EXCEVAL RS-1717

EXCEVAL RS-1717 is an ethylene-vinyl alcohol copolymer grade with a nominal ethylene content of 32 mol%, supplied as pellets for coextruded barrier layers in rigid sheet, blown film, cast film, and multilayer packaging structures. The grade is specified as an internal oxygen barrier layer rather than as a structural resin. Table 1 lists typical values obtained under standard laboratory conditioning; the values are not specification limits and should be verified against lot-specific certificates of analysis.

Oxygen permeability in ethylene-vinyl alcohol copolymers is not a single material constant. The permeation coefficient increases with moisture uptake because water plasticises the hydroxyl-bearing amorphous regions. Between 0% RH and 85% RH, the oxygen permeation coefficient of a 32 mol% EVOH grade typically rises by one to two orders of magnitude. Consequently, the barrier performance of RS-1717 in a finished package must be evaluated in relation to moisture ingress through adjacent polyolefin skins and tie layers, not on the basis of dry-film laboratory values alone.

Why Do Low-Ethylene EVOH Grades Suffer Microcracking in Thermoformed Trays?

Microcracking in thermoformed barrier trays occurs when the EVOH layer is stretched below its practical forming temperature or beyond the draw ratio that the grade can accommodate without discontinuous thinning. With RS-1717, the 32 mol% ethylene content shifts the practical plug-assist thermoforming window to 120°C to 150°C for sheet thicknesses from 0.8 mm to 1.5 mm. On a production pressure former with clamp force of 80 t, upper and lower oven zone settings of 350°C, and a forming-cycle time of 4 s, the grade remains processable at draw ratios up to approximately 2.5:1. Trial data from a 1,250 mm wide multilayer die showed that edge bead above 10 mm produced barrier-layer thinning below 3 μm at the corner shoulder, resulting in elevated oxygen transmission when tested after thermoforming. This failure mode is distinct from thermal degradation and is controlled by adjusting die-lip profiles and edge bead temperatures rather than by increasing EVOH layer thickness alone.

Tie-resin selection controls interlayer adhesion in these structures. Maleic anhydride-functionalised polypropylene with a melt flow rate of 1.0 g/10 min to 3.0 g/10 min at 190°C is commonly combined with RS-1717 in PP-based trays. Heat-seal peel adhesion above 8 N/15 mm, tested according to ASTM F904, indicates adequate tie-layer bonding. When regrind content exceeds 20 wt% in the tie layer, adhesion can fall below 4 N/15 mm, producing intermittent delamination along trimmed tray flanges.

Barrel Residence-Time Limits and Purging Incompatibilities

RS-1717 must be dried to 0.01% (100 ppm) moisture or lower before melt processing. Desiccant-bed drying at 80°C to 90°C for 4 h with a dew point of −40°C or lower is standard. Drying longer than 8 h at temperatures above 100°C may induce pellet yellowing and should be avoided. The recommended melt temperature measured at the die is 210°C to 240°C. Barrel zones above 250°C promote crosslinking and gel-particle formation. Maximum residence time from feed throat to die should not exceed 10 min at 240°C. Screw geometry is a processing boundary: single-flight polyolefin screws with L/D of 24:1 to 32:1 and a compression ratio of 3.0:1 to 3.5:1 are preferred. Avoid reverse-flow check rings with narrow clearances that can hold stagnant resin. Purging should be performed with medium-density polyethylene or high-density polyethylene. Polyvinyl chloride, acetal, and ionomer purging compounds are incompatible because acidic residues can catalyse cleavage of vinyl alcohol segments and generate gel particles.

Five-layer polypropylene sheet coextrusion lines typically place RS-1717 between two maleic anhydride-functionalised PP tie layers. The target barrier layer thickness is 5 μm to 15 μm. Below 5 μm, thickness variation across dies wider than 1,200 mm becomes a controlling risk for oxygen leakage at fold corners. Melt pumps with a capacity of 10 cm³/rev and speed variability below 0.1% are used to maintain layer uniformity. In cast-film lines running at 150 m/min, the internal barrier layer is quenched at 20°C on a chill roll. If the chill-roll surface temperature falls below the local dew point, condensation on the film edge can raise local moisture content and degrade the barrier layer before lamination.

When 32 mol% Ethylene Content Replaces 38 mol% in Retortable Barrier Structures

In retortable structures subjected to 121°C for 30 min, replacing a 38 mol% EVOH with RS-1717 lowers dry-state oxygen ingress but increases sensitivity to moisture loading through the sealant. The oxygen permeation coefficient after conditioning at 23°C and 65% RH is approximately 0.4 cm³·mm/m²·day·atm for RS-1717, compared with a typical value nearer 0.9 cm³·mm/m²·day·atm for a common 38 mol% EVOH under the same test. However, after steam retort exposure, the coefficient of RS-1717 does not recover until the sealant layer has reduced its internal moisture load below 0.1%. In a structure using a 70 μm cast polypropylene sealant, recovery can require 7 days at 23°C and 50% RH. With a 150 μm sealant, recovery can extend beyond 14 days. This behaviour limits the use of RS-1717 in direct hot-water boil-in bags without a polyolefin moisture barrier. Published package-permeation data for this exact grade under high-humidity retort are limited; the coeffective values above are raw material coefficients rather than finished package transmission rates.

Humidity-Dependent Barrier Coefficients from Standardized Film Conditioning

Table 2 compares typical oxygen permeation coefficients for RS-1717 with three alternative barrier polymers after equilibrium conditioning. The values are drawn from published laboratory film data and are not direct package permeability values. Layer structure, tie-resin compatibility, orientation, and heat history all change final package transmission rates.

PVdC maintains a relatively flat barrier response over the same humidity range, but RS-1717 provides lower oxygen permeation at 0% RH by approximately two orders of magnitude. Polyamide 6 shows an oxygen transmission coefficient at 65% RH that can be 20× to 80× higher than RS-1717 depending on grade and crystallinity. This difference explains why an EVOH oxygen barrier layer in multilayer packaging is usually 5 μm to 15 μm thick, while an equivalent polyamide 6 oxygen barrier layer often requires a thickness above 100 μm.

Compared with a 27 mol% EVOH grade, RS-1717 exhibits a wider processing window and improved thermoformability because the higher ethylene content reduces the stiffness of the hydrogen-bonded network. Compared with a 38 mol% EVOH grade, it provides lower oxygen permeation under dry conditions but requires more aggressive moisture management in high-humidity service. Compared with PVdC, RS-1717 avoids chloride-related disposal concerns but loses barrier advantage above 60% RH unless it is fully enclosed by polyolefin moisture-shielding layers.

Food-contact compliance is established under FDA 21 CFR 177.1360 for ethylene-vinyl alcohol copolymers and under EU Regulation (EU) No 10/2011 when the final multilayer structure meets the applicable overall migration and specific migration limits for ethylene glycol and vinyl alcohol oligomers. REACH, RoHS, and California Proposition 65 obligations apply to the finished article, not to the resin alone, because migration behaviour depends on tie-resin coverage, alcohol content, and processing history. The grade is not recommended for direct contact with ethanol above 20% by volume because high alcohol solubility plasticises the barrier and can increase monomer migration beyond test limits.

In aseptic paperboard packaging, RS-1717 is inserted between polyolefin tie layers at 6 μm to 10 μm in laminated board structures. Extrusion lamination at 150°C to 180°C is below the degradation threshold, but incoming paperboard moisture content must be below 8%. Higher paperboard moisture generates steam at the polymer-paper interface, causing pinholing and local barrier failure. On pilot lines with a 600 mm slot die, the EVOH layer temperature at the nip was maintained at 170°C ± 5°C. Excursions above 180°C for more than 5 min produced gel particles larger than 200 μm, which were visible in the finished laminate as raised specks and represented local oxygen transmission defects.