Page 46 - FDMAsia May/Jun 2026

44 MATERIALS MAY/JUN 2026 FDM ASIA | www.fdmasia.com

holzply.com Table 1. Characteristics of the three industrial panels
used in this study.
Nominal
Panel Panel Type Intended Mat Structure Adhesive Thickness
Code Use
(mm)
Three-layer
PB1 Particleboard Exterior (fine surface, PF 9.7
siding coarse core)
PB2 Particleboard Exterior Single-layer PF 12.1
siding (fine particles)
Outdoor
Medium- furniture, Homogeneous
MDF density exterior fibres pMDI 15.9
fibreboard
moulding

The vertical density profiles (VDPs) of the panels were
measured using X ray densitometry. Specimens measuring
50 mm × 50 mm were scanned across the panel thickness
at a spatial resolution of 0.01 mm.
For each VDP, three density parameters were obtained:

of 12.1 mm (1/2″) and consisted of a single layer of uniformly (i) mean density over the total panel thickness (average
distributed fine particles. density), (ii) maximum density in the surface layers (surface
Both particleboards were manufactured from a 50/50 density), and (iii) minimum density in the core layer zone (core
blend of softwood and hardwood particles and bonded with density). Twelve specimens from each panel type were used to
PF adhesive at the same adhesive content. PB1 and PB2 measure the VDPs. For each panel type, the VDP represents
are designed for siding applications, featuring one smooth the average profile calculated from all measured specimens.
face intended as the interior surface and one textured face Accelerated aging was conducted on the particleboards

with a distinctive embossed pattern created by the press caul and MDF panels according to the six cycle method specified
during manufacturing. in ASTM D1037 12 (2020), a standard aging test for mat
The textured face is intended to withstand weather exposure formed wood based panel products.
and serves as the exterior surface exposed to weathering in Each cycle consisted of the following sequential conditioning
service. It is important to note that in practical applications, steps: (1) immersion in water at 49 ± 2°C for 1 h, (2) exposure
the exterior surface is typically coated with a protective paint. to steam at 93 ± 3°C for 3 h, (3) freezing at –12 ± 3°C for
These uncoated particleboards exhibited a brown colour, 20 h, (4) oven drying in forced air at 99 ± 2°C for 3 h, (5)
resulting from PF reaction during hot pressing. re exposure to steam at 93 ± 3°C for 3 h, and (6) final oven
The MDF panel had a nominal thickness of 15.9 mm (5/8″) drying in forced air at 99 ± 2°C for 18 h.

and was manufactured from 100 percent softwood fibres and This six step sequence was repeated six times for all
bonded with pMDI adhesive. Due to proprietary considerations, samples subjected to accelerated aging. The overall duration
the manufacturer did not disclose detailed formulation parameters of the aging procedure was approximately three weeks. After
for any of the panels, including adhesive and wax contents, completion of the sixth cycle, all specimens were conditioned
particle/fibre size distribution, and the surface/core layer at 20 ± 3°C and 65 ± 2% relative humidity (RH) for at least
ratio in PB1. The principal characteristics of the panels are 48 h to reach equilibrium moisture conditions before testing.
summarised in Table 1. Residual thickness swelling (Residual TS) was measured to