The Coloration of Polypropylene

The Coloration of Polypropylene

JOHN SHORE

1CI Ltd, Organics Division Hexagon House Blackley Manchester M9 3DA

Introduction In spite of recent changes in the availability and price of chemical feedstocks and derived intermediates, continued growth in demand for synthetic fibres seems assured. The inherently valuable characteristics of mechanical strength and chemical resistance have been supplemented by chemical and physical modifications to produce a versatile range of variants appropriate to specific end-uses. The numerous varieties of nylon, polyester and polyacrylonitrile are therefore able to account for over 90% of the total world production of synthetic fibres [ 1 ] .

The most likely challenger to this established trio, apart from the unlikely possibility of a totally new and cheap fibrous polymer, is polypropylene, which currently is fourth in order of total production. As with polyacrylonitrile, which is also derived from propylene, polypropylene is made by a simple sequence from one essential hydrocarbon, compared with the more complicated processes for nylon 6.6 (cyclohexane and butadiene) or polyester (p-xylene and ethylene glycol).

Polypropylene fibres were first introduced in 1961 and consumption has grown rapidly in the period under review. Production in the USA [2], which represents almost half the world level [ I ] , more than trebled from 35,000 tons in 1966 [3] to 105-125,000 tons in 1968 [ 2 , 4 ] , and by 1971 had reached 145,000 tons [4] . Consumption of polypropylene face yarns for carpets had reached a level corresponding to about 30,000 tons p.a. by late 1973 [5].

Developments in Manufacture Uses of polypropylene filaments, such as filter fabrics and cordage, for which mass-coloured identification tints or the uncoloured appearance are suitable, soon became established. The scope for development of these applications is limited, however, and the period of maximum growth coincided with the development of dyeable polypropylenes. In 1966 the carpet industry was taking about 75% of the polypropylene production in the USA [3], but by 1968 this proportion had fallen to about 50% and newer outlets such as upholstery and apparel were being explored [2]. Corresponding data for the UK in 1970 show that cordage and sacking still accounted for half the total and carpet applications consumed only 25%, mainly as backing materials rather than face yarns [6].

The adoption of polypropylene as a carpet face yarn has not yet reached the level of consumption of the other three major synthetic fibres. It was estimated [3] that in 1966 polypropylene represented about 1 1% of the total consumption of carpet fibres in the USA. Statistics for the last quarter of 1973 revealed [ 5 ] that only 4.5% of the carpet face yarns

used in the USA were polypropylene, compared with acrylic (1 O%), polyester (1 2.5%) and nylon (67%).

Low cost, combined with high strength and resistance to chemicals and solvents, soon commended polypropylene as a useful fibre for twines, ropes, nets, sacking and filter fabrics. Abrasion resistance, knot strength, resilience and stain resistance are valuable properties for these outlets and for carpets, but the low melting point of polypropylene makes it unsuitable for PVC coated carpets [7]. The development of acid-dyeable variants suitable for batchwise dyeing and metallised polypropylene for printing or continuous dyeing has encouraged the adoption of bulked continuous filament yarns for tufted carpets. Resistance of polypropylene to insects and micro-organisms and its highly hydrophobic properties contribute to its usefulness in artificial grass, sandbags, webbing for outdoor furnishings and as staple fibre in needlefelt floor-coverings for outdoor use. Unmodified polypropylene shows only limited resistance to photodegradation and weathering and this was a serious drawback until improved stabilising additives were incorporated in order to increase the effective life of the material in outdoor exposure conditions [8 ,9] .

The low density of polypropylene, giving a high strength/weight ratio, and the introduction of stuffer-box textured yarns to increase covering power and heat insulation, have proved advantageous in blankets and woven upholstery. Fine-denier false-twist textured yarns have been developed to improve handle and comfort in wear of knitted garments. Dimensional stability is good but disadvantages of polypropylene in the apparel field include electrostatic problems arising from the zero regain, high flammability and softening during ironing at moderate temperatures (m.p. 165-170°C). The development of dyeable variants has permitted considera- tion of polypropylene as an apparel fibre, although the modification to confer dyeability tends to result in lowering of strength and melting point. The proportion of polypropylene fibre that is mass-coloured before extrusion is much higher than for nylon, polyester, or acrylic fibres. This reflects the wider range of suitable dyes and the relatively easier dyeing processes available for these three types, as well as the difficulty of rendering polypropylene dyeable without sacrificing other essential properties. The influence of coloured organic and inorganic pigments on the physical properties of molten polypropylene, nylon and polyester [ l o ] and of C.I. Pigment Yellow 37 and C.I. Pigment Red 108 on the tensile strength and abrasion resistance of mass-coloured polypropylene [ l 11 have been investigated. The mass-coloration of polypropylene was discussed authoritatively in the fifth volume of this Review [ 121.

Stabilisation against Degradation When uncoloured polypropylene filament ropes were exposed to weathering for 1500 h of sunlight at Hamburg, they showed a loss in strength of 35-50%, depending on filament diameter, compared with 25-45% for nylon and 5-20% for polyester [ 131 . Carbon black exerts a protective effect although certain

REV. PROG. COLORATION VOL. 6 1975 7

organic pigments increase the strength loss on weathering. Grafting of polypropylene with acrylic acid makes the polymer more susceptible to oxidative degradation [ 141 but conversion of the carboxylic acid groups to the calcium salt has a stabilising effect [ 151 .

The U.V. component of sunlight activates the oxidative decomposition of polypropylene, especially at the C-H bond of the tertiary carbon atom [8] .The degradation is initiated by peroxide residues remaining trapped in the polymer from the polymerisation stage [9]. Inorganic pigments, such as zinc oxide or a mixture of titanium and chromium oxides [ 161, provide some stabilising effect for opaque plastics. More expensive organic U.V. absorbers are necessary in transparent monofils or moulded articles.

The stabilisation of multifilament yarns is much more difficult because conventional additives provide little protection, owing to the relatively greater surface area exposed to oxidative attack. Stabilisers for polypropylene have been classified into four groups:

(a) an tioxidan t s (b) U.V. screeners (c) peroxide decomposers (d) energy quenchers

Simple antioxidants are virtually ineffective as stabilisers for fine-denier filaments. U.V. screeners such as 2-hydroxybenzo- phenone [17, 181 and its alkylated derivatives [19] are also inefficient alone but offer more protection when combined with a peroxide decomposer [9] . Various 2,4,6-irialkylphenols [18, 20, 211 and related phenols substituted in the 0- and p-positions to minimise discoloration on oxidation [22-241, and heterocyclic compounds such as substituted triazoles and triazines [25], piperidines [26, 271, indoles [28] and imidazoles [29] , have been recommended. Oxidised polymeric wax [17] and chlorinated polyphenols [30] increase the receptivity of polypropylene to the addition of stabilisers.

Certain organic compounds of phosphorus and sulphur decompose hydroperoxide radicals to give inert derivatives by a chain-terminating mechanism. Dialkyl esters of thiodiprop- ionic acid [20, 211, disubstituted thioxylenes [22], alkyl trialkylvinyl sulphides [3 1 ] and zinc dialkyldithiocarbamates [ 181 are representative of sulphur compounds patented for this purpose; alkylmercaptopropionates of alkylated phenols [32] are stabilisers containing a phenolic antioxidant grouping and an active sulphur atom to decompose hydroperoxide radicals. Dilauryl thiodipropionate and related additives are effective only after conversion of the sulphur to an oxidised form [9]. Phosphites are much more effective peroxide decomposers under low-temperature weathering conditions. Organophosphorus compounds specified include phosphite esters [ 181 , hydroxybenzylphosphonates [25] and piperidino- phosphines [26,27].

Nickel complex stabilisers are considerably more effective than U.V. absorbers in protecting multifilament polypropylene. They operate by quenching electronically excited carbonyl groups arising at the tertiary carbon atoms in the polymer during the chain propagation cycle. These complexes exhibit low U.V. absorption in general although the nickel complex of an alkylated 2,2'-dihydroxydiphenyl sulphide, probably the most important of this type of additive [ 251, is a U.V. absorber as well as an energy quencher. Nickel complexes of vicinal

diamines and halogenated P-diketones 1331 have been patented as stabilisers.

The activity of the reactive type of light stabiliser is less dependent on fiiament denier than that of conventional U.V. absorbers. A mixture of phosphite ester and a nickel complex stabiliser gives better stability than either alone because they operate by selective quenching. Interaction between some nickel complexes and organosulphur types of peroxide decomposer to form traces of nickel sulphide can occur during melt extrusion, however, resulting in discoloration of polypropylene stabilised with a mixture of these agents. An important characteristic of polypropylene stabilised with a nickel complex that is not shared by the other methods of stabilisation is dyeability with mordant dyes designed to form chelate complexes with the metal-atom sites in the fibres.

Modification to Improve Dyeability Incorporation of nickel-complex stabilisers before melt extrusion is only one example of the techniques adopted to improve the dyeability of this fibre. Few dyes are highly substantive towards unmodified isotactic polypropylene, owing to the highly crystalline and stereoregular structure of this polymer, which contains no aromatic nuclei or polar substituents to provide scope for van der Waals or dipole-dipole bonding. lnterference with the crystallinity of the fibre improves its dyeability with disperse dyes by lowering the glass-transition temperature but it may result in lower strength and lower thermal resistance, and can modify extrusion behaviour (341 . Polypropylene yarns modified with phenoxy [35] or epoxy [36] resins showed a change in crystallinity, decreased orientation, and were dyed more rapidly with disperse dyes.

Earlier work on methods of modifying polypropylene has been reviewed comprehensively [37] . Techniqw which have been explored can be classified as:

(a) copolymerisation of propylene with other monomers (b) grafting on to isotactic polypropylene (c) blending with other dyeable polymers before extrusion (d) dissolving or dispersing additives of low molecular weight

(e) treatments to modify the surface of the filaments after in the polymer melt

extrusion.

Many types of co-monomers will increase the accessibility to disperse dyes and specific dyeability for basic dyes can be conferred by the use of modifiers containing acidic groups, or by partial oxidative degradation. Copolymerisation with polar monomers is difficult because of poisoning of the stereospecific polymerisation catalyst, although vinyl monomers containing phosphoric acid groups have been patented for basic-dyeable properties [38]. Substantivity for a wide range of dyes is achieved by impregnating polypropylene with an alcoholic solution of an unsaturated monomer containing at least one liydrophilic group and subjecting it to high-energy radiation to effect graft polymerisation [39].

Most of the recent research in this field has been concerned with blending polypropylene with another polymer to make the composite material more accessible to dyes,or, more often, to provide dyeing sites for specific classes of ionic dyes. Disperse-dyeable characteristics are acquired by blending with relatively inert polyester or vinyl polymers; examples

8 REV. PROG. COLORATION VOL. 6 1975

include polyethylene terephthalate alone [40] and in admixture with N-alkylated p-toluenesulphonamides [41] , polyetheresters made by self-condensation of carboxy- phenoxyalkanols [42] , copolymers of vinylphosphine oxide and ethylene or an alkoxyethyl acrylate [43], and a mixture of a polyglycol and a styrene-acrylonitrile copolymer [44]. Improved dyeability and impact resistance at low temperatures are achieved by blending with an oxygenated polyethylene- -metal complex [45]. Receptivity for disperse, basic and metal-complex dyes is imparted by coating polypropylene fibres with an interpolymer of a polyunsaturated hydrocarbon monomer and a vinyl monomer containing only one copolymerisable group [46] .

The development of acid-dyeable characteristics by blending with nitrogenous polymers has proved to be the most useful and versatile method of modifying polypropylene to improve dyeability without excessive deterioration in other desirable properties. A successful method of achieving this effect is to form a network of acid-dyeable microfibrils passing through the interior, intersecting with one another, and extending to the surface of the polypropylene filament, so that water-soluble dyes do not have to penetrate the impervious polypropylene matrix before reaching the acid- dyeable component.

Numerous types of nitrogenous polymer have been investigated as dyesites in acid-dyeable polypropylene. They may contain alkylamine or arylamine groups [47], and be mixed with polyethylene glycol [48] or a copolymer of an alkylene hydrocarbon and acrylic acid [49], or be insolubilised by treatment with an epoxy compound [50] . Fusing nylon powder to the surface of the polypropylene [SI], or blending in the molten state with nylon and a thermally degradable acid [52] or with a linear aliphatic polyamide and a polyamine containing at least one tertiary amine group, e.g. methylbis(3-aminopropyl-)amine [53] , are methods which have been patented. Copolymers designed for modifying polypropylene in this way include ethylene copolymerised with an aminoacrylate [54], an interpolymer of a t-alkylated maleimide and an alkyl vinyl ether [55 ] , and polyethylene grafts of N-irinylamide polymers [56] .

Addition of compounds of low molecular weight before extrusion of the molten polymer does not cause drastic modification of structure or physical properties in general, but selection of suitable additives is limited by considerations of thermal stability and compatibility with the molten polypropylene. Optimum compatibility is observed when nonpolar additives of low molecular weight are applied at relatively high temperatures of extrusion. Sulphonated arylphosphates confer substantivity for disperse and basic dyes [57] and basic-dyeable characteristics are obtained by blending with up to 20% of a 50:50 mixture of a water-soluble metal sulphonate and an oil-soluble alkylarylsulphonate [58] .

Methods of chemical treatment of the polypropylene after extrusion are more difficult to control and are generally confined to modifying the filament surface, so that fastness properties and solidity of appearance of subsequent dyeings are sometimes limited. Surface application of decalin, ietralin, cyclohexane or cyclohexene is claimed to improve the penetration of disperse or acid dyes to nitrogenous dyesites in modified polypropylene [59] . Pretreatment of unmodified polypropylene under pressure with 40% acetic acid containing ochnoic acid imparts substantivity for acid dyes [60], and

dyeability with disperse or basic dyes can be increased by controlled oxidation with hypochlorite or chlorite [61].

Dyeing and Printing Isotactic polypropylene is highly crystalline and only about one third of the fibre volume may be accessible to dyes. However, the diffusion coefficients of NJ-dimethyl-p-amino- azobenzene (C.I. Solvent Yellow 2), p-aminoazobenzeneo- cresol (C.I. Disperse Yellow 7) and 1 -anilinoanthraquinone (C.I. Disperse Red 22) in polypropylene at 80°C were found to be considerably higher than for the same dyes in secondary cellulose acetate at the same temperature [62]. Linear adsorption isotherms were obtained, indicating that the mechanism is one of solid solution and it was found that these dyes were placed in the same order with respect to affinity for polypropylene at 80°C and solubility in n-hexane at 20°C. Saturation values on polypropylene were very low, however, being less than one-third of the corresponding values for the same dyes on secondary acetate.

Many conventional disperse and solvent-soluble dyes are not sufficiently hydrophobic to show good affinity for polypropylene. In general, hydrophilic auxochromic groups, such as primary amino, hydroxyalkyl or phenolic substituents, tend to lower affinity for polypropylene, but alkylamino groups, particularly those derived from butylamines or longerchain alkyls, confer increased affinity. Thus the 3 , s - bis( bu tylami no) derivative of 1 4pphenylazoanilino)- s-triazine is a yellow with good affinity for polypropylene [63]. The influence of substituents on the substantivity and light fastness of a series of benzeneazopyrazolone dyes for polypropylene has been investigated [64] . Selected dyes, including certain amylated or butylated phenoxyanthra- quinones, are particularly suitable for dyeing polypropylene backings for tufted nylon carpets, since they are compatible with the dyes used on the nylon pile, do not stain the nylon or impair the fastness of the dyed nylon, and dye the polypropylene at the same rate as that at which the nylon is dyed [65,66].

Fastness to light exposure in a carbon arc lamp was investigated for m- and p-substituted anilines coupled to 2-naphthol and applied to polypropylene powder [67]. The rate of fading in air or nitrogen was found to be directly proportional to the Hammett constant of the substituent, which was indicative of a reductive mechanism. The more electron-attracting the substituent, the lower the electron density of the azo group and hence the greater the sensitivity of the dye to photo-reduction. Initiation of the reduction by photolytic abstraction of hydrogen from the tertiary carbon atoms in the polypropylene structure was also suggested. Dyes of the aniline + 2-naphthol type exist as a tautomeric mixture of hydroxyazo and phenylhydrazone forms and the rate of fading under nitrogen increases with the hydrazone/ hydroxyazo ratio, indicating that the hydrazone tautomer fades preferentially. If the light exposure is carried out in oxygen, however, the fading rate is increased because the hydroxyazo form is decomposed by oxidation and the hydrazone by reduction [68].

In spite of the generally low fastness to light, washing and dry cleaning of disperse and solvent-soluble dyes on polypropylene, it is possible to use selected products for less demanding outlets, but the attainment of full depths is difficult on the unmodified fibre. Aliphatic or aromatic


hydrocarbons, chlorinated hydrocarbons, esters and alkyl- phenols can be used to accelerate the dyeing rate but this is seldom necessary; increasing the equilibrium exhaustion or the saturation limit are more difficult problems. Continuous dyeing offers a possibility of avoiding the effects of poor exhaustion, however, and optimum conditions for aqueous padding and dry heat fixation have been recommended [69]. Continuous application from solvents [70, 711, such as perchloroethylene [72] or an aqueous microemulsion of linseed oil or turpentine [73] has also been investigated. The practical exploitation of such methods, however, would require a level of demand not yet attained by polypropylene fabrics.

The dyeing properties of anionic dyes on acid-dyeable polypropylene are similar to those on wool and suitable dyes are selected from existing ranges of acid and metal-complex dyes. Affinity for acid-dyeable polypropylene increases as the dye structure becomes more hydrophobic. Meraklon DR (Montecatini) was titrated with acetic and hydrochloric acids and the results compared with a nylon 6.6 control [74]. The rate of absorption of acid was much more rapid than on nylon at a given pH. The saturation value corresponding to the content of basic groups in Meraklon DR was about 250 m equiv/kg, compared with only 32 m equiv/kg for the nylon 6.6 and about 800 m equiv/kg on wool. The heats of reaction of Meraklon DR with acetic and hydrochloric acids were of the same order as those of nylon and wool.

An amino-substituted polypropylene containing about 660 m. equiv/kg of primary amine groups was prepared by photo-catalysed bromination of polypropylene fibre and amination using liquid ammonia [75]. A stoichiometric relation between dye uptake and content of amine groups in accordance with the Langmuir absorption isotherm was observed for aniline + 2-naphthol-8-sulphonic acid (C.I. Acid Orange 8), sulphanilic acid --f 1-naphthol (Orange I), sulphanilic acid + 2-naphthol (Orange II), and a 1:2 metal-complex dye (C.I. Acid Black 60). Deamination of the aminopolypropylene with acidified nitrite solution to give an hydroxypolypropylene with only 5 m equiv/kg residual amine groups effectively destroyed the acid-dyeable characteristics of the polymer.

Differential-dyeing variants of acid-dyeable polypropylene have been patented, e.g. use has been made of blends of a vinylpyridine- or vinylquinoline-modified polypropylene with a similar polymer modified further with inert co-monomers designed to confer disperse-dyeable as well as acid-dyeable characteristics [76]. Metal-complex dyes, e.g. the 1 :2 cobalt complex of 3-amino4-inydroxybenzoylbenzoic acid+ aceto- acetyl- 2’-chloroanilide applied from aqueous dispersion, have been specifically claimed for the coloration of acid-dyeable polypropylene [77] . Preferred conditions for pad-steam application of dispersions of metal-complex dyes to acid-dyeable polypropylene fabrics have been given [78] .

The stabilisation of polypropylene with organometallic compounds, notably the nickel complex of 2,2’-dihydroxy-5,5‘. di-t-octyldiphenyl sulphide and related derivatives, followed by dyeing with dispersions of mordant dyes devoid of strongly polar groups and capable of ehelating with the metallic dye sites in the fibre, is the essential approach for optimum fastness to light and weathering and resistance of the fibre to photodegradation. Exhaust dyeing by this technique presents serious problems, however, and it has not proved acceptable in

practice. Rapid strike takes place in the early stages of dyeing and levelness depends on the uniformity of distribution of the metal dyesites; the kinetics of dyeing polypropylene fibres containing various amounts of nickel stearate have been studied [79, 801. The available dyes show poor compatibility with respect to rate of dyeing and chelation. Traces of other metals present may cause poor reproducibility of colour or lower the final exhaustion by undesirable complexing effects. Temperature range properties, migration and stripping behaviour are generally poor.

The structure of the chelatable dye is important in achieving the optimum balance of fastness properties on this substrate. Suitable types include certain phenylazocresols [ 8 1 ] , phenylazonaphthols [82, 831 , benzoylamino- azomethines [84] and benzylaminoanthraquinones [85] . The presence of an iminoazo structure -N=C-N=N- has been identified as a particularly important grouping for chelatable dyes exhibiting good fastness to dry cleaning on nickel- modified polypropylene [86]. The level of fastness achieved is also dependent on the type of substituents in the heterocyclic diazo component of these dyes. Dyes derived from benzothi- azole, 5-nitrothiazole or pyridine-N-oxide [87] , for example, show better fastness to dry-cleaning than those containing unsubstituted thiazole-azo or pyridine-azo groupings.

The green mordant dye 2-amino-5-methoxybenzothiazole + p-cresol has good all-round fastness on metal-modified polypropylene. Nuclear magnetic resonance spectroscopy of dyeings of this dye on polypropylene modified with nickel 2,2‘-dihydroxy-5,5’-di-t-octyldiphenyl sulphide indicate that there is a 1 : 1 molecular ratio of dye to dye site and the nickel remains complexed with the non-coloured ligand in an octahedral structure [88]. Organic acids such as acetic or tartaric promote chelation of the dye at the dye site.

Polypropylene carpets for indoor use may be printed with disperse and solvent-soluble dyes or with chelatable dyes. Build-up of disperse dyes is limited and solvent-soluble types are restricted in hue and brightness. Disperse dyes tend to be inferior t o solvent-soluble dyes in fastness to rubbing and wet treatments but better for fastness to dry-cleaning. The chelatable dyes exhibit low light fastness on unmodified polypropylene but when co-ordinated with the nickel atoms in metal-modified variants these dyes give the best yields and build-up, sharper definition in printing and superior fastness to light and bleaching [89].

Styles of printing on polypropylene carpets include (a) partial or complete coverage by the direct style, (b) pad dyeing and over-printing, and (c) mass-coloration and over-printing. All the available variants can be printed with disperse or solvent-soluble dyes but the best results with chelatable dyes can only be obtained by the direct style on metal-modified polypropylene. The fastness requirements for outdoor carpets exposed to sunlight and weathering can only be met in this way and the metal-chelation approach is also useful for stain-resistant indoor carpeting [90].

Novel approaches to the coloration of polypropylene are still under investigation. Modification by incorporating bis-amides , bis-urethanes and alkylamines gives enhanced affinity for vat dyes from a bath containing polyvinylpyrrol- ‘idone [91]. Even the possibilities of reactive dyeing have been explored, in spite of the intrinsic chemical inertness of polypropylene. Recommendations for the application of Vero- fix (BAY) dyes to acid-dyeable polypropylene have been made

I


[92], but probably the most interesting development is the synthesis of dyes containing carbonyl-azide [93] or sulphonyl- azide [94] groups as precursors for highly reactive transient species capable of reacting with polymeric substances containing C-H bonds.

The nitrogen in nitrene reactive dye species (D-N:) can be regarded as a di-radical and the essential reaction with polypropylene is to form dye-fibre bonds of the C-NH-D type, probably at the tertiary carbon atoms in the polymer chain. This mechanism is complicated by an undesirable side-reaction to give D-NH2 and two isolated free radicals in the substrate. Irradiation can be used to promote decomposition of the azide precursor and bonding of the nitrene dye to the fibre. Several methods of preparation of nitrenes are known but only the stable azides can be considered as suitable precursors for textile application. Selected triazinyl-, sulphonyl-, carbonyl- and aryl-azides have fulfilled most of the requirements, although none of them is free from disadvantages [95].

Many questions still remain unanswered about the coloration of polypropylene. The diversification of major outlets from non-textile into domestic and apparel textiles in the last decade resulted from a conflux of trends in development and

the impetus of these changes is not yet spent. Stereospecific polymerisation improved mechanical strength at the expense of dyeability and subsequent modifications to improve this characteristic have been limited by the need to preserve desirable physical properties. The incorporation of nickel complex stabilisers to impart resistance to light and weathering proved to be the cornerstone of the mordant dyeing process now important for lightfast prints on polypropylene floor coverings. The development of a matrix-fibril structure for modified polypropylene fibres containing acid-dyeable dyesite fibrils may have been influenced by the results of concurrent research on matrix-fibril biconstituent filaments and differential-dyeing nylon variants. Even dye-fibre reaction may offer a promise of future methods of colouring this intractable polymer. The structure of polypropylene is one of the simplest conceivable for a fibre-forming polymer. Since its introduction, a central feature of the arguments put forward in favour of polypropylene textiles has been economic attractiveness. In the present state of uncertainty over supply and price of oil-based intermediates, this is perhaps the most weighty imponderable in the equations which determine the future growth curve for dyeable polypropylene fibres.

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90. Idem, Text. Chem. Colorist, 2 (1970) 279. 91. Phillips Petroleum Co., USP 3,507,605 (27 Jan. 1966). 92. Fiorini, Tinctoria, 69 (1972) 105. 93. Fagbule, BP 1,341,199 (22 May 1970). 94. Upjohn Co., USP 3,711,244 (27 Nov. 1970). 95. Griffiths, Fagbule and McDarmald, Textilveredlung, 7

1968) 31.

(1 972) 807.


The Coloration of Polypropylene

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