EVOH vs PVDC Barrier Resins: Oxygen Transmission & Humidity Guide
In barrier flexible packaging, preventing atmospheric oxygen infiltration is the single most critical factor in inhibiting lipid oxidation, aerobic bacterial growth, and vitamin degradation. Two polymer resins have historically served as the benchmark for high-barrier co-extrusion: Ethylene Vinyl Alcohol (EVOH) and Polyvinylidene Chloride (PVDC).
While both resins achieve ultra-low oxygen transmission rates (OTR), their molecular chemistry behaves completely differently under real-world ambient conditions. EVOH possesses polar hydroxyl groups that make its gas barrier highly sensitive to relative humidity (RH). Conversely, PVDC maintains an impervious barrier across all humidity levels, but faces mounting regulatory bans across Europe and North America due to its chlorine content.
This technical guide compares the molecular barrier physics, humidity response curves, converting mechanics, and global circular economy compliance of EVOH and PVDC.
1. Quick Engineering Benchmark Matrix: EVOH vs. PVDC
| Engineering Parameter | EVOH (32 mol% Ethylene) | EVOH (44 mol% Ethylene) | PVDC (Saran Coating / Film) |
|---|---|---|---|
| Chemical Composition | Poly[(ethylene)-co-(vinyl alcohol)] | Poly[(ethylene)-co-(vinyl alcohol)] | Poly(vinylidene chloride-co-vinyl chloride) |
| OTR @ 23°C, 0% RH (cc·20µm / m²·day·atm) |
0.3 to 0.7 (Exceptional) | 1.2 to 2.0 | 1.5 to 3.0 |
| OTR @ 23°C, 85% RH (cc·20µm / m²·day·atm) |
3.5 to 8.0 (Degrades without outer moisture barrier) | 2.5 to 4.5 (More moisture stable) | 1.5 to 3.0 (Completely unaffected by humidity) |
| Water Vapor Transmission (WVTR) (g·20µm / m²·day @ 38°C, 90% RH) |
15 to 35 (Poor moisture barrier) | 12 to 25 | 0.8 to 1.8 (Dual O₂ + H₂O barrier) |
| Halogen / Chlorine Content | 100% Chlorine-Free | 100% Chlorine-Free | Contains ~73% Chlorine by weight |
| Recyclability & Incineration | Recyclable in PE/PP streams (< 5% w/w) | Recyclable in PE/PP streams (< 5% w/w) | Produces HCl and dioxins during incineration |
| EU PPWR & Retailer Blacklists | Approved & Preferred | Approved & Preferred | Blacklisted by major EU/US grocery chains |
| Typical Film Architecture | Symmetrical 7-to-9 layer co-extrusion | Symmetrical 7-to-9 layer co-extrusion | Emulsion surface coating on PET/BOPP |
| Tie-Layer Requirement | Maleic Anhydride-Grafted PE/PP | Maleic Anhydride-Grafted PE/PP | Self-adhering or polyurethane primer |
Explore our range of recyclable barrier structures in the Stand-Up Pouches Category and Flat Bottom Bags Category.
2. Molecular Chemistry & The Relative Humidity Curve
The core engineering distinction between EVOH and PVDC lies in how moisture interacts with their polymer backbones.
┌────────────────────────────────────────────────────────────────────────┐
│ OXYGEN BARRIER VS RELATIVE HUMIDITY │
│ │
│ OTR (cc/m²/day) │
│ 10 ┼ │
│ │ ╭── EVOH (32 mol%) │
│ 8 ┼ ╭╯ │
│ │ ╭─╯ │
│ 6 ┼ ╭╯ Rapid loss of │
│ │ ╭─╯ barrier above 75% RH │
│ 4 ┼ ╭╯ │
│ │ ╭──────────────╯ │
│ 2 ┼────────────────────┴───────────────────── PVDC (Constant OTR) │
│ │ EVOH (dry) │
│ 0 ┼──────────────────────────────────────────────────────────── │
│ 0% 25% 50% 75% 100% RH │
└────────────────────────────────────────────────────────────────────────┘The EVOH Humidity Paradox
EVOH’s gas barrier arises from dense intra- and intermolecular hydrogen bonding between polar hydroxyl ($-OH$) groups along the vinyl alcohol segments. In dry conditions (0% RH), this crystal lattice is so tight that $O_2$ molecules cannot permeate through.
However, water molecules are also small and polar. When relative humidity exceeds 70%, water penetrates the amorphous regions of EVOH, breaking the hydrogen bonds and acting as a plasticizer. This increases polymer chain mobility, causing free volume to expand and OTR to spike by a factor of 10x to 20x.
The Engineering Solution: Symmetric Co-extrusion Sandwich Packaging engineers shield the EVOH core by sandwiching it between thick hydrophobic polyolefin layers:
PE (Sealant) / Tie Layer / EVOH (Core Barrier) / Tie Layer / PE (Outer Protective)The outer polyethylene layers prevent ambient water vapor from reaching the EVOH core, maintaining the internal micro-climate below 60% RH. For deep insights on monomaterial engineering, see our guide on Recyclable MDO-PE Flexible Films.
PVDC: The Impervious Halogen Grid
Polyvinylidene chloride consists of repeating $(-CH_2-CCl_2-)$ units. The two electronegative chlorine atoms on alternating carbon atoms create a sterically hindered, symmetrical structure that crystallizes into an extremely dense barrier.
Because chlorine atoms are non-polar and hydrophobic, water vapor cannot penetrate the lattice. As a result, PVDC provides both an exceptional oxygen barrier and an exceptional moisture barrier simultaneously, regardless of whether the packaging is submerged in liquid or exposed to 99% RH cold-room storage.
3. Environmental Regulations & Circular Economy (EU PPWR)
While PVDC has superior all-weather barrier physics, regulatory pressures have dramatically accelerated its phase-out across international markets:
1. Chlorine Incineration & Dioxin Formation
When municipal solid waste containing PVDC is incinerated, chlorinated polymers break down into corrosive hydrochloric acid ($HCl$) gas and highly toxic polychlorinated dibenzodioxins (PCDDs). Facility scrubbers incur severe wear, and European waste directives penalize halogenated packaging materials.
2. Contamination of Recycling Streams
In mechanical recycling plants, PVDC degrades at typical polyolefin processing temperatures (180°C to 230°C). As PVDC chars and releases $HCl$, it causes severe discoloration, odor, and polymer degradation in recycled polyethylene (rPE) and polypropylene (rPP) pellets. Under the EU Packaging and Packaging Waste Regulation (PPWR), packaging containing PVDC is classified as non-recyclable, triggering maximum eco-modulation penalty fees.
3. Retailer Restrictions
Global consumer brands and European supermarket chains have universally mandated PVDC elimination from primary packaging, replacing it with EVOH, AlOx/SiOx Ceramic Coatings, or high-barrier metallized films.
4. Multi-Layer Co-Extrusion Engineering: Specifying EVOH
When specifying EVOH-based flexible barrier films, engineers must configure three critical parameters:
1. Ethylene Molar Percentage (mol%)
EVOH grades are classified by ethylene content, ranging from 27 mol% to 48 mol%:
- Low Ethylene (29–32 mol%): Highest gas barrier under dry conditions, but most sensitive to moisture and harder to thermoform. Ideal for shelf-stable retort trays and custom stand-up pouches.
- High Ethylene (38–44 mol%): Lower barrier in dry conditions, but significantly higher moisture tolerance and flexibility. Ideal for thermoformed vacuum skin trays and high-speed VFFS rollstock.
2. Tie-Layer Functionalization
Because EVOH is polar and polyolefins (PE, PP) are non-polar, they will not adhere to each other without functionalized tie-resins. Maleic anhydride-grafted polymers (MAH-g-PE) are co-extruded on both sides of the EVOH layer. Inadequate tie-layer thickness (< 3µm) or poor melt temperature control leads to catastrophic interlayer delamination during transport or drop impact.
3. Layer Ratio Rules for CEFLEX Recyclability
Under CEFLEX and APR design guides, polyolefin packaging can contain up to 5% EVOH by weight while remaining fully compatible with circular mechanical recycling streams. For a typical 100µm pouch film, a 3µm to 5µm EVOH core provides enterprise-grade oxygen protection while staying well below the 5% regulatory ceiling.
5. Decision Matrix for Processors & Brands
┌─────────────────────────────────────────────────────────────────────────┐
│ BARRIER RESIN SELECTION DECISION FRAMEWORK │
└─────────────────────────────────────────────────────────────────────────┘
│
Are you exporting to the European Union,
North America, or Australia?
│
┌───────────────┴───────────────┐
YES NO
│ │
Specify EVOH with Is the product
Hydrophobic PE/PP Skin submerged in liquid
│ under high humidity?
┌───────┴───────┐ │
Retort / Hot-Fill Ambient Pack ┌───────┴───────┐
│ │ YES NO
Use 32 mol% Use 38-44 mol% │ │
with R-CPP with LLDPE PVDC Permitted EVOH Preferred- Fresh Meat, Poultry & Cheese: Specify 9-layer blown EVOH films with anti-fog additives. Pair with our Vacuum Skin Packaging vs MAP Guide.
- Specialty Coffee & Dry Whole Beans: Use EVOH co-extrusions paired with One-Way Degassing Valves.
- Pet Food Kibble & Treats: Large bag formats benefit from EVOH barrier layers that prevent oil migration and aroma loss.
6. Frequently Asked Questions (FAQ)
Does EVOH replace aluminum foil entirely?
For products with shelf-life targets of 12 to 18 months (such as nuts, pet treats, and ground coffee), properly structured EVOH laminates deliver barrier performance comparable to foil while allowing product visibility and in-line metal detection. For shelf lives exceeding 24 months in tropical regions (38°C / 90% RH), aluminum foil remains the gold standard.
Can EVOH withstand high-pressure retort sterilization at 121°C?
Yes, when protected by Cast Polypropylene (CPP) sealant layers and specialized retort tie-resins. While EVOH temporarily absorbs steam during autoclaving, it releases moisture and recovers its original barrier within 48 to 72 hours of ambient cooling.
How do I verify EVOH barrier layer integrity before packaging production?
Laboratories use optical cross-section microscopy (microtome slicing with polarized light) to verify continuous EVOH thickness, combined with MOCON OTR coulometric testing per ASTM D3985.
For technical film specifications, barrier modeling, or sample testing, contact CraftPack Global’s engineering specialists today.