The influence of the polymerization on properties of an ethylacrylate/2-ethyl hexylacrylate pressure-sensitive adhesive suspension

In this paper, the batch suspension copolymerization process for production of microsphere acrylic pressure-sensitive adhesives (PSA) is presented. The effects of different process and chemical parameters on adhesion properties are discussed. The reaction was monitored in-line by using attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectroscopy. Properties of the adhesive suspension (particle size), adhesive (gel phase, molecular weight, glass transition temperature (T_g)) and adhesion properties (tack, peel strength and shear) were determined. The results have shown that reaction kinetics strongly depends on polymerization temperature and initiator concentration. On the other hand, adhesion properties depend mainly on the T_g of the polymer and on the amount of insoluble gel fraction in the adhesive.     

EFFECT OF FILLER TREATMENT ON THE RHEOLOGICAL AND MECHANICAL PROPERTIES OF POLYETHYLENE COMPOSITES

Mechanical and Theological properties of a high density polyethylene (HDPE) filled with mica flakes, rutile and carbon black are investigated. Experimental results show that the Young modulus and the tensile strength of mica and rutile-HDPE composites are significantly enhanced by surface treatment of fillers with silane and titanate coupling agents. Surface treatments are shown to reduce the peak of the loss tangent (tan δ) and slightly increase the glass transition temperature (T_g). This is an indication of improved adhesion at the filler-matrix interface. The carbon black composites, however, hardly show any improvement by these treatments. The Theological properties are also effected by surface treatments, particularly at low shear rates. The low-shear rate viscosities (η _O) and characteristic time (λ ₀) of these systems are determined and compared. It is found that η ₀ and λ ₀ of carbon black composites are much higher than those of mica composites. This is probably due to the poor dispersion and/or agglomerates formation of the carbon black in the HDPE matrix. It is also suggested that the coupling agent, depending on its chemical structure and nature of the filler, may act as an adhesion promoter or as a lubricating agent.     

Mechanical and lamination properties of alumina green tapes obtained by aqueous tape-casting

Mechanical characterisation and lamination were carried out on alumina green tapes prepared by aqueous tape casting using two acrylic emulsions having different glass transition temperatures (T_g) as binders. The tensile strength and strain were strongly dependent on the binder nature and content. Namely, the mechanical properties of the green tapes reflected those of the binders at room temperature: the green tapes obtained with the higher T_g binder showed a brittle behaviour, whereas those obtained with the lower T_g binder showed an elastoplastic behaviour. The mechanical properties of the green tapes prepared by mixing the two acrylic binders lies in between, giving the possibility of tailoring the flexibility and strength in the range of the values obtained for pure binders. Lamination gave rise to an increase of both green and sintered densities, compared with monolayer specimens, whatever the composition of the binder system. Such improvements significantly depended on lamination pressure, but were insensitive to lamination temperature for the two temperatures tested higher than the T_g of the two binders. ©     

蓖麻油基聚氨酯-丙烯酸酯复合乳胶膜的水白化研究

采用蓖麻油基聚氨酯作为大分子乳化剂制备聚氨酯-丙烯酸酯(PUA)复合乳液。采用红外光谱表征了PUA乳胶膜的结构;用紫外分光光度计、动态热机械分析仪和差示扫描量热仪对PUA乳胶膜的水白化进行了表征。结果表明:在实验的时间范围内,乳胶膜的水白化程度随其浸水时间和浸水温度的增加而增加;当浸水温度(4 ℃)远低于干膜的玻璃化转变温度(T_g=57.8 ℃)时,乳胶膜浸水24 h不会水白化,湿膜的T_g及其储能模量与干膜相比几乎没有变化;在28 ℃的水中浸泡24 h时,湿膜的T_g小于干膜的T_g,其储能模量也降低,乳胶膜出现轻微水白化,将乳胶膜再次烘干后,胶膜可恢复原有清晰度。当乳胶膜在高于干膜T_g的水中(70 ℃)浸泡24 h时,其储能模量下降,湿膜的T_g大于干膜的T_g,再次烘干乳胶膜不会恢复原有的清晰度,其原因是膜内出现了与PUA分子依靠氢键紧密相连的冻结键合水。     

Chemical approaches toward the definition of new high-solid and high-performance fluorocoatings

Hydroxy bifunctional fluoropolyether oligomers (ZDOL) are presented suitable for use as resins or for the preparation of polyurethane, polyester and polyether higher OH functionality resins. The synthesis procedures are described and discussed, and the effect of fluorine content and resin structure on glass transition temperature T_g and viscosity of final resin is stressed. It appears that the highly fluorinated polyether type resins, like the tetraolic derivative (TOL) and its mixtures with ZDOL, are characterized by only one, extremely low T_g and minimum viscosity values. Solvent–resin interactions and criteria for obtaining compatibility with polyisocyanate crosslinkers are discussed, pointing out the key role of hydrogen bonding. High solid coatings (solvent content less than 30%) are obtained by curing with blocked aliphatic polyisocyanates, and a preliminary characterization of final materials based on their thermal transitions and mechanical properties is reported.     

Film formation from cationic electropaint systems containing resins with different glass transition temperature

Some phenomena in the deposition process of electropainting have not been well elucidated till now. In this paper, to investigate an influence of glass transition temperature (T_g) on film formation, the deposited film was observed with an atomic force microscope and the electrochemistry was investigated, using two kinds of cationic acrylate resin with different T_g (methyl methacrylate system (MMAs): T_g=70°C, and methyl acrylate system (MAs): T_g=5°C). Electrodeposition was performed under constant voltage or current condition.

At constant voltage, the deposition behavior in the two resin systems differed extremely. The MMAs, the resin with high T_g, produced a high resistance film. The MAs, the resin with low T_g, was deposited forming a film at a voltage lower than 20 V. At constant current, the film formation did not result in a rise in voltage. It behaved like a conductive film. When the resin with high T_g was used, particulate deposits were observed by AFM even in the induction period. The resin with low T_g formed flat deposits. These results suggest that paint deposition is initiated once electrolysis of water starts. In addition, there are two types of film formation on the cationic electropainting: high resistance film formation for the resin with high T_g, and ion-permeable film formation for the resin with low T_g. In both cases, film growth occurs at the film/bulk solution interface.     

Cooperative relaxations in amorphous polymers studied by thermally stimulated current depolarization

Thermally stimulated current depolarization (t.s.c.) was used to study the relaxations in amorphous polymers including poly (ethyl methacrylate) (PEMA), poly (methyl methacrylate) (PMMA), polystyrene (PS), polycarbonate (PC) and polyarylate (PAR) over temperature ranges covering the β and (glass transition) regions. A.c. dielectric was used to obtain activation energies (E_a) for PS and PC to verify the accuracy of those values determined by the t.s.c. thermal sampling method. At temperatures below the glass transition (T_g) the values of E_a were found to agree with those predicted using an activated states equation with a zero activation entropy. This is evidence of the localized, non-cooperative nature of the low temperature secondary β relaxations which are found to be characterized by a continuous variation of activation energies as a function of temperature. The measured values of E_a depart from the zero activation entropy curve and exhibit a prominent maximum at T_g. This behaviour is known to be due to an enhanced degree of cooperativity of segmental relaxations near T_g. The results indicate that the main advantage of the thermal sampling method is the high sensitivity and high temperature resolution for cooperative relaxations. For the polymers studied here, only PEMA and PMMA show a substantial population of cooperative relaxations more than 60°C below T_g. This is tentatively explained in terms of structural heterogeneity due to variable tacticity in the methacrylates. Compensation of the t.s.c. relaxation spectra plotted in Arrhenius or Eyring plots was found for all polymers to differing degrees. Some discussion of compensation is made in terms of independently measured values of the coefficient of thermal expansion.     

Effect of physical aging and thermal stress on the behavior of polyester/TGIC powder coatings

Physical aging, thermal stress, dynamic mechanical characteristics and thermal expansion of powder coatings from model terephthalic acid (TPA) and isophthalic acid (IPA)-based polyesters (PEs) cross-linked with triglycidyl isocyanurate (TGIC) were studied. Enthalpy relaxation and maximum compressive thermal stress were the properties used to follow the physical aging. The better mechanical properties of TPA-based PE/TGIC powder coatings seem to be due to a combined effect of several properties, i.e., cross-link density (ν_e), thermal expansion coefficient (_F^T) and glass transition temperature (T_g). The higher the values of ν_e, (_F^T) and T_g, the tighter is the coating network, the greater is the coating ability to expand thermally and the slower the physical aging process, respectively, all factors favoring the TPA polyester-based powder coatings.     

Blends of amorphous and crystalline polylactides with poly(methyl methacrylate) and poly(methyl acrylate): a miscibility study

Blends of amorphous and crystalline polylactides (PDLA and PLLA) with poly(methyl methacrylate) (PMMA) and poly(methyl acrylate) (PMA) have been prepared. Thermal behaviour and miscibility of these blends along the entire composition interval were studied by differential scanning calorimetry (d.s.c.). The results were compared with those obtained by dynamic mechanical analysis (DMTA). Only one T_g was found in PDLA/PMA and PDLA/PMMA blends, indicating a high degree of miscibility in both systems. Nevertheless, the PDLA/PMMA blend presented enlargements of the T_g width at high PMMA contents. In this case, additional evidence of complete miscibility was obtained by studying the evolution of the enthalpic recovery peaks which appear after different thermal annealing treatments. When the polylactide used was semicrystalline (PLLA), once the thermal history of the blends had been destroyed, crystallization of PLLA was disturbed in both blends PLLA/PMMA and PLLA/PMA, but in a rather different fashion: in the first case crystallization was almost prevented while in the second one it was favoured. This behaviour was explained in terms of the effect of the higher stiffness as indicated by the value of T_g for PMMA compared to that for PMA.     

Preparation and properties of disyndiotactic poly(alkyl crotonate)s

Ethyl, n-propyl, iso-propyl and n-butyl crotonates were polymerized by group transfer polymerization (GTP) using ketene trialkylsilyl acetals as initiators in the presence of mercury (II) iodide as catalyst and iodotriethylsilane as co-catalyst. Predominantly disyndiotactic polymers with number-average molecular weights ranging from 56,000 to 90,000 were obtained almost quantitatively. Thermal and mechanical properties of poly(alkyl crotonate)s, such as glass transition temperature (T_g), refractive index, transmissivity, Izod impact strength, Young's modulus, hardness, tensile strength, tensile elongation at break, gas permeability coefficient and density were measured. All the polycrotonates have 65–90 °C higher T_g than the corresponding polymethacrylates.     

Small angle neutron scattering studies of composite latex film structure

The mechanical properties and structure of composite films made of high T_g polystyrene (PS) nodules dispersed in a low T_g polybutylacrylate (PBuA) matrix were studied by means of dynamic mechanical spectrometry and small angle neutron scattering. For films cast from mixtures of PS and PBuA latexes, film mechanical reinforcement was obtained above a percolation threshold of about 30% PS volume fraction. A segregation of PS particles into dense clusters in the PBuA continuous matrix, reminiscent of a phase separation, was observed. For films cast from core-shell particles, this segregation phenomenon may be prevented, depending on the coverage of the PS core by the PBuA shell. An efficient core encapsulation in the core-shell morphology leads to poor contact between PS cores, and the elastic moduli are then close to that of the PBuA matrix. Upon annealing the films above the T_g of PS, extensive coalescence of PS particles occurred when large contacts were already present in the dry film at room temperature, and a percolating network of coalesced PS domains provides large elastic moduli at temperatures between the T_g of PBuA and PS. The coalescence was prevented when PS particles were taken apart by the PBuA shell.     

Effects of freeze-drying on the glass temperature of cyclic polystyrenes

The calorimetric glass temperature was measured for three cyclic polystyrenes with apparent molecular weights ranging from 4.0×10³ to 195.5×10³ g/mol for both bulk material and for samples freeze-dried from dilute solution. Freeze-drying from dilute solution was found to reduce the glass temperature by 7–14 K depending on the sample. These T_g depressions are 5–12 K greater than those found previously for freeze-dried linear polystyrene. Annealing at 403.2 and 443.2 K (130 and 170 °C) resulted in recovery of the T_g back to the bulk value with the time scales depending on both temperature and the magnitude of the T_g reduction; the low apparent activation energy dependence of the recovery of T_g precludes its being due to viscous flow.     

Diffusion controlled kinetics of crosslinking

Reactions of polymer formation and crosslinking become diffusion controlled when, during the reaction, the increasing glass transition temperature T_g comes close to the reaction temperature, the reaction still goes on below T_g but the reaction rate decreases steeply. A theory is presented relating the apparent rate constant to the difference between the reaction temperature and T_g based on the free volume or the Adam-Gibbs theory of glass transition. The theory is correlated with experiments on curing of diglycidyl ether of bisphenol A with 1,3-propanediamine. The implications for formation of protective films chemically crosslinked are discussed. The presence of a solvent and its evaporation affects the reaction rate through a change in concentrations of reactants as well as in T_g.     

Energy storage during inelastic deformation of glassy polymers

In this paper, aspects of the microstructural state of glassy polymers that evolve during physical ageing and inelastic deformation were studied. Differential scanning calorimetric (d.s.c.) measurements were performed on specimens of three glassy polymers: polystyrene (PS), polycarbonate (PC) and poly(methyl methacrylate) (PMMA). Materials were subjected to both a quenched and a well annealed heat treatment and subsequently deformed in compression to various levels of strain. Stress-strain curves and companion d.s.c. scans were compared.

The well known enthalpy overshoot at T_g was observed for the annealed samples, showing that ageing is accompanied by enthalpy relaxation. The annealed material was also found to require a higher stress to yield, and the additional work required to strain-soften the annealed polymer to the flow stress level of its quenched companion was found to correlate well with the area of the enthalpy overshoot of the annealed specimen.

Inelastic deformation was found to increase the specific enthalpy of both annealed and quenched specimens. In the annealed material, the enthalpy overshoot at T_g was found to decrease with inelastic strain and was completely erased by about −20% strain. Simultaneously, a pre-T_g exotherm was observed to develop with inelastic strain over a wide range of temperature. The pre-T_g exotherm was found to evolve until essentially reaching a steady-state profile at approximately −25% strain. This evolution coincided with the strain-softening phenomenon observed in the corresponding stress-strain results. A pre-T_g exotherm was also found to evolve with straining of the quenched material. Furthermore, the steady-state exotherms of the quenched and annealed materials were found to be nearly identical, as were their corresponding flow stress values after strain softening.

Finally, a second, post-T_g exotherm was found to develop with further straining beyond strains of −25%. This exotherm was found to increase with inelastic strain and coincided with the occurrence of strain hardening (due to chain orientation) in the materials.

The presence of two distinct and separately evolving exotherms in the inelastically deformed polymers indicates the existence of two separate deformation resistances in glassy polymers, one related to the initial yield and strain-softening behaviour, and the other to the orientation-induced strain hardening of the material. The observation that the pre-T_g exotherm is spread over a wide temperature range reflects the distributed nature of the structural state and may be quantified using a distribution in activation energy for the local rearrangements. The results therefore provide valuable information about the processes that must be accounted for in the development of accurate constitutive models of mechanical behaviour.     

Influence of co-solvent content on electro-deposition behavior of acrylic lattices of different glass transition temperatures

The influence of co-solvent content on the constant-voltage electro-deposition behavior of three acrylic lattices was investigated. It was found that co-solvent effect is system-specific and the type and the extent of the influence depend on the specific features of the latex itself, specially its glass transition temperature, T_g. For a low-T_g high molecular weight latex, the addition of co-solvent makes the electro-coagulates more sticky but it does not show a quick influence on the deposition behavior. In contrast for higher T_g lattices the influence is more pronounced. For medium and high-T_g lattices, the co-solvent was found to have a significant influence on the electro-deposition behavior and the film morphology.     

Incidence of the polyol nature in waterborne polyurethane dispersions on their performance as coatings on stainless steel

Three waterborne polyurethane dispersions derived from polyester, polyether and polycarbonate diols with molecular weight of 1000 Da were synthesized by the acetone method and used as coatings on stainless steel 304 plates. The properties of the dispersions and the polyurethane films were influenced by the polyol nature. The polyurethanes obtained with polyether or polyester showed higher degree of phase separation between the soft and the hard segment. The higher adhesive strength under shear stresses was obtained in the joints produced with the waterborne dispersion obtained with polycarbonate diol. The properties of the polyurethane coating obtained with polycarbonate diol on stainless steel 304 were significantly higher as compared with the others. Improved performance of coatings obtained with polycarbonate diol was ascribed to the higher polarity of the carbonate groups that contributed to additional hydrogen bond formation between soft segments with respect to those obtained with polyether or polyester     

The glass temperature of polymer blends

The entropy theory of glasses is used to derive the glass temperature, T_g, of a binary polymer blend in terms of the glass temperatures of the two substituents. The formula is T_g = B₁T_g1 + B₂T_g2, where B_i is the fraction of flexible bonds of substituent i. A bond is flexible if rotation about it changes the shape of the molecule. Bonds in side groups as well as in the backbone are to be counted. This formula assumes that the free volume, taken here to be the volume fraction of empty lattice sites, is the same for each of the three materials. It has no parameters. The above equation expressed in weight fractions, W_i, is (T_g − T_g1)W₁(γ₁/ω₁) + (T_g − T_g2)W₂(γ₂/ω₂) = 0, where ω_i is the weight of a monomer unit and gg_i is the number of flexible bonds per monomer unit. A more general treatment is given. One variation of the more general treatment which expresses the properties of the blend in purely additive terms gives T_g = B₁T_g1 + B₂T_g2 + KB₁B₂(T_g1 − T_g2)(V₀₁ − V₀₂), where V_0i are the free volume fractions of the homopolymers at their glass temperatures and K is a constant. The added term is usually small. The most general form of the equation requires the energy of interaction between the two unlike molecules, which can be estimated by volume measurements on the blend.     

Ultraviolet light absorber mobility in crosslinked coatings: Experiments and modeling

The diffusion of an ultraviolet absorber (UVA) across a concentration step change in an acrylic melamine clearcoat was measured via micro-ultraviolet spectroscopy. Concentration profiles were obtained after diffusion times of 4–200 h at steady temperatures of 70, 80, and 90 °C. The glass transition temperature of the coating was measured via dynamic mechanical analysis for each time–temperature pair, and T_g was observed to increase with thermal aging, with a faster rate of increase at higher aging temperatures. The change in T_g was modeled using a first-order dependence on the deviation from a long-time T_g asymptote. The diffusion coefficient was then represented by a free volume expression, and the combination provided an accurate model of the measured concentration profiles. The time-dependent increases in glass transition temperature helped to explain why UVA diffusion does not alleviate concentration gradients created by photooxidation under natural weathering conditions.     

木器高光面漆用丙烯酸酯树脂的制备与性能研究

以甲基丙烯酸甲酯(MMA)和丙烯酸丁酯(BA)为主单体,多种交联体系为功能单体,采用水性固体丙烯酸树脂(SR-675、QZ-7001、QZ-7002)和聚合型乳化剂NRS-10搭配作为体系的表面活性剂,通过预乳化半连续乳液聚合工艺合成了木器高光面漆用丙烯酸酯树脂。探究了水性固体丙烯酸树脂酸值、T_g、相对分子质量以及用量;NRS-10用量、引发剂(APS)用量和树脂T_g对树脂及涂膜性能的影响。结果表明:当采用水性固体丙烯酸树脂SR-675且用量占单体总量的20%(下同)、NRS-10占0.5%、APS占0.75%,树脂T_g设计为40 ℃时,合成的丙烯酸酯树脂制备成木器面漆,涂膜光泽高、附着力好、耐水性好,铅笔硬度可达2H。     

Crystal lattice deformation and the mesophase in poly(ethylene terephthalate) uniaxially drawn by solid-state coextrusion

The development of crystalline and mesophase structure on drawing of poly(ethylene terephthalate) (PET) has been studied. The uniaxial drawing has been done by solid-state coextrusion from 50 to 90°C. The unit-cell parameters of stress-induced crystallites in extrudates have been determined as a function of extrusion draw ratio (EDR) up to 4.4 and at an extrusion temperature (ET) above T_g, at 70 and 90°C. The higher the EDR, the longer the c-axis chain direction, the shorter the a and b axes and the smaller the unit-cell volume. In comparison with the conventional lattice parameters obtained by Bunn and Fisher, the highest elongation of the c axis is near 10%. These features imply that the lattice of stress-induced crystallites is far from the closest packing. Coextrudates made below the T_g of PET differ markedly from those made above T_g. Wide-angle X-ray diffraction (WAXD) patterns of PET extruded at 50°C (below T_g) even at high draw ratio exhibit small and/or imperfect crystallites. They appear much as a mesophase. The distance between macromolecular chains ranges from 3.2 to 5.4 Å. The shortest value in the mesophase approaches the interplanar crystal distance of 3.4 Å for the (100) crystal face, on which the benzene rings lie. The crystalline peak separation of the PET, WAXD curve has been evaluated to obtain absolute crystallinities and the content of mesophase and amorphous phase.