WO2025137047A1 - Peelable polyester heat-shrink tubing - Google Patents

Abstract

A peelable heat-shrink tubing is formed from a composition including a base polymer comprising polyethylene terephthalate (PET) and at least one second polyester extruded or coextruded with the base polymer. The second polyester is selected from the group consisting of polyethylene terephthalate glycol (PETG), polycyclohexylenedimethylene terephthalate acid (PCTA), polycyclohexylenedimethylene terephthalate glycol-modified (PCTG), polybutylene terephthalate (PBT), and polycyclohexylenedimethylene terephthalate (PCT). The peelable heat-shrink tubing exhibits longitudinal peelability. Also disclosed herein are articles made from the peelable heat-shrink tubing.

Description

PEELABLE POLYESTER HEAT-SHRINK TUBING

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to and all benefit of U.S. Provisional Patent Application No. 63/612,641, filed on December 20, 2023, the entire disclosure of which is fully incorporated herein by reference.

BACKGROUND

[0002] Heat-shrink tubing is utilized in a variety of manufacturing processes, including the assembly of catheters. For example, catheter components such as a metal coil and one or more polymeric tubing layers can be positioned over a mandrel and inserted into heat-shrink tubing to form an assembly. The assembly can be heated, thereby causing the heat-shrink tubing to compress around the catheter components, thereby causing encapsulation of the metal coil by the polymeric tubing layer(s). Following encapsulation of the metal coil, the heat-shrink tubing can be removed and discarded.

[0003] However, conventional heat-shrink tubing can be difficult to remove because it lacks peelability. Because the heat-shrink tubing is not peelable, the heat-shrink tubing must be skived. Skiving is a difficult process, as over-skiving can damage the surface of the catheter while under-skiving may not enable easy removal from the catheter. Accordingly, there is a need for improved heat-shrink tubing having peelability.

SUMMARY

[0004] This summary is meant to provide some examples and is not intended to be limiting of the scope of the invention in any way. For example, any feature included in an example of this summary is not required by the claims, unless the claims explicitly recite the features. Also, the features, components, steps, concepts, etc. described in examples in this summary and elsewhere in this disclosure can be combined in a variety of ways. Various features and steps as described elsewhere in this disclosure may be included in the examples summarized here.

[0005] The present disclosure describes, in a first aspect, peelable heat-shrink tubing comprising a composition comprising a base polymer comprising polyethylene terephthalate (PET) and at least one second polyester extruded or co-extruded with the base polymer. The at least one second polyester is selected from the group consisting of polyethylene terephthalate glycol (PETG), polycyclohexylenedimethylene terephthalate acid (PCTA), polycyclohexylenedimethylene terephthalate glycol-modified (PCTG), polybutylene terephthalate (PBT), and polycyclohexylenedimethylene terephthalate (PCT). The peelable heat-shrink tubing exhibits longitudinal peelability.

[0006] According to a second aspect, a peelable heat-shrink tubing comprises the peelable heat-shrink tubing according to the first aspect, wherein the base polymer is present in an amount of from 10 wt.% to 95 wt.% of the composition forming the peelable heat-shrink tubing.

[0007] According to a third aspect, a peelable heat-shrink tubing comprises the peelable heatshrink tubing according to the first or second aspects, wherein the at least one second polyester is present in an amount of from 5 wt.% to 40 wt.% of the composition forming the peelable heat-shrink tubing.

[0008] According to a fourth aspect, a peelable heat-shrink tubing comprises the peelable heat-shrink tubing according to any preceding aspect, wherein, when expanded, the tubing has a wall thickness of greater than 0.25 mil.

[0009] According to a fifth aspect, a peelable heat-shrink tubing comprises the peelable heatshrink tubing according to any preceding aspect, wherein, when expanded, the tubing has a wall thickness of from 0.25 mil to 4 mil.

[0010] According to a sixth aspect, a peelable heat-shrink tubing comprises the peelable heatshrink tubing according to any preceding aspect, wherein the tubing has a minimum shrink ratio of 1.10: 1 to 1.45: 1.

[0011] According to a seventh aspect, a peelable heat-shrink tubing comprises the peelable heat-shrink tubing according to any preceding aspect, wherein, when expanded, the tubing has an inner diameter of from about 3 mm to about 10 mm.

[0012] According to an eighth aspect, a peelable heat-shrink tubing comprises the peelable heat-shrink tubing according to any preceding aspect, wherein the tubing has a peelability rate of greater than 70%.

[0013] According to a ninth aspect, a peelable heat-shrink tubing comprises the peelable heat-shrink tubing according to any preceding aspect, wherein the tubing has a peelability rate of greater than 85%. [0014] In a tenth aspect, a peelable heat-shrink tubing comprises a composition comprising a base polymer comprising polyethylene terephthalate (PET) and at least one second polyester extruded or co-extruded with the base polymer. The at least one second polyester is the polymerization product of terephthalic acid and one of: ethylene glycol, cyclohexanedimethanol, or combinations thereof. The peelable heat-shrink tubing exhibits longitudinal peelability.

[0015] According to an eleventh aspect, a peelable heat-shrink tubing comprises the peelable heat-shrink tubing according to the tenth aspect, wherein the at least one second polyester is the co-polymerization product of terephthalic acid, isophthalic acid, and cyclohexanedimethanol.

[0016] According to a twelfth aspect, a peelable heat-shrink tubing comprises the peelable heat-shrink tubing according to the tenth or eleventh aspects, wherein the base polymer is present in an amount of from 10 wt.% to 95 wt.% of the composition forming the peelable heat-shrink tubing.

[0017] According to a thirteenth aspect, a peelable heat-shrink tubing comprises the peelable heat-shrink tubing according to any one of the tenth through twelfth aspects, wherein the at least one second polyester is present in an amount of from 5 wt.% to 40 wt.% of the composition forming the peelable heat-shrink tubing.

[0018] According to a fourteenth aspect, a peelable heat-shrink tubing comprises the peelable heat-shrink tubing according to any one of the tenth through thirteenth aspects, wherein, when expanded, the tubing has a wall thickness of from 0.25 mil to 4 mil.

[0019] According to a fifteenth aspect, a peelable heat-shrink tubing comprises the peelable heat-shrink tubing according to any one of the previous aspects, wherein the tubing has a maximum shrink ratio of from 20% to 45%.

[0020] According to a sixteenth aspect, a peelable heat-shrink tubing comprises the peelable heat-shrink tubing according to any one of the tenth through fifteenth aspects, wherein, when expanded, the tubing has an inner diameter of from about 3 mm to about 10 mm.

[0021] According to a seventeenth aspect, a peelable heat-shrink tubing comprises the peelable heat-shrink tubing according to any one of the tenth through sixteenth aspects, wherein the tubing has a peelability rate of greater than 70%. [0022] According to an eighteenth aspect, a peelable heat-shrink tubing comprises the peelable heat-shrink tubing according to any one of the previous aspects, wherein the peelable heat-shrink tubing has a crystallinity of less than 10% by volume.

[0023] According to a nineteenth aspect, a peelable heat-shrink tubing comprises the peelable heat-shrink tubing according to any one of the previous aspects, wherein the peelable heatshrink tubing has a birefringence of from -0.09 to less than 0.00 or greater than 0.00.

[0024] According to a twentieth aspect, a peelable heat-shrink tubing comprises the peelable heat-shrink tubing according to any one of the previous aspects, wherein the peelable heatshrink tubing is clear, translucent, or colored.

[0025] According to a twenty-first aspect, a medical device comprises the tubing of any preceding aspect.

[0026] A further understanding of the nature and advantages of the present invention are set forth in the following description and claims, particularly when considered in conjunction with the accompanying drawings in which like parts bear like reference numerals.

BRIEF DESCRIPTION OF THE DRAWINGS

[0027] To further clarify various aspects of implementations of the present disclosure, a more particular description of the certain examples and implementations will be made by reference to various aspects of the appended drawings. It is appreciated that these drawings depict only example implementations of the present disclosure and are therefore not to be considered limiting of the scope of the disclosure. Moreover, while the figures can be drawn to scale for some examples, the figures are not necessarily drawn to scale for all examples. Examples and other features and advantages of the present disclosure will be described and explained with additional specificity and detail through the use of the accompanying drawings in which:

[0028] FIGS. 1 A and IB are photographs showing a comparative sample (a tube prepared using PET alone) that could not be peeled longitudinally;

[0029] FIG. 2 is a photograph of the samples of Sample 2 after the initial peeling tests;

[0030] FIGS. 3 A and 3B are photographs of the tubes of Sample 4 (top of each photograph) and a comparative tube formed with PET (bottom of each photograph) before peeling (FIG.

3 A) and after peeling (FIG. 3B); [0031] FIG. 4 is a schematic drawing of the optical train of the birefringence experiment of Example 2 in which the single-headed arrows indicate the polarization axis of the polarizer and analyzer and the double-headed arrow indicates the slow axis of the compensator; and

[0032] FIG. 5 is a schematic drawing of the Soliel-Babinet compensator used in Example 2 in which the arrow indicates the direction of the slow axis (larger refractive index) of the birefringent material, ‘o’ indicates the slow axis is normal to the page.

DETAILED DESCRIPTION

[0033] The following description refers to the accompanying drawings, which illustrate example implementations of the present disclosure. Other implementations having different structures and operation do not depart from the scope of the present disclosure.

[0034] In various aspects described herein, a peelable heat-shrink tubing comprises a composition comprising a base polymer and at least one second polyester extruded or coextruded with the base polymer. The composition can be formed into a single layer heatshrink tube, which may be incorporated into multilayer tube structures, as will be described in greater detail below. The base polymer of various aspects comprises polyethylene terephthalate (PET). The PET comprises the reaction product of the diacid terephthalic acid (TPA) and the diol ethylene glycol (EG). The base polymer in the heat shrink tubing is present in an amount of from about 10 wt.% to about 95 wt.%, based on a total weight of the composition forming the heat-shrink tubing. For example, the base polymer may be included in the composition forming the heat-shrink tubing in an amount of from about 10 wt.% to about 95 wt.%, from about 10 wt.% to about 92 wt.%, from about 10 wt.% to about 90 wt.%, from about 10 wt.% to about 87 wt.%, from about 10 wt.% to about 85 wt.%, from about 10 wt.% to about 80 wt.%, from about 10 wt.% to about 77 wt.%, from about 10 wt.% to about 75 wt.%, from about 10 wt.% to about 70 wt.%, from about 25 wt.% to about 95 wt.%, from about 25 wt.% to about 92 wt.%, from about 25 wt.% to about 90 wt.%, from about 25 wt.% to about 87 wt.%, from about 25 wt.% to about 85 wt.%, from about 25 wt.% to about 80 wt.%, from about 25 wt.% to about 77 wt.%, from about 25 wt.% to about 75 wt.%, from about 25 wt.% to about 70 wt.%, from about 50 wt.% to about 95 wt.%, from about 50 wt.% to about 92 wt.%, from about 50 wt.% to about 90 wt.%, from about 50 wt.% to about 87 wt.%, from about 50 wt.% to about 85 wt.%, from about 50 wt.% to about 80 wt.%, from about 50 wt.% to about 77 wt.%, from about 50 wt.% to about 75 wt.%, from about 50 wt.% to about 70 wt.%, from about 60 wt.% to about 95 wt.%, from about 60 wt.% to about 92 wt.%, from about 60 wt.% to about 90 wt.%, from about 60 wt.% to about 87 wt.%, from about 60 wt.% to about 85 wt.%, from about 60 wt.% to about 80 wt.%, from about 60 wt.% to about 77 wt.%, from about 60 wt.% to about 75 wt.%, from about 60 wt.% to about 70 wt.%, from about 70 wt.% to about 95 wt.%, from about 70 wt.% to about 92 wt.%, from about 70 wt.% to about 90 wt.%, from about 70 wt.% to about 87 wt.%, from about 70 wt.% to about 85 wt.%, from about 70 wt.% to about 80 wt.%, from about 70 wt.% to about 77 wt.%, or from about 70 wt.% to about 75 wt.%, including any ranges and subranges therein.

[0035] The second polyester included in the heat-shrink tubing, in any of the aspects disclosed herein, can be the polymerization or co-polymerization product of one or more diacid and one or more diol. Such polymerization products include polyesters or copolyesters, both of which are incorporated in the term “second polyester”. A suitable diacid used to make the polyesters or co-polyesters of the present disclosure includes terephthalic acid (TPA), and in some aspects, the diacid includes isophthalic acid (IPA) in addition to the TPA. Suitable diols that can be used to make the polyesters or co-polyesters of the present disclosure include ethylene glycol (EG), cyclohexanedimethanol (CHDM), or combinations or permutations thereof. In some aspects, the second polyester is a co-polyester can be the co-polymerization product of one or more diacids terephthalic acid (TPA) and isophthalic acid (IPA), and one or more diols ethylene glycol (EG) and cyclohexanedimethanol (CHDM). For example, the resulting polyester or co-polyester may be polyethylene terephthalate glycol (PETG), polycyclohexylenedimethylene terephthalate (PCTA), polycyclohexylenedimethylene terephthalate glycol-modified (PCTG), polybutylene terephthalate (PBT), or polycyclohexylenedimethylene terephthalate (PCT).

[0036] PETG is a co-polyester of both the polyester polymer formed from terephthalic acid (TPA) and cyclohexanedimethanol (CHDM), and the polyester polymer formed from TPA and ethylene glycol (EG). As such, while the base polymer PET has EG transesterification (ET) units, the co-polyester PETG has both EG transesterification (ET) unit and CHDM transesterification (CT) units. Accordingly, PETG has a relative flexible molecular chain structure and lower crystallinity as compared to PET. However, because the two polymers are in the same polyester family, when PET and PETG are compounded together, they exhibit good compatibility and stability and do not exhibit phase separation in the resultant tubing. Similarly, PCTA is a co-polyester of both the polyester polymer formed from TPA and CHDM and the polyester polymer formed form IPA and CHDM. PCTG is likewise a copolymer of TPA with EG and TPA with CHDM, and PCT is a polyester of TPA with CHDM. Like PETG, each of PCTA, PCTG, and PCT are in the same polyester family with PET and exhibit good compatibility with PET. [0037] In aspects disclosed herein, the second polyester is included in an amount of from about 5 wt.% to about 40 wt.%, based on a total weight of the composition forming the heatshrink tubing. For example, the second polyester can be included in an amount of from about 5 wt.% to about 35 wt.%, from about 5 wt.% to about 30 wt.%, from about 5 wt.% to about 25 wt.%, from about 5 wt.% to about 20 wt.%, from about 5 wt.% to about 15 wt.%, from about 5 wt.% to about 10 wt.%, from about 7 wt.% to about 40 wt.%, from about 7 wt.% to about 35 wt.%, from about 7 wt.% to about 30 wt.%, from about 7 wt.% to about 25 wt.%, from about 7 wt.% to about 20 wt.%, from about 7 wt.% to about 15 wt.%, from about 10 wt.% to about 40 wt.%, from about 10 wt.% to about 35 wt.%, from about 10 wt.% to about 30 wt.%, from about 10 wt.% to about 25 wt.%, from about 10 wt.% to about 20 wt.%, from about 10 wt.% to about 15 wt.%, from about 12 wt.% to about 40 wt.%, from about 12 wt.% to about 35 wt.%, from about 12 wt.% to about 30 wt.%, from about 12 wt.% to about 25 wt.%, from about 12 wt.% to about 20 wt.%, from about 15 wt.% to about 40 wt.%, from about 15 wt.% to about 35 wt.%, from about 15 wt.% to about 30 wt.%, from about 15 wt.% to about 25 wt.%, or from about 15 wt.% to about 20 wt.%, including any ranges and subranges therein. In any of the aspects of the disclosure, the composition forming the heatshrink tubing consists essentially of the base polymer and the second polyester.

[0038] Without being bound by theory, it is believed that conventional heat-shrink tubing that is manufactured from PET without the second polyester of the present disclosure has a matrix structure which does not lend itself to peelability. However, when the PET is blended and extruded or co-extruded with at least one second polyester as described in various embodiments herein, it is believed that the polymer chains are extended into orientations along the tubing direction that are compatible with peeling in the tubing direction (e.g., parallel orientations) because of the differences in the molecular chain structures of the PET and the second polyester. As a result, the heat-shrink tubing according to various aspects herein exhibits longitudinal peelability not exhibited by conventional heat-shrink tubing.

[0039] Orientation of the polymers, and more specifically, optical orientation, can be measured using a birefringence test method. One such birefringence test method is described in U.S. Patent No. 5,733,653, the entire contents of which is hereby incorporated by reference herein. For example, birefringence can be measured using a Zeiss AxioVision Imager using a tilting compensator (e.g., a Soliel-Babinet tilting compensator) mounted in a polarizing microscope (e.g., an Axio Imager M2m polarized microscope) on a film-like sample. Other methods, such as the method described in the Examples section hereinbelow may be employed. [0040] The heat-shrink tubing may have a birefringence of greater than about -0.09, but not equal to 0.00. For example, the heat-shrink tubing may have a birefringence of from about - 0.09 to less than 0.00, or a birefringence of greater than 0.00.

[0041] Without being bound by theory, the crystallinity of the polymers may also impact the longitudinal peelability of the heat-shrink tubing. Crystallinity can be measured by x-ray diffraction. Percent crystallinity of a tubing material can be determined based on the relative intensities of amorphous and crystalline peaks in an X-ray diffraction pattern. The percent crystallinity can be calculated based on the following formula:

where I_c is the intensity of the crystalline peak(s) and I_a is the intensity of the amorphous peak(s). Other methods, such as the method described in the Examples section hereinbelow may be employed.

[0042] The heat-shrink tubing may have a crystallinity of less than 10% by volume. For example, the heat-shrink tubing may have a crystallinity of less than 10% by volume, less than 7% by volume, or even less than 5% by volume, including any ranges and subranges therein. The heat-shrink tubing may have a crystallinity of from greater than 0% by volume to about 10% by volume, from about 0.1% by volume to about 10% by volume, from about 1% by volume to about 10% by volume, from greater than 0% by volume to about 7% by volume, from about 0.1% by volume to about 7% by volume, from about 1% by volume to about 7% by volume, from greater than 0% by volume to about 5% by volume, from about 0.1% by volume to about 5% by volume, from about 1% by volume to about 5% by volume, including any ranges and subranges therein.

[0043] Without being bound by theory, both the birefringence and XRD crystallinity analyses may help to define the morphological structure of the polymers that impacts the longitudinal peelability of the heat-shrink tubing. Additionally, the thermal properties analyzed by Differential Scanning Calorimetry (DSC) of the polymers may provide detailed information. In various aspects, the heat-shrink tubing can be further characterized by peak melting temperatures, melt onset temperatures, and/or enthalpy values as determined by DSC.

During DSC analysis, the sample is heated in a first heating cycle, then cooled during a cooling cycle, and re-heated in a second heating cycle. The first heating cycle detects thermal responses to the heat of the developed crystalline structure until the sample is completely melted. During the temperature scanning from low to high, the formed crystalline structure of the tested tube sample is gradually destroyed. The crystalline structure is therefore destroyed at melted stage. The cooling cycle detects and characterizes phase transitions like crystallization, where a material changes from a liquid or disordered state to a more ordered crystalline structure under stress-free conditions, which appears as an exothermic peak on the DSC curve. The second heating cycle remelts the re-crystallized material mixture that was formed during the cooling cycle. The crystalline structure of this re-crystallized material is formed under stress-free conditions and is different from the first heating cycle that is to detect the expanded tube samples that were made under stress conditions, such as the elongation conditions. In the context of DSC thermal analysis, the enthalpy refers to the amount of heat absorbed or released during a phase transition, while crystallinity represents the percentage of the material in a crystalline state. In general, a higher enthalpy of fusion (z.e., melting) in the DSC curve indicates a higher degree of crystallinity in a sample, as the more crystalline material is, the more heat is needed to melt it completely.

[0044] In various aspects, the heat-shrink tubing has a first heating cycle melting peak temperature (Tm peak) of less than about 255 °C. For example, the heat-shrink tubing may have a first heating cycle melting peak temperature of from about 250 °C to about 255 °C, from about 250 °C to about 254 °C, from about 250 °C to about 253 °C, from about 251 °C to about 255 °C, from about 251 °C to about 254 °C, from about 251 °C to about 253 °C, from about 252 °C to about 255 °C, from about 252 °C to about 254 °C, from about 252 °C to about 253 °C, from about 253 °C to about 255 °C, or from about 253 °C to about 254 °C, including any ranges and subranges therein.

[0045] The heat-shrink tubing may also have a second heating cycle melt onset temperature of less than about 243 °C. For example, the heat-shrink tubing may have a second heating cycle melt onset temperature of from about 235 °C to about 243 °C, from about 235 °C to about 241 °C, from about 235 °C to about 239 °C, from about 235°C to about 237 °C, from about 237 °C to about 243 °C, from about 237 °C to about 241 °C, from about 237 °C to about 239 °C, from about 239 °C to about 243 °C, or from about 239 °C to about 241 °C, including any ranges and subranges therein.

[0046] In aspects, the enthalpy (H) of the second heating cycle is higher than that of the first heating cycle. For example, the enthalpy (H) of the second heating cycle may be at least 5 J/g higher than the enthalpy of the first heating cycle. The difference between the enthalpy (AH) second heating cycle and the first heating cycle may be from about 5 J/g to about 30 J/g, from about 5 J/g to about 25 J/g, from about 5 J/g to about 22 J/g, from about 5 J/g to about 20 J/g, from about 5 J/g to about 18 J/g, from about 5 J/g to about 15 J/g, from about 5 J/g to about 12 J/g, from about 7 J/g to about 30 J/g, from about 7 J/g to about 25 J/g, from about 7 J/g to about 22 J/g, from about 7 J/g to about 20 J/g, from about 7 J/g to about 18 J/g, from about 7 J/g to about 15 J/g, from about 7 J/g to about 12 J/g, from about 10 J/g to about 30 J/g, from about 10 J/g to about 25 J/g, from about 10 J/g to about 22 J/g, from about 10 J/g to about 20 J/g, from about 10 J/g to about 18 J/g, from about 10 J/g to about 15 J/g, from about 10 J/g to about 12 J/g, from about 15 J/g to about 30 J/g, from about 15 J/g to about 25 J/g, from about 15 J/g to about 22 J/g, from about 15 J/g to about 20 J/g, or from about 15 J/g to about 18 J/g, including any ranges and subranges therein.

[0047] The heat-shrink tubing may further include one or more additives. Such additives can be blended with the base polymer and/or the second polyester prior to extrusion, or can be coextruded with the base polymer and the second polyester, as will be described below. Additives can include, for example, colorants, lubricants, and any other additive conventionally used in heat-shrink tubing to impart particular properties to the heat-shrink tubing. The resulting heat-shrink tubing may be clear, translucent, colored, or opaque, depending on the precursor extrusion process conditions, expansion process conditions, and presence or absence of colorants, such as pigment powders. When included, the additive(s) can be present in the composition forming the heat-shrink tubing in an amount of less than or equal to about 50 wt.%, less than about 25 wt.%, less than about 10 wt.%, less than about 7 wt.%, less than about 5 wt.%, or less than about 3 wt.%, depending on the particular additive. However, it should be understood that the incorporation of additives is optional and, as such, some aspects may not include additives.

[0048] The present disclosure is also directed to articles comprising the heat-shrink tubing. Heat-shrink tubing is widely used in many applications, including, but not limited to, catheter assembly, bond reinforcement, braid termination, bundling/encapsulation, custom precision printing, insulation, and masking for coating applications. Exemplary articles can include intravascular medical devices, including but not limited to, catheters and medical tubes comprising the heat-shrink tubing of the present disclosure. For example, a catheter may include a liner formed from a lubricious material (e.g., polytetrafluoroethylene (PTFE), a reinforcement layer to provide strength, and a jacket to provide durability and protection. The heat-shrink tubing of the present disclosure may be provided in an expanded state concentrically outside of the jacket. In such implementations, heat may be applied to the heat-shrink tubing, which causes the heat-shrink tubing to shrink and compress the jacket toward the reinforcement layer, finalizing the formation of the catheter. [0049] In aspects of the present disclosure, an intravascular medical device comprises multilayer tubes. Such multilayer tubes can include, by way of example and not limitation, a first layer and a second layer disposed about the first layer. Other layers, such as the heatshrink tubing described herein, reinforcement layers, tie layers, liners, and the like can be included in the multilayer tube. The multilayer tube may be of any type of construction known and used in the art. To form the articles any one of a variety of methods may be employed, including any methods conventionally known and used in the art. The various articles comprising the heat-shrink tubing are arranged concentrically, with the heat-shrink layer positioned in its expanded form as the outer-most layer of the arrangement. The heatshrink layer is then shrunken to encapsulate and compress the other layers. In aspects, the heat-shrink layer may be removed prior to use of the article.

[0050] To form the heat-shrink layer, the base polymer and the second polyester, along with any additives, are extruded or co-extruded to form an extruded tube. The tubing is provided in an expanded shape by virtue of applying heat to the material (e.g., as part of the extrusion process or as a subsequent application of heat during tube formation) and elongating the tube in both the longitudinal and transverse directions while the tube is warm and malleable to reduce the thickness of the tube wall and increase the inner diameter of the wall. The term “expanded heat-shrink tubing” refers to a heat-shrink tubing in its expanded form. The expanded heat-shrink tubing extends axially along a length of the tube. The expanded heatshrink tubing also includes an inner diameter, IDEHS, which is defined by an inner surface of the expanded heat-shrink tubing. Similarly, the inner diameter, IDEHS, can vary in some aspects of the present disclosure. In some aspects of the present disclosure, the inner diameter, IDEHS, is suitable for receiving other layers sized for use in catheter applications within the heat-shrink tubing (e.g., the first layer and the second layer of a multilayer tube). The expanded heat-shrink tubing may have a generally cylindrical shape, although other shapes are contemplated and possible.

[0051] In any of the aspects disclosed herein, the expanded heat-shrink tubing has an inner diameter of from about 0.1 mm to about 15.5 mm (e.g., from about 5 mils to about 600 mils), or from about 3 mm to about 10 mm. For example, the expanded heat-shrink tubing may have an inner diameter of from about 0.1 mm to about 15.5 mm, from about 0.1 mm to about 12.5 mm, from about 0.1 mm to about 10 mm, from about 0.1 mm to about 9 mm, from about 0.1 mm to about 8 mm, from about 0.1 mm to about 7 mm, from about 0.1 mm to about 6 mm, from about 1 mm to about 15.5 mm, from about 1 mm to about 12.5 mm, from about 1 mm to about 10 mm, from about 1 mm to about 9 mm, from about 1 mm to about 8 mm, from about 1 mm to about 7 mm, from about 1 mm to about 6 mm, from about 3 mm to about 15.5 mm, from about 3 mm to about 12.5 mm, from about 3 mm to about 10 mm, from about 3 mm to about 9 mm, from about 3 mm to about 8 mm, from about 3 mm to about 7 mm, from about 3 mm to about 6 mm, from about 3.5 mm to about 15.5 mm, from about 3.5 mm to about 12.5 mm, from about 3.5 mm to about 10 mm, from about 3.5 to about 10 mm, from about 3.5 mm to about 9 mm, from about 3.5 mm to about 8 mm, from about 3.5 mm to about 7 mm, from about 3.5 mm to about 6 mm, from about 4 mm to about 15.5 mm, from about 4 mm to about

12.5 mm, from about 4 mm to about 10 mm, from about 4 mm to about 10 mm, from about 4 mm to about 9 mm, from about 4 mm to about 8 mm, from about 4 mm to about 7 mm, from about 4 mm to about 6 mm, from about 4.5 mm to about 15.5 mm, from about 4.5 mm to about 12.5 mm, from about 4.5 mm to about 10 mm, from about 4.5 to about 10 mm, from about 4.5 mm to about 9 mm, from about 4.5 mm to about 8 mm, from about 4.5 mm to about 7 mm, or from about 4.5 mm to about 6 mm, including any ranges and subranges therein. The size of heat-shrink tubing within the scope of the disclosure (e.g., length, diameter and average wall thickness) is not particularly limited. For example, the diameters of the heatshrink tubing described herein can vary, in particular, depending upon the application for which the tubing is intended. Accordingly, heat-shrink tubing having expanded IDs outside this range are also encompassed by the present disclosure, particularly in the context of applications in different fields.

[0052] The expanded heat-shrink tubing further includes an outer surface that is separated from the inner surface by a thickness, tsns, of the expanded heat-shrink tubing. The wall thickness can generally be described as being substantially uniform, and does not vary significantly around the circumference of the expanded heat-shrink tubing or along the length of the expanded heat-shrink tubing. In any of the aspects described herein, the expanded heat-shrink tubing may have a wall thickness of greater than 0.05 mils. For example, the expanded heat-shrink tubing may have a thickness of from about 0.05 mils to 4.00 mils, 0.25 mils to about 10 mils, from about 0.25 mils to about 8 mils, from about 0.25 mils to about 6 mils, from about 0.25 mils to about 4 mils, from about 0.25 mils to about 2 mils, from about 0.5 mils to about 10 mils, from about 0.5 mils to about 8 mils, from about 0.5 mils to about 6 mils, from about 0.5 mils to about 4 mils, from about 0.5 mils to about 2 mils, from about 0.75 mils to about 10 mils, from about 0.75 mils to about 8 mils, from about 0.75 mils to about 6 mils, from about 0.75 mils to about 4 mils, from about 0.75 mils to about 2 mils, from about 1 mil to about 10 mils, from about 1 mil to about 8 mils, from about 1 mil to about 6 mils, from about 1 mil to about 4 mils, from about 1 mil to about 2 mils, from about

1.5 mils to about 10 mils, from about 1.5 mils to about 8 mils, from about 1.5 mils to about 6 mils, from about 1.5 mils to about 4 mils, or from about 1.5 mils to about 2 mils, including any ranges and subranges therein.

[0053] Upon heating and/or sintering, the expanded heat-shrink tubing shrinks to a size equivalent or close to its original size, commonly referred to as its “recovered” size, encapsulating article positioned within its inner diameter. The recovered heat-shrink tubing may also be referred to as the shrunken tubing. The heat-shrink tubing can be defined by its shrink ratio or shrink percentage. As used herein, the “shrink percentage” is calculated according to the following equation: 100

where IDEHS is the inner diameter of the expanded heat-shrink tubing, and IDRHS is the inner diameter of the recovered heat-shrink tubing. Inner diameters were measured by inserting standard pin gauges. Shrink percentage can be represented as the shrink ratio. For example, for a tubing having a shrink percentage of 10%, the shrink ratio can be expressed as 1.10: 1. In any of the aspects described herein, the heat-shrink tubing as a minimum shrink ratio of 1.10:1 to 1.45: 1. For example, the heat-shrink tubing may have a minimum shrink ratio of 1.10:1, 1.15: 1, 1.20: 1, 1.25:1, 1.30: 1, 1.35: 1, 1.40: 1, 1.45: 1, or even greater. In any of the aspects described herein, the shrink percentage may be calculated after heating the expanded heat-shrink tubing at 150 °C for approximately 5 minutes.

[0054] In any of the aspects described herein, the heat-shrink tubing is “peelable” and can be readily peeled or tom apart in the longitudinal direction (e.g., to remove the heat-shrink tubing from the other layers of the multilayer tube). Although measured herein on expanded heat-shrink tubing, the peelability of the tubing is maintained following shrinking during the heat-shrinking process. The peelability can enable the tubing to be provided, used, and removed without the need for scoring, break lines, or perforations extending the length of the tubing. In some aspects of the present disclosure, one or more (e.g., two) incisions may be made to one end of the heat-shrink tubing prior to recovery (e.g., the incisions may be made after expansion or before the heat-shrink process, such as during the reflow process). The recovered heat-shrink tubing of any of the aspects described herein can be peeled off longitudinally by the operator’s hands without causing damage to article it encompasses.

[0055] As used herein, “peelability rate” refers to a percentage of samples that are peeled at least 0.5 inches prior to breakage of the heat-shrink tubing. In any of the aspects described herein, the heat-shrink tubing has a peelability rate of greater than about 70%. For example, the heat-shrink tubing may have a peelability rate of greater than about 75%, greater than about 80%, greater than about 85%, greater than about 90%, greater than about 95%, greater than about 98%, or greater than about 99%, including any subranges and endpoints therein. In aspects of the present disclosure, the heat-shrink tubing has a peelability rate of 100%.

EXAMPLES

[0056] The following examples are meant to better illustrate various aspects of the present disclosure, but are not intended to limit the scope of the present disclosure.

[0057] The following materials were employed in the examples that follow:

[0058] PET Polymer A and PET Polymer B are two different PET polymers;

[0059] EASTAR™ MN210 is a co-polyester in the form of PETG, available from Eastman Chemical Company (Kingsport, TN); and

[0060] DURASTAR™ MN611 is a co-polyester in the form of PCTA, available from Eastman Chemical Company (Kingsport, TN).

[0061] Example 1

[0062] Three samples (Samples 1-3) including the heat-shrink tubing according to various aspects of the present disclosure were prepared by forming a heat-shrink tubing using PET Polymer A and EASTAR™ MN210. In particular, the PET and PETG were co-extruded with 1 wt.% blue colorant and 2 wt.% white colorant to form a heat-shrink tubing. Each of the samples were expanded to an expanded heat-shrink tubing having an inner diameter IDHST of 0.221 inches (5.6 mm) and a wall thickness of 0.002 inches (2 mils). The heat-shrink compositions are provided in Table 1 below.

[0063] Testing was conducted on the expanded heat-shrink tubing at a gauge length of 1 inch. Max peeling force was measured using a tensile tester, such as an Instron Tester. Ultimate elongation (UE) is calculated according to the following equation: 100

where LB is the elongated length at break and LG is the gauge length. [0064] For each of the samples, the sample size was 26, and the number of samples that were peeled at least 0.5 inch and less than 0.5 inch were recorded. The results are reported in Table 1 below.

[0065] Table 1

[0066] A comparative sample was prepared using conventional PET heat-shrink tubing, without the use of a co-extruded second polyester. The comparative sample could not be peeled longitudinally, as shown in FIGS. 1 A and IB, because the peeling path was in a curved, and not straight line. In particular, when V-shaped notches were put into the comparative sample, the thin wall of the heat-shrink tubing curled up.

[0067] In contrast, FIG. 2 is a photograph of the 26 samples of Sample 2 after the initial peeling tests. The peeled samples were separated into two groups. The group on the lefthand side of the photo shows the samples that were peeled less than 0.5 inch, while the group on the right-hand side of the photo shows the samples that were peeled at least 0.5 inch. The samples that were peeled at least 0.5 inch peeled in straight lines and are expected to be continuously peeled longitudinally.

[0068] Five additional samples (Samples 4-8) including the heat-shrink layer according to various aspects of the present disclosure were prepared by forming a heat-shrink tubing using PET Polymer B and DURASTAR™ MN611. In particular, the PET and PCTA were coextruded to form a heat-shrink tubing. The heat-shrink compositions, inner diameter IDHST, and wall thickness are provided in Table 2 below.

[0069] Testing was conducted on the expanded heat-shrink tubing. For each of the samples, the sample size was 5. Peelability was tested in two stages (e.g., expanded stage and after heat-shrink). The sample length was 12 inches and had incisions at one end (50%/50% split) that were about 0.5 - 1.0 inches length. Two hands were used to peel the samples. All of the samples peeled all the way to the end of the tubing opposite the incisions (i.e., the full length of the sample). Accordingly, each of the samples exhibited a peelability rate of 100%.

[0070] Table 2

[0071] FIGS. 3A and 3B are photographs of the tubes of Sample 4 (top of each photograph) and a comparative tube formed with PET (bottom of each photograph) before peeling (FIG.

3 A) and after peeling (FIG. 3B). As shown in FIG. 3B, the tube of Sample 4 exhibits excellent peelability from one end to the other (i.e., the entire longitudinal length), while the comparative tube peeled less than 1 inch.

[0072] Example 2

[0073] Eight additional samples (Samples 9-16) were prepared by forming a heat-shrink tubing using PET Polymer B and DURASTAR™ MN611. In particular, the PET and PCTA were extruded and expanded to form a heat-shrink tubing. Each of the samples were expanded to an expanded heat-shrink tubing having the inner diameter IDHST and wall thickness reported in Table 3. The heat-shrink compositions are also provided in Table 3 below. All of Samples 9-16 demonstrated good peelability.

[0074] For birefringence measurements, all samples were cut, unfurled, and then taped to microscopy slides for ease of measurement. The tube wall thickness was measured using a digital Mitutoyo coolant-proof micrometer Series 293 with resolution to 0.001mm. For samples too thin for measurement the flattened tube thickness was measured and halved to give the tube wall thickness. Five samples of each specimen were prepared, and the average of all measurements is reported.

[0075] Table 3

[0076] X-ray Diffraction (XRD) was used to determine crystallinity percentage of Samples 6 and 9-16. The X-ray diffraction measurements were performed with a Rigaku Smartlab equipped with a 9 kW rotating anode and Cu-Ka radiation ( = 1.54184 A) at 45 kV and 200 mA using parallel beam configuration. The measurements were performed over a 29 range from 5° to 70°, with a scan speed of 2°/min and 0.02° increments. All the scans were performed at room temperature.

[0077] All of the samples displayed a broad peak at -24.7° (29) corresponding to an X-ray Diffraction (XRD) amorphous behavior due to the lack of long-range order. Broader XRD peaks could be related to a greater structural disorder in the samples. It is believed that these structural disorders are influenced by mixed materials, molecular weight distributions of the two raw materials, and the expansion processes. [0078] The crystallinity percentage of Samples 6 and 9-16 was calculated by using the area under the sharp crystalline peaks and the broad amorphous peaks from the XRD data. However, none of the tube samples showed crystalline peaks. In essence, the patterns showed that all the samples were fully amorphous within the XRD detection limit. The lower limit of the XRD detection technique in polymers is about 2% to 5% by volume. Thus, the crystallinity of all the polyester samples could be below the lower limit of the XRD detection. i.e., less than 5%, as reported in Table 3.

[0079] These expanded tube samples were produced through expansion process. During the expansion process, the wall thickness of the precursor tubings were elongated in both longitudinal and transverse directions and became thinner walled. At the same time, the inner diameter (ID) of these expanded reached the targeted ID. The elongation of the tubing wall in the expansion process is like the process of bi-axial drawing of films. It is believed that the introduced stress by the elongation on the tubing wall is favored to suppress the crystalline structure formation on the final expanded tube samples.

[0080] Birefringence was also measured for Samples 6 and 9-13. AZeiss Axio Imager M2m polarized microscope with a StrainOptics Inc. PS-100-SF-Digivideo setup was used to measure the birefringence of the films. The optical train is shown in FIG. 4. A white light source located at the bottom of the instrument passes through a linear polarizer, the sample, and an analyzer (i.e., linear polarizer) oriented with its polarization axis 90° to the initial linear polarizer. A Soliel-Babinet compensator mounted in the polarized microscope was used to measure the retardation, 6, of each sample. The birefringence, An, was determined as:

| An| = 6/t

[0081] The sign of the birefringence was determined from the relative orientation of the sample machine director to the long-axis of the compensator as shown in FIG. 5. As shown in FIG. 5, the wedge is moved horizontally using a micrometer screw. The retardation is the product of the distance moved from the zero position, d, and the compensator calibration constant, 79.7 nm/mm. Samples with the machine direction oriented perpendicular to the slow axis of the compensator have a positive birefringence, while samples oriented with the machine direction perpendicular to the long axis of the compensator have a negative birefringence.

[0082] To set-up the birefringence measurement, the white balance of the camera was calibrated using white light passing through the polarizer and analyzer oriented with their polarization direction parallel. The compensator is at zero retardation when the magnitude of the retardation through the wedges matches the retardation through the slab. The retardation is adjusted using a micrometer screw to slide the movable wedge. The retardation is calculated by multiplying the micrometer position in mm by the calibration constant of the compensator, 79.7 nm/mm. The zero-retardation position of the compensator was calibrated using a full waveplate with a known retardation of 530 nm. The compensator was adjusted until an opposite retardation of 530 nm was applied, and then adjusted back 6.65 mm, based on the calibration constant of the compensator (530 nm / 79.7 nm/mm = 6.65 mm), and rezeroed.

[0083] For the birefringence measurement, the sample was first oriented with the machine direction perpendicular to the slow axis of the compensator, and the compensator was shifted to increase the retardation of the compensator. When the retardation of the sample is compensated (i.e., equal in magnitude, but opposite in sign between the sample and compensator) the sample image is black. The retardation measured in this orientation corresponds to positive birefringence. If a zero retardation could not be obtained in this sample orientation, the sample was rotated 90°, to place the machine direction parallel to the slow axis of the compensator and the measurement was repeated. The retardation measured in this orientation corresponds to negative birefringence.

[0084] Again, these expanded tube samples were produced through expansion process. During the expansion process, the wall thickness of the precursor tubing was elongated further in both longitudinal and transverse directions. The molecular chains of the well distributed two raw materials are further oriented in both directions. It is believed that the longitudinal orientation is increased and the expanded tubings have higher orientation than that of the precursor tubings. At the same time, the transverse orientation of the expanded tubing is also increased after expansion process. However, the bi-axial orientations of the molecular chains of these two mixed materials have competed one another dependent on the expansion process conditions.

[0085] As shown in birefringence results of the tube samples, Samples 6 and 9-13 each has a negative value because the extraordinary index of refraction parallel to the extended chain axis is less than that of the ordinary index of refraction perpendicular to the extended chain axis. Although the birefringence of the samples is reported in negative values, it is believed that the extraordinary index of refraction at longitudinal direction should have a certain high index so that these expanded tube samples resulted in good peelability. [0086] Differential Scanning Calorimetry (DSC) was used to analyze the thermal behavior of nine samples (Samples 4-7, 11-13, and 16-17) and a comparative sample (Sample A). Samples 4-7, 11-13, and 16 were prepared as described above. Sample 17 was prepared by forming a heat-shrink tubing using 20 wt.% PET Polymer B and 80 wt.% DURASTAR™ MN61 1. In particular, the PET and PCTA were co-extruded to form a heat-shrink tubing. Sample A was prepared using 100% PET. Each of the samples were expanded to an expanded heat-shrink tubing having the inner diameter IDHST and wall thickness reported in Table 4. The heat-shrink compositions are also provided in Table 4 below. All of Samples demonstrated good peelability.

[0087] Each tube sample was tested with heating-cooling-reheating cycles method, as described hereinabove. Again, the tube samples were made from the mixed semicrystalline polymers and through expansion processes. Temperatures and enthalpy (H) calculations are reported in Table 4, along with various differences in temperatures and enthalpy.

[0088] Table 4

[0089] Table 4 - Cont’d.

[0090] As shown in the first heating cycle, the melting peak temperatures of the tube samples made with the mixed materials at a PET/MN611 mixture range of from 85%/l 5% to 20%/80% are lower than that of the comparative sample (Sample A). This indicates the crystalline structure formation of the tube samples made with the mixed polymers is different from that of the tube sample made with 100% PET (Sample A).

[0091] In the second heating cycle, the melting points are lower than those of the first heating cycle because the morphological structure of the expanded tube samples was erased or destroyed through the first heating cycle. The results of the second heating cycle also provide information for comparison among the tested samples without the effect of structure formation from the expansion process conditions. All samples made with the mixed materials have a relative lower melt onset temperature (Tm Onset) than that of Sample A.

[0092] In addition, the DSC curves of the samples made with the mixed materials showed asymmetric pattern and start melting at a relative lower temperature at the second heating cycle when compared to that of the first heating cycle. A smaller crystallite size is melted more quickly as compared to relatively larger crystallite sizes. This indicates that the expanded tube samples made with the mixed materials had a relatively narrower crystallite size distribution under the stress during the expansion process conditions than that of the second heating cycle since these samples are re-crystallized and re-melted under stress-free conditions.

[0093] Comparing the enthalpy (AH) between the first and second heating cycles of the tube samples made with the mixed materials, the enthalpy of the second heating cycle is always higher than that of the first heating cycle, while Sample A shows the reverse result. This indicates that the crystallinity of the tube samples made with the mixed materials in the first heating cycle is lower than that of the second heating cycle, while Sample A shows a reverse result. This indicates that the crystalline structure of the tube samples made with the mixed materials resulted in suppressing the crystallization formation.

[0094] Overall, the samples made with the mixed materials have unique characteristics of good peelability, a crystallinity percentage of less than 5% by volume, negative birefringence value (likely due to the tube expansion process), and suppressed crystalline structure formation (as shown in the DSC test results).

[0095] While various inventive aspects, concepts and features of the disclosures may be described and illustrated herein as embodied in combination in the example aspects of the present disclosure, these various aspects, concepts, and features may be used in many alternative aspects of the present disclosure, either individually or in various combinations and sub-combinations thereof. Unless expressly excluded herein all such combinations and sub-combinations are intended to be within the scope of the present application. Still further, while various alternative aspects of the present disclosure as to the various aspects, concepts, and features of the disclosures — such as alternative materials, structures, configurations, methods, devices, and components, alternatives as to form, fit, and function, and so on — may be described herein, such descriptions are not intended to be a complete or exhaustive list of available alternative aspects of the present disclosure, whether presently known or later developed. Those skilled in the art may readily adopt one or more of the inventive aspects, concepts, or features into additional aspects of the present disclosure and uses within the scope of the present application even if such aspects of the present disclosure are not expressly disclosed herein.

[0096] Additionally, even though some features, concepts, or aspects of the disclosures may be described herein as being a preferred arrangement or method, such description is not intended to suggest that such feature is required or necessary unless expressly so stated. Still further, example or representative values and ranges may be included to assist in understanding the present application, however, such values and ranges are not to be construed in a limiting sense and are intended to be critical values or ranges only if so expressly stated.

[0097] Moreover, while various aspects, features and concepts may be expressly identified herein as being inventive or forming part of a disclosure, such identification is not intended to be exclusive, but rather there may be inventive aspects, concepts, and features that are fully described herein without being expressly identified as such or as part of a specific disclosure, the disclosures instead being set forth in the appended claims. Descriptions of example methods or processes are not limited to inclusion of all steps as being required in all cases, nor is the order that the steps are presented to be construed as required or necessary unless expressly so stated. The words used in the claims have their full ordinary meanings and are not limited in any way by the description in the specification.

Claims

1. A peelable heat-shrink tubing comprising a composition comprising: a base polymer comprising polyethylene terephthalate (PET); and at least one second polyester extruded or co-extruded with the base polymer, wherein the at least one second polyester is selected from the group consisting of polyethylene terephthalate glycol (PETG), polycyclohexylenedimethylene terephthalate acid (PCTA), polycyclohexylenedimethylene terephthalate glycol-modified (PCTG), polybutylene terephthalate (PBT), and polycyclohexylenedimethylene terephthalate (PCT), wherein the peelable heat-shrink tubing exhibits longitudinal peelability.

2. The peelable heat-shrink tubing of claim 1, wherein the base polymer is present in an amount of from 10 wt.% to 95 wt.% of the composition forming the peelable heat-shrink tubing.

3. The peelable heat-shrink tubing of any preceding claim, wherein the at least one second polyester is present in an amount of from 5 wt.% to 40 wt.% of the composition forming the peelable heat-shrink tubing.

4. The peelable heat-shrink tubing of any preceding claim, wherein, when expanded, the tubing has a wall thickness of greater than 0.05 mil.

5. The peelable heat-shrink tubing of any preceding claim, wherein, when expanded, the tubing has a wall thickness of from 0.05 mil to 4 mil.

6. The peelable heat-shrink tubing of any preceding claim, wherein the tubing has a minimum shrink ratio of 1.10: 1 to 1.45: 1.

7. The peelable heat-shrink tubing of any preceding claim, wherein, when expanded, the tubing has an inner diameter of from about 5 mil to about 600 mil.

8. The peelable heat-shrink tubing of any preceding claim, wherein the tubing has a peelability rate of greater than 70%.

9. The peelable heat-shrink tubing of any preceding claim, wherein the tubing has a peelability rate of greater than 85%.

10. A peelable heat-shrink tubing comprising a composition comrpising: a base polymer comprising polyethylene terephthalate (PET); and at least one second polyester extruded or co-extruded with the base polymer, wherein the at least one second polyester is the polymerization product of terephthalic acid and one of: ethylene glycol, cyclohexanedimethanol, or combinations thereof; wherein the peelable heat-shrink tubing exhibits longitudinal peelability.

11. The peelable heat-shrink tubing of claim 10, wherein the at least one second polyester is the co-polymerization product of terephthalic acid, isophthalic acid, and cyclohexanedimethanol.

12. The peelable heat-shrink tubing of claim 10 or claim 11, wherein the base polymer is present in an amount of from 10 wt.% to 95 wt.% of the composition forming the peelable heat-shrink tubing.

13. The peelable heat-shrink tubing of any one of claims 10-12, wherein the at least one second polyester is present in an amount of from 5 wt.% to 40 wt.% of the composition forming the peelable heat-shrink tubing.

14. The peelable heat-shrink tubing of any one of claims 10-13, wherein, when expanded, the tubing has a wall thickness of from 0.05 mil to 4 mil.

15. The peelable heat-shrink tubing of any one of claims 10-14, wherein, when expanded, the tubing has an inner diameter of from about 5 mil to about 600 mil.

16. The peelable heat-shrink tubing of any one of claims 10-15, wherein the tubing has a peelability rate of greater than 70%.

17. The peelable heat-shrink tubing of any preceding claim, wherein the tubing has a maximum shrink ratio of from 20% to 45%.

18. The peelable heat-shrink tubing of any preceding claim, wherein the peelable heatshrink tubing has a crystallinity of less than 10% by volume.

19. The peelable heat-shrink tubing of any preceding claim, wherein the peelable heatshrink tubing has a birefringence of from -0.09 to less than 0.00 or greater than 0.00.

20. The peelable heat-shrink tubing of any preceding claim, wherein the peelable heatshrink tubing is clear, translucent, or colored.

21. A medical device comprising the tubing of any preceding claim.