New stabilisers for polyvinyl chloride mixed salts of calcium carboxylates

Transcription

1 Plasticheskie Massy,, 2000, p. 19 New stabilisers for polyvinyl chloride mixed salts of calcium carboxylates R.F. Nafikova, E.I. Nagumanova, Ya.M. Abdrashitov and K.S. Minsker Translation submitted by P. Curtis Selected from International Polymer Science and Technology, 27, 9, 2000, reference PM 00/0/19; transl. serial no Among the leading multitonnage polymers produced industrially both in Russia and abroad are polyvinyl chloride and copolymers based on vinyl chloride. On their basis, up to 4000 materials and articles are produced, which are used in all areas of industry, in agriculture, and in the home. Along with their many advantages, vinyl chloride polymers, and primarily polyvinyl chloride (PVC), have a serious shortcoming low resistance during processing and service (ref. 1). Therefore, great importance is attached to the synthesis and production of different additives and secondary substances, without which the processing of vinyl chloride polymers into the corresponding materials and articles and their use are impossible. They include, above all, socalled primary stabilisers/acceptors of HCl for PVC, based on group II metal carboxylates and protecting the polymer against intense breakdown under the action of heat, mechanochemical effects, light, etc. They increase the service life of articles and improve their stability and reliability in operation. Different salts of group I III metals, mainly organic, based on saturated and unsaturated carboxylic and hydrocarboxylic acids (primarily stearates, laurates, and salicylates), mixtures of metal carboxylates, and also complex (coprecipitated) salts based on them are currently produced on an industrial scale (ref. 2). One of the most widely used metalcontaining stabilisers for PVC is calcium stearate (C H COO) Ca, which was first produced on an industrial scale in Calcium stearate is practically nontoxic and is one of the main stabilisers for the production of nontoxic polymeric materials. Meanwhile, as a stabiliser/acceptor of HCl, this compound is fairly ineffective. Therefore, it is often used in synergistic composites with other stabilisers. Wide use is also made of other effective stabilisers based on coprecipitated calcium barium, calcium zinc, and other carboxylates (refs. 1 and 2). Mixed calcium carboxylates and their coprecipitated salts RCOOCaOOCR, where R is a fragment of one acid, and R is a fragment of the other acid, for example calcium stearate laurate, etc., have been less studied. Meanwhile, the search for and synthesis of new primary stabilisers for PVC that are noted for increased effectiveness and lower cost are urgent problems. The aim of the present work was the production of mixed calcium carboxylates of the general formula C H COOCaR, where R is a mixture of higher α,αisomeric acids of the general formula OOC C(CH ) C H (molecular weight ~20), and also products of 14±2 29±4 the reaction of phthalic and maleic acids with mono, di, and triols (Table 1), of markedly lower cost and also considerably simpler to produce, and the study of their effectiveness in the stabilisation of PVC in comparison with industrial stabiliser calcium stearate (stearate K, TU ). Mixed calcium salts based on derivatives of maleic and phthalic acids were produced in two stages. At the first stage, phthalic or maleic anhydride and alcohol (butyl alcohol, ethylene glycol, or glycerin) were introduced in appropriate quantity into a threenecked flask equipped with a reflux condenser and a thermocouple. The mixture was stirred at 33 ± 2 K (during the synthesis of maleic acid monoesters) and 383 ± 2 K (during the synthesis of phthalic acid derivatives) until complete transparency of the contents of the reactor. Synthesis of the monoesters was The authors are in the Bashkir State University, Ufa, and the 'Kauchuk' Closed Stock Company, Sterlitamak T/69

2 ceased on the achievement of an acid number of 32 ± mg KOH/g for monobutyl maleate, 2 ± mg KOH/g for monobutyl phthalate, 30 ± mg KOH/g for monoethylene glycol maleate, 26 ± mg KOH/g for monoethylene glycol phthalate, 29 ± mg KOH/g for monoglycerine maleate, and 23 ± mg KOH/g for monoglycerine phthalate. Then (second stage), a calculated quantity (1:1 molar ratio) of stearic acid and dispersed phase (water or a water acetone mixture in a 70:30 mass ratio) was added to the same reactor, the necessary temperature was established (38 ± K for water and 32 K for a water acetone mixture), after which a calculated quantity of calcium hydroxide or oxide was introduced during intense stirring. The process took h when the reaction was carried out in water, and 1. h when it was carried out in a water acetone mixture, ending once an acid number in the reaction mixture of no more than 2 mg KOH/g was achieved. The reaction product was filtered out and dried in nitrogen at 368 K. Mixed calcium salts based on stearic and higher α,αisomeric acids (HIAs) were produced in one stage by the reaction of equimolar concentrations (1:1 molar ratio) of stearic and α,αisomeric acids with a suspension of Ca(OH) 2 in water for 1 1. h (38 ± K) or in a mixture of water with acetone (70:30 mass ratio) for 1 h (32 ± K). A melt of stearic acid was introduced over a 30 min period into a flask filled to 2% of its volume with a dispersion medium (water or a mixture of water with acetone) at the reaction temperature, and a suspension of calcium hydroxide was introduced. At the end of the reaction (monitored from the acid number), the reaction mass was filtered, washed with water, and dried to a moisture content of the product of over 3 wt.%. In all cases, a white, finely dispersed powder was produced in ~100% yield (96 ± 1%). Certain characteristics of the products obtained are given in Table 1. The stabilising action of the new stabilisers compared with an equimolecular amount of calcium stearate (00 g/mol) was evaluated from the processability and a number of service characteristics of the films produced with the use of the following base formulation: 100 parts PVC S709M, 40 parts dialkyl phthalate (DAP6), 00 mol calcium salt (3 parts calcium stearate). The base PVC composites were prepared by the mixing of components on a laboratory mixer after preliminary heating at 23 ± 1 K for 20 min. Specimens in film form were produced from PVC composites by the thermal plasticisation method on a laboratory mill for 7 min at a roll temperature of 433/423 K. The service characteristics and their variation during artificial ageing in an oven (448 K) were evaluated by standard procedures. The time of the thermal stability of PVC, τ t, was determined from the time of the induction period during change in the colour of the congo red indicator as HCl is released during the ageing of PVC according to GOST ('Method for determining the thermal stability of polyvinyl chloride, vinyl chloride copolymers, and composites based on them using the congo red indicator'). The melt flow index i was determined on a Franck m plastometer at 43 K and a load of 10 kg according to GOST ('Plastics. Method for determining the melt flow index of thermoplastics'). The tensile strength σ and breaking elongation ε were t b determined on an RM20 tensile testing machine at an elongation rate v = 100 mm/min (1.67 mm/s) according to GOST ('Polymer films. Tensile test method'). Bulk water absorption W was evaluated according to GOST ('Polyvinyl chloride materials for flooring. Monitoring methods'). The degree of whiteness and loss of whiteness during ageing of films of the PVC composite were evaluated on a Bleskomer FB2 instrument. The standard employed was a sheet of opal glass of type MS20 with a degree of whiteness of 93%, with illumination at an angle of 4 and observation at 0. The initial whiteness of the films was determined on a white substrate. The loss of whiteness (% of initial whiteness) during the ageing of PVC was evaluated after heating of specimens at 448 K ( h). The electrical conductivity of an aqueous extract was determined at 298 K to TU The test results of the new stabilisers mixed calcium stearates (carboxylates) compared with the effectiveness of industrial stabiliser calcium stearate are given in Table 2. It can be maintained that no difficulties were observed in the milling of PVC films containing the new stabilisers, except for the composite with, the use of which in the base formulation produces a deposit on the rolls at the end of the milling cycle. In addition, for this formulation, abnormally high bulk water absorption was found. In general, for all films produced with the new stabilisers, increased water absorption compared with calcium stearate was noted, which must be borne in mind in their practical use. The melt flow of a PVC composite with the new stabilisers is higher in virtually all cases than when calcium stearate is introduced, which indicates that the processing of the corresponding PVC composites is made easier. At the same time, as can be seen from Table 2, an analysis of the physicomechanical properties of PVC films produced using the new stabilisers reveals no increase in the breaking elongation of specimens. On the whole, the mechanical properties of PVC films produced using the new stabilisers are always slightly lower than those of specimens produced using calcium stearate. Relatively poorer results were obtained with and CV(S), i.e. on the basis of esters of maleic acid with glycerin, and also with calcium vicalate (stearate). Meanwhile, when introduced into PVC composites in equimolar quantities, all specimens of the new stabilisers provide greater thermal stability than calcium stearate. A similar picture is observed in T/70

3 practice with respect to colour fastness. Note, however, that, according to the initial colour of PVC films produced by milling of the corresponding composites, compared with calcium stearate, considerably better results are given by,,, and CV(S). A comparison of stabilisers produced in aqueous (for the case of and ) and water acetone (70:30) (for and ) media indicates clearly that the service properties of the corresponding PVC films with respect to the combination of physicomechanical properties and the colour fastness are always higher when the new stabilisers produced in an aqueous medium are used, but with respect to the time of thermal stability they are slightly poorer than in the case of using stabilisers produced in a water acetone medium, evidently on account of the poorer degree of dispersion. Table 1 Characteristics of mixed calcium stearate carboxylates Index Stabiliser (molecular weight) (mixed salts) Abbreviation * Yield, wt.% Acid number, mg koh/g Characteristics of products temperature of start of melting, K calcium content product theoretical of practical Electrical conductivity of aqueous extract, S/m 1 Calcium glycol phthalate (stearate) (MW 32.7) 1 Calcium glycol phthalate (stearate) (MW 32.7) 2 Calcium α(β)glycerin phthalate (stearate) ( calcium α(β) monophthalate (stearate)) (MW 62.7) 2 Calcium α(β) monophthalate (stearate) (MW 62.7) 3 Calcium glycol (MW 482.6) 3 Calcium glycol (MW 482.6) 4 Calcium α(β)glycerin ( calcium α(β) mono (MW.7) 4 Calcium α(β)mono (MW.7) Calcium monobutyl (MW 494.7) 6 Calcium vicalate (stearic) (mixed salts of higher isomeric α,αdimethyl lauric, α,αdimethyl myristic, and α,αacids dimethylpalmitic with calcium stearic acid) (MW 83) 7 Calcium stearate (TU ) (MW 607) CV(S) CS * w a synthesis in a wateracetone mixture (70:30 mass ratio) T/71

4 Table 2 Stabilising action of new mixed calcium carboxylates in PVC films (base formulation: 100 parts PVC, 40 parts DAP, 00 g/mol calcium salt) Mixed calcium salts and their content in base formulation Stabiliser CV(S) CS (standard) Content of calcium salt in base formulation, parts Service properties of PVC films produced Time of thermal stability τ t (448 K) Melt flow index i m, g/10 min at 43 K (10 kg) Tensile strength σ t, MPa Breaking elongation ε b Bulk water absorption of specimen, W Initial degree of whiteness B i nit Final whiteness B f (after h at 448 K) Relative loss of degree of whiteness Initial colour of specimen after milling of PVC composition Y * W Y Y W W W W Y Processability composite of PVC D * Y = yellowy; W = white; D = deposit on rolls during milling of PVC composites Table 3 Results of testing complex stabiliser calcium monobutyl in formulation of cable plasticised rubber of grade O40 GOST standards Calcium stearate (control) 1. parts Calcium monobutyl () 1. parts 1 2 Tensile strength σ t, kgf/cm Breaking elongation ε b Volume resistivity, Ω cm Weight losses at 433 K over 6 h period 0 1 Hardness, kgf/cm a t 20 C a t 70 C 2 : Density, g/cm Thermal stability at 43 K, τ t Brittle point, K 233 T/72

5 Table 4 Results of tests of complex stabilisers (produced in aqueous and in wateracetone media) in formulation of ON grade f ilm (438 ± K) (milling temperature K) 1 Tensile strength, gf/cm 2 : along across 2 Breaking elongation 3 Thermal stability at 43 K, τ t 4 MFI, g/10 min (T = K, P = 16.6 kgf) rittle point, K GOST , amendment 1, 2 higher grade >183 0 grade 1 >0 00 Control (base formulation 100 parts PVC, 4 parts DOP, 3 parts St 2 Ca) > parts PVC, 4 parts DOP, 1. parts stabiliser >144 3 > > > parts PVC, 36 parts DOP, 3 parts stabiliser > >187 1 > > B With stood Note: glycol phthalate (stearate); calcium α,β glycerin phthalate (stearate) Table Results of tests of complex stabilisers (produced in aqueous and water acetone media) in formulation of tacky PVC sheet 1 Tensile strength σ t, 2 kgf/cm 2 Breaking elongation ε b 3 Volume resistivity at 393 K, Ω cm TU parts PVC, 2 parts DOP, 6 parts TOSS (not defined Transl.), 3 parts stabiliser calcium stearate Brittle point, K 243 Thermal stability at >240 K, τ t 6 MFI i m, g/10 min On the whole, the new stabilisers based on mixed salts of stearic acid with derivatives of phthalic or maleic acid, and also with α,αbranched carboxylic (C C ) acids, noted for 16 lower cost and adequate effectiveness, can be recommended for use in industry instead of calcium stearate. In particular, some new stabilisers produced in an aqueous or in a water acetone medium have been tested in industrial formulations: cable plasticised rubber of grade O40, film of grade ON, and tacky PVC sheet (Tables 3 ). No difficulties arose in the preparation of PVC composites of these materials and their milling. The material specimens produced satisfied the requirements laid down: cable plasticised rubber of grade O40 to the GOST standards; films of grade ON to GOST , and tacky PVC sheet to TU REFERENCES 1. K.S. Minsker et al., Degradation and stabilisation of vinyl chloride based polymers, Pergamon Press, 1988, 08 pp. 2. Chemical additives to polymers (handbook), Khimiya, Moscow, pp (No date given) T/73