METHOD FOR PRODUCTIONAL THERMOSTABLE CHEMICAL RESISTANT PLASTICS

Abstract: Procedure for production of a chemical-resistant halogenous plastic. Reactive groups are added to a halogenous polymer and the polymer is cross-linked by reaction with a multifunctional organic compound under the influence of heat during or after the processing of the material. PVC is a favoured polymer, but the method is also applicable to the production of cross-linked products from other halogenous polymers. The invention also concerns a chemical-resistant cross-linked plastic consisting of 20-98 % copolymer of vinyl chloride and a glycidylic monomer, 0-80 % of plasticizer, 0.05-10 % of a multifunctional organic cross-linker, 0.1-10 % of stabilizer and 0-3 % of lubricant. The use of this plastic in oil-resistant and chemical-resistant products, especially foils, is also covered by the invention.

Description: Method for productional thermostable chemical resistant plasti The invention concerns a procedure for the production thermostable chemical-resistant plastic. Extremely hi resistance to chemicals can. be achieved if a strong, homogeno cross-linked network is introduced into the polymer. This type polymer will be particularly suitable for applications where oi resistance is important, for example in oil booms. It is al suitable for foils, tarpaulins, membranes and as a hard-weari top layer for floor coverings. Cables, pipes and rainwear c also be mentioned as potential application areas. In the case of PVC in particular, cross-linking has long be considered a good method of improving the mechanical properti of this plastic at high temperatures. Many attempts ha therefore been made to find technical solutions to this proble The introduction of cross-linking with the aid of so-calle reactive plasticizers, such as difunctional and trifunctiona acrylates or methacrylates, has had some commercial success These reagents are added in quantities of 20-50 pph (pph = part per hundred parts of polymer) , and they are cross-linked b exposure to radiation or free radicals. The network that i formed is strong and heterogeneous, which leads to a considerabl more brittle finished product. At the same time this techniqu can easily reduce the ther ostability of the product because o the degrading effect of the radiation or the free radicals (se for example W. A. Salmon & L. D. Loan; J. Appl. Polym. Sci., .16 671, (1972)). A homopolymer of polyvinyl chloride (PVC) has a certain conten of reactive groups, inasmuch as the carbon-chlorine bond is pol and may be attacked by nucleophilic compounds. In particula thiolate ions have proved to be good nucleophiles (see f example. K. Mori & Y. Nakamura; J. Macromol. Sci. Chem. A12, (2 209, (1978)). In a number of articles and patents, Mori and Nakamura ha described cross-linking of PVC with various types of dithi triazines. There are several reasons why the above method has not been commercial success, despite its many attractive aspects, sin the cross-linking in this case is triggered by heat, t reactivity of the system must be so good that the cross-linki can be done without breaking down the polymer. At the same ti there are many processing techniques which require that th cross-linking is only done after the actual processing of th material is concluded. All this means that a very difficul balancing act is necessary to create a functional system. further complicating factor is that the triazines which have th highest reactivity at the same time have a degrading effect o PVC. The method is therefore hardly suitable for producin thermostable chemical—resistant products. Cross-linking of PVC with organic alkoxysilanes has been th object of great interest in recent years. Several paten applications describe this technique - examples that can b mentioned are DE 3719151, JP 55151019 and NO 890543. The method described using alkoxysilanes have the disadvantage that th cross-linking requires the addition of water or water vapour. Tw separate processes thus become necessary to obtain the desire product. The object of the invention is therefore to produce thermostable chemical-resistant halogenous plastic, specificall a polyvinyl chloride. To achieve greatly enhanced chemical resistance in the case of PVC, it is necessary to introduce cross-linked network into the product. To retain ther ostability comparable to that of a standard PVC it necessary that the cross-linking reaction can be carried o concurrently with the working of the material without requiri very much extra heat. These and other objects of the invention are achieved by th procedure described below, and the invention is characterized an defined by the accompanying patent claims. The present invention concerns a procedure for producing chemical-resistant halogenous plastic. Reactive groups are adde to a halogenous polymer and cross-linked by reaction with multifunctional organic compound under the influence of hea during or after the processing. PVC is a preferred polymer, but the method is applicable to th production of cross-linked products from other halogenou polymers too. The invention also concerns a chemical-resistan cross-linked plastic which consists of 20-98% of copolymer o vinyl chloride and a glycidylic monomer, 0-80% of plasticizer 0.05-10% of a multifunctional organic cross-linker, 0.1-10% o stabilizer and 0-3% of lubricant. The application of thi plastic in oil and chemical-resistant products, especially foils is also covered by the invention. PVC is one of the great thermoplastics and is regarded as "mature" product. All the same, there is a steady increase in th consumption of PVC, and new areas of application are still bein developed. PVC is mainly produced by means of suspension emulsion, microsuspension or mass polymerization. The bulk of th PVC produced is homopolymeric. The unique feature of PVC is tha it can be mixed with a great number of organic solvents, and thi means that products at all grades of plasticity can b manuf ctured. The generally poor thermal stability of PVC is due to defec structures which arise in the polymer chain durin polymerization. These defect structures can be allylic an tertiary chlorine groups as illustrated below. normal structure llylic chlorine tertiary chlorine One advantage of these defect sites is that the chlorine group here are far more reactive than normal. This allows reaction with cross-linkers which are nucleophiles. Unfortunately, though the number of possible reaction sites is far too small to achiev sufficient cross-linking. It is therefore an essential part of the invention that halogenous polymer is used which has had extra reactive group added, which in reaction with suitable cross-linkers can produc a strong, homogenous network. It is an advantage if the extr reactive groups are already added during polymerization. Th polymer can then in itself be regarded as reactive. There are a number of relevant comonomers of vinyl chloride i this respect, and the choice of reactive group in the monomer ca be made from, for example, epoxy (glycidyl) , carboxylic acids, acid anhydrides, hydroxyl, amines, amides, isocyanates and silanes. Glycidylic acrylates or methacrylates have proved particularly favourable. This is because they are easily copolymerized with vinyl chloride in emulsion or suspension polymerization, and they are quickly used up so that there is no enrichment of them in the monomer phase. In addition, the epo groups have a suitable reactivity in the conditions in which t cross-linking has to be done. Copolymerization of vinyl chloride and a glycidylic acrylate methacrylate (GA) , e.g. glycidyl methacrylate, is as mention above an example of the way epoxy groups can be introduced in a halogenous polymer. Of the total monomer amount, GA should ma up 0.05-10 weight %, preferably 05.-5 weight %. The comono er c be added in a freely-selected way, but it is an advantage if even distribution of reactive groups in the polymer can achieved. The polymer can also be produced as a standard PVC wi the above-mentioned techniques. Glycidyl acrylate and buty glycidyl acrylate are also suitable monomers. In principle the cross-linker can be any multifunctional compoun which is coreactive with the polymer's reactive groups - fo example acid anhydrides, carboxylic acids, amines, amides mercaptans, thiol triazines, amidazoles. Special preferences ar phthalic anhydride, aleic anhydride, succinic anhydride succinic acid, malonic acid, oxalic acid, adipic acid, 2 dibutylamino-4,6-dithiol triazine, 2,4,6-trithiol triazine an 1,6-hexane diamine. To increase or adapt the reactivity of the system, catalysts e.g. of the tertiary a ine or Lewis acid types, can be used. Th cross-linker may also be another reactive polymer containing th above-mentioned groups. The type of cross-linker which will giv the desired result will depend on the total reaction system an reaction conditions. The cross-linker may be added at a arbitrarily chosen point in time, also before the actua polymerizate dries. The cross-linking take place when the copolymer produced is mixe with the cross-linker, and there is a direct reaction betwee these while the product is being processed. If the cross-linker is a difunctional amine the reactions can be illustrated follows : o ) ■ / \ / \ " < H 3 C - C - C - 0 - CK 2 - CH - CH 2 H 2 C - CH - CH 2 - 0 - C - C - CH 3 ) H 2 N ( CH 2 ) 6 NH 2 0 OH OH o ) " I I " ( H 3 C - C - C - O - CH^ - CH - CH 2 - NH ( CH 2 ) 6 - NH - CH 2 - CH - CH 2 .0 - C -C ■ CH 3 ) ( ) = polymer chain In this procedure, the disadvantage of poor thermostability whe using the above-men icned triazines can aisc be overcome becaus the system is so reactive that gocd results car. be achieved at lower working temperature and without the addition of " activatin metallic salts. The polymer is thus exposed to less heat stres and retains its ther ostability. One can study the chemical-resistance by exposing the finishe products to attacks by various types of solvents. For PVC, cyclohexanone and tetrahydrofuran (THF) are good solvents whic will completely dissolve the products. Acetone and diesel ar other relevant solvents which will attack and swell PVC to certain extent. For products which are to be used in contact wit chemicals and solvents, the time aspect is also important. Th product must retain its structure and its mechanical properties during storage. This means that additives and added plasticizers must not be allowed to migrate from the product to the ambient medium. Its has emerged that these product requirements can be met if cross-linking is introduced. The invention is described in more detail in the follow examples. Foils of varying composition are produced from b paste PVC and S-PVC. Different types of cross-linkers were us The production method for the foils and methods of testing t are described below. If not otherwise stated, quantities given in pph (weight parts per hundred parts of polymer) . PRODUCTION OF FOIL. 1. Paste PVC The paste is mixed in a Hobart mixer in accordance with ingredients given in Tables 1-3. The paste is stroked on release paper immediately after mixing and gelatinized/rolled if necessary pressed as described in Tables 1-3. 2. S-PVC The mixing is done in a small Papenmeier mixer. All solids mixed together from the start at "low" agitation. The plasticiz (DOP) is added when the temperature has reached 65°C. The mixi then continues at "high" speed until the temperature reac 110°C. The powder is then cooled down to 40°C. These mixtures (225 g) are rolled into a foil 1 mm thick on same day - the rolling specifications are given in Table 4. T foils are then aged with heat treatment as described in Table TESTING THE FOILS 1. Gel in THF. Jetons of foil are punched out and transferred to tetrahydrofur (THF) . After about 24 hours the gel jeton is evaluated (g (Yes)/non-gel(No)/partial) . The quantity of gel (%) is determined by a simplified meth where the jeton is weighed before and after storage in THF ( hours) . The percentage of cross-linked gel is determined by t formula: % Gel = Weight a f t β r /Weight b e f 0 r e x 100% Weight a f t e r - weight of gel after drying (50°C, 5 hour Weight fa e f 0 r e - weight of jeton. 2. Stress relaxation The degree of cross-linking in the foils is also assessed stress relaxation tests in a dynamic spectrometer (Rheometri RDS 7700). The conditions are given in Tables 1-2. The valu given as percentages are the ratio between the stress relaxatio module initially and after 100 seconds measured at 8% constan deformation. 3. Storage stability in diesel. The foils are stored in diesel for seven full days. Before an after storage in diesel the foils are analysed for tensil strength, elongation before breakage, cold-flex temperature an weight changes. Maximum tensile strength and elongation before breakage ar measured with a UTS 10 universal testing machine at a stretchin speed of 50/min. The specimens conform to the specifications o ISO R 527 (Test Type 2.) . Weight change after storage in diesel was calculated on the basi of the weight of the foil before and after storage. Before th foil was weighed after storage, it was dried with absorbent pape and only weighed 24 hours later. Cold-flex was done in accordance with ISO 458, Parts 1 and 2. Test 1 Six mixtures of paste PVC with different compositions were ma as shown in Table 1. One of the tests (Al) was done with P homopolymer, while in the others (A2-6) a copolymer of PVC a glycidyl methacrylate (GMA) was used. The percentage of GMA based on the added quantity of VCM. Equal amounts of plasticize stabilizer and epoxidized soya oil were added to the s mixtures. Different quantities of cross-linker were added three of the mixtures. The samples Al-4 were rolled for 3 min at 175°C and then pressed at the same temperature for 3+1 min Testing of these foils showed that the foils without added cros linker (A1-A3) were fully dissolved in tetrahydrofuran. The fo with least cross-linker (A-4) and 1% of GMA was partiall dissolved. Samples A5-6 both had 2% of GMA but differe quantities of cross-linker, and were treated in the same way wi gelatinization and pressing. It can be seen from the test resul that these were resistant in tetrahydrofuran. Cross-linking wa formed. However, the double quantity of cross-linker in A6 ha little extra effect compared with A5. The introduction of reactive groups into the PVC chains leads t a slight reduction in thermostability. The use of differen cross-linkers also leads to great differences, but th homopolymer will always be rather better than the reactiv samples. It is nevertheless possible to optimize the recipes wit respect to thermostability, for example by the choice of cross linker. The product is manufactured in process conditions whic do not require extra heat, so the thermostability of the produc is maintained. TABLE 1. Test with Zisnet DB as cross-linker Zisnet DB' 1.2 2.5 5.0 Gel time (mins. ) 3 3 Gel temp. (°C) 175 170 Rolling time (mins.) 3 3 3 3 Rolling temp. (°C) 175 175 175 175 Pressing time (mins.) 3+1 3+1 3+1 Pressing temp. (°C) 175 175 175 175 Gel in THF (Y/N) N N N partia Gel in THF (%) 0 0 0 Rheometrics (%) 37.2 34.1 25.7 37.0 1) DINP = di-isononyl phthalate 2) Lankromark LZ616 = Ca/Zn stabilizer from Lankro. 3) ESO = Epoxidized soya oil 4) Zisnet DB = 2-dibutylamino-4,6-dithiol triazine from Sanky Kasei. Test 2 Seven different mixtures were produced from paste PVC. These ar shown in Table 2. Homopolymer was used in Test B-l, while in th others a copolymer of PVC and 2% of glycidyl methacrylate w used. The same amount of additives was used in all mixtures. T quantity of cross-linker was varied. All samples except B-6 we gelatinized for 7 minutes, while the gelatinizing temperature w varied from 170 to 190°C. The results show that the two sampl Bl-2 without cross-linker were both dissolved in tetrahydrofura No major effect can be observe from doubling the amount of cross linker (see B-3 and B-6) . The gelatinizing temperature has positive effect on the result, as gelatinization at 190° produces better cross-linking than treatment at 170°C. A longe gelatinizing time also affects the result, as can be seen b comparing the mixtures B-6 and B-7. TABLE 2. Test with Zisnet F as cross-linker Zisnet F 1.4 2.8 2.8 2.8 2.8 1) Zisnet F = 2,4,6-trithiol triazine from Sankyo Kasei. Test 3 Three mixtures were made (Cl-3) with a copolymer of PVC and 2% glycidyl methacrylate. The mixtures C4-6 had a content of 3% glycidyl methacrylate. The same quantities of additives were u in all mixtures while the quantity of cross-linker (phtha anhydride) was varied from 1.7 to 4.4. A gelatinizing time of minutes at 190°C was used for all samples. The results show t only the samples with the highest content of GMA produced g cross-linking, and that the best result was achieved with highest content of cross-linker. TABLE 3. Test with phthalic anhydride as cross-linker Recipe C-1 C-2 C-3 C-4 C-5 C-6 Phthalic anhydride 1.7 2.3 2.9 2.6 3.5 4.4 Test 4 Five mixtures were made from S-PVC with 1% of glycid methacrylate. All mixtures had the same quantity of additive while the quantity of cross-linker varied. The mixtures we rolled for five minutes at 160°C and three of the samples we additionally heat-treated for 24 hours at 120°C. The results sh that a higher degree of cross-linking was achieved in the sampl D-3 and D-5, which contained different quantities of cros linker, but which were both heat-treated. It is also notable th it is possible to carry out rolling of the product without a great degree of cross-linking arising. This means that cross linking can be done on the finished, formed product. TABLE 4. S-PVC cross-linked with Zisnet F Recipe D-1 D-2 D-3 D-4 D-5 Zisnet F 1) DOP = dioctyl phthalate 2) LF3655 = Pb stabilizer from Akzo 3) AC316A = polyethylene wax from Allied Chemical Corp. Test 5 Five different mixtures, El-5, were made, one with P homopolymer and four mixtures of PVC and 2 and 3% of glycid methacrylate respectively and with different cross-linkers (s Table 5) . Specimens of the foils were tested before and aft seven days' storage in diesel. The results show that the tensil strength is more or less unchanged in all samples, as expected a room temperature. Measurement of elongation before breakage show that the samples with most gel (good cross-linking) retain thei properties, while those without and with little gel are reduce in elongation before breakage. The cold-flex temperature is a expression of brittleness. The table shows that Sample E-l, whic is not cross-linked, has been attacked by the solvent and ha become brittler. The other samples have retained thei flexibility. A weight reduction in the samples after storage i diesel may for example be due to loss of plasticizer. Samples E- and E-5, which have a high degree of cross-linking, exhibit n weight changes after storage in diesel. TABLE 5. Test of cross-linked foil before and after storage in diesel Recipe E-1 E-2 E-3 E-4 E-5 Homopolymer 100 Gel time (mins.) 10 10 10 Gel temp. (°C) 190 190 190 180 1 180' Tensile strength before (mPa) 17.2 17.8 15.1 15.1 12.0 after (Mpa) 20.3 18.8 17.1 17.1 12.7 Elongation before (%) 356 350 295 232 156 after (%) 317 313 281 236 154 Cold-flex temp, before (°C) -34.0 -32.0 -30.4 -31.0 -29.7 after (°C) -24.1 -34.6 -36.3 -41.0 -39.7 Weight change reduction (%) 10.0 4.7 3.1 0.08 increase (%) 0.2 Gel in THF (Y/N) N Y(-) Y Y Y Gel in THF (%) 0 23 35 53 53 1) Foils with Zisnet DB were gelatinized at a lower temperature and for shorter periods to avoid burnin the foils. Good results were still achieved. As shown in the examples, with this method one can achieve cros linked products with good resistance to solvents, and producti takes place in conditions which do not require extra heat. T thermostability of the product is therefore maintained. In selecting process conditions/chemicals one can customize t process and one can choose to carry out the cross-linking eith during or after working the material. The type of cross-linke chosen will be crucial for the degree of cross-linking in t product.

Claims: Patent claims 1. Procedure for the production of chemical-resistant halogen ous plastics, c h a r a c t e r i z e d i n t h a t reactive groups are added to a halogenous polymer, and th polymer is cross-linked by reaction with a multifunctiona organic compound which reacts with the polymer's reactiv groups under the influence of heat during or after th process of working the material. 2. Procedure according to Claim 1, c h a r a c t e r i z e d i n t h a t the reactive groups are added to the halogenous polymer b copolymerization. 3. Procedure according to Claim 1, c h a r a c t e r i z e d i n t h a t the reactive groups used are epoxy, carboxylic acids, acid anhydrides, hydroxyls, amines, amides, isocyanates or silanes. 4. Procedure according to Claim 1, c h a r a c t e r i z e d i n t h a t the multifunctional organic cross-linker used is phthalic anhydride, maleic anhydride, succinic anhydride, succinic acid, malonic acid, oxalic acid, adipic acid, 2-dibutyl amino-4,6-dithiol triazine, 2,4,6-trithiol triazine, 1,6- hexane diamine or a polymer containing any of these groups. 5. Procedure according to Claim 1, c h a r a c t e r i z e d i n t h a t the halogenous polymer is produced by copolymerization of vinyl chloride and a glycidylic acrylate. 6. Procedure according to Claim 5, c h a r a c t e r i z e d i n t h a t the glycidylic acrylate used is glycidyl methacrylate glycidyl acrylate or butyl glycidyl acrylate. 7. Procedure according to Claim 5, c h a r a c t e r i z e d i n t h a t a copolymer is used which contains 0.05-10 weight % of th glycidylic monomer. 8. Chemical-resistant cross-linked plastic, c h a r a c t e r i z e d i n t h a t the plastic consists of 20-98% of polymer of vinyl chlorid and a glycidylic monomer, 0-80% of plasticizer, 0.05-10% o a multifunctional organic cross-linker, 0.1-10% o stabilizer and 0-3% of lubricant. 9. Chemical-resistant cross-linked plastic according to Claim 8, c h a r a c t e r i z e d i n t h a t the multifunctional organic cross-linker is phthali anhydride, maleic anhydride, succinic anhydride, succinic acid, malonic acid, oxalic acid, adipic acid, 2- dibutylamino-4,6-dithiol triazine, 2,4,6-trithiol triazine or 1,6-hexane diamine. 10. Chemical-resistant cross-linked plastic according to Claim 8, c h a r a c t e r i z e d i n t h a t the glycidylic acrylate is glycidyl methacrylate, glycidyl acrylate or butyl glycidyl acrylate in a quantity of 0.05-10 weight %. 11. Use of a plastic produced by known processing methods for S- PVC or paste PVC based on a recipe specifying 20-98% of copolymer of vinyl chloride and a glycidylic monomer, 0-80% of plasticizer, 0.05-10% of a multifunctional organic cross- linker, 0.1-10% of stabilizer and 0-3% of lubricant, a cross-linked subject to heat, as oil-resistant and chemica resistant products.

Inventors: DAHL ROGER, MARTINSEN ANITA, PEDERSEN STEINAR, SKJELLAUG PER, DAHL, ROGER, MARTINSEN, ANITA, PEDERSEN, STEINAR, SKJELLAUG, PER
Applicants: NORSK HYDRO AS, NORSK HYDRO A.S
Application year: 1992
Main classification: C08F8
IPC codes: C08F8, C08J3