Organic peroxide aqueous emulsions

Abstract

The present disclosure relates to the use of an aqueous emulsion of an organic peroxide comprising 0 to 0.17 wt% of at least one emulsifier for the preparation of polyvinyl chloride having an increased drying rate.

Description

Technical Field

[0001] The present invention relates to aqueous organic peroxide emulsions containing a reduced amount of emulsifiers. The invention also relates to the use of such emulsions in the polymerization of vinyl chloride monomer (VCM) for the preparation of polyvinyl chloride (PVC) having improved drying characteristics. Background Art

[0002] Organic peroxides are known in the art as effective initiators for the polymerization of VCM to produce PVC. Commercially, these peroxides are available in the form of stable aqueous emulsions containing protective colloids, emulsifiers and antifreeze agents.

[0003] In WO 03 / 095500 it is disclosed how a combination of di(2-ethylhexyl)peroxydicarbonate, a protective colloid, a nonionic emulsifier and an antifreeze agent can produce a stable aqueous emulsion with a small peroxide droplet size and a narrow droplet size distribution, which is advantageous when used in PVC production. In Example 1, an aqueous emulsion was made with 55% w / w di(2-ethylhexyl)peroxydicarbonate, 0.8% w / w 62-68% saponified polyvinyl acetate, 0.3% w / w ethoxylated stearyl alcohol, water and methanol. When the ethoxylated stearyl alcohol emulsifier was omitted in Comparative Example A, the PVC polymer produced by the standard suspension polymerization of VCM was adversely affected.

[0004] Similarly, in WO 2011 / 015567, it is shown that an aqueous emulsion of an organic peroxide containing 40 wt% diisobutyryl peroxide, 1.1 wt% 62-68% hydrolyzed polyvinyl acetate, 0.3 wt% ethoxylated stearyl alcohol, water and methanol produces a stable aqueous emulsion with small peroxide droplet size and a narrow droplet size distribution, wherein 99% of the dispersed phase volume is much smaller than 10 microns.

[0005] However, it has been found that PVC produced using these stable aqueous organic peroxide emulsions requires a long time to dry and is unsatisfactory.

[0006] Therefore, there is a need for an aqueous organic peroxide emulsion that solves this problem. Summary of the invention

[0007] We have now surprisingly found that improved aqueous organic peroxide emulsions can be prepared using significantly smaller amounts of emulsifiers. These aqueous emulsions are not only stable, but have also been found to produce high-quality PVC with improved drying properties.

[0008] Thus, in a first aspect, the present disclosure relates to the use of an aqueous organic peroxide emulsion comprising 0 to 0.17 wt. % of at least one emulsifier for the preparation of polyvinyl chloride having an increased drying rate.

[0009] Advantageously, despite relatively low emulsifier concentrations (or the absence of emulsifier at all), stable aqueous emulsions having small peroxide droplet sizes and narrow droplet size distributions have been prepared, which is advantageous for PVC production. Furthermore, it has been found that the use of these emulsions in VCM polymerizations produces high quality PVC with unexpectedly improved drying properties (the drying rate of the resulting PVC polymer is significantly increased, thereby reducing the drying time of the polymer, which is important for the industrial scale production of PVC). BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1 The dimensionless drying rate of water in the pores of the PVC samples prepared in Example 2 of the present application and Comparative Example 2A is shown. DETAILED DESCRIPTION

[0011] Preferably, the aqueous organic peroxide emulsion used according to the first aspect of the present invention comprises:

[0012] (i) 25 to 70 weight percent of at least one organic peroxide having a self-accelerating decomposition temperature (SADT) of 25° C. or less;

[0013] (ii) 1.4 to 6.0% by weight of at least one protective colloid;

[0014] (iii) 0 to 0.17 wt % of at least one emulsifier; and

[0015] (iv) at least one antifreeze agent.

[0016] SADT is the lowest ambient temperature at which self-accelerating decomposition of a product occurs in a package intended for transport. The method for determining the SADT of an organic peroxide is described in detail in the United Nations Manual of Tests and Criteria, Seventh Revised Edition (2019), Test Series H.4: Heat accumulation storage test, which is incorporated herein by reference. The method determines the lowest constant air ambient temperature at which exothermic decomposition of a thermally unstable substance occurs under conditions representative of the substance when packaged. The method is based on the Semenov theory of thermal explosion, i.e., the assumption that the main resistance to heat flow is at the container wall. The method can be used to determine the SADT of a substance in its packaging (including IBCs (Intermediate Bulk Containers) and small tanks (up to 2m 3 For the avoidance of doubt, the SADT values ​​referred to herein are determined according to the method specified in the above-mentioned United Nations Manual (Test Series H.4: Heat Accumulation Storage Test) for organic peroxides in high density polyethylene (HDPE) packaging with a volume of 20 to 30 liters.

[0017] According to the first aspect of the present invention, the aqueous organic peroxide emulsion used preferably contains at least one organic peroxide with a low SADT (i.e. 25°C or lower), preferably 20°C or lower, preferably 15°C or lower, preferably 10°C or lower, preferably 5°C or lower, and can be about 0°C or lower. Preferred organic peroxides include peroxyesters, peroxydicarbonates and diacyl peroxides. Preferred are diacyl peroxides and peroxydicarbonates. Examples of preferred organic peroxides for use according to the invention are diisobutyryl peroxide (SADT 0° C.), cumyl peroxyneodecanoate (SADT 10° C.), 1,1,3,3-tetramethylbutyl peroxyneodecanoate (SADT 15° C.), cumyl peroxyneoheptanoate (SADT 10° C.), tert-amyl peroxyneodecanoate (SADT 20° C.), di-sec-butyl peroxydicarbonate (SADT 0° C.), di(2-ethylhexyl peroxydicarbonate) (SADT 5° C.), tert-butyl peroxyneodecanoate (SADT 20° C.), 1,1,3,3-tetramethylbutyl peroxypivalate (SADT 20° C.); tert-amyl peroxypivalate (SADT 25° C.), tert-butyl peroxypivalate (SADT 25° C.), di(3,5,5-trimethylhexanoyl) peroxide (SADT 25° C.), di-n-propyl peroxydicarbonate (SADT 25° C.). 0°C), diisopropyl peroxydicarbonate (SADT 5°C), di-n-butyl peroxydicarbonate (SADT 0°C), di(2-ethoxyethyl) peroxydicarbonate (SADT 10°C), 1,3-di(propane-2,2-diyl)benzenebis(neodecanoyl)peroxide (SADT 10°C), 3-hydroxy-1,1-dimethylbutyl peroxyneodecanoate (SADT 10°C), di-n-butyryl peroxide (SADT 25°C) or a mixture thereof.

[0018] The aqueous organic peroxide emulsion used according to the first aspect of the present invention generally contains 25 to 70 wt % of organic peroxide based on the total weight of the emulsion. Preferably, the amount of organic peroxide in the emulsion is 30 to 65 wt %, more preferably 35 to 60 wt %.

[0019] The amount of water in the emulsion of the first aspect is generally 20 to 60 wt%, preferably 25 to 50 wt% and more preferably 25 to 40 wt%, based on the total weight of the emulsion.

[0020] The organic peroxide aqueous emulsion used according to the first aspect of the present invention preferably contains at least one protective colloid. Any conventional protective colloid can be used. The example of a suitable protective colloid is cellulose and partially hydrolyzed (or saponified) polyvinyl acetate. Partially hydrolyzed polyvinyl acetate (PVA) is a preferred protective colloid to be present in the aqueous emulsion. Preferably, the hydrolysis degree of PVA is at least 50 mol %, more preferably at least 55 mol % and most preferably at least 60 mol %, and preferably at most 90 mol %, more preferably at most 80 mol % and most preferably at most 70 mol %. Preferably, PVA is randomly hydrolyzed, rather than block hydrolyzed.

[0021] In addition to using only one type of PVA, a blend of two or more PVAs may be used. In this case, the blend may be considered to be a PVA having a degree of hydrolysis that is the weight average degree of hydrolysis of the PVAs. Preferably, such a blend of PVAs does not contain more than 0.2% of a PVA having a degree of hydrolysis of less than 50 mol % or greater than 90 mol %.

[0022] The amount of protective colloid used in the emulsion of the first aspect of the invention will depend on the type and amount of the organic peroxide and the desired viscosity of the final emulsion, but is generally used in an amount of 1.4 to 6.0 wt % and preferably 1.5 to 5 wt % based on the total weight of the emulsion. For example, when the organic peroxide is di(2-ethylhexyl) peroxydicarbonate, the amount of protective colloid used is generally 1.4 to 3.0 wt %, preferably 1.5 to 2.0 wt %, based on the total weight of the emulsion.

[0023] The emulsion used according to the first aspect of the invention contains 0 to 0.17 wt %, preferably 0 to 0.15 wt %, preferably 0 to 0.10 wt %, preferably 0 to 0.05 wt % and more preferably 0 wt % of at least one conventional emulsifier, based on the total weight of the emulsion.

[0024] Conventional emulsifiers are known to those skilled in the art and include nonionic, anionic, cationic and amphoteric surfactants and mixtures thereof. Examples of surfactants commonly used in organic peroxide aqueous emulsions include alkylene oxide block copolymers, alkoxylated fatty alcohols (including ethoxylated and / or propoxylated C6-C22 fatty alcohols, such as ethoxylated stearyl alcohol, ethoxylated cetyl alcohol and mixtures thereof) and alkoxylated fatty acids (including ethoxylated and / or propoxylated C6-C22 fatty acids). Other examples include sorbitan fatty acid esters, ethoxylated sorbitan fatty acid esters, ethoxylated castor oils and oxyalkylene vegetable and animal oils (hydrogenated or unhydrogenated).

[0025] When an emulsifier is added to the emulsion used according to the first aspect of the present invention, a nonionic surfactant is preferably used, more preferably it has an HLB value of 8 or more, preferably 10 or more, even more preferably 14 or more. The HLB value represents the hydrophilic-lipophilic balance, as described in "The Atlas HLB-System, a time saving guide to emulsifier selection (Atlas HLB system, time-saving emulsifier selection guide)" (published by Atlas Chemical Industries Inc. in 1963). However, it is preferred to omit the emulsifier from the emulsion. That is, the emulsion used according to the first aspect of the present invention is preferably substantially free of emulsifier.

[0026] The emulsion used according to the first aspect of the present invention preferably also contains at least one antifreeze and can comprise the combination of two or more antifreeze. Any conventional antifreeze can be used. Preferably, methanol, ethanol, propanol, isopropanol, (second) glycol, propylene glycol, glycerine and mixtures thereof are used, more preferably methanol, ethanol, propylene glycol and mixtures thereof. Known these compounds have almost no effect on the polymerization process using peroxide emulsion. Most preferably, methanol is used as antifreeze.

[0027] The amount of antifreeze is usually selected so that the emulsion does not freeze at a temperature of -10°C, preferably -15°C, most preferably -20°C or -25°C. The amount of freezing point depressant to be used will depend on the type of antifreeze or antifreeze mixture used. Suitably, a mixture of antifreeze and water is first prepared, which contains a sufficient amount of antifreeze so that it can be poured at the indicated temperature. This mixture can then be used in further processes to prepare the emulsion. The skilled person has no difficulty in balancing the ratio of water to antifreeze. Typically, the amount of antifreeze used in the emulsion according to the present invention will be lower than the amount of water.

[0028] In a second aspect, the present disclosure relates to an aqueous organic peroxide emulsion comprising:

[0029] (i) 30 to 45% by weight of diisobutyryl peroxide;

[0030] (ii) 2.0 to 6.0% by weight of at least one protective colloid;

[0031] (iii) 0 to 0.17 wt % of at least one emulsifier; and

[0032] (iv) at least one antifreeze agent.

[0033] By combining high concentrations of diisobutyryl peroxide (SADT 0°C) with low concentrations of emulsifiers, stable aqueous emulsions have been prepared which surprisingly benefit PVC production. In particular, it has been found that including less emulsifier (or no emulsifier at all) in the resulting PVC polymer achieves faster drying characteristics which, coupled with the possible continuous and / or intermittent dosing of the peroxide emulsion, saves considerable production time.

[0034] The organic peroxide aqueous emulsion of the second aspect of the present invention contains 30 to 45 wt% of diisobutyryl peroxide (CAS No. 3437-84-1) based on the total weight of the emulsion. Preferably, the amount of diisobutyryl peroxide in the aqueous emulsion is 35 to 42 wt%.

[0035] The amount of water in the aqueous organic peroxide emulsion of the second aspect is generally 20 to 60% by weight, preferably 25 to 50% by weight, and more preferably 25 to 40% by weight, based on the total weight of the emulsion.

[0036] The organic peroxide aqueous emulsion of the second aspect of the present invention contains at least one protective colloid, based on the total weight of the emulsion, in an amount of 2.0 to 6.0 weight %, preferably 2.5 to 4.0 weight % and more preferably 2.7 to 3.5 weight %. As in the first aspect of the present invention, any conventional protective colloid can be used. Examples of suitable protective colloids are cellulose and partially hydrolyzed (or saponified) polyvinyl acetate. Partially hydrolyzed polyvinyl acetate (PVA) is a preferred protective colloid to be present in the aqueous emulsion. Preferably, the hydrolysis degree of PVA is at least 50 mol %, more preferably at least 55 mol % and most preferably at least 60 mol %, preferably at most 90 mol %, more preferably at most 80 mol % and most preferably at most 70 mol %. Preferably, PVA is randomly hydrolyzed, rather than block hydrolyzed.

[0037] In addition to using only one type of PVA, a blend of two or more PVAs may also be used. In this case, the blend may be considered to be a PVA having a degree of hydrolysis that is the weight average degree of hydrolysis of the PVA. Preferably, the blend of PVAs does not contain more than 0.2% of PVAs having a degree of hydrolysis of less than 50 mol % or greater than 90 mol %.

[0038] The aqueous organic peroxide emulsion according to the second aspect of the invention contains 0 to 0.17 wt %, preferably 0 to 0.15 wt %, preferably 0 to 0.10 wt %, preferably 0 to 0.05 wt % and more preferably 0 wt % of at least one conventional emulsifier, based on the total weight of the emulsion.

[0039] Conventional emulsifiers are known to those skilled in the art and include nonionic, anionic, cationic and amphoteric surfactants and mixtures thereof. Examples of surfactants commonly used in aqueous organic peroxide emulsions include alkylene oxide block copolymers, alkoxylated fatty alcohols (including ethoxylated and / or propoxylated fatty alcohols) and alkoxylated fatty acids (including ethoxylated and / or propoxylated fatty acids).

[0040] As with the first aspect of the invention, when an emulsifier is added to the emulsion of the second aspect of the invention, it is preferred to use a nonionic surfactant, more preferably with an HLB value of 10 or higher, even more preferably 14 or higher. However, it is preferred to omit the emulsion from the emulsion. That is, the emulsion of the second aspect of the invention is preferably substantially free of an emulsifier.

[0041] The organic peroxide aqueous emulsion according to second aspect of the present invention also contains at least one antifreeze agent, and can comprise the combination of two or more antifreeze agents.Any conventional antifreeze agent can be used.Preferably, use methyl alcohol, ethanol, propyl alcohol, isopropanol, (second) glycol, propylene glycol, glycerine and mixture thereof, more preferably, use methyl alcohol, ethanol, propylene glycol and mixture thereof.Known these compounds almost do not have any influence on the polymerization process using peroxide emulsion.Most preferably, use methyl alcohol as antifreeze agent.

[0042] The amount of antifreeze is usually selected so that the emulsion does not freeze at a temperature of -10°C, preferably -15°C, preferably -20°C and most preferably -25°C. The amount of freezing point depressant to be used will depend on the type of antifreeze or antifreeze mixture used. Suitably, a mixture of antifreeze and water is first prepared, which contains a sufficient amount of antifreeze so that it can be poured at the indicated temperature. This mixture can then be used in other processes to prepare the emulsion. The skilled person has no difficulty in balancing the ratio of water to antifreeze. Typically, the amount of antifreeze used in the emulsion according to the present invention will be lower than the amount of water.

[0043] The organic peroxide aqueous emulsions of the first and second aspects of the present invention may also optionally contain other additives, including pH regulators (such as phosphate and citrate buffers), chelating agents, biocides (e.g., fungicides), antiozonants, antioxidants, antidegradants, UV stabilizers, coagents, comonomers, antistatic agents, foaming agents, release agents, and process oils. These additives may be added in their usual amounts.

[0044] The organic peroxide aqueous emulsion of first and second aspects of the present invention can be produced in a conventional manner.Usually, use well-known equipment that each component of emulsion is mixed and / or homogenized, described equipment is such as high-speed stirrer, colloid mill, bead mill (pearl mills), pressure homogenizer, fluidizer and ultrasonic homogenizer.Because superoxide may be unstable at higher temperatures, therefore mixing and / or homogenizing should be carried out under the self-accelerating decomposition temperature (SADT) that is lower than organic peroxide.

[0045] The aqueous organic peroxide emulsions of the first and second aspects of the present invention may also be produced continuously using an in-line emulsifier by first cooling a pre-emulsion mixture containing the organic peroxide to a temperature at least 12°C lower than the SADT of the organic peroxide before feeding it into the in-line emulsifier, and then cooling the organic peroxide emulsion to a temperature at least 12°C lower than the SADT of the organic peroxide using a downstream heat exchanger.

[0046] The organic peroxide may be introduced into the emulsification process in the form of a desensitized organic peroxide. In this regard, any suitable desensitizer may be used to dilute and / or dissolve the peroxide, such as an inert desensitizing solvent. Such inert desensitizing solvents are well known in the art and include, for example, isododecane and mineral oil. For example, 3-hydroxy-1,1-dimethylbutyl peroxyneodecanoate (SADT 10°C) is provided in desensitized form as a 75% solution in odorless mineral oil (" 193-CH75”) from Commercially available.

[0047] The present disclosure also relates to the use of the above-mentioned aqueous diisobutyryl peroxide emulsion of the second aspect in polymerization processes, cross-linking reactions, curing of unsaturated polyester resins, polymer modification processes and other reactions involving free radicals (such as the synthesis of certain chemicals).

[0048] The diisobutyryl peroxide emulsion of the second aspect of the present invention is preferably used in a polymerization process, more preferably in the polymerization of VCM and the copolymerization of VCM with styrene or (meth) acrylate. Most preferably, the emulsion according to the present invention is used in a suspension polymerization process for preparing PVC. The polymerization process preferably includes the step of continuously and / or intermittently dosing the emulsion to a polymerization reactor at the polymerization temperature. Such a process is described in WO 2000 / 017245.

[0049] The improved drying characteristics (i.e., increased drying rates) of the resulting PVC polymers are quantified in the following examples and are intended to include a normalized drying rate greater than 0.840 at a time t* of 0.5, as determined by the method described in the journal article "Dehydration and drying poly(vinyl) chloride (PVC) porous grains: 2. Thermogravimetric analysis and numerical simulations", P. Agaciak et al., Colloids and Surfaces A: Physicochem. Eng. Aspects 470 (2015) 120-129, which article and test methods are hereby incorporated by reference herein.

[0050] Therefore, the present disclosure also relates to a method for preparing a polyvinyl chloride (PVC) polymer having a normalized drying rate greater than 0.840 at a time t* of 0.5 (determined by the method described in "Dehydration and drying poly(vinyl) chloride (PVC) porous grains: 2. Thermogravimetric analysis and numerical simulations", P. Agaciak et al., Colloids and Surfaces A: Physicochem. Eng. Aspects 470 (2015) 120-129), the method comprising polymerizing monovinyl chloride monomer (VCM) using an aqueous organic peroxide emulsion, wherein the aqueous organic peroxide emulsion comprises 0 to 0.17 weight percent of an emulsifier.

[0051] In the method, the aqueous organic peroxide emulsion may be as defined above in the first aspect.

[0052] It is noted that the various elements of the present invention (including but not limited to the preferred ranges of various parameters) can be combined unless the elements are mutually exclusive.

[0053] The present invention will be described by the following examples and drawings, but the present invention is not limited thereto.

[0054] Example

[0055] Example 1 and Comparative Example 1A

[0056] Two emulsions were prepared according to the following procedure to have the final contents of components (i)-(iv) shown in Table 1.1.

[0057] 1. Introduce methanol and water into a double-jacketed vessel.

[0058] 2. Add PVA (polyvinyl acetate, degree of hydrolysis 65-70%) and optional emulsifier (C16 / C18 ethoxylated alcohol, HLB=18) to the water / methanol mixture at room temperature and stir at a stirring speed of about 250 rpm for 30 minutes to dissolve them.

[0059] 3. Cool the aqueous mixture to below -10°C with stirring.

[0060] 4. The oil phase containing 70 wt% of diisobutyryl peroxide in isododecane was added to the aqueous mixture using an Ultra Turrax S25N-25GM model apparatus at low speed.

[0061] 5. Disperse the oil phase at maximum Ultra Turrax speed (2.5 min / kg emulsion) while maintaining the temperature below 0° C. If it is necessary to keep below this temperature, temporarily stop the action of the Ultra Turrax.

[0062] 6. Store the emulsion at -25°C.

[0063] Table 1.1

[0064] Components Example 1A Example 1 (i) Diisobutyryl peroxide (wt%) 40 40 (ii) PVA (wt%) 1.3 3.0 (iii) Emulsifier (weight percentage) 0.5 - (iv) Methanol (wt%) 14.5 14.5

[0065] The storage stability of the emulsions was determined by measuring the droplet volume distribution with the aid of light scattering techniques using a Malvern 3000 model apparatus.

[0066] In Table 1.2, d99 (expressed in μm) is the 99th percentile of the droplet volume distribution of the organic peroxide in the emulsion, and d50 (expressed in μm) is the 50th percentile of the droplet volume distribution of the organic peroxide in the emulsion. The emulsion samples were stored at -25°C and the data were collected at room temperature.

[0067] Table 1.2

[0068] Droplet size after storage at -25°C (μm) Example 1A Example 1 1 day - d50 / d99 0.5 / 1.0 0.8 / 1.4 1 week - d50 / d99 1.3 / 2.5 nd 2 weeks - D50 / D99 nd 1.8 / 3.9 4 weeks - d50 / d99 2.2 / 3.8 2.6 / 5.0 8 weeks - D50 / D99 2.8 / 5.0 3.5 / 6.4 12 weeks - D50 / D99 3.1 / 5.8 4.0 / 8.2

[0069] nd – not determined

[0070] The above data demonstrate that both emulsions are highly stable for at least 12 weeks (a 12-week droplet size d99 value <10 μm indicates that the organic peroxide aqueous emulsion is highly stable). Thus, contrary to expectations, the inventors have managed to produce a highly stable, well-dispersed, emulsifier-free diisobutyryl peroxide aqueous emulsion. Furthermore, despite the absence of an emulsifier during emulsification, the organic peroxide aqueous emulsion formed in Example 1 advantageously has a small peroxide droplet size and a narrow droplet size distribution.

[0071] PVC suspension polymerization process

[0072] Vinyl chloride (VCM) polymerization was carried out following standard suspension polymerization techniques using a 10 liter Buchi reactor equipped with baffles, a flat blade stirrer, pressure transducer, VCM feed line, nitrogen purge line, peroxide feed line and peroxide injection point.

[0073] 3480 g of deionized water including 75.4 g of 2% (w / w) B72 (polyvinyl acetate / alcohol) solution and 11.6g 2% (w / w) Gohsenol GH23 (polyvinyl acetate / alcohol) solution. The reactor was then pressurized to 12 bar with nitrogen. If no leaks were found, the reactor was decompressed to 75 mbar (while stirring) to remove air and nitrogen. Subsequently, 2900g VCM was added to the reactor. While adding VCM, the reactor was heated to 52°C in 30 minutes. At 52°C, the organic peroxide emulsion was continuously added, and after reaching a maximum polymerization rate of 30% / hour in 40 minutes, the exothermic temperature was further raised to its polymerization temperature of 57°C. When the conversion rate reached 83% (calculated by temperature and pressure using CiD software), the polymerization was stopped. The reactor was then cooled and degassed. After the residual VCM was removed by vacuuming, the reactor contents were sampled and analyzed.

[0074] Example 2 and Comparative Example 2A

[0075] PVC samples were produced according to the above-described polymerization process.

[0076] Example 2: PVC prepared using the aqueous organic peroxide emulsion of Example 1 (diluted to 0.5% diisobutyryl peroxide with cold water for relatively small scale polymerization (10 liters) and stored in an ice bath with stirring during polymerization).

[0077] Comparative Example 2A: PVC prepared using the aqueous organic peroxide emulsion of Comparative Example 1A (diluted to 0.5% diisobutyryl peroxide with cold water for relatively small scale polymerizations (10 liters) and stored in an ice bath with stirring during polymerization).

[0078] The drying rates of the two PVC samples were investigated using thermogravimetric experiments under a stream of dry nitrogen, as described in the journal article “Dehydration and drying poly(vinyl)chloride(PVC)porous grains: 2. Thermogravimetric analysis and numerical simulations”, P. Agaciak et al., Colloids and Surfaces A: Physicochem. Eng. Aspects 470 (2015) 120-129.

[0079] As explained in the paper, the total time for a PVC sample to dry depends on the free water, interstitial water, and internal water content. To compare the two PVC samples, the drying rate was normalized for internal water content, as described on page 123 of the paper, such that:

[0080] -v* is the normalized drying rate;

[0081] -t* is the dimensionless time, normalized by the time required to dry the same mass of pure water;

[0082] -When t<0, water evaporates between PVC particles;

[0083] -When t>0, water evaporates (or boils off) from the PVC particles.

[0084] Standardized drying rate Figure 1 Here, it can be seen that the PVC of Example 2 dries quickly (where v* is 0.861 when t* is 0.5 and v* is 0.694 when t* is 1), while the PVC of Comparative Example 2A dries slowly (where v* is 0.837 when t* is 0.5 and v* is 0.673 when t* is 1). Specifically, the PVC of Example 2 is almost completely dried at t*=1.6, while the PVC of Comparative Example 2A takes longer to reach the same dry state.

[0085] These results indicate that including less (or no) emulsifier in the resulting PVC polymer results in faster drying characteristics, which in turn saves time in PVC production runs.

[0086] Example 3 and Comparative Example 3A

[0087] Two emulsions were prepared according to the following procedure to have the final contents of components (i)-(iv) shown in Table 3.1.

[0088] 1. Introduce methanol and water into a double-jacketed vessel.

[0089] 2. Add PVA (polyvinyl acetate, degree of hydrolysis 65-70%) and optional emulsifier (C16 / C18 ethoxylated alcohol, HLB=18) to the water / methanol mixture at room temperature and stir at a stirring speed of about 250 rpm for 30 minutes to dissolve them.

[0090] 3. Cool the aqueous mixture to below -10°C with stirring.

[0091] 4. An organic peroxide composition containing 98 wt% di(2-ethylhexyl) peroxydicarbonate was added to the aqueous mixture using Ultra Turrax S25N-25GM equipment at a slow speed.

[0092] 5. Disperse the organic peroxide composition at maximum Ultra Turrax speed (2.5 minutes / kg emulsion) while maintaining the temperature below 0° C. If it is necessary to maintain the temperature below this, temporarily stop the action of the Ultra Turrax.

[0093] 6. Store the emulsion at -20°C.

[0094] Table 3.1

[0095] Components Example 3A Example 3 (i) Di(2-ethylhexyl) peroxydicarbonate (wt%) 60 60 (ii) PVA (wt%) 0.6 1.6 (iii) Emulsifier (wt%) 0.3 - (iv) Methanol (wt%) 12 13

[0096] The storage stability of the emulsions was determined by measuring the droplet volume distribution with the aid of light scattering techniques using a Malvern 3000 model apparatus.

[0097] In Table 3.2, d99 (expressed in μm) is the 99th percentile of the droplet volume distribution of the organic peroxide in the emulsion, and d50 (expressed in μm) is the 50th percentile of the droplet volume distribution of the organic peroxide in the emulsion. The emulsion samples were stored at -20°C and the data were collected at room temperature.

[0098] Table 3.2

[0099] Droplet size after storage at -20°C (μm) Example 3A Example 3 1 day - d50 / d99 1.1 / 2.4 1.3 / 2.6 1 week - d50 / d99 nd nd 2 weeks - D50 / D99 1.3 / 2.5 1.5 / 2.9 4 weeks - d50 / d99 1.4 / 2.7 1.7 / 3.3 8 weeks - D50 / D99 1.5 / 3.0 2.0 / 3.6 12 weeks - D50 / D99 1.8 / 3.3 2.3 / 4.4

[0100] nd - not determined

[0101] The above data demonstrate that both emulsions are highly stable for at least 12 weeks (a 12-week droplet size d99 value <10 μm indicates that the organic peroxide aqueous emulsion is highly stable). Thus, contrary to expectations, the inventors have managed to produce a highly stable, well-dispersed, emulsifier-free aqueous emulsion of di(2-ethylhexyl) peroxydicarbonate. Furthermore, despite the absence of an emulsifier during emulsification, the organic peroxide aqueous emulsion formed in Example 3 advantageously has a small peroxide droplet size and a narrow droplet size distribution.

[0102] Although the invention has been described with reference to exemplary embodiments, it will be understood that various modifications may be made within the scope of the invention.

[0103] In this specification, unless expressly stated otherwise, the word "or" is used to refer to an operator that returns a true value when one or both of the stated conditions are met, as opposed to an "exclusive or" which requires that only one condition is met. The word "comprises" is used to mean "comprising" rather than "consisting of". All prior teachings acknowledged above are incorporated herein by reference. The acknowledgement herein of any previously published document is not to be taken as an acknowledgment or representation that its teachings were common general knowledge at the date of publication of this document, in Europe or elsewhere.

Claims

1. Use of an aqueous organic peroxide emulsion comprising 0 to 0.17% by weight of at least one emulsifier for the preparation of polyvinyl chloride having an increased drying rate.

2. The use according to claim 1, wherein the organic peroxide aqueous emulsion comprises: (i) 25 to 70 wt. % of at least one organic peroxide having a self-accelerating decomposition temperature (SADT) of 25° C. or less; (ii) 1.4 to 6.0% by weight of at least one protective colloid; (iii) 0 to 0.17 wt % of at least one emulsifier; and (iv) at least one antifreeze agent, The SADT value is determined for organic peroxides in high-density polyethylene (HDPE) packaging with a volume of 20 to 30 liters according to the method given in the United Nations Manual of Tests and Criteria, seventh revised edition (2019), test series H.4: Heat accumulation storage test.

3. The use according to claim 1 or claim 2, wherein the organic peroxide has a self-accelerating decomposition temperature (SADT) of 20°C or less, preferably 15°C or less, preferably 10°C or less, preferably 5°C or less, preferably 0°C or less, the SADT value being determined according to the method given in the United Nations Manual of Tests and Criteria, seventh revised edition (2019), test series H.4: heat accumulation storage test for organic peroxides in high-density polyethylene (HDPE) packaging with a volume of 20 to 30 liters.

4. The method according to claim 1, wherein the organic peroxide is selected from peroxyesters, peroxydicarbonates, diacyl peroxides or mixtures thereof and is preferably selected from diisobutyryl peroxide (SADT 0°C), isopropyl peroxyneodecanoate (SADT 10°C), 1,1,3,3-tetramethylbutyl peroxyneodecanoate (SADT 15°C), isopropyl peroxyneoheptanoate (SADT 10°C), tert-amyl peroxyneodecanoate (SADT 20°C), di-sec-butyl peroxydicarbonate (SADT 0°C), di(2-ethylhexyl peroxydicarbonate) (SADT 5°C), tert-butyl peroxyneodecanoate (SADT 20°C), 1,1,3,3-tetramethylbutyl peroxypivalate (SADT 20°C); tert-amyl peroxypivalate (SADT 25°C), tert-butyl peroxypivalate (SADT 25°C), di(3,5,5-trimethylhexanoyl) peroxide (SADT 25°C), di-n-propyl peroxydicarbonate (SADT 0°C), diisopropyl peroxydicarbonate (SADT 5°C), di-n-butyl peroxydicarbonate (SADT 0°C), di(2-ethoxyethyl peroxydicarbonate) (SADT 10°C), 1,3-di(propane-2,2-diyl)benzenebis(neodecanoyl)peroxide (SADT 10°C), 3-hydroxy-1,1-dimethylbutyl peroxyneodecanoate (SADT 10°C), di-n-butyryl peroxide (SADT 25°C) or a mixture thereof, the SADT value being determined for high density polyethylene (HDPE) packaging with a volume of 20 to 30 litres according to the method given in the United Nations Manual of Tests and Criteria for Organic Peroxides, Seventh Revised Edition (2019), Test Series H.4: Heat Accumulation Storage Test.

5. The method according to claim 1 , wherein the protective colloid is polyvinyl acetate having a degree of hydrolysis between 60 and 75% and / or the at least one emulsifier is a compound selected from alkylene oxide block copolymers, ethoxylated fatty alcohols, ethoxylated fatty acids and combinations thereof and having an HLB (hydrophile-lipophile balance) value of 8 or more, preferably 10 or more, more preferably 14 or more.

6. Use according to any of the preceding claims, wherein no emulsifier is added to the aqueous emulsion.

7. Use according to any one of the preceding claims, wherein the at least one antifreeze agent is a compound selected from methanol, ethanol, propanol, isopropanol, (ethylene) glycol, propylene glycol, glycerol and combinations thereof, preferably methanol, and is used in an amount such that the emulsion does not freeze at a temperature of -10°C.

8. An organic peroxide aqueous emulsion comprising: (i) 30 to 45% by weight of diisobutyryl peroxide; (ii) 2.0 to 6.0% by weight of at least one protective colloid; (iii) 0 to 0.17 wt % of at least one emulsifier; and (iv) at least one antifreeze agent.

9. The aqueous emulsion according to claim 8, comprising 35 to 42% by weight of diisobutyryl peroxide.

10. Aqueous emulsion according to claim 8 or claim 9, comprising 2.5 to 4.0% by weight, preferably 2.7 to 3.5% by weight, of at least one protective colloid.

11. Aqueous emulsion according to any one of claims 8 to 10, wherein the protective colloid is polyvinyl acetate having a degree of hydrolysis between 60% and 75%.

12. The aqueous emulsion according to any one of claims 8 to 11, wherein the at least one emulsifier is a compound selected from alkylene oxide block copolymers, ethoxylated fatty alcohols, ethoxylated fatty acids and combinations thereof and having an HLB (hydrophile-lipophile balance) value of 10 or more, more preferably 14 or more.

13. The aqueous emulsion according to any one of claims 8 to 12, wherein no emulsifier is added to the aqueous emulsion.

14. The aqueous emulsion according to any one of claims 8 to 13, wherein the at least one antifreeze agent is a compound selected from methanol, ethanol, propanol, isopropanol, (ethylene) glycol, propylene glycol, glycerol and combinations thereof, preferably methanol, and is used in an amount such that the emulsion does not freeze at a temperature of -10°C.

15. A method for preparing a polyvinyl chloride polymer having a normalized drying rate greater than 0.840 at a time t* of 0.5, the normalized drying rate being determined by the method described in "Dehydration and Drying of Porous Polyvinyl Chloride (PVC) Particles:

2. Thermogravimetric Analysis and Numerical Simulation", P. Agaciak et al., Colloids and Surfaces A: Physicochem. Eng. Aspects 470 (2015) 120-129, the method comprising polymerizing monovinyl chloride monomer using an aqueous organic peroxide emulsion, wherein the aqueous organic peroxide emulsion comprises 0 to 0.17 weight percent of an emulsifier.

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