Wood: The Good, the Bad, and the “Neutral”
Hello, everyone. The unit I’m going to introduce to you today will focus on the good, the bad and neutrality of wood. This is a very meaningful unit, which will help you to have a new understanding of wood.
First of all, there are some limitations on the use of wood and the strength of wood itself. As a hygroscopic material, wood can absorb moisture according to the humidity of surrounding air. Therefore, the drying technology of wood is very important. Most wood is put into caves for high temperature drying. However, there is always a problem of warping when the wood is air-dried or dried. For example, if the wood is not fully dried or excessively dried in the kiln, it will warp when the wood comes into contact with the air. In addition, the uneven shrinkage caused by the sawing mode of wood and the inherent defects of wood will also lead to warpage. This is one of the limitations (Lesson 14 Part 1).
Secondly, wood is regarded as orthotropic material, so the strength of wood is different in longitudinal direction, tangential direction and radial direction. This also leads to the phenomenon that wood is easy to bend under the condition of uneven stress, and it is easy to break at the place where the stress is concentrated (Lesson 14 Part 2).
Besides the limitations of wood, wood itself has many advantages. According to relevant data, by 2050, our demand for wood will be twice that of today, which is why wood is becoming more and more important to us. As an essential material in our life, wood can be used for building and decorating buildings, printing and packaging paper products and generating energy. The following picture shows the wide range of uses of wood (Industry key to conserving forests as demand for wood projected to triple by 2050).
Our demand for paper is increasing, but few people pay attention to the source of paper and the specific demand for paper. By 2017, the global output of paper and paperboard is about 410 million tons. The figure below shows the global output of paper and paperboard from 1993 to 2017. We can see that the global output of paper and paperboard is increasing year by year (Lesson 16).
After understanding the global demand for paper, I will introduce how paper came into being. Generally, papermaking is mainly divided into three steps. Firstly, from the preparation of raw materials, the logs are peeled and cut into small pieces. When the required wood is ready, it can be pulped mechanically or chemically. And then bleaching the finished wood pulp and removing residual lignin. Finally, the wood pulp is consolidated on the paper machine (Lesson 16)
In the process of carbon cycle, trees will absorb carbon dioxide, but when they die, all the carbon dioxide stored in their bodies will be released back into the atmosphere. Therefore, I think wood also has certain neutrality. When a tree dies naturally, the carbon absorbed by it will release carbon dioxide with the degree of corrosion, which generally lasts for ten to twenty years; When wood is harvested as furniture, the carbon release in its body will depend on the service life of these furniture; When wood is burned as energy, the carbon dioxide absorbed in it will be instantly released back into the atmosphere. In addition, when wood is used as a building material, it can keep the absorbed carbon dioxide in its body for 100 to 200 years. However, no matter what the circumstances, the carbon dioxide absorbed by trees will eventually return to the atmosphere, which is only a matter of time. Therefore, I think that besides its advantages and disadvantages, wood also has certain neutrality (Lesson 17).
Work Cited
Lesson 14 (Part 1), Moisture Pertaining to Wood Use, BBE 1002, UMN
Lesson 14 (Part 2), Strength Requirements for Wood Use, BBE 1002, UMN
Lesson 16, Paper Products, BBE 1002, UMN
Lesson 17, Is Wood Good?, BBE 1002, UMN
Title: Industry key to conserving forests as demand for wood projected to triple by 2050
URL:https://fanyi.sogou.com/text?keyword=Industry%20key%20to%20conserving%20forests%20as%20demand%20for%20wood%20projected%20to%20triple%20by%202050%0A&transfrom=zh-CHS&transto=en&model=general
