CN113844109A

CN113844109A - Multilayer composite flexible pipeline and manufacturing method thereof

Info

Publication number: CN113844109A
Application number: CN202010593571.6A
Authority: CN
Inventors: 耿煜; 张伟
Original assignee: Suzhou Yingnawei Technology Co ltd
Current assignee: Suzhou Yingnawei Technology Co ltd
Priority date: 2020-06-27
Filing date: 2020-06-27
Publication date: 2021-12-28

Abstract

A multilayer flexible polymeric tube includes a polymeric backing layer and a polymeric outer layer adjacent the polymeric backing layer. The polymeric backing layer comprises a polypropylene-based polymeric continuous phase, and a crosslinked rubber phase dispersed within the continuous phase; and a polymeric outer layer having an inner surface directly bonded to the outer surface of the polymeric liner layer, the polymeric outer layer comprising a continuous phase comprising a polypropylene-based polymer, and a non-crosslinked styrene block copolymer elastomer miscible with the polypropylene-based polymer dispersed within the continuous phase. The invention also includes a method of forming the multilayer flexible polymer tube.

Description

Multilayer composite flexible pipeline and manufacturing method thereof

Technical Field

The present disclosure relates to a flexible pipe, in particular to a multilayer flexible pipe and a method for manufacturing the same.

Background

Flexible tubing is widely used in a variety of industrial and household products. Such as flexible filled tubing for the food and beverage industry, flexible fuel delivery tubing for engines and motors for automobiles and portable tools, flexible tubing for food contact, drinking water and liquid dairy product delivery, laboratory fluid delivery applications, peristaltic pump tubing applications, biopharmaceutical applications, medical tubing, and other medical tubing. However, conventional pipes used in such applications in the past have mostly been made from polyvinyl chloride PVC materials using plasticizers.

Flexible pipe products of PVC have been widely used in numerous fields. However, such PVC products are hazardous to both the environment and to personal health. The incineration of PVC containing these wastes results in the release of hydrochloric acid, and PVC is considered to be a major contributor to the source of hydrogen chloride in the incineration flue gas. In addition, PVC may also contribute to the formation of polychlorinated dibenzodioxins and furanic toxins during incineration.

In addition to concerns over incineration, the problem of avoiding plasticizer in PVC from entering blood, food, beverages, or other liquids being transported is also considered a potential risk issue to be addressed when using products made from PVC tubing. In order to produce flexible PVC products, the use of plasticizers or processing aids is inevitably required. If exposed to these processing aids or plasticizers, such as diethyl phosphite (DEHP), many health concerns arise. In particular, DEHP is suspected of reducing the oxygen transport capacity of platelets in the blood and of being genotoxic, particularly in the reproductive system of young males. Therefore, research and search for solutions capable of replacing PVC flexible pipes are carried out at home and abroad in recent years.

Polyolefin-based flexible tubing developed in recent years abroad has begun to find wide application in industry, and such tubing, which is generally free of plasticizers, has broad prospects for use in the medical, food, beverage and pharmaceutical industries. However, such polyolefin-based hoses have a large flow rate difference during use or during metering and conveying, particularly under the action of repeated mechanical forces depending on the use conditions, within 200 hours and after 200 hours of initial use, become unstable, and require continuous calibration of equipment, thereby affecting their use in equipment requiring stable flow rate metering and in such fields.

Disclosure of Invention

Under unexpected conditions, the invention finds that a multi-layer flexible hose product with excellent mechanical properties and stable flow can be obtained by adopting a multi-layer flexible hose with a polyolefin structure and using different polyolefin resin materials on a lining layer and an outer layer, and has wide application prospects in food contact applications, dairy products, beverages and drinking water contact applications, laboratory fluid transmission applications, medical applications, pharmaceutical applications or peristaltic pumps and the like.

A multilayer flexible pipe having an annular cross-section with an inner surface, an outer surface, an inner diameter and an outer diameter, the annular cross-section defining a wall thickness of the flexible pipe, wherein the flexible pipe is characterized by:

a) a polymeric backing layer comprising a polypropylene-based polymeric continuous phase, and a crosslinked rubber phase dispersed within the continuous phase; and

b) a polymeric outer layer having an inner surface directly bonded to the outer surface of the polymeric liner layer, the polymeric outer layer comprising a continuous phase comprising a polypropylene-based polymer, and a non-crosslinked styrene block copolymer elastomer miscible with the polypropylene-based polymer dispersed within the continuous phase.

Drawings

The present invention may be better understood, and its numerous features and advantages made apparent to those skilled in the art by referencing the accompanying drawings.

FIG. 1 includes an illustration of an exemplary multi-layer flexible tubing material.

The use of the same reference symbols in different drawings indicates similar or identical items.

Detailed Description

As used herein, the terms "comprises," "comprising," "includes," "including," "has," "having" or any other variation thereof, are intended to cover a non-exclusive inclusion. For example, a method, article, or apparatus that comprises a list of features is not necessarily limited to only those features but may include other features not expressly listed or inherent to such method, article, or apparatus. Further, unless expressly stated to the contrary, "or" refers to an inclusive or, and not to an exclusive or. For example, condition a or B is satisfied by either: a is true (or present) and B is false (or not present), a is false (or not present) and B is true (or present), and both a and B are true (or present).

Also, the use of "a" or "an" is used to describe elements and components described herein. This is done merely for convenience and to provide a general sense of the scope of the invention. This description should be read to include one or at least one and the singular also includes the plural and vice versa unless it is obvious that it is meant otherwise. For example, when a single item is described herein, more than one item may be used in place of a single item. Similarly, when more than one item is described herein, a single item may replace the more than one item.

Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. The materials, methods, and examples are illustrative only and not intended to be limiting. To the extent not described herein, many details regarding specific materials and processing acts are conventional and may be found in the written description and other sources within the field of construction and corresponding manufacturing.

The liner layer and outer layer polymers of the multilayer flexible pipe include a continuous phase that includes a polypropylene-based polymer that is a polypropylene containing a propylene copolymer or a syndiotactic metallocene catalyzed polypropylene. The propylene copolymer may be a random copolymer of propylene and a comonomer. Examples of one comonomer include ethylene, 1-butene, 1-pentene, 1-hexene, 4-methyl-1-pentene, 2-methylpropene, 3-methyl-1-pentene, 5-methyl-1-hexene, or any combination thereof. The propylene random copolymer may be produced by a catalytic technique, for example, ziegler-natta or metallocene catalysis. In addition, the propylene-based polymer may be a syndiotactic metallocene-catalyzed polypropylene or a syndiotactic propylene copolymer. For example, the syndiotactic propylene copolymer may comprise a monomer such as ethylene or an alpha-olefin such as those described above.

The amount of the polypropylene-based polymer may be adjusted within the following ranges to achieve the desired processability and elasticity properties of the flexible pipe. In certain embodiments of the flexible pipe as further described herein, the amount of polypropylene-based polymer may be present in a range of 10 wt% to 70 wt% of the total polymer amount. For example, in various particular embodiments of the flexible pipe as otherwise described herein, the amount of polypropylene-based polymer can be present in a range of 10 wt% to 60 wt%, or 10 wt% to 50 wt%, or 10 wt% to 40 wt%, or 10 wt% to 30 wt%, or 20 wt% to 70 wt%, or 20 wt% to 50 wt%, or 20 wt% to 40 wt%, or 30 wt% to 70 wt%, or 30 wt% to 60 wt%, or 30 wt% to 50 wt%, or 40 wt% to 70 wt%, or 40 wt% to 50 wt%, or 50 wt% to 70 wt% of the total polymer amount.

The polymeric liner layer of the multilayer flexible tube comprises a continuous phase including a polypropylene-based polymer, and a crosslinked rubber phase dispersed within the continuous phase. The following conditions are satisfied in order to obtain a blend of a thermoplastic polypropylene-based polymer and a rubber phase having desired properties. The surface energy of the polypropylene polymer and the rubber polymer needs to be matched, the length of the rubber entanglement molecular chain is lower, and the crystallinity of the polypropylene polymer is more than 12 percent. Therefore not all polyolefin based polymers can meet the above requirements, wherein the crosslinked rubber phase comprises a fully vulcanized crosslinked polyolefin with a phenolic resin and a non-conjugated diene based copolymer, characterized by a degree of vulcanization of more than 95%; or peroxide-cured crosslinked polyolefin and non-conjugated diene copolymer; or mixtures or blends thereof. The polyolefin comprises a monomer (e.g., ethylene, propylene, butene, pentene, methylpentene, hexene, octene, or any combination thereof). The non-conjugated diene comprises ethylidene norbornene, vinyl norbornene, cyclopentadiene, dicyclopentadiene or mixtures thereof. The crosslinked rubber phase is a homopolymer, copolymer, terpolymer, alloy, or any combination thereof formed from the above-described polyolefins, non-conjugated dienes, phenolic resins, or peroxides. As used herein, "fully cured cross-linking" refers to a final cross-link density of greater than 95% as determined, for example, by rheometer data (95% cure means that the material reaches 95% of maximum torque as measured by ASTM D5289). In certain embodiments of the flexible pipe as further described herein, the crosslinked rubber is crosslinked to an extent such that less than 5 wt% is extractable, i.e., considered to achieve fully vulcanized crosslinking. Extractability was determined by boiling xylene test, where a film sample was left in boiling xylene for 30 minutes, after which the dry residue was weighed, and the appropriate corrections for soluble and insoluble components were based on knowledge of the composition or analysis of the extractant.

Based on the present disclosure, one of ordinary skill in the art can adjust the amount of the crosslinked rubber phase within the following ranges to achieve the desired processability and elasticity properties of the flexible pipe. In certain embodiments of the flexible pipe further described herein, the crosslinked rubber phase is present in a range from 15 wt% to 85 wt% of the total polymer amount. For example, in various particular embodiments of the flexible pipe as otherwise described herein, the crosslinked rubber phase is present in a range of 15 wt% to 80 wt%, or 15 wt% to 75 wt%, or 15 wt% to 65 wt%, or 15 wt% to 60 wt%, or 15 wt% to 50 wt%, or 15 wt% to 40 wt%, or 30 wt% to 85 wt%, or 30 wt% to 80 wt%, or 30 wt% to 75 wt%, or 30 wt% to 65 wt%, or 30 wt% to 60 wt%, or 30 wt% to 50 wt%, or 40 wt% to 85 wt%, or 40 wt% to 80 wt%, or 40 wt% to 75 wt%, or 40 wt% to 65 wt%, or 40 wt% to 60 wt%, or 50 wt% to 85 wt%, or 50 wt% to 80 wt%, or 50 wt% to 75 wt%, or 60 wt% to 85 wt%, or 60 wt% to 80 wt% of the total polymer amount.

The polymeric outer layer of the multilayer flexible tube includes a continuous phase that includes polypropylene and a non-crosslinked styrenic block copolymer elastomer that is miscible with the polypropylene. The non-crosslinked styrene block copolymer elastomer includes styrene-butadiene-styrene (SBS), styrene-isoprene-styrene (SIS), styrene-ethylene-butylene-styrene (SEBS), styrene-ethylene-propylene-styrene (SEPS), styrene-ethylene-butadiene-styrene (SEEBS), styrene-ethylene-propylene-styrene (SEEPS), styrene-isoprene-butadiene-styrene (SIBS), or combinations thereof. Based on the present disclosure, one of ordinary skill in the art can adjust the amount of the non-crosslinked styrenic block copolymer elastomer within the following ranges to achieve the desired processability and elastic properties of the flexible pipe. In certain embodiments of the flexible pipe further described herein, the non-crosslinked styrenic block copolymer elastomer is present in a range of 15 wt% to 85 wt% of the total polymer amount. For example, in various particular embodiments of the flexible pipe as otherwise described herein, the non-crosslinked styrenic block copolymer elastomer is present in a range of 15 wt% to 80 wt%, or 15 wt% to 75 wt%, or 15 wt% to 65 wt%, or 15 wt% to 60 wt%, or 15 wt% to 50 wt%, or 15 wt% to 40 wt%, or 30 wt% to 85 wt%, or 30 wt% to 80 wt%, or 30 wt% to 75 wt%, or 30 wt% to 65 wt%, or 30 wt% to 60 wt%, or 30 wt% to 50 wt%, or 40 wt% to 85 wt%, or 40 wt% to 80 wt%, or 40 wt% to 75 wt%, or 40 wt% to 65 wt%, or 40 wt% to 60 wt%, or 50 wt% to 85 wt%, or 50 wt% to 80 wt%, or 50 wt% to 75 wt%, or 60 wt% to 85 wt%, or 60 wt% to 80 wt% of the total polymer amount.

In one example, the polymer of the multilayer flexible tube further comprises an oil. It is contemplated that any suitable oil may be used, such as paraffinic oils, mineral oils, dearomatized aliphatic hydrocarbons, high purity hydrocarbon fluids, and the like. As used herein, an "oil" must be a liquid at 25 ℃. In another particular embodiment, the oil is a mineral oil having a zero aromatic content, said mineral oil being a paraffinic, or a naphthenic, or a mixture of paraffinic or naphthenic. For example, mineral oil may be used in an amount of about 10% to about 70% by weight of the total weight of the polymer. In a particular embodiment, oils approved by the U.S. FDA or European Union certification are used for food, medical and pharmaceutical related applications.

A multilayer flexible pipe according to claim 1, wherein the shore a hardness of the polymer lining layer and the polymer outer layer is not particularly limited, but in one embodiment, the hardness of the polymer lining layer, or the polymer outer layer, or the multilayer flexible pipe as a whole may be in the range of 30 to 95 shore a hardness, preferably in the range of 45 to 85 shore a hardness, and more preferably in the range of 55 to 75 shore a hardness, in consideration of practical application.

In one embodiment, the polymeric liner layer and the polymeric outer layer of the multilayer flexible pipe include any additive that is contemplated, such as a lubricant, a filler, an antioxidant, or any combination thereof. Exemplary lubricants include silicone oils, waxes, slip aids, anti-tacking agents, and the like. Exemplary fillers may be reinforcing or non-reinforcing, and may be used for various other purposes as will be apparent to those of ordinary skill in the art. For example, one or more of calcium carbonate, talc, silica (e.g., functional or fumed silica), clay, carbon (e.g., carbon black), and titanium dioxide, or any combination thereof, and the like are included. Typically, the additive may be present in an amount of no greater than about 50% by weight of the total weight of the polymer, such as no greater than about 40% by weight of the total weight of the polymer, or even no greater than about 30% by weight of the total weight of the polymer. Alternatively, the polymer may be free of lubricants, fillers, and antioxidants. As understood by one of ordinary skill in the art, many other additives may be present in the polymer of the multilayer flexible tube, such as residual curatives (i.e., curatives from crosslinked rubber), antioxidants, flame retardants, acid scavengers, antistatic agents, and processing aids (e.g., melt index enhancers).

Figure 1 includes an illustration of a cross-section of an exemplary multi-layer flexible pipe 100. In one embodiment, the flexible tube 100 includes a polymeric liner layer 140 and a polymeric outer layer 120. The polymeric backing layer 140 is an inner layer or lining that forms an inner surface 150, the inner surface 150 defining a lumen 160 through which fluid flows. In one example, the polymer outer layer 120 forms the outer surface 110 of the flexible tube 100. In a particular embodiment, the polymeric backing layer 140 and the polymeric outer layer 120 are in direct contact with each other and are directly joined to each other at the surface 130 without the presence of any intermediate layers. In one embodiment, the polymeric backing layer 140 and the polymeric outer layer 120 are bonded to each other without a primer or adhesive. The surface 130 may be free of adhesive or other treatment to increase the adhesive properties of the polymeric backing layer 140 to the polymeric outer layer 120, such as free of surface treatment. In an alternative embodiment, the flexible tube 100 may include any reasonable intermediate layer between the polymer backing layer 140 and the polymer outer layer 120, such as a tie layer, an adhesive layer, a reinforcement layer, and the like (not shown). For example, the reinforcing layer may be disposed between the polymeric backing layer 120 and the polymeric outer layer 140, or substantially embedded within the polymeric outer layer 140. As used herein, "substantially embedded" refers to a reinforcing layer wherein at least 25%, such as at least about 50%, or even 75% of the total surface area of the reinforcing layer is in direct contact with the polymeric outer layer. In one embodiment, the polymeric backing layer 140 directly contacts the reinforcement layer (not shown). In one example, the reinforcement layer can be a polymer, such as a polyolefin, a polyester, a polyamide, a polyaramid, or a combination thereof. In one exemplary embodiment, the reinforcement layer is a polyolefin, such as polypropylene. In a more specific embodiment, the reinforcement layer is braided such that the polymer is in the form of interwoven yarns. The use of a reinforcing layer may provide additional advantageous properties to the flexible pipe. For example, by selection of the reinforcing layer polymer material, a compatible material with the desired adhesion can be provided, thereby improving the peel strength of the flexible pipe polymer liner layer and the polymer outer layer. In a particular embodiment, "desired adhesion" can be defined as cohesive failure, wherein the polymeric backing layer, the polymeric outer layer, or the reinforcing layer breaks before the bonds between the polymeric backing layer, the reinforcing layer, and the polymeric outer layer fail. The required adhesion will provide the following benefits compared to flexible pipes without a reinforcement layer or with a reinforcement layer as an incompatible material: for example, improved burst pressure and increased mechanical performance properties (especially at fluid pressures up to 5 to 6 bar). In case the reinforcement layer has the desired adhesion to the polymer backing layer and the polymer outer layer, the risk of leaching out small molecule volatiles from the yarns of the polymer reinforcement layer into the transported fluid is avoided, since the reinforcement layer is sandwiched between the polymer backing layer and the polymer outer layer.

In one example, the backing layer 140 can include one or more antimicrobial additives. For example, the antimicrobial additive may be a silver-based antimicrobial additive in an amount between 0.1 weight percent and 5 weight percent, more preferably between 0.5 weight percent and 2.5 weight percent, based on the total liner layer polymer amount.

In one example, the polymer backing layer 140 forms 5% to about 50%, more preferably 6% to 30%, and most preferably 7 to 20% of the overall thickness of the flexible pipe 100; the polymeric outer layer 120 forms about 50% to about 95% of the thickness of the flexible tube 100.

In one embodiment, the multilayer flexible tube 100 can be made by any reasonable means, such as extrusion molding using a single screw extruder. The polymeric backing layer and the polymeric outer layer may be extruded separately or coextruded. In one exemplary embodiment, an inner liner formed from a liner layer polymer may be extruded sequentially with an outer layer formed from an outer layer polymer. The lining layer polymer is first extruded into pipe in one single screw extruder and cooled to obtain flexible pipe product. And then the outer layer polymer is sent into a single screw extruder, is directly extruded on the outer surface of the lining layer pipe after being led into a special die, and is cut into a multilayer flexible pipe product through cooling and traction. In one exemplary embodiment, an inner liner formed from a liner layer polymer may be coextruded with an outer layer formed from an outer layer polymer. Two single screw extruders were connected to a multilayer coextrusion die. The liner layer polymer is fed into one extruder and the outer layer polymer is fed into another extruder and extruded simultaneously through a multilayer coextrusion die into a multilayer flexible tube which is cooled, drawn and cut into articles. The polymeric backing layer can directly contact the polymeric outer layer and be directly bonded to the inner surface of the polymeric outer layer without an intermediate layer or adhesive. Further, the polymeric backing layer may be extruded in the absence of additives, plasticizers, or other processing aids.

The multilayer flexible pipe according to the invention can be used in applications such as: drinking water (e.g., drinking water contact applications as specified by NSF 51), food and beverage (food contact applications as specified by the chinese food safety act, the U.S. FDA and european union), dairy contact applications, laboratory fluid transport applications, medical fluid transport device applications, peristaltic pump applications, fluid transport applications in biopharmaceutical or chemical pharmaceutical engineering, and the like. In one exemplary embodiment, the multilayer flexible tube of the present invention may be used in applications such as: the flexible water pipe is used as a flexible water pipe of sports and entertainment equipment, a fluid transmission flexible pipe in food and beverage processing equipment, a fluid transmission flexible pipe of liquid medicines, body fluids and the like in the medical and health care fields, a peristaltic pump pipe used in laboratories, medical equipment and biopharmaceuticals, and a disposable system fluid transmission pipeline used in the biopharmaceutical manufacturing process. For example as part of a molding assembly for pumping, bioreactor processing, sampling, filling, etc. In one embodiment, the multilayer flexible pipe of the present invention may be configured for high purity high pressure resistant braided flexible tubing products with an intermediate reinforcing layer. In another embodiment, the multilayer flexible tube of the present invention has been validated by regulatory approval of the chinese food and drug administration, the united states Food and Drug Administration (FDA), the United States Pharmacopeia (USP), the European Pharmacopeia (EP), the International Standard Organization (ISO), other regulatory approval, or combinations thereof. For example, the multilayer flexible tube has been validated using USP class VI standards, ISO 10993 standards, and the like.

Examples of the invention

Comparative example 1

The preparation method of the polymer particles adopts a melt blending method, wherein 39phr of polypropylene polymer (Korean LG chemical PPR754), 100phr of non-conjugated diene copolymer (medium petrochemical three-well oil-filled grade, 125-degree Mooney viscosity 45), 40phr of oil and silica additive are fed into a double screw extruder for melt blending, 40phr of oil and 1phr of dicumyl peroxide (DCP) are respectively fed into a side feed for full melt blending, and the polymer particles are prepared by underwater granulation after extrusion. The hardness of the prepared polymer particles is tested to be 66 Shore A hardness. And feeding the polymer particles into a single-screw extruder, and performing melt extrusion to obtain a standard No. 17 single-layer flexible pipe with the inner diameter of 6.35 mm and the outer diameter of 9.53 mm.

Experimental example 1

The preparation method of the multilayer flexible pipe comprises the following steps: the polymer particles for the liner layer were the polymer particles of comparative example 1, and the polymer particles for the outer layer were prepared by melt-blending 39phr of a polypropylene polymer (korean LG chemical PPR754), 100phr of a SEPS block copolymer (middle petro balsamine oil extended grade YH-4053), 70phr of an oil and a silica additive in a twin-screw extruder, melt-blending the mixture, feeding 70phr of an oil from a side feed, and fully melt-kneading the mixture, followed by underwater pelletization after extrusion. The hardness of the prepared outer layer polymer particles is 69 Shore A hardness. In order to prepare the multilayer flexible pipe, a 25-type single-screw extruder is connected to another 65-type single-screw extruder through a co-extrusion die head, the lining layer and the outer layer polymer particles are respectively fed into the 25-type single-screw extruder and the 65-type single-screw extruder, and a standard No. 17 multilayer flexible pipe with the inner diameter of 6.35 mm and the outer diameter of 9.53 mm is prepared by co-extrusion, wherein the thickness of the lining layer is 0.3 mm.

Taking the single-layer flexible pipe of the comparative example 1 and the multi-layer flexible pipe of the experimental example 1 prepared as described above, under the condition of using water as a medium and under the condition of an outlet pressure of 1.5 bar at room temperature, after the multi-layer flexible pipe is operated on a peristaltic pump using a YZ15 standard pump head at 600rpm for 200 hours, the measured flow change percentage taking an initial flow value as a comparison is shown in Table 1, and it can be known that the flow change of the comparative example 1 for 200 hours is significantly larger than that of the corresponding experimental example 1.

TABLE 1

	Flow rate change from initial flow rate after 200 hours of use (%)
		Comparative example 1	13.2
Experimental example 1	5.5

The foregoing illustrates and describes the principles, general features, and advantages of the present invention. It will be understood by those skilled in the art that the present invention is not limited to the embodiments described above, which are described in the specification and illustrated only to illustrate the principle of the present invention, but that various changes and modifications may be made therein without departing from the spirit and scope of the present invention, which fall within the scope of the invention as claimed. The scope of the invention is defined by the appended claims and equivalents thereof.

Claims

1. A multilayer flexible pipe having an annular cross-section with an inner surface, an outer surface, an inner diameter and an outer diameter, the annular cross-section defining a wall thickness of the flexible pipe, wherein the flexible pipe is characterized by:

a polymeric backing layer comprising a polypropylene-based polymeric continuous phase, and a crosslinked rubber phase dispersed within the continuous phase; and

a polymeric outer layer having an inner surface directly bonded to the outer surface of the polymeric liner layer, the polymeric outer layer comprising a continuous phase comprising a polypropylene-based polymer, and a non-crosslinked styrene block copolymer elastomer miscible with the polypropylene-based polymer dispersed within the continuous phase.

2. The multilayer flexible tube of claim 1, wherein the styrene block copolymer elastomer comprises styrene-butadiene-styrene (SBS), styrene-isoprene-styrene (SIS), styrene-ethylene-butylene-styrene (SEBS), styrene-ethylene-propylene-styrene (SEPS), styrene-ethylene-butadiene-styrene (SEEBS), styrene-ethylene-propylene-styrene (SEEPS), styrene-isoprene-butadiene-styrene (SIBS), or combinations thereof.

3. A multilayer flexible pipe according to any one of claims 1 to 2, wherein the polymer lining layer thickness forms 5% to 50% of the total thickness of the multilayer flexible pipe.

4. The multilayer flexible tube of any one of claims 1 to 2, wherein the multilayer flexible tube is useful for the following applications: food contact applications, dairy, beverage and drinking water contact applications, laboratory fluid transport applications, medical applications, pharmaceutical applications, peristaltic pump applications, or combinations thereof, as defined by the national food safety act, the U.S. FDA and european union.

5. The multilayer flexible tube of any one of claims 1 to 2, having a flow variation of no more than 20%, such as less than 15% or even less than 10%, between 200 hours on a peristaltic pump using a YZ15 standard pump head at 600rpm, using water as the medium, at an outlet pressure of 1.5 bar in a room temperature environment.

6. The multilayer flexible tube of any one of claims 1 to 2, further comprising a reinforcement layer disposed between the polymeric liner layer and the polymeric outer layer.

7. A method of forming a multilayer flexible pipe according to any one of claims 1 to 2, the method comprising first extruding a polymeric lining layer, cooling, drawing, rolling; and then directly extruding a polymer outer layer on the polymer lining layer, cooling, drawing, rolling and cutting to prepare a finished product of the multilayer flexible pipe.

8. A method of forming a multilayer flexible tube as claimed in any one of claims 1 to 2, the method comprising co-extruding a polymer liner layer and a polymer outer layer simultaneously, cooling, drawing, rolling, slitting to produce a finished multilayer flexible tube.