Jennifer Elena

4. Discussion

50%

60%

70%

80%

90%

100%

ADP

AP

PED

EP

GWP

RI

S1-original scenario

analyzed

S2-reduce the stage

of drying

Figure 5. Analysis to reduce drying stage.

4.2.2. Change Technology in Gluing and Drying

The subsystems of compositing and drying exerted major impacts on all environmental categories

due to large releases of formaldehyde, NOX, SO2, CO2, and volatile organic compounds (Figure 2),

which come from waste materials and fossil oil combusted to generate heat to dry veneers before

gluing. New technologies can be tested to identify impacts on the environment. Gluing green wood is

a new technology that can be applied in plywood vacuum molding wherein veneer-composited wood

Int. J. Environ. Res. Public Health 2019, 16, 2037 8 of 10

in a green stage is glued without drying because it is vacuum-dried when pressure is applied to the

press [25]. This method reduces the number of subsystems in manufacturing and avoids release of free

formaldehyde and other noxious emissions during compositing and gluing. Figure 5 shows the results

of LCA for plywood production that can reduce the drying stage.

Int. J. Environ. Res. Public Health 2019, 16, x 8 of 10

(Figure 2), which come from waste materials and fossil oil combusted to generate heat to dry

veneers before gluing. New technologies can be tested to identify impacts on the environment.

Gluing green wood is a new technology that can be applied in plywood vacuum molding wherein

veneer-composited wood in a green stage is glued without drying because it is vacuum-dried when

pressure is applied to the press [25]. This method reduces the number of subsystems in

manufacturing and avoids release of free formaldehyde and other noxious emissions during

compositing and gluing. Figure 5 shows the results of LCA for plywood production that can reduce

the drying stage.

Figure 5. Analysis to reduce drying stage.

Results show that using the new technology of gluing green wood can promote improvements

in all impact categories, especially for GI, GWP, and AP, which were reduced by 38.96%, 34.18%,

and 33.18%, respectively. This new technology seems promising in decreasing the environmental

impacts of plywood. When reducing the drying stage, traditional internal recycling of waste

material (e.g., barks and edges) will be influenced. These forms of waste may represent a

gasification process to produce resultant gas that could be utilized to generate electricity and

process heat [26]. Compared with traditional combustion treatment, gasification could eliminate

approximately 90.0% of particulate material and 50.0% of NOX without releasing carbon monoxide.

5. Conclusions

This paper focuses on the environmental impact of plywood production in south China.

Several impact categories (ADP, AP, PED, EP, GWP, and RI) were assessed to obtain results and

serve as decision-making indicators to help the wood-based panel industry develop and introduce

alternatives in plywood processing to improve the environmental performance of production.

According to our results, in the process of plywood production, manufacturing of veneers in all raw

materials had the greatest impact on the environment, mainly attributed to the drying stage of the

veneer manufacturing process. The compositing stage was the largest contributor in all subsystems

to all impact categories for the environment, followed by log debarking due to fossil fuel

combustion as energy and bark waste. This study covers the plywood manufacturing process from

a cradle-to-gate perspective and analyzes each subsystem and raw material in the plywood

production process. To improve environmental performance, advanced technologies and green

materials can be used instead of traditional processes. In this study, we suggested that pyrolysis

bio-oil replace phenol (nonrenewable) to produce green phenolic resin to decrease contributions in

impact categories including GWP, PED, AP, and PM during the plywood manufacturing process,

especially to lessen the impacts of ADP and EP. In addition, the new technology of gluing green

50%

60%

70%

80%

90%

100%

ADP

AP

PED

EP

GWP

RI

S1-original scenario

analyzed

S2-reduce the stage

of drying

Figure 5. Analysis to reduce drying stage.

Results show that using the new technology of gluing green wood can promote improvements

in all impact categories, especially for GI, GWP, and AP, which were reduced by 38.96%, 34.18%,

and 33.18%, respectively. This new technology seems promising in decreasing the environmental

impacts of plywood. When reducing the drying stage, traditional internal recycling of waste material

(e.g., barks and edges) will be influenced. These forms of waste may represent a gasification process to

produce resultant gas that could be utilized to generate electricity and process heat [26]. Compared

with traditional combustion treatment, gasification could eliminate approximately 90.0% of particulate

material and 50.0% of NOX without releasing carbon monoxide.

5. Conclusions

This paper focuses on the environmental impact of plywood production in south China. Several

impact categories (ADP, AP, PED, EP, GWP, and RI) were assessed to obtain results and serve as

decision-making indicators to help the wood-based panel industry develop and introduce alternatives

in plywood processing to improve the environmental performance of production. According to our

results, in the process of plywood production, manufacturing of veneers in all raw materials had the

greatest impact on the environment, mainly attributed to the drying stage of the veneer manufacturing

process. The compositing stage was the largest contributor in all subsystems to all impact categories

for the environment, followed by log debarking due to fossil fuel combustion as energy and bark waste.

This study covers the plywood manufacturing process from a cradle-to-gate perspective and analyzes

each subsystem and raw material in the plywood production process. To improve environmental

performance, advanced technologies and green materials can be used instead of traditional processes.

In this study, we suggested that pyrolysis bio-oil replace phenol (nonrenewable) to produce green

phenolic resin to decrease contributions in impact categories including GWP, PED, AP, and PM during

the plywood manufacturing process, especially to lessen the impacts of ADP and EP. In addition, the

new technology of gluing green wood can reduce the veneer-drying stage and decrease NOX and

COX emissions generated by fossil fuel and waste wood (containing adhesive) combustion during

veneer production. This environmentally friendly technology can also decrease all impact categories,

especially RI, GWP, AP, and EP. Moreover, the location of the factory near a rich supply of quality

wood resources can control environmental impact substantially.

Int. J. Environ. Res. Public Health 2019, 16, 2037 9 of 10

Author Contributions: Conceptualization, L.J.; project administration, J.C.; formal analysis, L.M.; supervision,

X.Q.; visualization, A.K.

Funding: This research was funded by Jie Chu of Yang Ling science and technology plan project under grant

agreement No. 2017NY-04.

Conflicts of Interest: The authors declare no conflict of interest

emissions than traditional plywood

emissions than traditional plywoodWhen PF was replaced by up to 60%, impacts on plywood production decreased by 4.47% for ADP, 4.11% for EP, 2.74% for RI, 2.68% for GWP, and 1.67% for AP as shown in Figure 4. Replacing PF

resin can thus evoke environmental benefits, especially in terms of diminishing EP and ADP impacts.

Previous research on wood-based panels has found that using green bonding agents instead of PF to

produce HB elicited similar results as those in this study [24]. Therefore, renewable resources should

be encouraged to replace fossil energy to decrease impacts on ADP, EP, RI, GWP, and AP.

4.2.1. Change to Conventional Resin Consumption

In this study, petrochemical resins (phenolic) were used as adhesives in plywood production.

The preceding discussion suggests traditional resin as a hot spot for formaldehyde emissions. This

synthetic resin greatly influences primary environmental impact categories for two reasons: First, the

composition of PF is basically of fossil origin, especially phenol obtained from fossil resources due

to environmental factors related to the use of fossil fuels; and second, free formaldehyde is released

into the air during the subsystems of veneer compositing, gluing, and hot pressing [19–21]. Therefore,

we propose solutions to improve the environmental performance of plywood based on reducing

consumption of PF resin and replacing petroleum-based phenol with bio-oil produced by biomass

fast pyrolysis; such pyrolysis contains many phenolic compounds, such as phenol, guaiacol, and

4-methyl guaiacol that can be condensed with formaldehyde [22]. Sensitivity analyses were conducted

in five scenarios that simulate replaced percentages of PF resin in the plywood manufacturing process:

S1—original scenario in this study; S2—replace PF resin with 30% bio-oil; S3—replace PF resin with

40% bio-oil; S4—replace PF resin with 50% bio-oil; and S5—replace PF resin with 60% bio-oil. It is

found that replacing phenol with bio-oil can reach 60% under a catalyst loading of 1.25 g of NaOH;

results showed that dry shear strength and wet shear strength were comparable between pure PF and

bio-oil-PF for plywood. Additionally, plywood produced by bio-oil-PF emitted lower formaldehyde

emissions than traditional plywood

4.2. Perspectives on Improving Environmental Assessment

This section presents ways to reduce pollution in the plywood process based on analysis of alternate

scenarios and previous studies [5,17,18]. In this study, the three targets for environmental improvement

are adhesive components (i.e., adhesive based on bio-oil), veneer drying, and compositing.

The hot-pressing subsystem was responsible for a small share of impact categories (AP, PED,

EP, GWP, and RI), mainly due to the release of organic compounds, benzene, formaldehyde, CO2,

and SO2 [13,14]. However, some studies on wood-based panel manufacturing in other regions

revealed different results, namely a larger contribution to environmental impact compared to this

study [15]. As with the transportation of materials and products, this difference is mainly due to

uncertainty regarding the environmental impact of hot pressing, the extent of emissions from hot

pressing (depending on moisture content and veneer species), the type and amount of adhesive, and

aging time after gluing [16].

The compositing subsystem made the greatest contribution (more than 40%) to all impact

categories, followed by the drying subsystem at 22.4% (Figure 2). Composition of plywood panels

proceeds as follows: Glue-making, gluing, assembly, and aging. The main sources of emissions include

the gluing and aging processes, which release excessive amounts of formaldehyde and other hazardous

air pollutants.

4.1. Environmental Hotspot Analysis

In the preparation of all raw materials, veneer production presented the highest contribution to

all environmental categories (Figure 3). Veneer manufacturing consists of five main processes: Log

debarking, log cut-off, softening of logs, peeling the logs into veneers, and drying the veneers [12].

The first step of debarking by debarking machines represents remaining waste in the forest industry;

thus, the debarking subsystem was a primary contributor to all impact categories. Then, blocks were

heated to approximately 93 ◦C (200 ◦F) using various methods (e.g., hot water baths, steam heat,

and hot water spray with heat energy from diesel combustion). The log-softening stage was another

important step in the emissions of CO2, CO, NOx, formaldehyde, and volatile organic compounds,

especially in contributing to wastewater. When heating was completed, logs were processed to generate

veneers by a veneer lathe. Finally, veneers were taken from the clipper to a veneer dryer, where they

were dried to the required moisture content (between 6% and 15%). The veneer dryer acted as the main

emission pollution source because heat from fossil fuel and by-product (waste material) combustion

emits large quantities of organic compounds (e.g., CO2, CO, SO2, NOx, and formaldehyde) that greatly

influence GWP, PED, AP, and RI. The stages of log debarking and bucking release filterable particulate

matter of less than 10 micrometers in aerodynamic diameter (PM-10) along with organic compounds

(AP) from steaming and drying operations.

4. Discussion

The results of impact assessment indicated that veneer production and the subsystems of drying

and composting appeared to be the greatest contributors to environmental impact. Then, we conducted

a detailed analysis of these environmental hotspots to consider alternate scenarios.

An analysis of LCA for plywood production was carried out according to the CML 2 baseline 2000

V2.4 method to quantify environmental impacts of the manufacturing process [11]. The LCA software

eBalance (IKE, Chengdu, China) was used for environmental impact assessment. The total amount

Int. J. Environ. Res. Public Health 2019, 16, 2037 4 of 10

of life cycle inventory analysis (LCI) for each impact category can be calculated using the following

formula (1):

LCIi =

X

p

Sp× ∈ Vip(1) (1)

In the above formula, I denotes the list of substances in the life cycle of the product (e.g., wood

raw materials and water consumption); LCIi

, denotes the total quantity of in the product life cycle; P,

denotes a unit process in the product life cycle; inVip denotes the number of list I in a unit process P;

and Sp denotes the process P of the baseline stream by the given LCA.

Several impact categories were analyzed in this study: ADP, AP, PED, EP, GWP, and RI. Results of

the characterization step are displayed in Table 2.

Table 2. Impact assessment results (characterization step) of plywood manufacturing for 1 m3 of

finished plywood.

Impact Category Unit Value

ADP kg antimony eq.

* 2.90 × 10−1

EP kg PO3−

4

eq. 3.32 × 10

RI kg PM2.5 eq. 3.43 × 10

AP kg SO2 eq. 1.38 × 102

GWP Kg CO2 eq. 1.88 × 104

PED MJ 9.85 × 106

* Indicator for assessing product and measure unit.

To conduct an accurate LCA evaluation of plywood, we separated the processing of plywood

production and preparation of raw materials to analyze environmental impacts as shown in Figures 2

and 3.

Int. J. Environ. Res. Public Health 2019, 16, x 4 of 10

3. Results of Impact Assessment

An analysis of LCA for plywood production was carried out according to the CML 2 baseline

2000 V2.4 method to quantify environmental impacts of the manufacturing process [11]. The LCA

software eBalance (IKE, Chengdu, China) was used for environmental impact assessment. The total

amount of life cycle inventory analysis (LCI) for each impact category can be calculated using the

following formula (1):

𝐿𝐶𝐼௜ ൌ෍𝑆௣ ൈ∈ 𝑉௜௣

௣

ሺ1ሻ (1)

In the above formula，I denotes the list of substances in the life cycle of the product (e.g.,

wood raw materials and water consumption); LCIi, denotes the total quantity of in the product life

cycle; P, denotes a unit process in the product life cycle; inVip denotes the number of list I in a unit

process P; and Spdenotes the process P of the baseline stream by the given LCA.

Several impact categories were analyzed in this study: ADP, AP, PED, EP, GWP, and RI.

Results of the characterization step are displayed in Table 2.

Table 2. Impact assessment results (characterization step) of plywood manufacturing for 1 m3 of

finished plywood.

Impact Category Unit Value

ADP kg antimony eq. * 2.90 × 10−1

EP kg PO3−

4 eq. 3.32 × 10

RI kg PM2.5 eq. 3.43 × 10

AP kg SO2 eq. 1.38 × 102

GWP Kg CO2 eq. 1.88 × 104

PED MJ 9.85 × 106

* Indicator for assessing product and measure unit.

To conduct an accurate LCA evaluation of plywood, we separated the processing of plywood

production and preparation of raw materials to analyze environmental impacts as shown in Figures

2 and 3.

Figure 2.

Figure 2. Contribution per subsystem (in %) to each impact category.

Contribution per subsystem (in %) to each impact category.

Int. J. Environ. Res. Public Health 2019, 16, 2037 5 of 10 Int. J. Environ. Res. Public Health 2019, 16, x 5 of 10

Figure 3. Relative contributions of material production (%) to each impact category; veneer includes

debarking and drying stages.

3.1. Abiotic Depletion Potential (ADP)

As Figure 3 indicates, among all materials, veneer production was responsible for ADP

(86.53%). Among all plywood production processes, the subsystem of veneer compositing

accounted for the highest ADP contribution (82.36%); veneer composting includes resin making,

gluing, and aging. ADP is mainly caused by use of fossil fuels in the veneer-producing stage and

use of phenolic formaldehyde (PF) in the composting stage.

3.2. Acidification Potential (AP)

In plywood processing, drying and compositing were the most important contributors to AC

at 34.18% and 29.75%, respectively, followed by the plywood packing subsystem at 13.29% (Figure 2).

This result is largely due to NOX and SO2 emissions from the generation of heat energy and

electricity consumption. Veneer production contributed 73% to the AC in preparation of all raw

materials, mainly due to wastewater, combustion of waste wood, and fossil fuel.

3.3. Primary Energy Depletion (PED)

The debarking subsystem had the largest contribution to PED at 66.82%. Compositing and

drying were responsible for 15.27% and 9.63%, respectively. The PED of the system was primarily

caused by bark, representing remaining waste and other material waste as wood defects, such as

burrows, dead knots, and slipknots. Veneer production contributed 98.76% to PED, mainly due to

the consumption of fossil fuel and electricity.

3.4. Freshwater Eutrophication (EP)

PF resin was the main contributor to EP impact, causing the compositing subsystem to

contribute most to this impact category at 60.55%; this was followed by board drying (15.26%) and

debarking (11.13%). Veneer production was the main contributing sector to EP, with 78.23% of the

impact of all materials production on the environment (as shown in Figure 3), followed by curing

agents at 13.12%. This finding is mainly due to NOX emissions during energy production.

Figure 3. Relative contributions of material production (%) to each impact category; veneer includes

debarking and drying stages.

3.1. Abiotic Depletion Potential (ADP)

As Figure 3 indicates, among all materials, veneer production was responsible for ADP (86.53%).

Among all plywood production processes, the subsystem of veneer compositing accounted for the

highest ADP contribution (82.36%); veneer composting includes resin making, gluing, and aging. ADP

is mainly caused by use of fossil fuels in the veneer-producing stage and use of phenolic formaldehyde

(PF) in the composting stage.

3.2. Acidification Potential (AP)

In plywood processing, drying and compositing were the most important contributors to AC at

34.18% and 29.75%, respectively, followed by the plywood packing subsystem at 13.29% (Figure 2).

This result is largely due to NOX and SO2 emissions from the generation of heat energy and electricity

consumption. Veneer production contributed 73% to the AC in preparation of all raw materials, mainly

due to wastewater, combustion of waste wood, and fossil fuel.

3.3. Primary Energy Depletion (PED)

The debarking subsystem had the largest contribution to PED at 66.82%. Compositing and drying

were responsible for 15.27% and 9.63%, respectively. The PED of the system was primarily caused by

bark, representing remaining waste and other material waste as wood defects, such as burrows, dead

knots, and slipknots. Veneer production contributed 98.76% to PED, mainly due to the consumption of

fossil fuel and electricity.

3.4. Freshwater Eutrophication (EP)

PF resin was the main contributor to EP impact, causing the compositing subsystem to contribute

most to this impact category at 60.55%; this was followed by board drying (15.26%) and debarking

(11.13%). Veneer production was the main contributing sector to EP, with 78.23% of the impact of all

materials production on the environment (as shown in Figure 3), followed by curing agents at 13.12%.

This finding is mainly due to NOX emissions during energy production.

Int. J. Environ. Res. Public Health 2019, 16, 2037 6 of 10

3.5. Global Warming Potential (GWP)

The drying and compositing subsystems were responsible for GWP contributions of 33.18% and

33.68%, respectively. Veneer production was responsible for 76.41% of the impact category. CO2 was

emitted from the combustion of waste wood and fossil fuel for generating heat energy, chemicals,

and electricity.

3.6. Particulate Matter (RI)

The drying subsystem accounted for the largest contribution to the environmental profile at 38.96%.

Veneer production was responsible for 82.25%, followed by curing agent production (10.20%). Detailed

analysis of the RI considers emissions of PM2.5, NOX, and SO2. Two features warrant attention—the

contributions of fossil fuel and coal consumption in processes such as chemicals, electricity, and thermal

energy; and small amounts of RI were released from cutting and packing. Log debarking, log bucking,

and sawdust handling were additional sources of RI emissions.

All data in this study related to the input and outputs of plywood processing were obtained

via on-site measurements and investigation of the Eco-invent and CLCD databases. Data on

the consumption of materials, electricity, ancillary materials, water, and diesel came from on-site

measurements used in the database. Key data included the technology used for plywood production

and energy input and output per procedure.

Building a logical data processing method is also important for LCA assessment. Two data

selection criteria were applied in this study—when the contribution of single-material input and per

subsystem exceeds 0.001% of environmental impact, it cannot be neglected; and when the auxiliary

material quality is less than 0.01% of total raw material consumption, it can be ignore

The product system is detailed in Figurefigure 1 and includes the following main stages: raw material and

material tracking and cross-boundary energy flows The system boundaries in this study included what

occurred during production on-site along with off-site measurements, such as resources consumed in

energy production, raw material production, additives and transport, and electricity generation; these

features were partially collected and analyzed

1220 × 2440 mm2, and its approximate moisture content was 7%. This study covered the manufacturing life cycle of plywood from a cradle-to-gate perspective

and ignored background data for raw materials (internal) and data on products sales (external).

The product system is detailed in Figure 1 and includes the following main stages: raw material and

energy production, transport, plywood production, and waste disposal. Boundary setting facilitated

material tracking and cross-boundary energy flows

based on the LCA method as impact categories to identify hotspots.This paper used material from medium-sized plywood manufacturers in Suqian, Jiangsu Province,with an annual output of more than 600,000 m3 and fast-growing poplar as the wood species.

The appropriate function unit was defined as 1 m3 of product. The conventional size of the board was

1220 × 2440 mm2, and its approximate moisture content was 7%.