Film with high weathering resistance

Abstract

The present disclosure refers to a modified low density polyethylene derivable from a radical polymerization process using propylene as modifier, which can be used for an agricultural film or greenhouse film, or scattering film without adding any UV stabilizers with improved weathering resistance, increased lifetime obtained by a process, which is either processed in a tubular reactor. Lifetime, weathering resistance and stability against UV light is increased compared to other well known low density polyethylene grades.

Description

FILM WITH HIGH WEATHERING RESISTANCEFIELD OF THE DISCLOSURE

[0001] The present disclosure refers to a propylene controlled branched low density polyethylene, for use e.g., for film applications, such as agricultural films, greenhouse films, or scattering films with improved weathering resistance, increased lifetime, comprising a propylene controlled low density polyethylene which has been obtained by a radical initiated propylene controlled process to obtain a branched low density polyethylene with low density.BACKGROUND OF THE DISCLOSURE

[0002] The modification of properties for using polyethylene in different applications, such as e.g. for agricultural films, made of low density polyethylene polymers, or the like play an essential and ubiquitous role in everyday life. One way to obtain polymers is high-pressure polymerization of monomers such as ethylene leading to polyethylene differing in density, optionally in combination with one or more comonomers, to obtain valuable polyolefin products.

[0003] Polyethylene, a widely used commercial polymer, can be prepared by different processes, such as polymerization in the presence of free-radical initiators at elevated pressures.

[0004] Low density polyethylene can be obtained by different processes varying dependent on the process in mechanical und structural properties. Which is valuable when it comes to different applications, e.g. LDPE's flexible and versatile nature is highly appreciated for some well known applications including the use for plastic bags, in food packaging, or medical packaging, besides industrial wraps and the use in films, e.g. agricultural films. So, typical agricultural films are made of blends on LDPE, or LDPE and LLDPE and at least an UV stabilizer.

[0005] In the state of the art different chain transfer agents are well known. The use of propylene as chain transfer agent is already known in the state of the art. To control the molecular mass during the radical polymerization of ethylene. The chain transfer agent terminates then the growing polymer chain by transferring a hydrogen or other atom, which leads to the production of a new radical which then reinitiates the polymerization with a new polymer chain.

[0006] For the polymerization process there is one significant difference between propylene and propionaldehyde, due to the fact that propylene also copolymerizes with ethylene. With the incorporation of propylene into the backbone of the polymer the number of short chain branches (SCB) increase significantly and reduce the density at the same time. This means that using propylene as modifier is not favorable for the production of low density polyethylene's where a higher density is required, e.g. for a high mechanical stability for film applications for example, especially in agricultural films where a high tensile strength is required.

[0007] Therefore the density of the polyethylene should be high, which means that reduction of density is unfavorable.

[0008] Furthermore, adding UV stabilizers are mostly required, to extend lifecycle of the agricultural films due to the exposure to challenging weather conditions, like sun, UV radiation, wind, snow and the like.

[0009] UV light and the other weathering conditions deteriorate the structure of the polyethylene applied in agricultural films through a process known as photodegradation. UV radiation contains high-energy photons interacting with the polymer chains in LDPE. This interaction leads to the breaking of chemical bonds, causing the material to weaken, become brittle, and lose its mechanical strength overtime. Additionally, exposure to environmental factors like moisture, temperature variations, and atmospheric pollutants, further accelerates the degradation process. This combined effect of UV light and weathering conditions ultimately leads to the deterioration of polyethylene, e.g. LDPE derived agricultural films.

[0010] Especially for low density polyethylene, when used for agricultural films, the lifetime correlates directly to economy and sustainability. Therefore there is a high demand for polyethylene providing longer and extended lifetime when used as agricultural films. With increased resistance to exposure of weather conditions.

[0011] Furthermore, extension of lifetime is directly connected to an environmental friendly production of vegetables and plants, and helps to benefit for economic reasons and also helps to save energy and resources resulting in eco-friendly agriculture as it helps to reduce carbon dioxide emission and prevent PE waste.

[0012] As described above, photodegradation is a main issue in agriculture. Therefore the most important property of polyethylene used in agricultural films is a high weathering resistance. Depending on time, the properties of polyethylene processed to films suffer always from UV light and weathering conditions.

[0013] So, various low density polyethylene films using propylene as modifier have already been known, however, all of these films exhibit very poor weathering resistance.

[0014] Hence, there is a strong need to find alternative low density polyethylene which can be used in films, e.g. agriculture applications which offer longer and extended lifetime and improved weathering resistance than those known from the state of the art.SUMMARY OF INVENTION

[0015] Surprisingly it has been found, a modified low density polyethylene (LDPE), comprising low density polyethylene with high weathering resistance and increased lifetime obtained by a polymerization process using propylene as modifier, whit high resistance and resilience against exposure to UV radiation, wind and weather conditions. It has been found that the use of propylene as chain transfer agent in the polymerization process described further herein, increases the weathering resistance and / or lifetime of the polymer. Therefor a modified low density polyethylene grade is disclosed, comprising low density polyethylene with high weathering resistance, obtained by a polymerization process using propylene as modifier.BRIEF DESCRIPTION OF THE DRAWINGS

[0016] These and other features, aspects, and advantages of the present invention will be better understood with reference to the following description and claims, and accompanying drawings where:

[0017] Figure 1 shows the influence of different modifiers on the weathering resistance and / or lifetime of the disclosed modified low density polyethylene and also the relatively poor UV stability of all the other samples comprising UV-stabilizers or without an UV-stabilizer, already known from the state of the art. It is shown that after 500 hours under the testing conditions the samples Comp. Ex. 2 one with and the other without Irganox 1010, the material has lost more than 80% of the elongation properties, whereas the disclosed non-polar modified low density polyethylene grade, grades Comp. Ex. 1 and Comp. Ex. 2 remain still more than 50% of their elongation properties. After 1000 hours under testing conditions all samples have lost almost all of their mechanical resistance, but also the propionaldehyde modified Comp. Ex. 3 samples are significant worse compared to the Example comprising the modified low density polyethylene disclosed herein.

[0018] At this stage it was only possible for the disclosed modified low density polyethylene, to measure its mechanical properties in transverse direction (TD) and it is obvious from the provided data that also after 500 hours of exposure to artificial weathering conditions also the disclosed modified low density polyethylene, shows the best UV resistance and show also still the best mechanical properties.

[0019] Figure 2 shows the influence on mechanical film properties of artificial weathering conditions according to ISO 527 and ISO 4892-2 before and after weathering of before (0 h), after 500 h and after 1000 h of exposure time under artificial weathering resistance, for the elongation at break in MD [%] for all samples Comp. Ex. 1-3 also the Example.

[0020] Figure 3 shows the I R spectra of the test samples Comp. Ex. 2 and the Example before exposure to artificial weathering conditions.

[0021] Figure 4 shows the IR spectra after exposure for 500 hours to artificial weathering conditions. Changes in the IR - spectra the come along with the variations in the mechanical properties, where the carbonyl band becomes more pronounced with increasing weathering time. The IR spectra for Comp. Ex. 2 and the Example is almost similar, but the CO-band is more pronounced.

[0022] Figure 5 shows a IR spectra for the disclosed low density polyethylene grade after 0, 500 and 1000 hours of artificial weathering. The increase in the carbonyl band for the Example, the modified low density polyethylene shows the time-dependent transmittance decrease of the CO- band at a wavelength of 1720-1680 cm'1, compared to other low density polyethylene grades the present modified polyethylene grade shows the exceptional weathering resistance and an extended lifetime even after 1000 hours under testing conditions. The Figure 5 shows the increase of the carbonyl band for modified low density polyethylene disclosed herein after 0, 500 and 1000 hours artificial weathering and the following table lists for all tested grades the time-dependent transmittance decrease of the C=O band.

[0023] Figure 6 shows the temperature-depending reactor profile of the radical polymerization process to produce the modified low density polyethylene.DETAILED DESCRIPTION OF THE INVENTION

[0024] A modified low density polyethylene is disclosed, having a high weathering resistance and / or extended and / or increased lifetime, obtained by a polymerization process using propylene as modifier in a reactor, which can be a tubular reactor. It has been surprisingly found that using propylene instead of propionaldehyde increases the weathering resistance and / or extends the lifetime of the polymer significantly. Which means, that after 500 hours or even 1000 hours under artificial weathering conditions, according to the testing conditions according to ISO 527 and ISO 4892-2, which means exposure to artificial weathering conditions, the mechanical properties, measured as elongation at break [%], tensile strength at break [MPa], according to the results, shown in (Table 4, Table 5 and Table 6) measured in MD (machine direction) and TD (testing direction), the results are still exceptionally good for the Example, comprising the disclosed modified low density polyethylene as disclosed herein.

[0025] Furthermore in Table 6, the increasing number of CO-bonds is shown, which causes brittleness and finally destruction of the polyethylene structure, and finally the damage of the e.g. agricultural films. Depending on the exposure time under artificial weathering conditions, an increase of carbonyl-groups can be detected, due to reactions of double bonds and oxygen. Only the disclosed modified low density polyethylene keeps its extraordinary high mechanical properties, due to a low amount of the emerged carbonyl-groups. So, the remaining good mechanical properties of the disclosed modified low density polyethylene with increased and extended lifetime compared to the Comparative Examples results from low amount of CO-bands in the polyethylene structure. Due to the fact, that propylene has been incorporated into the structure of polyethylene, leading to a more branched PE- than without propylene. So the branched structure increases the ageing stability and prevents decomposition when exposed to artificial weathering conditions and UV-radiation. And reduces the formation of CO-bands and slows down the deconstruction of the branched polymer.

[0026] So by using propylene as modifier or chain transfer agent to produce the modified low density polyethylene in a high pressure and high temperature in reactors, such as tubular reactors, e.g., the obtained modified low density polyethylene shows not only good optical and mechanical properties, besides high gloss and less haze, but also increased lifetime and exceptional weathering resistance, good draw down, wherein the production itself is also highly cost efficient.

[0027] The modified low density polyethylene has a density of 0.917 to 0.926 g / cm3, preferably 0.919 to 0.924 g / cm3, preferably 0.920 to 0.922 g / cm3, a Mw of 300,000 to 400,000 g / mol measured by GPC-LS, preferably 350,000 g / mol, an amount of short chain branches (SCB) of 18 to 22 -CH3 1 / 1000C measured by IR, preferably 19 to 21 , and a MFR of 0.15 g / 10 min to 0.35 g / 10 min (2.16 kg / 190°C, ISO 1133), preferably 0.18 g / 10 min to 0.30 g / 10 min, preferably 0.20 g / 10 min to 0.28 g / 10 min, preferably 0.22 g / 10 min.

[0028] The use of a technology with conditions under pressure and high temperature in a polymerization process with propylene as chain transfer agent leads to modified low density polyethylene grades with extraordinary properties. Processed in a tubular reactor comprising a tube length of 800 up to 2800 m, and a pressure from 2000 up to 3000 bar, preferably 2100 up to 2600 bar, at temperatures of 300 °C with a conversion rate up to 35 %, leads to low density polyethylene withrelatively high density in a range from 0.917 to 0.926 g / cm3, preferably a product having a density of 0.922 g / cm3.

[0029] The disclosed material is therefore suitable for use as agricultural film and or greenhouse film, or scattering film and shows compared to other agricultural films improved mechanical properties, increased lifetime and extraordinary weathering resistance although one would have expected the opposite as the density is lower.

[0030] The use of a high pressure high temperature process is also cost efficient and also highly sustainable as non-reacted monomers are constantly recovered and recycled in the process. Operating costs with low consumption of raw material and energy, low investment costs due to a highly efficient design, while also the process can be seen as sustainable as the resulting heat due to the exothermal reaction is used to produce steam which can be used elsewhere in the petrochemical complex for heating up other reactions and processes.

[0031] The disclosed modified low density polyethylene disclosed herein has preferably an MFR (2.16 kg / 190°C) of from 0.1 to 1 g / 10 min, preferably 0.13 to 0.5 g / 10 min, preferably 0.15 to 0.35 g / 10 min, preferably 0.18 g / 10 min to 0.30 g / 10 min, preferably 0.20 g / 10 min to 0.28 g / 10 min, preferably 0.22 g / 10 min, according to ISO 1133, according to ASTM D1238.

[0032] The disclosed modified low density polyethylene, shows an MFRw (10 kg / 190°C), which is in the range from 1 to 15 g / 10 min, preferably from 2 to 10 g / 10 min, preferably from 3 to 7 g / 10 min, preferably from 3.5 to 5 g / 10 min, preferably 3.7 to 4 g / 10 min according to ISO 1133, according to ASTM D1238.

[0033] It has been found, that as described in the present disclosure, the modified low density polyethylene can be used for agricultural and / or greenhouse film, and / or scattering film applications, although the density is lower than that of comparable LDPE known from the state of the art (without propylene used in the process). The film application shows that comprising the modified low density polyethylene results in longer and increased lifetime and exceptional good weathering resistance tested under artificial weathering conditions of at least 500 hours, preferably 1000 hours. So the films can be used longer than other films already known in the state of the art, and even can be reused for several seasons.

[0034] When it comes to applications and articles, films comprising the disclosed propylene controlled modified low density polyethylene helps to save costs, also to avoid more plastic waste as it can be seen as a sustainable film, as it reduces carbon dioxide emission, and leads to establish a “greener” more eco-friendly and more sustainable agricultural business.

[0035] Per definition the term “sustainable” means, that the production and use of the material and the use of the films comprising the low density polyethylene as described herein is environmentally friendly and resource-efficient, aiming to minimize negative impacts on the environment. It may also imply that the LDPE films are recyclable.

[0036] The term “greener” as per definition means, that the production and use of this material are environmentally friendly than conventional alternatives. This may involve aspects such as a lower ecological footprint, the use of renewable resources, or improved recycling capabilities. It aims to reduce environmental impacts and represents a more sustainable option compared to traditional alternatives.

[0037] The disclosed modified low density polyethylene shows exceptional mechanical properties and high processability due to its molecular structure and molecular weight distribution, which is influenced and determined by the process conditions such as temperature, pressure, content of ethylene and also propylene present in the reactor during the radical polymerization.

[0038] To control the molecular weight during the radical polymerization of ethylene, a so called chain transfer agent or modifier as it is also called, is applied and used. The chain transfer agent terminates the growing polymer by transferring a hydrogen or other atom to the growing chain, which leads in the production of a new radical which then reinitiates the polymerization. In high pressure high temperature processes propylene and propionaldehyde can be used as modifiers to obtain low density polyethylene. These modifiers show a significantly different behavior and lead to different products with different mechanical properties, different molecular structures, crystallinity, and density, besides different processing behavior resulting in different weathering resistance, lifetime, and UV stability used for film applications. A high weathering resistance indicates that such conditions can be endured without or less significant degradation or loss of properties in relation to the starting conditions.

[0039] The use of polar propionaldehyde as modifier leads to a low density polyethylene , with unsatisfying weathering resistance (please see comparative examples 1 , 2 and 3 discussed in the following). The polar modified LDPE shows insufficient weathering resistance when exposed to artificial weathering conditions, in form of a film sample, due to the loss of almost all mechanical properties, e.g., elongation at break, or tensile strength (Table 4, Table 5 or Table 6), just like other comparative films known in the state of the art. The films lose all their mechanical properties and show a significant decrease in elongation at break tests after being exposed to artificial weathering conditions (Figure 1 and 3, showing the IR Spectra after 0, 500 and 1000 hours under artificial weathering conditions).

[0040] The exposure to artificial weathering conditions show according to ISO 4892-2 (method A under black standard temperature of 65 °C), that the molecular structure of the polyethylene changes, which results in a degradation and / or loss of mechanical properties. Due to reactions under UV radiation, temperature and oxygen, carbonyl groups are formed. IR measurements show, that after 500 hours of exposure to artificial weathering conditions, the carbonyl band becomes more pronounced.

[0041] Figure 2 shows the IR - spectra of the disclosed modified low density polyethylene, compared to the samples known from the state of the art. All samples were obtained by radical polymerization processes, while Comp. Ex. 1 and the Example comprising modified LDPE were processed with propylene as modifier, and for obtaining Comp. Ex. 2 and 3 propionaldehyde as chain transfer agent was used.

[0042] Taking a closer look at the IR results, the influence of the modifier leads to significantly different mechanical properties of the obtained polymers. The IR transmission at 1720 cm-1 (for the C=O-band) is an indicator for the thermal (oxidative induced) damage of the polyethylene. As the samples obtained with propylene show significant lower absorption bands in the region of and no significant difference between the bands (Figure 2). Even the results for Comp. Ex. 3 a low density material, processed with propionaldehyde as modifier, wherein Irganox 1010, an antioxidant stabilizer was added, to protect thermo-oxidative degradation of the polyethylene, the resistance against artificial weathering is significantly lower compared to samples processed with propylene (Comp. Ex. 1 andExample, being the modified LDPE as disclosed herein). So the addition of an antioxidant stabilizer does not improve the weathering resistance sufficiently.

[0043] Although the amount of initial carbonyl groups inserted by the decomposition of propionaldehyde (e.g. in the compared films) is extremely low, it has a great influence on the weathering resistance of LDPE used in agricultural film applications (results can be seen in Figure 3). It is known that all carbonyl groups absorb UV in the region of 300 nm and that the concentration of these groups accelerates the degradation of polyethylene chains. Aliphatic ketones degrade under UV light by chain scissions after either Norrish type I or Norrish type II mechanism. These scissions create free radicals which then react with oxygen or other polymer chains causing a decrease in polymer length and thus cause the decrease of mechanical properties. Therefore all test samples (wherein propionaldehyde is used) are heavily damaged by the applied artificial weathering and completely destructed after 1000 h of testing, which can be tested by an increase of the CO- band. Besides the disclosed modified low density polyethylene, which shows the best weathering resistance of all test materials.

[0044] In a further form of the present disclosure the modified polyethylene film shows high weathering resistance which is measured via IR spectra over time by the increase in the carbonyl band which is at 1710-1680 cm1(Figure 3), and indicates the thermal and oxidative damage of the polyethylene.

[0045] Also UV light, sunlight, and normal weather can cause degradation of LDPE; especially of agricultural films made from low density polyethylene (LDPE) through a process called photodegradation. When LDPE is exposed to UV radiation from the sun, the energy from the UV light promotes the breakage of chemical bonds in the polymer chain. This leads to a weakening of the material's structure, resulting in a loss of mechanical properties like strength and flexibility.

[0046] Additionally, the oxygen in the air and other environmental factors can contribute to the degradation PE-process. Oxygen molecules can interact with free radicals formed during photodegradation, accelerating the degradation process. So, even when no propionaldehyde is used and propylene serves as modifier, carbonyl groups can be formed. Even when there are no initial carbonyl groups e g., derived from propionaldehyde, the interaction of the formed radicals induced by UV light and environmental factor, with the low density polyethylene in combination with oxygen due to aging processes.

[0047] Furthermore, the disclosed modified low density polyethylene counts as homopolymer, when propylene's only function is to regulate chain transfer. But when added to the structure, the resulting low density polyethylene is a copolymer, when propylene is also contributing to chain growth. As propylene also copolymerizes with ethylene, resulting in a different structure where short chain branching (SCB) occurs, leading to different mechanical properties. This occurs through oxidative processes where oxygen molecules react with the LDPE chains. As a result, carbonyl groups which contain a double bond between carbon and oxygen (C=O) are formed. These groups can adversely affect all mechanical properties, lifetime and weathering resistance of the material and lead to embrittlement and destruction of the low density polyethylene.

[0048] This leads to the formation of small cracks, brittleness, and a decrease in the polyethylene overall mechanical properties especially when used in film applications the performance is extremely poor. To mitigate these effects, low density polyethylene when used for films, especially usedfor agricultural films, are often treated with UV stabilizers or additives that absorb or scatter the UV light, providing a protective barrier against photodegradation. However, over time, these stabilizers can also become depleted, making it important to monitor the condition of the film and replace it as needed to maintain its effectiveness. So if the low density polyethylene was obtained by processes using propylene as modifier, the initial carbonyl-content is so low, that there is no need to add UV stabilizers, and even without the lifetime of the modified low density polyethylene used for e.g., agricultural films comprising the disclosed LDPE is increased and the test results (please see Table 6, Example) are exceptionally good.

[0049] Film applications, comprising the disclosed propylene controlled modified low density polyethylene, are more resilient to external climate conditions, such as temperature (artificial weathering conditions according to ISO 4892-2, method A and black-standard temperature of 65°C to evaluate the weather resistance of the samples, performed under 65°C), or solar irradiation, UV radiation, UV intensity, global energy, weathering conditions, rain, snow, wind, storm, and also to mechanical stress, when the films are applied to greenhouses or fields etc. leading to a longer period of use.

[0050] The use of propylene instead of propionaldehyde prevents to have a further source of carbonyl groups in the polymer. Although the amount of initial carbonyl-g roups via using propionaldehyde is extremely low, it has a great influence on the weather resistance of LDPE blown films for the use in agricultural film applications as greenhouse films and scattering films. It is known that all aliphatic CO- groups absorb UV in the region of 300 nm and that the concentration of these groups accelerates the degradation of polyethylene chains.

[0051] Furthermore, aliphatic ketones degrade under UV- light by chain scissions after either Norrish type I or Norrish type II mechanism. These scissions create free radicals which then react with oxygen or other polymer chains causing a decrease in polymer length and thus cause the decrease of mechanical properties.

[0052] The "weathering resistance" of low density polyethylene with respect to the IR spectrum carbonyl band in the region of 300 nm refers to the material's ability to withstand the detrimental effects of environmental factors such as UV radiation, moisture, and temperature fluctuations, which tend to degrade the structural integrity and performance of the material overtime. A well-developed weathering resistance indicates that the LDPE material exhibits increased resistance to the degrading effects of these environmental factors, leading to an extended lifespan and enhanced functionality of the product.

[0053] In yet another form of the present disclosure, the modified low density polyethylene, shows high UV stability without adding an UV stabilizer. The non-additivated low density polyethylene (LDPE) film exhibits good tear strength and toughness, and offers good flexibility and processability, and a higher weathering resistance, compared to the comparative examples 1 , 2 and 4.

[0054] The modified low density polyethylene does not comprise any UV stabilizers, not comprising any UV stabilizers, its UV stability is higher compared to other polyethylene films and grades produced with propylene as modifier in a comparable pressure process (Comp. Ex. 3). Due to the different structure of the low density polyethylene, having higher amounts of short chain branches, the density is lower, and the mechanical properties and processability is improved.TEST RESULTS

[0055] For testing after 0 h of artificial weathering resistance testing

[0056] In one embodiment the disclosed low density polyethylene shows high values after testing for 0 h at elongation at break [%] in (MD) in the range of 510 to 550, preferably 515 to 540, preferably 520 to 535, more preferably 525 to 530, still more preferably 528.

[0057] In one embodiment the disclosed low density polyethylene shows high values after testing for 0 h at tensile strength at break [MPa] in (MD) in the range of 22 to 27, preferably 23 to 26, preferably 24 to 25, still more preferably 24.8.

[0058] In one embodiment the disclosed low density polyethylene shows high values after testing for 0 h at elongation at break [%] in (TD) in the range of 620 to 660, preferably 625 to 650, more preferably 630 to 640, still more preferably 637.

[0059] In one embodiment the disclosed low density polyethylene shows high values after testing for 0 h at tensile strength at break [MPa] in (TD) in the range of 22 to 27, preferably 21 to 26, 22 to 25, more preferably 23 to 24, still more preferably 24.1 .

[0060] For testing after 500 h of artificial weathering resistance testing:

[0061] In one embodiment the modified low density polyethylene shows high values for the elongation at break [%] in (MD) after testing for 500 h under artificial weathering conditions being greater than 300 %, preferably in the range of 320 to 380, preferably 330 to 370, preferably 340 to 360, more preferably 350 to 355, still more preferably 357, compared to the initial starting value.

[0062] In one embodiment the modified low density polyethylene shows high values after testing for 500 h under artificial weathering conditions at tensile strength at break [MPa] in (MD) being greater than 10, preferably in the range of 8 to 15, preferably 9 to 13, more preferably 10 to 12, still more preferably 11 , compared to the initial starting value.

[0063] In one embodiment the modified low density polyethylene shows high values after testing for 500 h under artificial weathering conditions at elongation at break [%] in (TD) being greater than 300 %, preferably in the range of 280 to 350, preferably 300 to 340, preferably 310 to 330, more preferably 315 to 325, still more preferably 320, compared to the initial starting value.

[0064] In one embodiment the disclosed low density polyethylene shows high values after testing for 500 h under artificial weathering conditions at tensile strength at break [MPa] in (TD) greater than 10, preferably in the range of 7 to 15, preferably 8 to 14, preferably 9 to 13, more preferably 10 to 12, still more preferably 11 , compared to the initial starting value.

[0065] For testing after 1000 h of artificial weathering resistance testing

[0066] In one embodiment the disclosed low density polyethylene shows high values after testing for 1000 h under artificial weathering conditions at elongation at break [%] in (MD) greater than 11 % in the range of 16 to 25, preferably 16.5 to 24, preferably 17 to 23, preferably 17.5 to 22, more preferably 18 to 21 , more preferably 18.5 to 20, still more preferably 19, compared to the initial starting value.

[0067] In another embodiment the modified low density polyethylene, shows high values after testing for 1000 h under artificial weathering resistance at tensile strength at break [MPa] in (MD) greater than 9, preferably in the range of 8 to 16, preferably 9 to 14, 10 to 13, more preferably 11 to 12, still more preferably 11 .6, compared to the initial starting value.

[0068] In one embodiment the disclosed low density polyethylene shows high values after testing for 1000 h at elongation at break [%] in (TD) in the range of 5 to 14, preferably 6 to 12, preferably 7 to 11 , more preferably 8 to 10, still more preferably 9, compared to the initial starting value.

[0069] In one embodiment the disclosed low density polyethylene shows high values after testing for 1000 h under artificial weathering conditions at tensile strength at break [MPa] in (TD) greater than 7, preferably in the range of 4 to 12, preferably 5 to 11 , preferably 6 to 10, more preferably 7 to 8, still more preferably 7.6, compared to the initial starting value.

[0070] As the temperature profile (according to Figure 6) for barrel and die was applied in the starting phase a temperature of 200°C was applied, wherein the temperature was going up at a maximum temperature of 320 °C and down in dependence of the reactor position.

[0071] In a further embodiment, the polyethylene film, comprises at least one additive chosen from the following group, e.g., one or more of kaolin, hindered amine light stabilizer (HALS) and heavy metals are used to stabilize LDPE films. A comparison between this group and non-stabilized LDPE films show, that the by the additives various properties can be improved.

[0072] Low density polyethylene is produced exclusively by high pressure free radical polymerization. High pressure and high temperature conditions, together with the monomers and a chain transfer agent result in numerous competing side reactions such as branching and premature chain termination. Therefore product properties are only controlled via concentration, temperature, pressure, vinyl monomers and co-monomers, e.g., polar vinyl acetate and methacrylic acid and the chain transfer agents.

[0073] The modified low density polyethylene was obtained using a polymerization process to produce a polyethylene film using a Lupotech T process.

[0074] As high temperatures promote branching and also the choice of chain transfer agents, such as propylene or propionaldehyde, influences short chain branching and long-chain branching. The increased branching level reduces the degree of crystallinity, resulting in a lower density of the obtained low density polyethylene.

[0075] Depending on the reaction conditions the molecular weight of the obtained modified low density polyethylene can be varied. The modified low density polyethylene In one embodiment, the molecular weight Mw of the low density polyethylene ranges from 300.000 to 400.000 g / mol, preferably 350,000 g / mol measured by GPC-LS. The density of the low density polyethylene tends to increase, differing also in a more broader or narrower molecular weight distribution when different reaction conditions such as a higher or lower pressure is applied besides a certain number of short chain branches (SCB) of 18 to 22 -CH31 / 1000C by IR.

[0076] So, the reason for the extraordinary weathering resistance can be found in the reaction conditions. The conditions for producing the modified low density polyethylene are a) a pressure of 2300 barb) a starting temperature in zone 1 of 170 °C, c) a maximum temperature in zones 1 to 4 of 300 °C, d) a propylene dosing of 8 kg / t of resulting product, e) at a conversion rate of 26.4 %, f) and a reactor cooling water of 160 to 180 °C.

[0077] In the polymerization process (Figure 6 shows the temperature profile of the reactor conditions), both homopolymers and copolymers can be obtained. So the polymer disclosed is to be understood as homopolymer, when the propylene is only used as chain transfer agent, but also as copolymer, when the propylene is added to the primary chains, resulting in short chain branches, or even long chain branches when so called backbiting reactions occur. Besides that, the disclosed low density polyethylene may also be understood as both, a homo- and a copolymer, and blends therefrom. So, the use of propylene influences also significantly the MFR of the obtained homo- and / or copolymer. Therefore, besides ethylene and propylene and optionally one or more comonomers are used in the process, such as ethylene, propylene, butene, hexene, heptene and / or octene.

[0078] The term “low density polyethylene” (LDPE) includes polyethylene homopolymers and copolymers, using comonomers as defined above. So, a low density polyethylene is a versatile thermoplastic polymer characterized by its molecular structure. As a homopolymer it is composed solely of ethylene monomers, or as a copolymer, where ethylene is copolymerized with amounts of other monomers, e.g., propylene, or butene, hexene, heptene, or octene.

[0079] In a further embodiment the polyethylene film, used as reference for testing etc. is obtained by an extrusion process. The extrusion process comprises the following steps and process conditions to prepare a 100 pm film using an Alpine sing HS 50 S-30. The 100 pm film was produced according to the following standard operating conditions: the Alpine Extruder HS 50 S-30, was applied using a barrier screw, a BFC 4-16, with a die diameter of 120 mm and die gap width of 1 .0 mm. As air cooling ring a HK 300 / ML was used, with a freeze height of 0.3 m, BUR 2.5.

[0080] In an alternative embodiment, the disclosed modified low density polyethylene can be used to produce an agricultural film, a greenhouse film, or a scattering film comprising the polyethylene film. Preferably the films are produced via blow film extrusion and film extrusion processes. Optical properties of the films, comprising the modified low density polyethylene are measured with standard methods, gloss according to ASTM D 2457, and haze according to ASTM D 1003. And gloss and haze are measured and given in table 3.

[0081] Furthermore, the use of the disclosed modified polyethylene for application as agricultural film is disclosed, or use as greenhouse film, or use as scattering film, with high weathering resistance and good processability, as defined above.

[0082] Furthermore, the disclosed modified low density polyethylene, is used for producing films, e.g. single or for production of multilayer films.

[0083] Article comprising the modified low density polyethylene according to any one of the preceding claims. Producing agricultural films using the modified low density polyethylene is preferred. Such films include scattering film applications, wherein the scattering film has a function of adjusting temperature, light, humidity, and diffuse scattering.DEFINITIONS

[0084] In the sense of this disclosure “weathering resistance” means and refers to the ability to withstand the effects of exposure to outdoor weather conditions, or artificial weathering conditions, over time. Furthermore, it can be understood, that it also means, that the material is exposed to sunlight, moisture, temperature variations, and other environmental factors. A high weathering resistance indicates that such conditions can be endured without or less significant degradation or loss of properties in relation to the starting conditions. The exposure to artificial weathering conditions showed according to ISO 4892-2 (method A under black standard temperature of 65 °C),

[0085] In addition to that, “deterioration” of the polyethylene means also, a loss in mechanical properties, which is caused by sun, UV radiation, temperature, climate conditions such as rain, snow wind storm etc., compared to the state of the art (according to ISO 4892-2).

[0086] In the sense of this disclosure, the term “improved lifetime” refers to an extended or enhanced lifetime of low density polyethylene compared to standard samples comprising LDPE, obtained by using propylene or propionaldehyde as chain transfer agent.

[0087] The term LDPE refers to a low density polymer containing a copolymer of ethylene and one or more a-olefins polymerized in the presence of one or more single-site catalysts, such as one or more Ziegler-Natta catalysts, one or more metallocene catalysts, and combinations thereof. Such LDPE can have density within the range from a low 0.917 g / cm3to a high of 0.935 g / cm3.

[0088] The term “LDPE composition” refers to a composition containing a LDPE polymer. The LDPE polymer composition can be in any form. Some examples include: the form of a reactor grade (e g., granules or resin) containing the LDPE polymer; the form of a molten or at least partially molten composition containing the LDPE polymer and one or more additives undergoing or about to be undergoing the process of finishing (such as in the process of compounding extrusion), which is may be referred to as a pre; in the form of a finished LDPE polymer product such as LDPE polymer pellets containing the LDPE and any additives (such as PPA); or in the form of a finished LDPE product such as LDPE resin undergoing the process of mixing (e.g., via coextrusion, melt blending, or other processing) with additives, such as in the case of LDPE being extruded to form blown film, cast film or other polymer-containing article.

[0089] The term “photodegradation” is UV light, sunlight, and normal weather can cause degradation of LDPE; especially of agricultural films made from low density polyethylene (LDPE). Photodegradation of polyethylene refers further to the process by which the polyethylene in general, undergoes degradation and breakdown due to exposure to light, especially sunlight. This exposure can lead to chemical and physical changes in the polyethylene structure, causing it to lose some of its original properties. UV radiation is a common trigger for the photodegradation of polyethylene, and this process can result in the formation of smaller molecular fragments and, eventually, impact the materials performance.

[0090] Furthermore, the term “modified low density polyethylene” can be seen as homopolymer and also as copolymer. As randomly the propylene can act as chain transfer agent and can also be incorporated into the PE-chain. Besides that also at least one monomer differing from ethylene, such asbutene, hexene, heptane or octene can be additionally applied in the production process and incorporated into the polyethylene.

[0091] The term “ageing stability” is to be understood as the resisting to external and internal degradation influences on the structure of polyethylene resulting in loss of structure and properties.EXAMPLES

[0092] The following examples are included to demonstrate some preferred embodiments of the invention. The disclosed techniques used to analyze the samples are found to function well in the practice of the present disclosure and thus can be considered to constitute some preferred modes for its practice. However, those skilled in the art considering the present disclosure, appreciate that many changes can be made in the specific embodiments which are disclosed and still obtain a similar result without departing from the spirit and scope of the invention.RESULTS AND METHODS

[0093] Testing methods, and samples are explained in more detail in the following. In table 1 all properties of the testing materials, the Example and Comp. Examples 1-3 are listed.

[0094] All samples were analyzed, and of each sample 100-micron-films were prepared according to the following standard operation conditions.

[0095] For measuring the weathering resistance of the samples, artificial weathering conditions were used according to ISO 4892-2, method A and black-standard temperature of 65°C to evaluate the weather resistance of the samples.

[0096] Measurement of the MFR was performed according to IS 1133-1.

[0097] To determine the molecular weight of the modified low density polyethylene a GPS-LS,(Gel Permeation Chromatography) coupled with light scattering is used. Measurement, was performed according to ISO 16014-42012.

[0098] Short chain branches (SCB) of 18 to 25 -CH3 1 / 1000C, preferably in the range of 19 to 23 -CH3 1 / 1000C are measured by IR. The determination is carried out in accordance with ASTM D 6248-98.

[0099] As mentioned above, for both Comp. Ex. 1 and the Example, propylene was used to adjust the MFR (see Table 1). Comp. Ex. 2 and Comp. Ex. 3 were processed using propionaldehyde as regulation agent.

[0100] A common set-up for preparing polyethylene comprises a polymerization reactor, which can be a tubular reactor or a combination of such reactors, and additional equipment. For pressurizing the reaction components, usually a set of two compressors, a primary compressor and a secondary, or hyper, compressor, is used. At the end of the polymerization sequence, a set-up for high-pressure polymerization normally further includes apparatuses like extruders and granulators for pelletizing the resulting polymer. Furthermore, such a set-up generally also comprises means for feeding monomers and comonomers, free-radical initiators, modifiers or other substances at one or more positions to thepolymerization reaction. With the incorporation of propylene into the backbone of the polymer the number of short chain branches (SCB) increase, and this reduce the density of the resulting LDPE. This means that using propylene as modifier is not favorable for the production of low density polyethylene with higher density.

[0101] All materials were analyzed and from each sample 100-micron films were produced according to the following standard operation conditions.Table 1 : Test materials and samples.

[0102] In Table 1 an overview is given of the comparative Examples, and the properties of the compared LDPE materials.

[0103] As mentioned above, in Table 1 Comparative examples and the disclosed example comprising the modified LDPE are listed. Two examples comprising propylene, two examples regulated with propionaldehyde.

[0104] The density of Comp. Ex. 1 , and of modified low density polyethylene are quite similar, whereas the density for Comp. Ex. 3 is significantly higher, which results in a higher melting temperature measured via DSC and a higher elastic modulus measured on the blown films in TD.

[0105] The MFR2values are also quite similar for all products but the differences in the MFR10values indicates a higher degree in long chain branching of the Comp. Ex. 1, which can be related to differences in the polymerization process between the present herein described and other processed known from the art. A comparison of the film properties shows the advantages of Comp. Ex. 2 in comparison with the other grades. Due to the higher density of Comp. Ex. 2 this grade offers the best optical film properties, the best yield strength and the highest stiffness. Furthermore attention should be paid to the relative good dart drop performance of Comp. Ex. 2 even if the Example of the disclosed LDPE is the benchmark in dart drop test amongst the test grade. In Table 2 the Mw measured with GPC- LS , the inventive LDPE preferably Mw in the range of 300.000 to 400.000 g / mol, preferably in the range of 330,000 to 350,000 g / mol measured by GPC-LS.

[0106] The short chain branches (SCB) of 18 to 25 -CH3 1 / 1000C, preferably in the range of 19 to 23 measured by IR.

[0107] The following tables summarize the results measured from different grades, known from the state of the art, derived from pellets and as film source material:Table 2: The following tables summarize the measured results at the LDPE pellets and the film as source material.Table 3: Test results on films.Table 4: Table shows test results after 0 hours of artificial weathering.

[0108] In Table 4 the results of examined samples under the same weathering conditions, according to the standardized method, as defined above. Compared to the disclosed polyethylene film, the state of the art materials all suffer from worse results for elongation break resistance. So the mechanical properties of the disclosed film, are much better than those from the other examples.Table 5: Table shows test results after 500 hours of artificial weathering.

[0109] In Table 5 the results are show after 500 hours in artificial weathering conditions, according to the standardized method, as defined above. Also the disclosed polyethylene film show far better results compared to the other examples.Table 6: Table shows test results after 1000 hours of artificial weathering.

[0110] Table 6 shows the test results after 1000 hours of artificial weathering conditions. It was not possible to run every test with the examples. Surprisingly, the performance of the disclosed modified low density polyethylene grade (please compare the date for the disclosed Example) exceeds the examples known from the state of the art.

[0111] These results show clearly the influence of different modifiers on the weathering resistance of LDPE grade used in agricultural film applications and also the relatively poor UV stability of all products without an UV-stabilizer.

[0112] After 500 hours under the testing conditions Comp. Ex. 2, either with or without Irganox1010, has lost more than 80% of its elongation properties, whereas the non-polar modified disclosed modified low density polyethylene have still more than 50%. The reason of the relatively poor performance of Comp. Ex. 1 is unclear. After 1000 hours all samples have lost almost all of their mechanical resistance, but also here the polar modified samples are significant worse than the other ones. At this stage it was only possible for the modified low density polyethylene derived film Example to measure its mechanical properties in transverse direction (TD) and it is obvious that also for 500 hours it shows the best UV resistance and herewith the best keeping of mechanical properties compared to the other examples known in the state of the art.MFR10Table 7: IR Transmission at wave length of 1720 cm-1(C=O band)

[0113] In Table 7 the IR transmission at a wave length of 1720 cm1of the C=O band measured by IR is shown. The results clearly show, that the band for the C=O- band increases corresponding with the weathering exposure, but that the results for the IR transmittance of C=O- band in the modified polyethylene film, compared to the other examples known from the state of the art are still far better.Table 8: Film properties after exposure to weathering conditions.

[0114] In Table 8 all tested examples and their corresponding results are listed. The disclosed Comp. Ex. 2, Comp. Ex. 3 and the example of the modified low density polyethylene offers the best optical film properties, when it comes to haze and gloss, and the best yield strength and the best stiffness amongst all test materials due to its increased density.

Claims

CLAIMS1. A modified low density polyethylene having a weathering resistance under artificial weathering conditions of at least 500 h (according to ISO 4892-2, method A under black standard temperature of 65 °C), , having a) a density of in the range of 0.915 to 0.930 g / cm3, preferably in the range of 0.917 to 0.926 g / cm3, b) a Mw in the range of 300.000 to 400.000 g / mol, preferably in the range of 330,000 to 350,000 g / mol measured by GPC-LS, c) a Short chain branches (SCB) of 18 to 25 -CH3 1 / 1000C, preferably in the range of 19 to 23 measured by I R, d) a MFR2 of 0.15 g / 10min to 0.35 g / 10min, preferably 0.18 g / 10 min to 0.30 g / 10 min, preferably 0.20 g / 10 min to 0.28 g / 10 min, preferably 0.22 g / 10 min (2.16 kg / 190°C, according to ISO 1133), e) wherein no UV stabilizers are added and UV stability is measured according to DIN EN ISO 4892-2.

2. The modified low density polyethylene according to claim 1 , wherein the weathering resistance under artificial weathering resistance is measured via I R spectra overtime by an increase in the carbonyl band at 1710-1680 cm1, preferably at 1720 cm1, wherein the transmission of the wave length is at least 0.3.

3. Modified low density polyethylene, according to any one of the preceding claims, wherein the MFR10 [g / 10 min] is in the range from 1 to 15, preferably 2 to 10, preferably 4 to 7 (according to according to 10 kg, 190°C, ISO 1133).

4. Modified low density polyethylene, according to any one of the preceding claims, wherein the elongation at break [%] in (MD) after testing for 500 h under artificial weathering conditions is greater than 300 %, preferably is in the range of 320 to 380, preferably 330 to 370, preferably 340 to 360, more preferably 350 to 355, still more preferably 357, and / or for 500 h under artificial weathering conditions at elongation at break [%] in (TD) is greater than 250 %, preferably is in the range of 280 to 350, preferably 300 to 340, preferably 310 to 330, more preferably 315 to 325, still more preferably 320, compared to the initial starting value, (according to ISO 527-2).

5. Modified low density polyethylene, according to any one of the preceding claims, wherein the tensile strength at break [MPa] in (MD) after testing for 500 h under artificial weathering conditions is greater than 5 MPa, preferably is in the range of 8 to 15, preferably in the range of 9 to 13, more preferably in the range of 10 to 12, and / or for 500 h under artificial weathering conditions at tensile strength at break [MPa] in (TD) in the range of 7 to 15, preferably in therange of 8 to 14, preferably in the range of 9 to 13, more preferably in the range of 10 to 12, compared to the initial starting value, (according to ISO 527-2).

6. Modified low density polyethylene, according to any one of the preceding claims, wherein the elongation at break in [%] in (MD) after testing for 1000 h under artificial weathering conditions is greater than 11 %, preferably is in the range of 16 to 25, preferably in the range of 16.5 to 24, preferably in the range of 17 to 23, preferably in the range of 17.5 to 22, more preferably in the range of 18 to 21 , more preferably in the range of 18.5 to 20, and / or after testing for 1000 h under artificial weathering conditions (TD) is greater than 7 %, preferably is in the range of 5 to 14, preferably in the range of 6 to 12, preferably in the range of 7 to 11 , more preferably in the range of 8 to 10, compared to the initial starting value, (according to ISO 527-2)..

7. Modified low density polyethylene, according to any one of the preceding claims, wherein the tensile strength at break in [MPa] in (MD) after testing for 1000 h under artificial weathering conditions is greater than 8 MPa, preferably in the range of 8 to 16, preferably in the range of 9 to 14, preferably in the range of 10 to 13, more preferably in the range of 11 to 12, and / or in (TD) after testing for 1000 h under artificial weathering conditions is greater than 4 MPa, preferably in the range of 4 to 12, preferably in the range of 5 to 11 , preferably in the range of 6 to 10, more preferably in the range of 7 to 8, , compared to the initial starting value, (according to ISO 527-2)..

8. Polymerization process for the preparation of the modified low density polyethylene according to any of the preceding claims, the process comprising the steps of a) Preparing the modified low density polyethylene and propylene by polymerizing ethylene in presence of propylene as modifier, under high pressure and high temperature conditions, b) Adding a chain transfer agent (CTA), propylene or a combination of propylene and propionaldehyde, to the system during the polymerization to control the molecular weight distribution of the polymer; c) Conducting the polymerization in an autoclave reactor, followed by a tubular reactor, to achieve the desired properties of the polymer: d) Cooling and extruding the polymer to form the final product with a single or double screw extruder.

9. Use of the modified low density polyethylene, according to any one of the preceding claims for films, single layer or multilayer film.

10. Article, according to any of the preceding claims, comprising the modified low density polyethylene according to any one of the preceding claims, such as an agricultural film.

11. Article, according to claim 10, wherein the agricultural film is a scattering film and / or a greenhouse film.

12. Article, according to claim 11 , wherein the agricultural film has a function of adjusting temperature, light, humidity, and diffuse scattering.

13. Film comprising the modified low density polyethylene, according to any of the preceding claims.

Images