Álcool polivinil (PVA) para filmes de conservação de alimentos

Polyvinyl alcohol (PVA) intended for food preservation films is not a single-compound commodity but a family of semi-crystalline vinyl polymers obtained through controlled alcoholysis of polyvinyl acetate. The proportion of residual acetate groups defines the degree of hydrolysis (DH), and commercial models are typically designated by a four-digit code in which the first two digits indicate the approximate DH and the last two digits represent the 4 wt% solution viscosity at 20 °C (in mPa·s). For solvent-cast or blown-film food barriers, grades such as PVA 1799 (DH ≥ 99 %) and PVA 1788 (DH 87–89 %) dominate production schedules. The 99 % hydrolysed variant delivers the lowest oxygen permeability—typically 0.5–1.5 cm³·µm·m⁻²·day⁻¹·atm⁻¹ at 23 °C and 0 % RH—but requires melt processing with a plasticiser package and extremely tight moisture control, while the partially hydrolysed grade remains cold-water-soluble and is therefore applied via aqueous casting for edible sachets and single-dose soluble packaging where the film intentionally dissolves during food preparation. A further model, PVA 0588 (DH 86–89 %, viscosity 5.0–6.5 mPa·s), is formulated for rapid dissolution below 10 °C, broadening its use in refrigerated food-contact scenarios.

How Does Oxygen Transmission Rate Compare Under Realistic Shelf-Life Humidity Profiles?

The oxygen barrier of PVA is intrinsically moisture-dependent, and comparison with co-extruded polyamide or EVOH structures must be performed at multiple relative humidity (RH) setpoints rather than a single dry-state figure. Measurements under ASTM D3985 at 23 °C show that an unplasticised PVA 1799 film of 30 µm thickness yields an oxygen transmission rate (OTR) of 0.8–1.2 cm³·m⁻²·day⁻¹·atm⁻¹ at 0 % RH, equivalent to a permeability coefficient near 0.04 cm³·mm·m⁻²·day⁻¹·atm⁻¹. When the RH is raised to 50 %, OTR escalates to 4–8 cm³·m⁻²·day⁻¹·atm⁻¹ due to plasticisation of the amorphous phase. By 75 % RH, the value can exceed 20 cm³·m⁻²·day⁻¹·atm⁻¹, making monolayer PVA unsuitable for high-water-activity foods unless laminated between moisture-impermeable skins. In contrast, an EVOH (38 mol% ethylene) film of equal gauge commonly registers OTR 0.5–1.0 at 65 % RH, whereas PVA already loses barrier integrity at that humidity if not protected. This asymmetrical humidity response explains why PVA is rarely employed as a mono-material flexible pouch for ambient-stored meat; instead it is positioned as a coated or interlayer oxygen scavenger in retort laminates where the surrounding PP or PE layers shield it from moisture ingress during retort and subsequent storage.

Oxygen and water vapour transmission values for single-layer films (23 °C, 30 µm nominal thickness)

Material	OTR at 0 % RH (ASTM D3985)	OTR at 65 % RH	WVTR at 90 % RH (ASTM F1249)
PVA 1799 (plasticised)	0.8–1.2	15–25	380–550 g·m⁻²·day⁻¹
EVOH L171 (Kuraray)	0.4–0.8	1.5–3.0	20–35 g·m⁻²·day⁻¹
PVdC (vinylidene chloride copolymer)	2.0–4.0	2.5–5.0	3–6 g·m⁻²·day⁻¹
PLA (polylactic acid, amorphous)	250–450	300–500	150–250 g·m⁻²·day⁻¹

Because the above data reveal that PVA imparts almost no water vapour barrier, coextrusion die technology—particularly a multi-manifold die with dedicated skin-layer metering pumps—must be tuned to achieve uniform PVA interlayer gauge without rupture. On a Collin E30M blown-film line with a ¾-inch extruder feeding a 1.2 mm annular die gap, processing PVA 1788 with 15 phr glycerol demands a barrel temperature profile flat within 185–195 °C; deviation beyond 205 °C initiates chain scission and gel particle formation, which causes bubble instability and periodic draw resonance.

Cold-Water-Soluble PVA 0588 for Rapid-Dissolve Single-Dose Condiment Sachets

Where the preservation function shifts from long-term barrier to momentary enclosure until intentional dissolution, partially hydrolysed grades replace fully hydrolysed ones. PVA 0588 films cast from a 12 wt% aqueous solution containing 2.5 wt% polyethylene glycol (PEG-400) as internal plasticiser routinely achieve complete disintegration in distilled water at 5 °C within 45–60 seconds when the dry film thickness is held at 35 ± 3 µm. Tensile strength measured under ISO 527-3 at 23 °C and 50 % RH falls between 28–35 MPa, which is adequate to resist puncture during automated form-fill-seal operations on a Volpak SI-280 horizontal sachet machine running at 120 cycles/min. However, published data for long-term storage of oil-based condiments inside PVA-0588 sachets is limited; anecdotal line trials suggest that migration of free fatty acids can accelerate dissolution during storage if the moisture content of the film exceeds 4.5 wt%, necessitating pre-conditioning of the finished sachets at ≤35 % RH and 20 °C.

When PVA Replaces PVdC in Multilayer Meat Packaging, What Adhesive Migration Must Be Controlled?

Substituting PVdC with PVA in thermoformed barrier trays for modified-atmosphere packaging (MAP) of processed meat eliminates chlorinated compound concerns but introduces interfacial adhesion management. Typical tray structures run PP/tie/PVA/tie/LDPE, where the tie layer is a maleic anhydride-grafted polypropylene (MAH-PP) with a graft level of 1.0–1.5 wt% maleic anhydride. At the PP–PVA interface, adhesion strength as measured by T-peel (ASTM F904) must sustain ≥3.0 N/15 mm after pasteurisation at 85 °C for 45 min. Any migration of unreacted MAH or low-molecular-weight oligomers into the food contact side must remain below the specific migration limit (SML) of 10 mg/dm² as specified in EU Regulation 10/2011, Annex I. Production data from a Battenfeld MEZ 1500 co-injection system indicate that the PVA interlayer thickness must be capped at 20–25 µm to prevent delamination during the thermoforming draw step when the preheat temperature exceeds 130 °C. This contrasts sharply with PVdC, which thermally degrades above 120 °C but does not suffer the same draw-induced delamination due to its higher melt extensibility.

Representative PVA grades utilised in food preservation films

Model	Degree of hydrolysis (mol%)	Viscosity 4 % aq. sol. (mPa·s at 20 °C)	Primary application method	Key regulatory reference
PVA 1799	≥ 99.0	25.0–31.0	Melt extrusion (plasticised)	FDA 21 CFR 177.1670; GB 9685-2016
PVA 1788	87.0–89.0	20.0–26.0	Melt extrusion, solution casting	FDA 21 CFR 175.300; EU 10/2011 FCM No. 485
PVA 0588	86.0–89.0	5.0–6.5	Aqueous casting	GB 9685-2016; JHOSPA positive list (Japan)
PVA 2499	≥ 99.0	55.0–67.0	Specialty blow moulding	FDA 21 CFR 177.1670

The differential crystallisation kinetics of PVA grades also affect film clarity, a property monitored for premium transparent packaging. PVA 1799 films extruded with 12 phr sorbitol plasticiser and rapidly cooled on a chill roll at 12 °C can reach a haze value as low as 2.3 % per ASTM D1003 with a 50 µm specimen. However, if the cooling rate is reduced—as occurs when the film gauge rises above 80 µm on a single-chill-roll stack—crystallite dimensions grow and haze can climb to 18–25 %, rendering the film milky. Scrap re-extrusion under these conditions lowers the effective molecular weight, shifts the polydispersity index, and can produce gel counts exceeding 15 particles/kg if filtration through a screen pack finer than 50 µm is omitted. In practice, line operators on Reifenhäuser cast-film lines mitigating regrind inclusion cap regrind at 30 wt% and employ online continuous screw washing cycles every 6 hours to avoid carbonised residue build-up. Beyond film transparency, PVA-based edible films for delicatessen coating require rigorous compliance with microbiological safety. A formulation of 85 wt% PVA 1788 and 15 wt% glycerol, when solution-cast and crosslinked with 0.5 wt% citric acid at 105 °C for 30 minutes, achieves a swell ratio in water of 1.8–2.2, sufficient to maintain film integrity on a sliced roast beef surface for 48 hours under refrigerated display lighting. This crosslinking step, however, must be validated against overall migration limits under EU 10/2011; testing with simulant D1 (ethanol 50 % v/v) for 10 days at 40 °C reveals that uncrosslinked PVA readily exceeds the 10 mg/dm² limit, whereas citric acid-treated films remain compliant below 8 mg/dm². Published data for the effect of such films on lipid oxidation measured via thiobarbituric acid reactive substances (TBARS) in sliced mortadella over a 14-day display period is limited, yet initial trials suggest that the oxygen barrier, once the film absorbs surface moisture and plasticises, is so degraded that no meaningful oxidative protection is conferred compared to an uncoated control. Thus the main function becomes moisture retention on the meat surface rather than active oxygen exclusion. Biodegradation credentials are often referenced in product literature; however, the extent and speed of PVA mineralisation in food-waste composting streams must be scrutinised against EN 13432. Under the controlled aerobic conditions of ISO 14855-1 at 58 °C, a 25 µm PVA 1788 film can achieve 60–70 % mineralisation within 45 days when inoculated with acclimated compost containing specific polyvinyl alcohol-degrading bacteria (Pseudomonas sp. and Sphingopyxis sp.). Yet the same film tested in a mesophilic home composting environment (ambient temperature, 20–30 °C) often results in less than 30 % mineralisation after 90 days, a disparity that prevents broad “home compostable” certification. In contrast, starch-based blown films filled with 20 wt% glycerol routinely meet the 90 % mineralisation requirement within 90 days under home conditions, though their oxygen barrier is up to 100× poorer than dry PVA. Consequently, PVA’s role in compostable packaging is constrained to industrial organic waste streams where consistent thermophilic conditions are guaranteed; it is not a direct replacement for soluble starch films in ambient composting schemes. Where PVA appears as an internal bag for dry soup powders, the dissolution kinetics must not interfere with the food’s rehydration. A water-soluble PVA 0588 pouch containing 20 g of powdered tomato soup, when submerged in water at 95 °C in a 1-litre vessel with gentle agitation, must release its contents within 30 seconds without residue visible to the naked eye (≤0.2 mg insoluble matter per litre as per a simplified hot-water extraction). To achieve this, the film is microperforated with 0.3 mm needle punches or cast with a thickness gradient; however, microperforation introduces a pathway for moisture ingress during storage, so the outer carton must include a desiccant sachet maintaining headspace RH below 25 % at 25 °C. This trade-off exemplifies a fundamental design conflict unique to PVA: the very solubility that enables convenience also demands meticulous supply-chain humidity management, a constraint not shared with melt-blown compartmented trays of polyhydroxyalkanoate (PHA) where barrier function relies on bulk hydrophobicity.