The sandwich-structured composites comprising a RH core
sandwiched between the randomly aligned wood strand faces were
manufactured in the laboratory conditions, using standardized procedures
that simulated industrial production. The wood strands
forming the surface layers of the sandwich-structured composite
were placed in a drum blender. The PF resin was then sprayed onto
blending the particles with pneumatic nozzles and blended for
5 min at ambient temperature to obtain a homogenized mixture.
The RH particles forming the core layer of the particleboard were
separately resined with the PF resin in a box using an air atomized
metered spray system for 5 min. The RH particles (core) and wood
strands (face layers) for three-layer boards were separately weighed
and distributed evenly by hand into a 300 mm 300 mm forming
box. The layer construction of the experimental boards are presented
in Table 1. Release agent was used to avoid direct contact
of the wood strands with the steel caul plates during heating and
pressing. The hand formed mats comprising a core layer of the RH
particles sandwiched between the randomly aligned the wood
strand layers were cold pressed at 1 N/mm2 for 1 min to ensure
the stability of the mat and to reduce mat height prior to the hotpressing.
The mats were then subjected to the hot-pressing process,
using a manually controlled, electrically heated press. The mats
were pressed into the 10 mm thick boards using 2.5 N/mm2 at
180 C press temperature and 7 min hot-press time. To achieve
complete cure of the PF resin in the core, the curing time (7 min)
and temperature (180 C) were determined according to the results
of the pre-experiments for all types of boards and curing properties
of the PF resin. The boards were then trimmed to a final size of
280 mm 280 mm after the cooling process. A total of 12 particleboards,
two for each type of formulation and controls, were manufactured
(Table 1). The average density values of the panels varied