摘要:

AbstractA series of polyacrylamides covering a wide molecular weight range were synthesized and employed as retention aids in a model papermaking system of cellulose fibers and titanium dioxide. The ability of the polymer to increase the proportion of added titanium dioxide that is retained in the formed paper sheet is strongly dependent on molecular weight, but not on pH. Adsorption isotherms on both pigment and fibers are strongly molecular weight dependent. Polyacrylamides have no more than a weak flocculating effect on fiber suspensions and stabilize dispersions of titanium dioxide. However, with mixed dispersions of fibers and pigment, in the same ratio (10:1) as in paper formation, strong coflocculation is evidenced by the higher molecular weight polyacrylamides. In this model system pigment retention is a consequence of a heteroflocculation by adsorbed polymer bridging between the particles of titanium dioxide and cellulose fibers, possibly augmented by improved filtration in the forming sheet. Electrostatic effects appear to be unimportant in the system under study.

ISSN:0021-8995    

DOI:10.1002/app.1977.070210101

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1977

数据来源: WILEY

摘要:

AbstractThree poly(4‐vinylpyridines) and a poly(2‐vinylpyridine) were studied for their effectiveness at increasing the retention of titanium dioxide a model papermaking system at pH 3.8. All the polymers are very efficient retention aids and do not greatly increase the time for the paper sheet to be formed. They are well adsorbed by both cellulose fibers and titanium dioxide. Although fiber suspensions are weakly flocculated by the poly(vinylpyridines), pigment suspensions are stabilized. Flocculation studies on mixed suspensions show that the poly(vinylpyridines) have a powerful heterocoagulation effect which mirrors the retention results. Some results are also reported in which the pH is brought to 6.5; under these conditions, polymer adsorption and its consequent effects compete with polymer precipitat

ISSN:0021-8995    

DOI:10.1002/app.1977.070210102

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1977

数据来源: WILEY

摘要:

AbstractThe pigment retention efficiency, in a model papermaking system, of anionically and cationically modified polyacrylamides was compared to that of the unmodified homopolymer. The anionic polyacrylamide is a much less efficient retention aid, especially at high pH's; the nonionic and cationic polymers perform similarly and without any marked pH dependence. However, it is the nonionic and anionic polyacrylamides which are similarly poor at fiber flocculation, at pH's between 4.5 and 7.5, whereas the cationic polymer is a good fiber flocculant. All three polymers stabilize pigment suspensions. The anionic polymer is not effective in heteroflocculation of mixed dispersions of fibers and pigment, whereas both the nonionic and cationic are good flocculants, the latter being less susceptible to overdosing. Equilibrium adsorption isotherms were determined; the cationic polymers is, unlike the other modified polyacrylamide, very well adsorbed by cellulose fibers. Onto titanium dioxide, polymers adsorbed in the order anionic

ISSN:0021-8995    

DOI:10.1002/app.1977.070210103

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1977

数据来源: WILEY

摘要:

AbstractIn an attempt to relate the retention behavior of water‐soluble polymers in paper formation from cellulose fibers and titanium dioxide, several copolymer types were synthesized. These were acrylamide–acrylonitrile random copolymers; block copolymers of acrylamide, acrylonitrile, and 2‐vinylpyridine with poly(ethylene oxide); and acrylamide graft copolymers of ethyl hydroxyethyl cellulose. Good retention and heteroflocculation behavior is shown only by the first of the above types of copolymers. Generally speaking, block copolymeric structures synthesized were of molecular size too small to act as good retention aids, although in a number of cases their performance was noticeably superior to that of the homopolymer analog. Adsorption isotherms are also reported and the overall results discussed in terms of a polymer bridging mechanism of heterofloccul

ISSN:0021-8995    

DOI:10.1002/app.1977.070210104

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1977

数据来源: WILEY

摘要:

AbstractThe degradation of dicumyl peroxide‐cured natural rubber was studied by the stress relaxation method. Experiments were carried out in air, in nitrogen, and by irradiation of UV light in the temperature range of 30–200°C. We attempted to divide factors of the degradation into two parts: that caused by heat and that by light, and to study the respective degradation quantitatively. The degradation caused by UV light in nitrogen was almost independent of temperature. However, the degradation caused by UV light in air increased with temperature and the rate of degradation caused by the interaction between light and oxygen was greater at high temperature than at low temperature. It was found that scission along main chains occurs for dicumyl peroxide‐cured natural rubber by photo‐oxidation as well as thermal o

ISSN:0021-8995    

DOI:10.1002/app.1977.070210105

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1977

数据来源: WILEY

摘要:

AbstractCopolymers of caprolactam with caprylolactam and laurolactam were prepared by activated anionic copolymerization under adiabatic conditions, at an initial polymerization temperature ofT0= 130°C. The drop of the crystalline phase content and changes of the copolymer morphological structure depending on the content of comonomers result in increasing toughness and deformability due to enhanced yielding ability. The dependences of the copolymer structure and properties on the concentration of comonomers are different for the two series of copolymers. This results from different courses of the polymerization and crystallization history as a consequence of a large difference between polymerization rates of caprylolactam and laurolactam

ISSN:0021-8995    

DOI:10.1002/app.1977.070210106

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1977

数据来源: WILEY

摘要:

AbstractA sample of the commercial copolymer vinyl chloride–vinyl acetate was fractionated by the GPC method in the preparative scale. The fractions thus obtained were characterized by light scattering, viscometry, GPC in the analytical scale, chemical analysis, and IR spectroscopy. They were compared with those obtained by precipitation fractionation. TheM̄wand [η] values from the light scattering and viscometry of fractions of the commercial copolymer were employed for the calculation of the Mark‐Houwink equation valid in THF at 25°C for a copolymer with vinyl acetate content of 10–13%. Universal calibration of the [η]·Mtype was confirmed experimentally for the above polymer. Effects which could change the correct interpretation of the GPC data were discussed in detail. Correct interpretation of the GPC data showed an agreement between the GPC, light scattering, and viscometric data w

ISSN:0021-8995    

DOI:10.1002/app.1977.070210107

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1977

数据来源: WILEY

摘要:

AbstractThe kinetics of the bulk thermal polymerization of phenyl glycidyl ether induced by trimethoxyboroxine were investigated. Infrared absorption spectroscopy and gel permeation chromatography were used to follow the course of polymerization, while proton and boron‐11 NMR spectroscopy were used to support the kinetic model developed. The postulated mechanism involves a fast‐initiated, nonstationary cationic polymerization with five elementary steps, including spontaneous and monomer transfer as well as a termination reaction. The trimethoxyboroxine was found to be incorporated into the structure of the cured polymer. The polymerization was followed at several temperatures and with several ratios of initial concentrations of trimethoxyboroxine to phenyl glycidyl et

ISSN:0021-8995    

DOI:10.1002/app.1977.070210108

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1977

数据来源: WILEY

摘要:

AbstractGas permeabilities of a copolymer of acrylonitrile and methyl acrylate were examined at the temperature range of 25° to 80°C. The change of activation energy of gas permeability constant at the glass transition temperature (65°C) was observed with N2, Ar, O2, and CO2, but no change was observed with He. The observation of the change of slope of the Arrhenius plot of gas permeability is discussed as a function of the diffusion constant (D) of a permeant gas at the glass transition temperature (Tg). The change occurs only if the value ofDatTgis smaller than a certain value (i.e., 5 × 10−8), according to the analysis of data appearing in the liter

ISSN:0021-8995    

DOI:10.1002/app.1977.070210109

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1977

数据来源: WILEY

摘要:

AbstractWhen used as a thickening agent in aqueous suspension, hydrolyzed starch–polyacrylonitrile graft copolymer (H‐SPAN) has broadly variable rheological properties, such as viscosity, storage modulus, and stress overshoot characteristics. A series of H‐SPAN preparations with variable swelling ratioQwere made by pretreating portions of stock material. As 1% suspensions in water, they had viscosities η that were non‐Newtonian. At a constant shear rate, η of the suspensions depended onQand had a sharp maximum in the midrange ofQ. In terms of reduced concentrationcQ, wherecis weight fraction of polymer, the highest η occurred whencQwas approximately 2. With isoionic dilution, each suspension had a constant reduced viscosity function, η/cQ, providedcQ>2. The value of η/cQfell rapidly whencQapproached 1. All thickeners of the closely packed gel–particle type so far examined have this relation of the reduced variables. The shear modulus calculated from measurements of primary normal force and corrected for solvent swelling, according to theory for rubber for elasticity, was essentially constant for each suspension measured during isoionic dilution tocQ= 2. The density of crosslinks calculated from the modulus was extremely low for all samples. The variable rheological properties of the preparations resulted primarily from differences in their low effective cross

ISSN:0021-8995    

DOI:10.1002/app.1977.070210110

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1977

数据来源: WILEY