-vinyl tetrahydroabietate copolymer. Elastie moduli for the uncured copolymers range from 80,200 to 338,000 psi. Cured compositions of vinyl chloride–vinyl tetrahydroabietate copolymer exhibited both lower and higher moduli than that of the uncured copolymer. Some of the cured compositions appear to have an improved impact resistance over that of the uncured polymers.     

Influence of the Spew Fillet and other Parameters on the Stress Distribution in the Single Lap Joint

Even the most recent closed form analyses of single lap joints assume that the adhesive terminates in a square end. In practice a fillet of adhesive (hereafter called the spew) usually forms at the overlap ends. This spew can considerably reduce peak adhesive stresses and so strengthen the joint. An investigation has been made into the role of the spew for a wide range of joint parameters. The stress distribution across the adhesive thickness was also considered, and was found to be essentially uniform over a large part of the overlap length. However, near the overlap end, the stress variation across the thickness can be high, resulting in higher stresses and so lower strengths than would be expected considering average stress levels in the joint, but even after including the effect of this variation the maximum adhesive stresses have usually been found to be considerably lower than corresponding peak values predicted by closed form analysis of square ended joints.     

Improved adhesion of EVAs with different vinyl acetate contents treated with sulphuric acid

Four ethylene vinyl acetate copolymers (EVAs) containing 9, 12, 18 and 20 wt% vinyl acetate (VA) were treated with concentrated sulphuric acid to improve their adhesion to polychloroprene (PCP) adhesive. The tensile strength and Young's modulus of EVAs decreased as the VA content increased, due to the reduction in crystallinity of the polyethylene blocks in the copolymer. The modifications produced in the EVAs by treatment with sulphuric acid were followed using contact angle measurements (water, 25 °C), ATR-IR spectroscopy and scanning electron microscopy (SEM). Adhesive-bond strength was obtained by T-peel tests on treated EVA/polychloroprene adhesive joints. The vinyl acetate content in the EVA affected the extent, but not the nature, of the surface modification produced by treatment with sulphuric acid. The treatment produced both sulfonation and oxidation on the EVA surfaces. The higher the vinyl acetate content in the EVA, the more significant the modifications produced. Increased T-peel strengths of EVA/polychloroprene adhesive + 5 wt% polyisocyanate joints were obtained and a mixed failure (adhesion failure + cohesive failure in the adhesive) was produced. It was found that, to be effective, the treatment of EVAs must be carried out with 96 wt% sulphuric acid.     

Development of methanol selective membranes for separation of methanol–methyl tertiary butyl ether mixtures by pervaporation

Several copolymers of acrylonitrile (AN) were synthesized. Methanol selective membranes were prepared from these copolymers of AN. The other monomers in the copolymers were selected on the basis of their solubility parameter values relative to those of methanol. These were hydroxyethyl methacrylate, methacrylic acid, and vinyl pyrrolidone. Thus, pervaporative separation of methanol from its mixture with methyl tertiary butyl ether over the entire concentration range of 0–100% methanol was studied using these copolymer membranes of AN. For each copolymer of AN three different membranes with different copolymer compositions were prepared. Copolymers of AN with hydroxyethyl methacrylate and methacrylic acid showed high selectivity and moderate flux for methanol (2561, 773, 0.057, and 0.045 kg/m² h, respectively, with a membrane of 50‐μm thickness for a feed mixture containing 5% methanol at 30°C). A copolymer of AN with vinyl pyrrolidone showed comparable flux, but methanol selectivity of this membrane was poor. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 2645–2659, 1999     

Graft polymerization of vinyl acetate onto starch. Saponification to starch–g–poly(vinyl alcohol)

Graft polymerizations of vinyl acetate onto granular corn starch were initiated by cobalt-60 irradiation of starch-monomer-water mixtures, and ungrafted poly(vinylacetate) was separated from the graft copolymer by benzene extraction. Conversions of monomer to polymer were quantitative at a radiation dose of 1.0 Mrad. However, over half of the polymer was present as ungrafted poly-(vinyl acetate) (grafting efficiency less than 50%), and the graft copolymer contained only 34% grafted synthetic polymer (34% add-on). Lower irradiation doses produced lower conversions of monomer to polymer and gave graft copolymers with lower % add-on. Addition of minor amounts of acrylamide, methyl acrylate, and methacrylic acid as comonomers produced only small increases in % add-on and grafting efficiency. However, grafting efficiency was increased to 70% when a monomer mixture containing about 10% methyl methacrylate was used. Grafting efficiency could be increased to over 90% if the graft polymerization of vinyl acetate-methyl methacrylate was carried out near 0°C, although conversion of monomers to polymer was low and grafted polymer contained 40-50% poly(methyl methacrylate). Selected graft copolymers were treated with methanolic sodium hydroxide to convert starch–g–poly(vinyl acetate) to starch–g–poly(vinyl alcohol). The molecular weight of the poly(vinyl alcohol) moiety was about 30,000. The solubility of starch–g–poly(vinyl alcohol) in hot water was less than 50%; however, solubility could be increased by substituting either acid-modified or hypochlorite-oxidized starch for unmodified starch in the graft polymerization reaction. Vinyl acetate was also graft polymerized onto acid-modified starch which had been dispersed and partially solubilized by heating in water. A total irradiation dose of either 1.0 or 0.5 Mrad gave starch–g–poly(vinyl acetate) with about 35% add-on, and a grafting efficiency of about 40% was obtained. A film cast from a starch–g–poly(vinyl alcohol) copolymer in which homopolymer was not removed exhibited a higher ultimate tensile strength than a comparable physical mixture of starch and poly(vinyl alcohol).     

可固化性环氧-丙烯酸酯聚合物压敏胶的研究

在丙烯酸酯类单体的乳液聚合过程中加入环氧树脂,可以制得可固化性乳液压敏胶.研究了环氧树脂含量、聚合物的玻璃化温度、聚合工艺等因素对压敏胶主要性能的影响,并通过对交联度的测量,确认了环氧树脂参与聚合交联的事实.实验得出:采用核-壳聚合工艺、当环氧树脂的含量为30%(wt)、共聚物玻璃化温度为243.15K时,制得的可固化性乳液压敏胶的初黏力为9号球,固化后对铝合金的粘接强度可达10MPa.