CN111819239B

CN111819239B - Agricultural film

Info

Publication number: CN111819239B
Application number: CN201980017630.0A
Authority: CN
Inventors: 向井健太; 山本幸一郎; 五户久夫; 高冈博树
Original assignee: Du Pont Mitsui Polychemicals Co Ltd
Current assignee: Dow Mitsui Polychemicals Co Ltd
Priority date: 2018-03-19
Filing date: 2019-03-19
Publication date: 2023-03-07
Anticipated expiration: 2039-03-19
Also published as: WO2019181986A1; KR102410418B1; JP7144508B2; BR112020018924A2; JPWO2019181986A1; CN111819239A; KR20200132933A

Abstract

One embodiment of the present invention provides an agricultural film having a mixture layer containing an ethylene-vinyl acetate copolymer (a) in which a content of a structural unit derived from vinyl acetate is 12% by mass or more and 35% by mass or less and a melt flow rate (MFR, JIS K7210-1999, 190 ℃,2160g load) is 4g/10 minutes or more and 100g/10 minutes or less, and a polyolefin (B) containing at least one selected from the group consisting of a high-density polyethylene and a metallocene-catalyzed polyethylene, wherein a content ratio of the ethylene-vinyl acetate copolymer (a) and the polyolefin (B), (a): (B) ] in a mass ratio of 35: 65-85: 15.

Description

Agricultural film

Technical Field

The present invention relates to agricultural films.

Background

As agricultural films, agricultural films having high light transmittance are generally desired, but depending on the type of crop, it is desirable to reduce the proportion of direct light as much as possible and to increase the proportion of scattered light. For example, in a nursery room for delicate vegetables such as tobacco leaves and lettuce, it is essential to use an agricultural film with little direct light in order to prevent leaves from being sunburned. In addition, in the drying chamber of tobacco leaves, it is essential to use an agricultural film with little direct light in order to prevent quick drying or to prevent the emergence of clumped leaves or rotted leaves. Therefore, as an agricultural film, a pear peel type (satin like) film is used.

As an agricultural film of pearskin type, for example, patent No. 3219319 discloses the following agricultural film: at least one of the outermost layer and the innermost layer is a mixture layer, and the mixture layer and another olefin resin layer form a multilayer structure, and the total light transmittance is 80% or more, and the conversion rate is 10% or less, wherein the mixture layer is formed of a mixture of an ethylene-vinyl acetate copolymer (a) having a vinyl acetate content of 24 to 34% by weight and a Melt Flow Rate (MFR) of 4 to 50g/10 minutes, and a low-density polyethylene (B) having an MFR of 0.04 to 2.0g/10 minutes, the mixing ratio of (a) to (B) is (a)/(B) =35 to 90/65 to 10 (weight ratio), the average vinyl acetate content of the mixture is 12 to 22% by weight, and the MFR ratio thereof (MFR of (a) =10 to 100 (MFR of (B)).

Disclosure of Invention

Problems to be solved by the invention

As shown in patent No. 3219319, various attempts have been made to obtain agricultural films (plastic films) having various functionalities and pearskin-like surfaces.

An object of one embodiment of the present invention is to provide an agricultural film that maintains values of total light transmittance and haze within allowable ranges and has more excellent mechanical properties than conventional agricultural films.

The pearskin-like shape is a surface state having a rough texture, such as the fruit skin of pears, with a large number of fine, spotty irregularities of indefinite shape.

The allowable range of the total light transmittance value is 85% or more and less than 95%, and the allowable range of the haze value is 70% or more and less than 95%.

Means for solving the problems

Means for solving the above problems include the following.

<1 > an agricultural film having a blend layer containing an ethylene-vinyl acetate copolymer (A) and a polyolefin (B),

the ethylene-vinyl acetate copolymer (A) has a vinyl acetate-derived structural unit content of 12 to 35 mass%, a melt flow rate (MFR, JIS K7210-1999, 190 ℃,2160g load) of 4 to 10 minutes, and 100g/10 minutes,

the polyolefin (B) comprises at least one selected from the group consisting of high density polyethylene and metallocene-catalyzed polymerized polyethylene,

the ethylene-vinyl acetate copolymer (A) and the polyolefin (B) have a content ratio of [ (A): (B) ] in a mass ratio of 35: 65-85: 15.

< 2 > the agricultural film according to <1 >, wherein the polyolefin (B) further comprises a low density polyethylene.

< 3 > the agricultural film according to <1 > or < 2 >, wherein the average content of the structural units derived from vinyl acetate is 9% by mass or more and less than 30% by mass when the resin component in the mixture layer is 100% by mass.

< 4 > the agricultural film according to any one of <1 > -3 >, wherein the mixture layer is an outermost layer.

< 5 > the agricultural film according to any one of <1 > < 4 >, wherein the MFR of the ethylene-vinyl acetate copolymer (A) ^A MFR with the aforementioned polyolefin (B) ^B Ratio of (MFR) ^A /MFR ^B ) Is 10 or more and 100 or less.

Effects of the invention

According to one embodiment of the present invention, an agricultural film having excellent mechanical properties can be provided while maintaining the values of the total light transmittance and the haze within the allowable ranges.

Detailed Description

Hereinafter, an embodiment as an example of the agricultural film of the present invention will be described. The present invention is not limited to the following embodiments, and can be carried out with appropriate modifications within the scope of the object of the present invention.

In the present invention, "to" in the numerical range means to include numerical values before and after the "to". In the numerical ranges recited in the present specification, the upper limit or the lower limit recited in a certain numerical range may be replaced with the upper limit or the lower limit recited in another numerical range. In the numerical ranges described in the present specification, the upper limit or the lower limit described in a certain numerical range may be replaced with the values shown in the examples.

In the present specification, the amount of each component in the composition refers to a structural unit of a plurality of substances present in the composition when the plurality of substances belonging to each component are present in the composition unless otherwise specified.

[ agricultural film ]

The agricultural film of the present invention has a mixture layer containing an ethylene-vinyl acetate copolymer (a) having a content of a structural unit derived from vinyl acetate of 12% by mass or more and 35% by mass or less and a melt flow rate (MFR, JIS K7210-1999, 190 ℃,2160g load) of 4g/10 min or more and 100g/10 min or less, and a polyolefin (B) containing at least one selected from the group consisting of a high-density polyethylene and a metallocene-catalyzed polyethylene, wherein the content ratio [ (a): (B) ] in a mass ratio of 35: 65-85: 15.

the agricultural film of the present invention can provide an agricultural film having excellent values of total light transmittance and haze by blending the ethylene-vinyl acetate copolymer (a) having an MFR within the above range in the content ratio within the above range.

Further, the polyolefin (B) is blended with at least one selected from the group consisting of high-density polyethylene and metallocene-catalyzed polyethylene at a content ratio within the above range, whereby an agricultural film having excellent mechanical properties can be obtained while maintaining the values of the total light transmittance and the haze within the allowable ranges.

Hereinafter, each component contained in the agricultural film of the present invention will be described in detail.

Unless otherwise specified, the Melt Flow Rate (MFR) in the present invention is a value [ g/10 min ] measured at 190 ℃ under a load of 2160g in accordance with JIS K7210-1999.

[ layer of mixture ]

The agricultural film of the present invention has a mixture layer containing an ethylene-vinyl acetate copolymer (a) and a polyolefin (B).

The mixture layer may contain other polymers, additives, as needed.

< ethylene-vinyl acetate copolymer (A) >)

The ethylene-vinyl acetate copolymer (a) used in the present invention contains at least a structural unit derived from ethylene and a structural unit derived from vinyl acetate, and may be a random copolymer, a block copolymer, or an alternating copolymer.

In addition, the ethylene-vinyl acetate copolymer (a) may further contain other monomer units than vinyl acetate and ethylene. In the present invention, it is preferable that: the ethylene-vinyl acetate copolymer is composed of a structural unit derived from vinyl acetate and a structural unit derived from ethylene, and contains no monomer unit other than vinyl acetate and ethylene.

The ethylene-vinyl acetate copolymer (a) in the present invention contains a structural unit derived from ethylene and a structural unit derived from vinyl acetate in a specific amount, and other monomers may be further copolymerized as the case may be.

The ethylene-vinyl acetate copolymer (a) in the present invention has a content of a structural unit derived from vinyl acetate of 12 mass% or more and 35 mass% or less. When the content of the structural unit derived from vinyl acetate is 12 mass% or more and 35 mass% or less, the haze of the obtained film is a suitable haze as an agricultural film.

From the viewpoint of the haze value, the content of the structural unit derived from vinyl acetate is preferably in the range of 16 mass% or more and 30 mass% or less, and more preferably 18 mass% or more and 25 mass% or less.

The content of the structural unit derived from ethylene is preferably 65% by mass or more and 88% by mass or less, and more preferably 70% by mass or more and 84% by mass or less.

The content of the structural unit derived from another monomer may be 10% by mass or less, and is preferably 0% by mass.

The ethylene-vinyl acetate copolymer (A) in the present invention has an MFR of 4g/10 min to 100g/10 min, preferably 8g/10 min to 60g/10 min, more preferably 10g/10 min to 50g/10 min, and still more preferably 12g/10 min to 30g/10 min.

When the MFR of the ethylene-vinyl acetate copolymer (A) is from 4g/10 min to 100g/10 min, the haze value of the resulting film becomes a value suitable for an agricultural film.

The ethylene-vinyl acetate copolymer (a) may be used alone in 1 kind or in combination with 2 or more kinds having different copolymerization ratios or the like.

From the viewpoint of obtaining an agricultural film having excellent mechanical strength, the content of the ethylene-vinyl acetate copolymer (a) contained in the blend layer of the agricultural film of the present invention is preferably 35% by mass or more and 85% by mass or less with respect to the entire blend layer.

< polyolefin (B) >, a process for preparing a polyolefin composition

The polyolefin (B) comprises at least one selected from the group consisting of high density polyethylene and metallocene-catalyzed polymerized polyethylene.

The polyolefin (B) contains the above-mentioned polyolefin, and thus the agricultural film of the present invention has excellent mechanical properties.

The polyolefin (B) preferably contains high-density polyethylene from the viewpoint of obtaining an agricultural film excellent in mechanical properties, particularly in grab tear strength (grazing elongation) and elongation at break.

Here, the high-density polyethylene is a polyethylene obtained in accordance with JIS K6748:1995 density of 935kg/m ³ The polyethylene is usually produced by a low pressure process or a medium pressure process. The low pressure method may be a ziegler method, and the medium pressure method may be a phillips method.

The metallocene-polymerized polyethylene refers to polyethylene produced by using a homogeneous catalyst such as a metallocene catalyst, and examples thereof include linear low-density polyethylene (LLDPE) produced by using a metallocene catalyst.

The polyethylene may be an ethylene- α -olefin copolymer obtained by copolymerizing ethylene and an α -olefin.

In addition, the polyolefin (B) may contain other polyolefins than the above.

As other polyolefins, mention may be made of: low-density polyethylene such as high-pressure low-density polyethylene, ethylene-unsaturated carboxylic acid-based copolymers, ethylene-vinyl acetate copolymers, ethylene- α -olefin copolymer elastomers in which the crystallinity is reduced or substantial crystallinity is not exhibited by increasing the amount of α -olefins other than ethylene (propylene, 1-butene, 1-pentene, 1-hexene, 1-octene, 1-decene, 1-dodecene, 4-methyl-1-pentene, etc.) to be copolymerized with ethylene, polypropylene, propylene-based copolymers (copolymers of propylene and α -olefins other than propylene), polybutene, and other olefin-based copolymers/polymers, and blends thereof.

From the viewpoint of obtaining excellent mechanical strength, the content of the polyolefin (B) contained in the blend layer of the agricultural film of the present invention is preferably 15 mass% or more and 65 mass% or less with respect to the entire blend layer.

Here, the polyolefin (B) included in the mixture layer may further include low-density polyethylene as another polyolefin. The low-density polyethylene is a polyethylene obtained by blending the following components in accordance with old JIS K6748:1995 density of less than 930kg/m ³ The polyethylene (2) is a polyethylene produced by a high pressure process (bulk polymerization process). The low-density polyethylene in the present invention means a low-density polyethylene excluding linear low-density polyethylene (LLDPE).

In this case, the content of the low-density polyethylene is preferably less than 30% by mass, more preferably less than 20% by mass, still more preferably less than 15% by mass, and particularly preferably 0% by mass, based on the entire blend layer, from the viewpoint of obtaining excellent mechanical properties.

From the viewpoint of obtaining a pearskin-like film, the MFR of the polyolefin (B) in the present invention is preferably 5g/10 min or less, more preferably 3g/10 min or less, and still more preferably 1.5g/10 min or less. The lower limit is preferably 0.04g/10 min or more.

MFR of ethylene-vinyl acetate copolymer (A) ^A MFR with polyolefin (B) ^B Ratio of (MFR) ^A /MFR ^B ) Preferably 10 or more and 100 or less, more preferably 10 or more and 80 or less, and further preferably 10 or more and 60 or less.

In the mixture layer of the agricultural film of the present invention, the content ratio of the ethylene-vinyl acetate copolymer (a) and the polyolefin (B) (a): (B) ] in a mass ratio of 35: 65-85: 15.

when the mass ratio of the ethylene-vinyl acetate copolymer (a) is in the above range, an agricultural film having a suitable haze value and grip tear strength can be obtained.

Therefore, when the mass ratio of the ethylene-vinyl acetate copolymer (a) to the polyolefin (B) is in the above range, an agricultural film having an excellent mechanical strength while maintaining the haze value within an allowable range can be obtained.

In the above range, the content ratio of the ethylene-vinyl acetate copolymer (a) and the polyolefin (B) is in the range of [ (a): (B) ] is preferably 40: 60-80: 20, more preferably 45:55 to 75:25, more preferably 45:55 to 70:30.

< other Polymer >

Other polymers may be included in the mixture layer. Examples of the other polymer include an ethylene- (meth) acrylic acid copolymer and an ionomer. The content of the other polymer is preferably 30% by mass or less based on the entire agricultural film.

< other additives >

Other additives may be included in the mixture layer.

As other additives, conventionally known chemical crosslinking agents, crosslinking aids, softeners, fillers, antioxidants, heat stabilizers, weather stabilizers, acetic acid extenders, heat insulating agents, ultraviolet absorbers, anti-clouding agents (anti-clouding agents), and antifogging agents can be appropriately blended. As the heat retaining agent, a known heat retaining agent having a refractive index similar to that of the mixture layer can be used. The most preferable heat-insulating agent is hydrotalcite which has particularly good heat-insulating property and does not adversely affect the light transmittance.

The content of the other additives is preferably 30% by mass or less with respect to the entire agricultural film.

< layer of mixture >

The average content of the structural units derived from vinyl acetate in the mixture layer of the agricultural film of the present invention is preferably 9 mass% or more and less than 30 mass%, more preferably 9 mass% or more and 25 mass% or less, and most preferably 10 mass% or more and 23 mass% or less, assuming that the resin component in the mixture layer is 100 mass%.

In the resin component of the mixture layer, the adhesiveness can be suppressed and the pearskin properties can be maintained by setting the average content of the structural units derived from vinyl acetate within the above range.

The "average content of structural units derived from vinyl acetate" may be determined in accordance with JIS-K7192:1999, determined. This method is a method in which a polymer is decomposed by heating to 500 ℃ or higher in an electric furnace, and acetic acid derived from the obtained vinyl acetate is determined by neutralization titration, and can be determined as the average content of the structural units derived from vinyl acetate, whether it is an ethylene-vinyl acetate copolymer monomer or a mixture with various polyethylenes.

From the viewpoint of film processability, the MFR of the mixture layer is preferably 2g/10 min or more and 7g/10 min or less, and more preferably 2g/10 min or more and 5g/10 min or less. When the MFR of the mixture layer is within the above range, the film processability is excellent.

The total content of the ethylene-vinyl acetate copolymer (a) and the polyolefin (B) in the mixture layer is preferably 70% by mass or more, more preferably 80% by mass or more, and most preferably 90% by mass or more.

The thickness of the mixture layer is preferably 3 μm or more and 500 μm or less, and more preferably 10 μm or more and 200 μm or less.

[ layers other than mixture layers ]

The agricultural film of the present invention may have a layer other than the above-described mixture layer from the viewpoint of obtaining necessary characteristics such as mechanical strength, durability, heat retaining property and the like which exist in agricultural films.

Examples of the layer other than the mixture layer include an olefin resin layer and a barrier resin layer using a barrier resin such as EVOH (ethylene-vinyl alcohol copolymer resin).

The mixture layer in the present invention is preferably the outermost layer from the viewpoint of suppressing excessive direct light irradiation to the plant.

[ method for producing agricultural film ]

The method for producing the agricultural film of the present invention includes, for example, a method of preparing a mixture containing the above components and then forming the mixture into a film by a known method.

Hereinafter, a method for producing an agricultural film having a mixture layer alone will be described. However, the method for producing the agricultural film of the present invention is not limited to the following method.

The above mixture is prepared, for example, by dry blending (dry blend) or melt blending (melt blend) the above ingredients. In the case of dry blending, the mixing is carried out in a molding machine at the stage of melt plasticization of the components. In the case of melt blending, the melt blending may be carried out using various extruders such as a single-screw or twin-screw extruder, various mixers such as a Banbury mixer, compounding machines such as rolls and a kneader, and a mixer. The mixing order in melt blending is not particularly limited.

Thereafter, the film is formed by a known method such as inflation or casting.

Examples

The present embodiment will be described in more detail below with reference to examples and comparative examples, but the present embodiment is not limited to these examples. Unless otherwise specified, "part(s)" and "%" are based on mass.

Details of the ingredients used to make the agricultural film are as follows.

<1. Ethylene-vinyl acetate copolymer (EVA) >

(EVA-1)：

Content of structural units of vinyl acetate (VA content): 28% by mass

MFR (JIS K7210-1999, 190 ℃, load 2160 g) 15g/10 min

(EVA-2)：

Content of structural units of vinyl acetate (VA content): 19% by mass

MFR (JIS K7210-1999, 190 ℃, load 2160 g) 15g/10 min

(EVA-3)：

Content of structural units of vinyl acetate (VA content): 19% by mass

MFR (JIS K7210-1999, 190 ℃, load 2160 g) 2.5g/10 min

(EVA-4)：

Content of structural units of vinyl acetate (VA content): 41% by mass

MFR (JIS K7210-1999, 190 ℃, load 2160 g) 65g/10 min

(EVA-5)：

Content of structural units of vinyl acetate (VA content): 10% by mass

MFR (JIS K7210-1999, 190 ℃, load 2160 g) 9g/10 min

< 2. Polyolefin (PO) >

(PO-1)：

The types are as follows: low Density Polyethylene (LDPE)

Density: (JIS K7112-1999) 920kg/m ³

MFR: (JIS K7210-1999, 190 ℃, load 2160 g) 0.15g/10 min

(PO-2)：

The types are as follows: high Density Polyethylene (HDPE)

Density: (JIS K7112-1999) 950kg/m ³

MFR: (JIS K7210-1999, 190 ℃, load 2160 g) 1.1g/10 min

(PO-3)：

The types are as follows: high Density Polyethylene (HDPE)

Density: (JIS K7112-1999) 940kg/m ³

MFR: (JIS K7210-1999, 190 ℃, load 2160 g) 0.45g/10 min

(PO-4)：

The types are as follows: linear low-density polyethylene (mPE: metallocene catalyzed polyethylene)

Density: (JIS K7112-1999) 923kg/m ³

MFR (JIS K7210-1999, 190 ℃, load 2160 g) 1.3g/10 min

[ example 1]

(preparation of agricultural film)

The following ingredients were prepared.

< ingredient >

EVA-1:80 parts by mass

PO-3:20 parts by mass

Preparation of the mixture

The above components were melt-blended using a single-screw extruder (extruder screw diameter: 65 mm) under conditions of a die temperature of 180 ℃ and a melting zone temperature of 180 ℃ to thereby stably pelletize.

Then, the content of the structural unit of vinyl acetate (average content (unit: mass%) of the structural unit derived from vinyl acetate; expressed as VA content in Table 1) and MFR of the melt-blended mixture were measured by the methods described above. The results are shown in Table 1.

In table 1, a symbol such as "-" indicates that the component is not included.

Molding-

The above-mentioned mixture after melt blending was formed into a tubular shape by using a single layer inflation molding machine (bore: 150mm, extruder screw diameter: 50 mm), under conditions of a mold temperature of 180 ℃, a melt zone temperature of 180 ℃, an LS (line speed) of 5.0m/min, and a BUR (blow-up ratio) of 2.1, thereby forming a mixture layer, and an agricultural film having a fold diameter of 520mm and a thickness of 50 μm was obtained.

[ evaluation ]

The obtained agricultural film was evaluated for the following items. The results are shown in Table 2.

Total light transmittance-

The total light transmittance of the obtained agricultural film was measured by a haze meter (manufactured by Suga Test Instruments) in accordance with JIS-K7136 (2000), and used as an index for evaluating the light transmittance of the agricultural film. If the total light transmittance is 85% or more and less than 95%, there is no practical problem.

Haze-

The haze of the obtained agricultural film was measured by a haze meter (manufactured by Suga Test Instruments) in accordance with JIS-K7136 (2000), and the haze was used as an index for evaluating the pearskin-like degree of the agricultural film. If the haze is 70% or more and less than 95%, there is no practical problem.

Stress at break-

According to JIS-K6760:1995, the obtained agricultural film was measured with the machine axis direction as MD direction and the direction orthogonal to the machine axis direction as TD direction. If the stress at break point is 18MPa or more (MD direction), it is judged that the stress at break point is excellent.

Elongation at break-

According to JIS-K6760:1995, the agricultural film obtained was measured with the machine axis direction as MD direction and the direction orthogonal to the machine axis direction as TD direction. When the elongation at break point is 400% or more, it is judged that the elongation at break point is excellent.

Grab tear Strength

According to JIS-K7128-3:1998, the obtained agricultural film was measured with the machine axis direction as the MD direction and the direction orthogonal to the machine axis direction as the TD direction.

If the grab tear strength is 70N/mm or more (MD direction), the grab tear strength is judged to be excellent.

Examples 2 to 8 and comparative examples 1 to 7

Agricultural films were produced in the same manner as in example 1, except that the composition of the agricultural film in example 1 was changed as shown in table 1.

As in example 1, examples 2 to 8 were able to stably granulate even when preparing the mixture, and comparative example 3 was unstable in the granulation property.

The obtained agricultural film was evaluated in the same manner as in example 1. The results are shown in Table 2.

[ Table 1]

[ Table 2]

As is clear from tables 1 to 2, the agricultural film of the present example can maintain the values of the total light transmittance and the haze within the allowable ranges, and is excellent in any of the stress at break, the elongation at break, and the grab tear strength. That is, the agricultural film of the present example is an agricultural film which has the values of the total light transmittance and the haze maintained within the allowable ranges and has excellent mechanical strength. On the other hand, the agricultural film of the comparative example is inferior in at least one of the value of haze or mechanical strength to the agricultural film of the example. For example, in comparative example 7, the haze value was within the allowable range, but the mechanical strength such as the stress at break, the elongation at break and the grab tear strength was inferior to that of the agricultural film of the example.

The disclosure of Japanese application Ser. No. 2018-051725 filed on 3/19/2018 is incorporated herein by reference in its entirety.

All documents, patent applications, and technical standards described in the present specification are incorporated by reference into the present specification to the same extent as if each document, patent application, and technical standard was specifically and individually described.

Claims

1. An agricultural film having a mixture layer containing an ethylene-vinyl acetate copolymer (A) and a polyolefin (B),

the ethylene-vinyl acetate copolymer (A) has a content of a structural unit derived from vinyl acetate of 12 to 35 mass%, a melt flow rate of 4g/10 min to 100g/10 min,

the polyolefin (B) comprises a high density polyethylene,

the ethylene-vinyl acetate copolymer (A) and the polyolefin (B) have a content ratio of [ (A): (B) ] in a mass ratio of 35: 65-85: 15,

the melt flow rate is a value measured at 190 ℃ under a load of 2160g in accordance with JIS K7210-1999,

the haze measured according to JIS-K7136 (2000) is 70% or more and less than 95%.

2. The agricultural film according to claim 1, wherein the polyolefin (B) further comprises a low density polyethylene.

3. The agricultural film according to claim 1 or 2, wherein the average content of the structural units derived from vinyl acetate is 9% by mass or more and less than 30% by mass when the resin component in the mixture layer is set to 100% by mass.

4. The agricultural film of claim 1 or 2, wherein the mixture layer is the outermost layer.

5. The agricultural film of claim 1 or 2, wherein the ethylene-vinyl acetate copolymer (a) has an MFR ^A MFR with said polyolefin (B) ^B Ratio of (MFR) ^A /MFR ^B ) Is 10 or more and 100 or less.

6. The agricultural film of claim 1 or 2, wherein the polyolefin (B) further comprises a metallocene-catalyzed polymeric polyethylene.