Non-sustainable single-use plastics used for food packaging needs to be phased out. Films made from cellulose nanofibrils (CNFs) are suitable candidates for biodegradable and recyclable packaging ...materials as they exhibit good mechanical properties, excellent oxygen barrier properties and high transparency. Yet, their poor water vapour barrier properties have been a major hindrance in their commercialisation. Here, we describe the preparation of 25 μm thick CNF films with significantly improved water vapour barrier properties after deposition of ultrathin polymeric and metallic coatings, parylene C and aluminium, respectively. When first adding a 40 nm aluminium layer followed by an 80 nm parylene layer, i.e. with a combined thickness of less than one percent of the CNF film, a water vapour transmission rate of 2.8 g m−2 d−1 was achieved at 38 °C and 90 % RH, surpassing a 25 μm polypropylene film (4–12 g m−2 d−1). This is an improvement of more than 700 times compared to uncoated CNF films, under some of the harshest possible conditions a packaging material will need to endure in commercial use. The layers showed a good and even coverage, as assessed by atomic force microscopy, and the parylene-coated surfaces were hydrophobic with a contact angle of 110°, providing good water repellency.
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A new vapour intrusion contaminant transport model was designed specifically to allow an assessment of the impact of a hydrocarbon fuel spill on air quality in cold region buildings. The model is ...applied to a recent situation in Antarctica, where a diesel spill impacted the construction of a new building. For the first time, this model allows consideration of the diffusive resistance of different vapour barrier to the transport of hydrocarbons into the building and an assessment of the effectiveness of different products. Site specific indoor air criteria are derived. Five scenarios are modelled at field temperatures: (1) build on current contaminated site; (2) excavate contaminated soil, backfill with clean soil and assess impact of residual contamination; (3) excavate and backfill with remediated (biopile) soil; (4) backfill with remediated soil and assess impact of residual contamination; (5) backfill with remediated soil and assess impact of a potential future fuel spill. Two different vapour barriers, a co-extruded ethylene vinyl alcohol (EVOH) geomembrane (VB1) and a linear low-density (LLDPE) geomembrane (VB2), are investigated for each scenario and compared to a base case with no vapour barrier, providing quantifiable evidence of the benefit of installing an engineered vapour barrier Contaminant concentrations were below regulatory limits for Scenarios (2–5) with VB1 and air exchange in the building. For all scenarios, the EVOH geomembrane (VB1) was consistently superior at reducing vapour transport into the building indoor air space over the LLDPE geomembrane (VB2) and no vapour barrier. The risk mitigation measures developed for this contaminated Antarctic site may be relevant for other buildings in cold regions.
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•First vapour intrusion model to include a vapour barrier and evaluate performance.•Model specific to cold climate, field temperatures and seasonal groundwater.•Investigates reuse of remediated soil as backfill in an Antarctic building application.•Indoor air quality is managed by a specific vapour barrier and air exchange.•Co-extruded EVOH vapour barrier was superior at protecting indoor air quality.
Diffusion of volatile organic compounds (VOCs) through a 4.1 mm elastomeric bituminous geomembrane (BGM) is investigated using a dilute aqueous solution of four aromatic hydrocarbons: benzene, ...toluene, ethylbenzene, and xylenes (BTEX). Due to the very different diffusion characteristics of the BGM components, double-compartment diffusion experiments are separately conducted on the bituminous and non-bituminous components of the BGM to assess their diffusion parameters. A two-layer computer model is developed to obtain the diffusion parameters of the BGM that correlates with the 890-day laboratory diffusion test data obtained for the multicomponent BGM and allows the modelling of transient diffusion. Using contaminant transport modelling, the BGMs performance as a diffusive barrier for different applications is evaluated and compared to different polymeric geomembranes (GMBs). It is shown that using BGM as part of the cover system for a hydrocarbon-contaminated soil landfill or as a vapour barrier below concrete building foundations can decrease the BTEX mass flux through the cover system and the peak concentration of contaminant in the indoor air compared to monolayer polymeric GMBs. It is also predicted to reduce the impact on the aquifer when modelled as a part of the composite liner without holes for a hypothetical solid waste landfill.
•Establishes the methodology to examine the diffusion of contaminants through multicomponent BGMs.•Assesses the diffusion parameters of different voltaile organic compounds for BGMs.•Compares the effectiveness of BGMs as diffusive barriers to aromatic hydrocarbons with different polymeric geomembranes.
•Bilayer coating to achieve bifunctional paper for packaging.•Synergistic interaction to enhance each function.•Confocal laser scanning microscope to identify the presence of each coating layer and ...understand its role.
In order to overcome the deficiencies of single layer coating, bilayer coated papers were prepared by two separate coating procedures using various combinations of proteins or polysaccharides with beeswax. Among those combinations, chitosan–beeswax bilayer coated paper showed the best water vapour barrier property. It was observed that as the concentration of chitosan solution increased from 1.0 to 3.0wt%, its water vapour transport rate (WVTR) decreased from 171.6 to 52.8g/m2/d but using reduced beeswax coating weight (from 10.1 to 4.9g/m2). It also displayed an enhanced performance of grease resistance. Scanning electron microscopy (SEM) showed that beeswax layer was fitted to chitosan layer so closely that these two layers are indistinguishable. Confocal laser scanning microscope (CLSM) further confirmed the existence of an integrated chitosan film between beeswax layer and paper base and a thin composite layer consisting of chitosan and beeswax.
Effects of high pressure treatment (0, 200 and 400 MPa) on water vapour barrier, microstructure, thermal, and mechanical properties of poly (lactic acid) (PLA)/Ag nanocomposite films were ...investigated. The migration behavior of nano-Ag from the nanocomposite films in the presence of 50% (
/
) ethanol as a food simulant was also studied. The water vapour barrier properties increased as pressure was applied to film-forming solutions. High pressure treatment enhanced the mutual effect between PLA and nanoparticles, leading to a more compact network structure in PLA/Ag nanocomposite films. Furthermore, PLA/Ag nanocomposite films treated by high pressure were significantly affected by microstructure, thermal, and mechanical properties when, compared with untreated samples. High pressure treatment at 200 to 400 MPa significantly (
< 0.05) reduced the migration of nano-Ag from the films. Overall, high pressure treatment on film-forming solutions showed potential in improving the functional properties of nanocomposite films, especially in relation to water vapour barrier properties.
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•Carboxymethyl and hydroxypropyl xylans (CMX and HPX) were thoroughly characterized.•Self-supporting films were formed from CMX and HPX without plasticizer addition.•Films from CMX ...and HPX with glycerol addition showed a lower water vapour permeability.•Film from CMX with 25% glycerol addition showed an exceptionably good oxygen barrier.•Overall, strength and barrier properties were better for CMX films than for HPX films.
In this work, the successful derivatization of a beechwood xylan (BX) by carboxymethylation and hydroxypropylation was achieved aimed to produce bio-based films. Carboxymethyl xylan (CMX) and hydroxypropyl xylan (HPX) with a substitution degree of 0.3 and 1.1, respectively, as determined by 1H NMR, were synthesised. The xylan’s characterization by thermogravimetric analysis showed that HPX is thermally more stable than CMX or BX. The ability of the xylan derivatives to form films and the effect of the glycerol addition on the films performance were evaluated. Tensile strength, Young’s modulus and water vapour permeability of self-supporting CMX films were higher and the elongation at break lower than those of the corresponding HPX films. The water vapour barrier properties of CMX and HPX films were improved with 10% glycerol addition. Oxygen barrier property was exceptionably good for a CMX film plasticized with 25% of glycerol (oxygen permeability of 0.5cm3μmm−2d−1kPa−1) while higher oxygen permeability values were obtained for HPX films. Favourable characteristics were found that may enable the use of these films in, e.g., coatings for packaging.
An in situ experiment on a full-scale timber frame test building was carried out to study the hygrothermal performance of wood-hemp composite insulation in timber frame wall panels with and without a ...vapour barrier. The heat transfer properties and the likelihood of mould growth and condensation in the panels were compared. Step changes in the internal relative humidity were performed to explore the effects of high, normal and low internal moisture loads on the wall panels. No significant difference in the average equivalent thermal transmittance (U-values) between the panels with and without a vapour barrier was observed. The average equivalent U-values of the panels were close to the U-values calculated from the manufacturers’ declared thermal conductivity values of the insulation. The likelihood of condensation was higher at the interface of the wood-hemp insulation and the oriented strand board (OSB) in the panel without a vapour barrier. In terms of the parametric assessment of the mould germination potential, the relative humidity, the temperature and the exposure conditions in the insulation-OSB interfaces of the panel without a vapour barrier were found to be more favourable to the germination of mould spores. Nonetheless, when the insulations were dismantled, no mould was visually detected.
•Hygrothermal performance of wood-hemp insulation is assessed in a test cell.•U-values of the wall panels with and without a vapour barrier are measured.•U-values of the panels are lower than the calculated U-values.•Moisture response is faster if the lining of the vapour open panel has low μ value.•In situ observation does not support the prediction of interstitial mould growth.
The effect of hyperbaric storage (HS) on food packaging materials was evaluated. PA/PE, PP/EVOH/PE, PET and PLA pouches filled with hydroethanolic simulant (D1) were stored at 0.1 and 200 MPa for up ...to 35 days and analyzed for optical, structural, mechanical and diffusional properties. HS weakened PLA seals, which easily failed after 7 days releasing the simulant. Both PET and PLA films swelled during HS, reducing PET physical ageing and PLA crystallinity. These structural effects caused PET and PLA mechanical properties to vary during HS, and a slight WVTR increase in PLA. Optical, structural and mechanical properties of multi-material films did not change upon HS. Nevertheless, both PA/PE and PP/EVOH/PE released critical amounts of adhesives after 7 and 35 days under pressure, respectively. Results indicate the critical role of the packaging material of foods intended for HS, and the need for its careful selection in future studies on the topic.
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•The effect of hyperbaric storage (HS, 200 MPa for 35 d) on food packaging was studied.•HS swelled films with simulant, hindering PET ageing and reducing PLA crystallinity.•HS impaired PLA barrier loss but promoted stress-induced seals failure after 7 days.•HS did not affect optical, structural and mechanical properties of multi-material films.•Multi-material films released critical amounts of migrates in the simulant during HS.
Porous membranes find natural application in various fields and industries. Water condensation on membranes can block pores, reduce vapour transmissibility, and diminish the porous membranes' ...performance. This research investigates the rate of water vapour transmission through microporous nylon and nanofibrous Gore-Tex membranes. Testing consisted of placing the membrane at the intersection of two chambers with varied initial humidity conditions. One compartment is initially set to a high (
R
h
=
95
%
)
water vapour concentration and the other low (
R
h
=
<
10
%
)
, with changes in humidity recorded as a function of time. The impact of pore blockage was explored by pre-wetting the membranes with water or interposing glycerine onto the membrane pores before testing. Pore blockage was measured using image analysis for the nylon membrane. The mass flow rate of water vapour (ṁv) diffusing through a porous membrane is proportional to both its area (A) and the difference in vapour concentration across its two faces (
Δ
C
)
, such that
m
˙
v
=
K
A
Δ
C
where K is defined as the moisture diffusion coefficient. Correlations are presented for the variation of K as a function of
Δ
C
. Liquid contamination on the porous membrane has been shown to reduce the moisture diffusion rate through the membrane due to pore blockage and the subsequent reduced open area available for vapour diffusion. Water evaporation from the membrane's surface was observed to add to the mass of vapour diffusing through the membrane. A model was developed to predict the effect of membrane wetting on vapour diffusion and showed good agreement with experimental data.
It is often assumed that reduced heat flux to a ventilated attic reduces the temperature and thereby increases the relative humidity. Consequently, the importance of having a tight air and vapour ...barrier in the ceiling becomes more important with increased insulation. Therefore, in Denmark, the recommendation is to have a tight vapour barrier when re-insulating ceilings against cold ventilated attics to a total of 150-mm insulation material. The recommendation is independent of the insulation material’s hygroscopic properties or the indoor moisture level. The aim of this project was to test the relevance of the recommendation through testing in a full-scale test building (7 × 22 m) with a series of six different ceilings with or without a vapour barrier and variation in the insulation material comprising insulation thickness and its hygroscopic properties. The examination was performed with a controlled indoor climate after an European humidity classes 1–3 and a natural outdoor climate. The study showed very little differences in temperature and relative humidity in the cold ventilated attics, while the humidity class of the indoor climate significantly affects the absolute moisture content in the attic. However, the climate in the attic did not cause mould growth in the test sections, even for humidity class 3. Consequently, in the test building the thickness or hygroscopic properties of the insulation material did not have a significant effect on the moisture level in attics and did not determine whether a vapour barrier should be installed. In this study with the given climate, a vapour barrier is unnecessary in well-ventilated attics if the ceiling is airtight.
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