GB2038848A - A process for preparing bitumen polymer compounds - Google Patents

Abstract

A process for preparing compounds of bitumen and polymers, comprising mixing 80 to 98% by weight of a bitumen having a penetration of from 30 to 220 with 2 to 20% by weight of a styrene-diene conjugated block copolymer having a mean molecular weight of from 30,000 to 300,000, with agitation, at a temperature of 130 to 230 DEG C, maintaining the resulting mixture at this temperature for at least 2 hours and then adding 0.2 to 3% of elemental sulphur, based on the weight of the bitumen, while maintaining the same agitation and temperature conditions for at least a further 20 minutes, characterised in that the conjugated diene component is carboxylated butadiene or isoprene. These compounds are useful for surfacing roads, and have various industrial applications, e.g. waterproofing.

Description

SPECIFICATION A process for preparing bitumen polymer compounds We have previously developed a process for preparing compounds of bitumens and polymers, consisting of contacting 80 to 98% by weight of a bitumen having a penetration of 30 to 220 with 2 to 20% by weight of a block conjugate styrene-diene copolymer having a mean molecular weight from 30,000 to 300,000, at a temperature from 130 to 2300 C, with agitation, maintaining the resulting mixture for at least 2 hours, then adding 0.1 to 3% by weight of elemental sulphur (based on the weight of the bitumen) and maintaining the agitation of the resulting mixture for at least 20 minutes, thereby achieving vulcanisation in situ of the block copolymer.

The diene portion of the di- or poly-sequenced copolymers described in this application basically comprise butadiene.

The present invention extends this process to the preparation of bitumen polymers in which the copolymers are styrene-isoprene or carboxylated styrene-butadiene, since the elastomer and/or crosslinking phenomena of these products in the presence of elemental sulphur allow a possible reduction in the proportion of sequenced copolymers to be introduced into the bitumen polymer compounds according to the invention.

The di-sequen ced polystyrene-polyisoprene or carboxylated polystyre ne-polybutadiene copolymers preferably have a polystyrene content from 15 to 25% by weight. Their molecular weight is preferably from 70,000 to 90,000.

The proportion of carboxylic groups is low, and they preferably constitute from 0.05 to 0.1% of the weight of the polymer. These groups are preferably situated at the end of the polydiene chains and may be achieved either by a termination reaction with CO2, or by anionic polymerisation, or by a maleinisation reaction, or by grafting acrylic acid onto the non-carboxylated polymer.

Vulcanisation in situ of a di-sequenced carboxylated polystyrene-polybutadiene copolymer in a bitumen affords the advantage of endowing it with improved elastomeric properties when cold, while still preserving in the product a viscosity when hot which is substantially identical to that of a bitumen with a di-sequenced polystyrene polybutadiene copolymer.

This improvement may be explained by the fact that twofold cross-linking operates between the polymer chains.

The first, reversible, cross-linking process is provided by the carboxylic groups of the polymer, which form salts with the metal ions present in the bitumen (e.g. Fe, Ni,V) when the temperature of the mixture drops, transforming the non-elastomeric di-sequence chains into elastomer polysequence chains.

The other, irreversible, cross-linking process is provided by the covalent sulphur bridges created between the polymer chains, which bridges are retained at high temperature.

By improving the elastomeric properties of the bitumen, the double cross-linking makes it possible to'contemplate reducing the level of polymers so as to obtain properties which are exactly adequate to satisfy the specification for the intended application and thus to influence production costs for the product directly.

The reversibility of the ionic cross-linking makes possible easy application of the substance when hot, since an identical viscosity to that obtained with a non-carboxylated di-sequenced copolymer used at the same rate is preserved.

The following examples, which are given without limiting the invention, will enable the improvement in the properties obtained by the addition of carboxylated styrene-isoprene and styrene butadiene copolymers to be appreciated.

EXAMPLE I 100 parts of an 80-100 bitumen, with a ball and ring temperature of 480C and a Fraass point of -1 80C, are mixed with 10 parts of an isoprene styrene di-sequenced copolymer with a mean molecular weight of 80,000 and with an isoprene styrene ratio equal to 0.3. The mixture is maintained at 1 700C for 3 hours 30 min., with agitation; 0.2 parts of elemental sulphur are added and the agitation continued for half an hour. The characteristics of the bitumen polymer obtained are shown in Table I.

EXAMPLE II Example I is repeated, but with the omission of sulphur, and agitation of the mixture is maintained for 4 hours. it is established that the compound is brittle in traction tests at -100C 100 mm/mn.

EXAMPLE Ill The procedure as in Example I is used, but the isoprene blocks in the di-sequenced copolymer is replaced by carboxylated butadiene blocks, which improve the elastic properties, as can be seen in Table I.

EXAMPLE IV This Example is similar to Example Ill, except that elemental sulphur is not added. It is established that brittleness appeared in the traction tests at -1 OOC 500 mm/mn.

EXAMPLE V Based on the improvement of the elastic properties provided by the butadiene Carboxylated at the chain ends, the procedure as in the previous examples is followed, but with the introduction of a smaller proportion of copolymer; only 3%.

EXAMPLE VI A comparative procedure is followed, relating to Example V, using 3% by weight of a noncarboxylated styrene-butadiene copolymer.

Products in accordance with the present invention, being substances which have strong elastic properties and a considerable interval of plasticity, produce particularly favourable results when they are used: - for the production of road coverings and industrial coatings (surfacing, surface rendering, asphalt capping), - for industrial applications such as waterproofing (capping, felts, shingles, paints, products for undersealing vehicle bodies, products for thermal, electrical or acoustic insulation).

TABLE I

o o ao In (1, I I I Charac- Traction a cj O CU tics +2000500 mm/mn -100 10 mm/mn 1000 500 mm/mn Test Eraass Ex. P B+A C Point bars bars bars bars bars bars No. (1) (2) oS or er os or ES Er o5 or ES Er 53 71.5 cal 2.14 1.17 100 625 8.5 OOCr)O II E 76 -23 4.93 2.25 25 eoo g 8 1 III 36 120 -28.5 2.25 4.25 200 900 10 22.9 50 700 31 45.5 125 540 IV 39 101 -21 2.8 1.68 30 900 19.4 10.9 (0 X X V 59 61 -22 X ' N O o VI 60 57.5 -21 1.44 0.74 30 800 27.5 9.6 12.5 200 - - - uz O O O O O E ae ~ (\l a 8 È aR 68 ot o X e ov Csl n ~ N t - O O XC U) U C) 0) F ~ ie NO o eD U) Q~ CO t O Fg9 > (-) Brittleness not measurable (1) P = penetration (2) B + A = Ball and Ring

Claims (3)

1. A process for preparing compounds of bitumen and polymers, comprising mixing 80 to 98% by weight of a bitumen having a penetration of from 30 to 220 with 2 to 20% by weight of a styrene-diene conjugated block copolymer having a mean molecular weight of from 30,000 to 300,000, with agitation, at a temperature of 130 to 2300C, maintaining the resulting mixture at this temperature for at least 2 hours and then adding 0.1 to 3% of elemental sulphur, based on the weight of the bitumen, while maintaining the same agitation and temperature conditions for at least a further 20 minutes, characterised in that the conjugated diene component is carboxylated butadiene or isoprene.

2. A process according to Claim 1, characterised in that the copolymers added to the bitumen are isoprene or carboxylated styrene-butadiene block copolymers having a polystyrene level content from 15 to 25% by weight, a molecular weight from 70,000 to 90,000 and a content of carboxylic groups from 0.05 to 0.1% based on the weight of the polymer.

3. A polymer-bitumen compound obtained according to the process claimed in Claim 1 or Claim 2.