WO1992018173A1

WO1992018173A1 - Medical tubing

Info

Publication number: WO1992018173A1
Application number: PCT/EP1992/000871
Authority: WO
Inventors: Norbert Rohse; Daniel Eugene Nerinckx
Original assignee: Exxon Chemical Patents Inc.
Priority date: 1991-04-17
Filing date: 1992-04-16
Publication date: 1992-10-29
Also published as: GB9108242D0

Abstract

Medical tubing is made from a polyolefin having a density of from 0.900 to 0.880 and a melt index from 1 to 12 to provide a processable material resistant to collapse upon kinking which can be disposed in an environmentally friendly manner.

Description

MEDICAL TUBING

Field of invention

The invention relates to medical tubing used especially but not exclusively for intravenous sets, cathethers and breathing tubes.

Background of invention

Medical tubing currently is principally made of PVC. Whilst it can be kinked tightly without collapse of the internal tube passage, it may absorb drugs on its internal surface so varying dosage. It is difficult to dispose of PVC materials in an environmentally friendly manner.

DPE has been used but it collapses easily when kinked. LLDPE is more flexible but it is difficult to extrude at commercially acceptable production rates.

US 3865776 describes a complex block copolymer blend which is kink resistant but costly.

It is the aim of the invention to provide medical tubing which possesses a reasonable balance of desirable properties such as low cost, kink-resistance (to avoid tube collapse) , toxicity, processability, non-adsorbence of drugs and ease of disposal so that it can replace PVC tubing.

*.* i Summary of Invention

According to the invention there is provided medical tubing of a polyolefin having a density of from 0.900 to 0.880 and a melt index of from 1 to 12. Above 0.900 the tube will collapse too easily upon kinking; below 0.880 the tube will have non-slip, sticky surfaces. Below a melt index of one the material will not extrude easily; above a melt index of 12 melt strength is insufficient.

Preferably the polyolefin has an Mw/Mn of from 1.5 to 3.5 and especially from 1.7 to 3.0. Surprisingly such materials may be extruded at a sufficiently high speed in spite of the relatively narrow molecular weight distribution, because the extrusion speed can be increased manifold by the use hydrofluorocarbons as processing aids. It is believed that extrusion speeds of 50 meter per minute can be reached. Whilst such processing aids where known for LLDPE, it was not foreseeable that such a drastic increase in processability could be obtained with materials which if anything have a more narrow molecular weight distribution than LLDPE.

The tubing may have a variety of dimensions. For intravenous sets preferably the tubing has a smooth interior and exterior and a wall thickness of from 0.4 to 2 mm, preferably 0.5 to 1.5 mm and an overall diameter of from 3 to 15 mm preferably from 4 to 12 mm.

The polyolefin may be made by any suitable process and catalyst system which gives the high level of comonomer incorporation and so the low density. The process may be a gas-phase process, an elevated pressure, solvent free process or a solution or slurry process. Preferably the catalyst system incorporates a transition metal component in the form of a metallocene and a cocatalyst component which is bulky, such as alumoxane.

The catalyst system may include as metallocene a compound of the general formula

R Z L M

wherein M is a transition metal of group IV B of the periodic table, wherein R is a ligand having a conjugated electron bonded to M;

wherein L is a leaving group bonded to M; and

wherein Z represent one or more further conjugated ligand and/or a amionic leaving groups.

R and optionally Z may be or include a substituted or unsubstituted cycloalkadienyl group such as cyclopentadiene or tetrahydro-indenyl. Where more than one such cycloalkadienyl group is present, the groups may be bridged (See Exxon EP 129368) .

L and optionally Z may be or include an aryl group, alkyl group, an aralkyl group, a halogen atom, a hetero atom containing ligand containing an oxygen sulfur, nitrogen or phasphorus atom; these groups may be connected by single or multiple bonds to M; optionally these groups may be linked to groups R or Z. The other catalyst component, generally alumoxane, may be prepared in a pre-reaction and then introduced into the polymerisation system but may also be formed wholly or partly in situ by reaction of water and a trialkylaluminum, preferably trimethylaluminum.

The Al/transition metal mol ratio may be from 10 to 5000, preferably from 50 to 1000.

Depending on the process and catalsyt system selected low molecular weight species may be present which can be extracted with hexane and are undesirable. The polyolefin has a hexane extractable portion which varies with density and can be minimised by using higher densities. The materials do not extract with the aqueous fluids generally conveyed through medical tubing. The material may be multimodel to enhance extrudability (See EP 128 045) . Low molecular weight fractions should be kept to a minimum.

The polyolefin may be derived from ethylene or one or more comonomers. Butene-1 may be the comonomer, it may be present at from 15 to 17 wt% in the polymer. Hexene-1 may also be used, preferably at from 21 to 32 wt%. It is also possible to use propylene suitably at from 19 to 28 wt%. The molar proportion for comonomers is from 5 to 25 mol % preferably from 8 to 20 mol % or especially up to 17 mol % for most higher alpha-olefin comonomers having from 3 to 12 preferably from 4 to 10 carbonatoms.

Examples

A VLDPE material was prepared as follows by the general method described in EP 260999. The VLDPE material had the following characteristics :

Melt index 3.8

Mn 36250

Mw 77750

Mw/Mn 2.1

Density 0.885

Comonomer butene-1

Com. wt% 19.3

The materials were extruded on conventional machinery. As a processing additive 4 wt% of Viton A (Registered Trade Mark) may be used for example. The tubes obtained had the dimensions shown in Table 1.

Toxicity tests showed low toxicity.

The tube of the VLDPE was investigated for the presence of leachable toxic substances by means of the Growth Inhibition Test. Extracts of test materials were added to cell cultures. Reduced growth of cell cultures in the presence of toxic substances is determined by comparing the protein content of the cell cultures with protein content of untreated control cultures after 72 h incubation.

The tube was filled with the cell culture medium (DMEM-FCS) or organic solvent dimethylsulfoxide (DMSO) , respectively, and were extracted for 24 h at 37°C. The extracts (DMSO extracts diluted 1:100) were incubated with L 929 cell cultures for 72 h.

The results showed that the VLDPE material does not release substances in cytotoxic concentrations. Kinking and tube collapse were tested, Table I gives comparative data for PVC and EVA.

Tubes of 12 cm length were clamped between the grips of a tensile tester (Zwick) . Initial grip distance was 10 cm. Clamps were moved towards each other with a constant speed of 50 mm/min thus forcing the tube to bend and to close off at a certain distance. The distance-load curve was recorded. Typically the load increased initially, reaching an equilibrium, and then leading to a further increase in load shortly before closing off of the tube cross-section, with a final decrease after closing off of the tube..

TABLE 1

INTERNAL OUTSIDE WEIGHT KINKING DIAMETER DIAMETER g/m TEST RESULT

VLDPE 2.5 4.2 7.7 78.3

Plasticized 3.2 4.64 11.4 79.6 PVC

EVA 3.1 4.65 8.8 71.04

MI 7,

28 wt% VA

The polymers used are free of appreciable levels of chlorine and can be disposed of without harming the environment, for example by burning.

Claims

1. Medical tubing of a polyolefin having a density of from 0.900 to 0.880 and a melt index of from 1 to 12.

2. Tube according to claim 1 in which the polyolefin has an Mw/Mn of from 1.5 to 3.5.

3. Tube according to claim 1 or claim 2 having a smooth interior and exterior and a wall thickness of from 0.4 to 4 mm and an overall diameter of from 3 to 15 mm.