LU102640B1 - A straw recombination integration material and its preparation method - Google Patents

Abstract

The present invention provides a straw recombined glulam and a method for preparing the same, which are used to solve the problems of complicated straw pretreatment, formaldehyde pollution of a board and a poor quality of the board in the prior art. The present invention provides a straw recombined glulam and a method for preparing the same, which uses an efficient straw pretreatment process, a non-polluting adhesive, and optimized sizing, paving, and hot pressing processes to obtain the straw recombined glulam with a high strength and a high hardness.

Description

Description A straw recombination integration material and its preparation method

TECHNICAL FIELD The present invention relates to the technical field of a water-based artificial board, and specifically, to a straw recombined glulam and a method for preparing the same.

BACKGROUND The artificial board industry is a resource-dependent industry based on forest resources. With a worldwide shortage of forest resources, the implementation of China’s natural forest protection projects and the increasingly prominent problems in population, energy, and environments, contradiction between wood supply and demand has intensified. China's artificial board industry will face a serious shortage of raw materials for a long time. Artificial boards has an increasing demand year by year, which makes the artificial boards using wood as the raw materials increasingly tight. China's forest resources are relatively scarce. With the rapid development of economy and society, the demand for wood continues to increase. In face of a huge wood demand gap, the development of wood conservation and substitution is an important measure.

China has abundant crop straw resources, especially corn stalks with an annual output of about 200 million tons. However, China has a low comprehensive crop stalk resource utilization rate, and most corn stalks are burned on a spot, which is not only harmful to environments but also causes serious pollution and serious waste of resources, and also affects traffic safety, social production and residents’ lives.

Under the background of increasingly tight wood resources and shortage of the raw materials for the artificial boards, using corn stalks, an important crop straw resource, for artificial board production can not only alleviate problems in supply and demand of the raw materials, but also achieve good economic, environmental and social benefits, which has great practical significance.

In the prior art, a corn stalk board is prepared by mainly using an outer diameter stalk skin part as raw materials, and a urea-formaldehyde resin as an adhesive.

Alternatively, with peeling and separation technology, the corn stalks are peeled, and straw husks are used as shaving raw materials. Larch tannin resin is used as an adhesive to manufacture the corn stalk boards.

However, the forgoing methods have the following disadvantages:

1. A peeling and separation process of corn stalk husks is complicated and has a low utilization rate, which increases costs of products;

2. Surfaces of the corn stalks mostly contain substances that are not conducive to gluing. If urea-formaldehyde resin or phenolic resin glue are used, it is difficult to obtain a satisfactory bonding strength. Further, there is a problem of formaldehyde pollution;

3. After straw scraps are processed, there are problems of different thicknesses, which affect strength of the board.

SUMMARY The technical solutions used to solve the forgoing problems is a straw recombined glulam and a method for preparing the same.

The present invention provides a method of preparing a straw recombined glulam, including the following steps: a step of pretreating straws of raw materials to form a core layer raw material and a surface layer raw material; a step of sizing the core layer raw material and the surface layer raw material, respectively; and a step of paving and hot pressing the core layer raw material and the surface layer raw material after sizing, to form the straw recombined glulam.

Preferably, the step of pretreating the straws of the raw materials to form the core layer raw material and the surface layer raw material includes:

Removing the straws of the raw materials, as well as leaves and roots of the straws of the raw materials, cutting the straws into sections to form spare straws; For softening treatment, using a sodium hydroxide solution to spray or steam the spare straws.

For combing treatment, rolling the softened straws until net-like straws are formed; For a drying process, drying the combed straw to form a surface layer raw material with a moisture content of 8-10% and a core layer raw material with a moisture content of 5-7%.

Preferably, when spraying, the amount of the sodium hydroxide solution is

1.5-2.0% of a dry weight of the straws after the softening treatment, and the sodium hydroxide solution has a mass concentration of 1%; When steaming the straws under a temperature of 90-95°C for 2-2.5 h, the sodium hydroxide solution has a mass concentration of 1%.

Preferably, the step of sizing the core layer raw material and the surface layer raw material respectively includes: Mixing evenly the core layer raw material and the surface layer raw material with the adhesive, respectively, wherein the amount of the adhesive is 8-10% of the mass of the core layer raw material or the surface layer raw material.

Preferably, the adhesive is prepared by mixing corn starch-based API glue and non-blocked PMDI.

Preferably, the corn starch-based API glue and the non-blocked PMDI have a mass ratio of 100:15-20. The corn starch-based API glue and the non-blocked PMDI were purchased from Jilin Chenlong Biomass Materials Co., Ltd.

Preferably, the adhesive is a larch bark powder modified phenolic resin adhesive.

Preferably, the larch bark powder modified phenolic resin adhesive contains 2% by mass of a dimethyl silicone oil and 1% by mass of a silane coupling agent.

The larch bark powder modified phenolic resin adhesive was purchased from Jilin Chenlong Biomass Materials Co., Ltd.

Preferably, the evenly mixing process uses a drum-type glue mixer and a ring-type glue mixer that are connected in series.

Preferably, the step of paving and hot pressing the core layer raw material and the surface layer raw material after sizing to form the straw recombined glulam includes: paving the surface layer raw material in equal amounts on both sides of the core layer raw material, wherein the surface layer raw material and the core layer raw material have a mass ratio of 0.75-0.85:1.

Preferably, the step of paving and hot pressing the core layer raw material and the surface layer raw material after sizing to form the straw recombined glulam includes: using a three-stage hot pressing method for hot pressing: The first stage has a pressure of 4.0MPa, a temperature of 145-150°C, and time of 10-12 min.

The second stage has a balanced pressure of 1.0MPa, a temperature of 145-150°C, and time of 2 min; The third stage has a balanced pressure of 0.5MPa, a temperature of 145-150°C, and time of 30 s.

The present invention also provides a straw recombined glulam, which is prepared by using the forgoing method for preparing the straw recombined glulam.

The present invention provides a straw recombined glulam and a method for preparing the same, which have the following advantages:

1. Using integrated preparation technology of stalks and scoops of a corn, which reduces a process flow and avoids process and cost problems caused by separation of the scoops.

2. Using starch-based API as a main agent and a non-blocked PMDI as a cross-linking agent to prepare an isocyanate adhesive, which is a reactive type adhesive and can react with active groups such as hydroxyl and carboxyl groups on surfaces of the straws to produce a better bonding strength, wherein the prepared straw recombined glulam has features of a high strength and a high density, and solves a problem of formaldehyde pollution caused by urea-formaldehyde and phenolic resin.

3. Using larch bark powder modified phenolic resin as an adhesive to solve a problem of a low bonding strength and a high formaldehyde emission of traditional outdoor corn stalk glulam.

4. The optimization of a combing process and sizing, paving, hot pressing and other processes of corn stalks overcomes the shortcomings of traditional adhesives such as a sticky board and a poor initial viscosity, and greatly improves production efficiency and product quality.

DESCRIPTION OF THE INVENTION In order to enable the person skilled in the art to better understand the technical solutions of the present invention, the present invention is further described in detail below in conjunction with specific embodiments.

Embodiment 1 This embodiment provides a straw recombined glulam and a method for preparing the same, including the following steps:

1. A step of pretreating straws of raw materials to form a core layer raw material and a surface layer raw material;

1.1 Removing the straws of the raw materials, as well as leaves and roots of the straws of the raw materials, cutting the straws into sections to form spare straws; Specifically, a circular saw can be used to cut off roots of corn stalks, remove leaves manually, and cut the corn stalks into straw sections of about 350 mm to form spare straws.

1.2. For softening treatment, using a sodium hydroxide solution to spray the spare straws. When spraying, the amount of the sodium hydroxide solution is 1.5% of a dry weight of the straws after the softening treatment, and the sodium hydroxide solution has a mass concentration of 1%.

The forgoing softening treatment of the straws prevents the damage to straw fibers due to brittleness when the straws are combed into net-like straws, thereby generating too much scraps.

1.3. For combing treatment, rolling the softened straws until the net-like straws are formed; Specifically, the softened straws are combed. After the corn straws are flattened by a crushing roller, the corn straws are further combed by a combing roller to form the net-like straws. The decomposed corn straws are sorted and treated to remove the finely divided materials, and the larger straws are again unraveled until the net-like straws are formed.

The combed straws are relatively soft, which is beneficial to paving a uniform and dense board blank. After hot pressing, a board has a relatively uniform density, a small internal stress, and high dimensional stability.

1.4. For a drying process, drying the combed straw to form a surface layer raw material with a moisture content of 8% and a core layer raw material with a moisture content of 5%.

Because a moisture content of the surface layer raw material is greater than that of the core layer raw material, in a hot pressing process, the surface layer raw material first contacts a pressing board. A temperature rises rapidly. Increasing the moisture content of the surface layer raw material is beneficial to heat transferred from a surface layer to a core layer, accelerates the temperature of the core layer temperature, and promotes curing of a core layer adhesive.

In addition, under action of high temperature steam, plastic and viscoelastic deformation of the straws are increased and hence are easy to be compressed. Fiber contact is closer, thereby reducing an internal stress, improving dimensional stability of the board, and increasing a static bending strength of the board.

2. A step of sizing the core layer raw material and the surface layer raw material, respectively: Mixing evenly the core layer raw material and the surface layer raw material with the adhesive, respectively, wherein the amount of the adhesive is 8% of the mass of the core layer raw material or the surface layer raw material.

The adhesive is prepared by mixing corn starch-based API glue and non-blocked PMDI. It should be understood that the forgoing corn starch-based API glue is used as a main agent, and the non-blocked PMDI is used as a cross-linking agent. The forgoing two substances can use commercially available products.

The forgoing isocyanate adhesive is a reactive adhesive, can react with active groups such as hydroxyl and carboxyl groups on surfaces of the straws to produce a better bonding strength.

The corn starch-based API glue and the non-blocked PMDI have a mass ratio of 100:15.

The forgoing adhesive solves the problem of formaldehyde pollution caused by urea-formaldehyde and phenolic resin.

The evenly mixing process uses a drum-type glue mixer and a ring-type glue mixer that are connected in series. That is, a mixture is first stirred by a drum-type glue mixer and then by a ring-type glue mixer.

Compared with manual mixing, this mixing method has a better mixing

H LU102640 effect and provides an internal bonding strength of the board.

3. À step of paving and hot pressing the core layer raw material and the surface layer raw material after sizing, to form the straw recombined glulam.

3.1. Paving the surface layer raw material in equal amounts on both sides of the core layer raw material, wherein the surface layer raw material and the core layer raw material have a mass ratio of 0.75:1.

The specific paving can be manually paving. A mold frame is used to control a width size. When paving, the mold frame is placed on a stainless steel backing board. The corn straws mixed with glue is well matched based on an even thickness and placed in the mold frame. A board blank has a flat surface that is compacted hard to make the board blank have a certain strength and transportation performance. Then, the mold frame is carefully removed, and the same stainless steel backing board is placed on an upper surface of the board blank. In order to facilitate air exhaust and prevent sticking of the board, a wire mesh equivalent to the size of a width of the board blank is placed between the upper and lower backing boards and the board blank, and is put into a press machine together with the board blank and the backing board during the hot pressing.

3.2 Using a three-stage hot pressing method for the hot pressing: The first stage has a pressure of 4.0MPa, a temperature of 145°C, and time of 10 min.

The second stage has a balanced pressure of 1.0MPa, a temperature of 150°C, and time of 2min; The third stage has a balanced pressure of 0.5MPa, a temperature of 145°C, and time of 30 s.

Preferably, the forgoing hot-pressed board is performed with preservation treatment, and artificial treatment is performed in a standard climate, so that the internal moisture content is moved until a balance is reached.

The forgoing straw recombined glulam is tested with a static bending strength, elastic modulus, compression resistance along grain, a screw holding force and impact toughness. The test results are shown in Table 1.

Embodiment 2 This embodiment provides a straw recombined glulam and a method for preparing the same, including the following steps:

1. A step of pretreating straws of raw materials to form a core layer raw material and a surface layer raw material;

1.1 Removing the straws of the raw materials, as well as leaves and roots of the straws of the raw materials, cutting the straws into sections to form spare straws;

Specifically, a circular saw can be used to cut off roots of corn stalks, remove leaves manually, and cut the corn stalks into straw sections of about 350 mm to form spare straws.

1.2. For softening treatment, using a sodium hydroxide solution to steam the spare straws. When steaming the straws under a temperature of 90°C for 2 h, the sodium hydroxide solution has a mass concentration of 1%.

The forgoing softening treatment of the straws prevents the damage to straw fibers due to brittleness when the straws are combed into net-like straws, thereby generating too much scraps.

1.3. For combing treatment, rolling the softened straws until the net-like straws are formed; Specifically, the softened straws are combed. After the corn straws are flattened by a crushing roller, the corn straws are further combed by a combing roller to form the net-like straws. The decomposed corn straws are sorted and treated to remove the finely divided materials, and the larger straws are again unraveled until the net-like straws are formed.

The combed straws are relatively soft, which is beneficial to paving a uniform and dense board blank. After hot pressing, a board has a relatively uniform density, a small internal stress, and high dimensional stability.

1.4. For a drying process, drying the combed straw to form a surface layer raw material with a moisture content of 10% and a core layer raw material with a moisture content of 7%.

Because a moisture content of the surface layer raw material is greater than that of the core layer raw material, which is conducive to reducing a thickness expansion rate of water absorption of a board material, in a hot pressing process, the surface layer raw material first contacts a pressing board. A temperature rises rapidly. Increasing the moisture content of the surface layer raw material is beneficial to heat transferred from a surface layer to a core layer, accelerates the temperature of the core layer temperature, and promotes curing of a core layer adhesive.

In addition, under action of high temperature steam, plastic and viscoelastic deformation of the straws are increased and hence are easy to be compressed. Fiber contact is closer, thereby reducing an internal stress, improving dimensional stability of the board, and increasing a static bending strength of the board.

2. The step of sizing the core layer material and the surface layer material respectively: Mixing evenly the core layer raw material and the surface layer raw material with the adhesive, respectively, wherein the amount of the adhesive is 10% of the mass of the core layer raw material or the surface layer raw material.

The adhesive is prepared by mixing corn starch-based API glue and non-blocked PMDI. It should be understood that the forgoing corn starch-based API glue is used as a main agent, and the non-blocked PMDI is used as a cross-linking agent. The forgoing two substances can use commercially available products.

The forgoing isocyanate adhesive is a reactive adhesive, can react with active groups such as hydroxyl and carboxyl groups on surfaces of the straws to produce a better bonding strength.

The corn starch-based API glue and the non-blocked PMDI have a mass ratio of 100:20.

The forgoing adhesive solves the problem of formaldehyde pollution caused by urea-formaldehyde and phenolic resin.

The evenly mixing process uses a drum-type glue mixer and a ring-type glue mixer that are connected in series. That is, a mixture is first stirred by a drum-type glue mixer and then by a ring-type glue mixer.

Compared with manual mixing, this mixing method has a better mixing effect and provides an internal bonding strength of the board.

3. A step of paving and hot pressing the core layer raw material and the surface layer raw material after sizing, to form the straw recombined glulam.

3.1. Paving the surface layer raw material in equal amounts on both sides of the core layer raw material, wherein the surface layer raw material and the core layer raw material have a mass ratio of 0.85:1.

The specific paving can be manually paving. À mold frame is used to control the width size. When paving, the mold frame is placed on a stainless steel backing board. The corn straws mixed with glue is well matched based on an even thickness and placed in the mold frame. À board blank has a flat surface that is compacted hard to make the board blank have a certain strength and transportation performance. Then, the mold frame is carefully removed, and the same stainless steel backing board is placed on an upper surface of the board blank. In order to facilitate air exhaust and prevent sticking of the board, a wire mesh equivalent to the size of a width of the board blank is placed between the upper and lower backing boards and the board blank, and is put into a press machine together with the board blank and the backing board during the hot pressing.

3.2 Using a three-stage hot pressing method for the hot pressing: The first stage has a pressure of 4.0MPa, a temperature of 150°C, and time of 12 min.

The second stage has a balanced pressure of 1.0MPa, a temperature of 150°C, and time of 2 min; The third stage has a balanced pressure of 0.5MPa, a temperature of

150°C, and time of 30 s.

Preferably, the forgoing hot-pressed board is performed with preservation treatment, and artificial treatment is performed in a standard climate, so that the internal moisture content is moved until a balance is reached.

The forgoing straw recombined glulam is tested with a static bending strength, elastic modulus, compression resistance along grain, a screw holding force and impact toughness. The test results are shown in Table 1.

Embodiment 3 This embodiment provides a straw recombined glulam and a method for preparing the same, including the following steps:

1. A step of pretreating straws of raw materials to form a core layer raw material and a surface layer raw material;

1.1 Removing the straws of the raw materials, as well as leaves and roots of the straws of the raw materials, cutting the straws into sections to form spare straws; Specifically, a circular saw can be used to cut off roots of corn stalks, remove leaves manually, and cut the corn stalks into straw sections of about 350 mm to form spare straws.

1.2. For softening treatment, using a sodium hydroxide solution to spray the spare straws. When spraying, the amount of the sodium hydroxide solution is 2.0% of a dry weight of the straws after the softening treatment, and the sodium hydroxide solution has a mass concentration of 1%.

The forgoing softening treatment of the straws prevents the damage to straw fibers due to brittleness when the straws are combed into net-like straws, thereby generating too much scraps.

1.3. For combing treatment, rolling the softened straws until the net-like straws are formed; Specifically, the softened straws are combed. After the corn straws are flattened by a crushing roller, the corn straws are further combed by a combing roller to form the net-like straws. The decomposed corn straws are sorted and treated to remove the finely divided materials, and the larger straws are again unraveled until the net-like straws are formed.

The combed straws are relatively soft, which is beneficial to paving a uniform and dense board blank. After hot pressing, a board has a relatively uniform density, a small internal stress, and high dimensional stability.

1.4. For a drying process, drying the combed straw to form a surface layer raw material with a moisture content of 9% and a core layer raw material with a moisture content of 6%.

Because a moisture content of the surface layer raw material is greater than that of the core layer raw material, which is conducive to reducing a thickness expansion rate of water absorption of a board material, in a hot pressing process, the surface layer raw material first contacts a pressing board. A temperature rises rapidly. Increasing the moisture content of the surface layer raw material is beneficial to heat transferred from a surface layer to a core layer, accelerates the temperature of the core layer temperature, and promotes curing of a core layer adhesive.

In addition, under action of high temperature steam, plastic and viscoelastic deformation of the straws are increased and hence are easy to be compressed. Fiber contact is closer, thereby reducing an internal stress, improving dimensional stability of the board, and increasing a static bending strength of the board.

2. A step of sizing the core layer raw material and the surface layer raw material, respectively: Mixing evenly the core layer raw material and the surface layer raw material with the adhesive, respectively, wherein the amount of the adhesive is 9% of the mass of the core layer raw material or the surface layer raw material.

The adhesive is prepared by mixing corn starch-based API glue and non-blocked PMDI. It should be understood that the forgoing corn starch-based API glue is used as a main agent, and the non-blocked PMDI is used as a cross-linking agent. The forgoing two substances can use commercially available products.

The forgoing isocyanate adhesive is a reactive adhesive, can react with active groups such as hydroxyl and carboxyl groups on surfaces of the straws to produce a better bonding strength.

The corn starch-based API glue and the non-blocked PMDI have a mass ratio of 100:17.

The forgoing adhesive solves the problem of formaldehyde pollution caused by urea-formaldehyde and phenolic resin.

The evenly mixing process uses a drum-type glue mixer and a ring-type glue mixer that are connected in series. That is, a mixture is first stirred by a drum-type glue mixer and then by a ring-type glue mixer.

Compared with manual mixing, this mixing method has a better mixing effect and provides an internal bonding strength of the board.

3. A step of paving and hot pressing the core layer raw material and the surface layer raw material after sizing, to form the straw recombined glulam.

3.1. Paving the surface layer raw material in equal amounts on both sides of the core layer raw material, wherein the surface layer raw material and the core layer raw material have a mass ratio of 0.8:1.

The specific paving can be manually paving. A mold frame is used to control the width size. When paving, the mold frame is placed on a stainless steel backing board. The corn straws mixed with glue is well matched based on an even thickness and placed in the mold frame. A board blank has a flat surface that is compacted hard to make the board blank have a certain strength and transportation performance. Then, the mold frame is carefully removed, and the same stainless steel backing board is placed on an upper surface of the board blank. In order to facilitate air exhaust and prevent sticking of the board, a wire mesh equivalent to the size of a width of the board blank is placed between the upper and lower backing boards and the board blank, and is put into a press machine together with the board blank and the backing board during the hot pressing.

3.2 Using a three-stage hot pressing method for the hot pressing: The first stage has a pressure of 4.0MPa, a temperature of 145°C, and time of 11 min.

The second stage has a balanced pressure of 1.0MPa, a temperature of 145°C, and time of 2 min; The third stage has a balanced pressure of 0.5MPa, a temperature of 145°C, and time of 30 s.

Preferably, the forgoing hot-pressed board is performed with preservation treatment, and artificial treatment is performed in a standard climate, so that the internal moisture content is moved until a balance is reached.

The forgoing straw recombined glulam is tested with a static bending strength, elastic modulus, compression resistance along grain, a screw holding force and impact toughness. The test results are shown in Table 1.

Embodiment 4 This embodiment provides a straw recombined glulam and a method for preparing the same, including the following steps:

1. A step of pretreating straws of raw materials to form a core layer raw material and a surface layer raw material;

1.1 Removing the straws of the raw materials, as well as leaves and roots of the straws of the raw materials, cutting the straws into sections to form spare straws; Specifically, a circular saw can be used to cut off roots of corn stalks, remove leaves manually, and cut the corn stalks into straw sections of about 350 mm to form spare straws.

1.2. For softening treatment, using a sodium hydroxide solution to steam the spare straws. When steaming the straws under a temperature of 95°C for

2.5 h, the sodium hydroxide solution has a mass concentration of 1%.

The forgoing softening treatment of the straws prevents the damage to straw fibers due to brittleness when the straws are combed into net-like straws, thereby generating too much scraps.

1.3. For combing treatment, rolling the softened straws until the net-like straws are formed; Specifically, the softened straws are combed. After the corn straws are flattened by a crushing roller, the corn straws are further combed by a combing roller to form the net-like straws. The decomposed corn straws are sorted and treated to remove the finely divided materials, and the larger straws are again unraveled until the net-like straws are formed.

The combed straws are relatively soft, which is beneficial to paving a uniform and dense board blank. After hot pressing, a board has a relatively uniform density, a small internal stress, and high dimensional stability.

1.4. For a drying process, drying the combed straw to form a surface layer raw material with a moisture content of 9% and a core layer raw material with a moisture content of 7%.

Because a moisture content of the surface layer raw material is greater than that of the core layer raw material, which is conducive to reducing a thickness expansion rate of water absorption of a board material, in a hot pressing process, the surface layer raw material first contacts a pressing board. A temperature rises rapidly. Increasing the moisture content of the surface layer raw material is beneficial to heat transferred from a surface layer to a core layer, accelerates the temperature of the core layer temperature, and promotes curing of a core layer adhesive.

In addition, under action of hign temperature steam, plastic and viscoelastic deformation of the straws are increased and hence are easy to be compressed. Fiber contact is closer, thereby reducing an internal stress, improving dimensional stability of the board, and increasing a static bending strength of the board.

2. A step of sizing the core layer raw material and the surface layer raw material, respectively: Mixing evenly the core layer raw material and the surface layer raw material with the adhesive, respectively, wherein the amount of the adhesive is 10% of the mass of the core layer raw material or the surface layer raw material.

The adhesive is prepared by mixing corn starch-based API glue and non-blocked PMDI. It should be understood that the forgoing corn starch-based API glue is used as a main agent, and the non-blocked PMDI is used as a cross-linking agent. The forgoing two substances can use commercially available products.

The forgoing isocyanate adhesive is a reactive adhesive, can react with active groups such as hydroxyl and carboxyl groups on surfaces of the straws to produce a better bonding strength.

The corn starch-based API glue and the non-blocked PMDI have a mass ratio of 100:18.

The forgoing adhesive solves the problem of formaldehyde pollution caused by urea-formaldehyde and phenolic resin.

The evenly mixing process uses a drum-type glue mixer and a ring-type glue mixer that are connected in series. That is, a mixture is first stirred by a drum-type glue mixer and then by a ring-type glue mixer.

Compared with manual mixing, this mixing method has a better mixing effect and provides an internal bonding strength of the board.

3. A step of paving and hot pressing the core layer raw material and the surface layer raw material after sizing, to form the straw recombined glulam.

3.1. Paving the surface layer raw material in equal amounts on both sides of the core layer raw material, wherein the surface layer raw material and the core layer raw material have a mass ratio of 0.78:1.

The specific paving can be manually paving, and the mold frame is used to control the width size. When paving, the mold frame is placed on the stainless steel backing board, and the thickness of the glued corn straw is evenly matched and placed in the mold frame. The surface should be flat and compacted hard to make the board blank have a certain strength and transportation performance. Then, the mold frame is carefully removed, and the same stainless steel backing board is placed on an upper surface of the board blank. In order to facilitate air exhaust and prevent sticking of the board, a wire mesh equivalent to the size of a width of the board blank is placed between the upper and lower backing boards and the board blank, and is put into a press machine together with the board blank and the backing board during the hot pressing.

3.2 Using a three-stage hot pressing method for the hot pressing: The first stage has a pressure of 4.0MPa, a temperature of 150°C, and time of 12 min.

The second stage has a balanced pressure of 1.0MPa, a temperature of 148°C, and time of 2 min; The third stage has a balanced pressure of 0.5MPa, a temperature of 147°C, and time of 30 s.

Preferably, the forgoing hot-pressed board is performed with preservation treatment, and artificial treatment is performed in a standard climate, so that the internal moisture content is moved until a balance is reached.

The forgoing straw recombined glulam is tested with a static bending strength, elastic modulus, compression resistance along grain, a screw holding force and impact toughness. The test results are shown in Table 1.

Embodiment 5 This embodiment provides a straw recombined glulam and a method for preparing the same, including the following steps:

1. A step of pretreating straws of raw materials to form a core layer raw material and a surface layer raw material;

1.1 Removing the straws of the raw materials, as well as leaves and roots of the straws of the raw materials, cutting the straws into sections to form spare straws; Specifically, a circular saw can be used to cut off roots of corn stalks, remove leaves manually, and cut the corn stalks into straw sections of about 350 mm to form spare straws.

1.2. For softening treatment, using a sodium hydroxide solution to steam the spare straws. When steaming the straws under a temperature of 92°C for

2.2 h, the sodium hydroxide solution has a mass concentration of 1%.

The forgoing softening treatment of the straws prevents the damage to straw fibers due to brittleness when the straws are combed into net-like straws, thereby generating too much scraps.

1.3. For combing treatment, rolling the softened straws until the net-like straws are formed; Specifically, the softened straws are combed. After the corn straws are flattened by a crushing roller, the corn straws are further combed by a combing roller to form the net-like straws. The decomposed corn straws are sorted and treated to remove the finely divided materials, and the larger straws are again unraveled until the net-like straws are formed.

The combed straws are relatively soft, which is beneficial to paving a uniform and dense board blank. After hot pressing, a board has a relatively uniform density, a small internal stress, and high dimensional stability.

1.4. For a drying process, drying the combed straw to form a surface layer raw material with a moisture content of 9% and a core layer raw material with a moisture content of 7%.

Because a moisture content of the surface layer raw material is greater than that of the core layer raw material, which is conducive to reducing a thickness expansion rate of water absorption of a board material, in a hot pressing process, the surface layer raw material first contacts a pressing board. A temperature rises rapidly. Increasing the moisture content of the surface layer raw material is beneficial to heat transferred from a surface layer to a core layer, accelerates the temperature of the core layer temperature, and promotes curing of a core layer adhesive.

In addition, under action of high temperature steam, plastic and viscoelastic deformation of the straws are increased and hence are easy to be compressed. Fiber contact is closer, thereby reducing an internal stress, improving dimensional stability of the board, and increasing a static bending strength of the board.

2. A step of sizing the core layer raw material and the surface layer raw material, respectively: Mixing evenly the core layer raw material and the surface layer raw material with the adhesive, respectively, wherein the amount of the adhesive is 10% of the mass of the core layer raw material or the surface layer raw material.

The adhesive is prepared by mixing corn starch-based API glue and non-blocked PMDI. It should be understood that the forgoing corn starch-based API glue is used as a main agent, and the non-blocked PMDI is used as a cross-linking agent. The forgoing two substances can use commercially available products.

The forgoing isocyanate adhesive is a reactive adhesive, can react with active groups such as hydroxyl and carboxyl groups on surfaces of the straws to produce a better bonding strength.

The corn starch-based API glue and the non-blocked PMDI have a mass ratio of 100:16.

The forgoing adhesive solves the problem of formaldehyde pollution caused by urea-formaldehyde and phenolic resin.

The evenly mixing process uses a drum-type glue mixer and a ring-type glue mixer that are connected in series. That is, a mixture is first stirred by a drum-type glue mixer and then by a ring-type glue mixer.

Compared with manual mixing, this mixing method has a better mixing effect and provides an internal bonding strength of the board.

3. À step of paving and hot pressing the core layer raw material and the surface layer raw material after sizing, to form the straw recombined glulam.

3.1. Paving the surface layer raw material in equal amounts on both sides of the core layer raw material, wherein the surface layer raw material and the core layer raw material have a mass ratio of 0.82:1.

The specific paving can be manually paving, and the mold frame is used to control the width size. When paving, the mold frame is placed on the stainless steel backing board, and the thickness of the glued corn straw is evenly matched and placed in the mold frame. The surface should be flat and compacted hard to make the board blank have a certain strength and transportation performance. Then, the mold frame is carefully removed, and the same stainless steel backing board is placed on an upper surface of the board blank. In order to facilitate air exhaust and prevent sticking of the board, a wire mesh equivalent to the size of a width of the board blank is placed between the upper and lower backing boards and the board blank, and is put into a press machine together with the board blank and the backing board during the hot pressing.

3.2 Using a three-stage hot pressing method for the hot pressing: The first stage has a pressure of 4.0MPa, a temperature of 147°C, and time of 12 min.

The second stage has a balanced pressure of 1.0MPa, a temperature of 147°C, and time of 2 min; The third stage has a balanced pressure of 0.5MPa, a temperature of 147°C, and time of 30 s.

Embodiment 6 This embodiment provides a straw recombined glulam and a method for preparing the same, including the following steps:

1. A step of pretreating straws of raw materials to form a core layer raw material and a surface layer raw material;

1.1 Removing the straws of the raw materials, as well as leaves and roots of the straws of the raw materials, cutting the straws into sections to form spare straws; Specifically, a circular saw can be used to cut off roots of corn stalks, remove leaves manually, and cut the corn stalks into straw sections of about 350 mm to form spare straws.

1.2. For softening treatment, using a sodium hydroxide solution to steam the spare straws. When steaming the straws under a temperature of 92°C for

2.2 h, the sodium hydroxide solution has a mass concentration of 1%.

The forgoing softening treatment of the straws prevents the damage to straw fibers due to brittleness when the straws are combed into net-like straws, thereby generating too much scraps.

1.3. For combing treatment, rolling the softened straws until the net-like straws are formed; Specifically, the softened straws are combed. After the corn straws are flattened by a crushing roller, the corn straws are further combed by a combing roller to form the net-like straws. The decomposed corn straws are sorted and treated to remove the finely divided materials, and the larger straws are again unraveled until the net-like straws are formed.

The combed straws are relatively soft, which is beneficial to paving a uniform and dense board blank. After hot pressing, a board has a relatively uniform density, a small internal stress, and high dimensional stability.

1.4. For a drying process, drying the combed straw to form a surface layer raw material with a moisture content of 9% and a core layer raw material with a moisture content of 7%.

Because a moisture content of the surface layer raw material is greater than that of the core layer raw material, which is conducive to reducing a thickness expansion rate of water absorption of a board material, in a hot pressing process, the surface layer raw material first contacts a pressing board. A temperature rises rapidly. Increasing the moisture content of the surface layer raw material is beneficial to heat transferred from a surface layer to a core layer, accelerates the temperature of the core layer temperature, and promotes curing of a core layer adhesive.

In addition, under action of high temperature steam, plastic and viscoelastic deformation of the straws are increased and hence are easy to be compressed. Fiber contact is closer, thereby reducing an internal stress, improving dimensional stability of the board, and increasing a static bending strength of the board.

2. A step of sizing the core layer raw material and the surface layer raw material, respectively: Mixing evenly the core layer raw material and the surface layer raw material with the adhesive, respectively, wherein the amount of the adhesive is 10% of the mass of the core layer raw material or the surface layer raw material.

The larch bark powder modified phenolic resin was purchased from Jilin Chenlong Biomass Materials Co., Ltd. The larch bark powder modified phenolic resin is prepared according to the following method:

1. Using larch as a main raw material and mineral acid (for example, hydrochloric acid) as a catalyst, liquefying a larch bark powder with phenol, and using an obtained product to replace part of phenol to prepare a modified phenolic resin adhesive;

2. There is a thin layer of silicate and wax on surfaces of corn stalks. Conventional phenolic resin has no penetrating power on this layer of film, and hence is difficult to form an effective gluing. However, the larch bark powder modified phenolic resin adhesive has a smaller molecular weight, which can penetrate surface films of the corn stalks to form an effective gluing; In this embodiment, 2% by mass of dimethyl silicone oil and 1% by mass of silane coupling agent are added to the larch bark powder modified phenolic resin adhesive, which can further improve bonding performance of a corn stalk recombined material.

The forgoing larch bark powder modified phenolic resin solves problems of a low bonding strength and a high formaldehyde emission of a traditional outdoor corn stalk glulam. The evenly mixing process uses a drum-type glue mixer and a ring-type glue mixer that are connected in series. That is, a mixture is first stirred by a drum-type glue mixer and then by a ring-type glue mixer.

Compared with manual mixing, this mixing method has a better mixing effect and provides an internal bonding strength of the board.

3. À step of paving and hot pressing the core layer raw material and the surface layer raw material after sizing, to form the straw recombined glulam.

3.1. Paving the surface layer raw material in equal amounts on both sides of the core layer raw material, wherein the surface layer raw material and the core layer raw material have a mass ratio of 0.82:1.

The specific paving can be manually paving, and the mold frame is used to control the width size. When paving, the mold frame is placed on the stainless steel backing board, and the thickness of the glued corn straw is evenly matched and placed in the mold frame. The surface should be flat and compacted hard to make the board blank have a certain strength and transportation performance. Then, the mold frame is carefully removed, and the same stainless steel backing board is placed on an upper surface of the board blank. In order to facilitate air exhaust and prevent sticking of the board, a wire mesh equivalent to the size of a width of the board blank is placed between the upper and lower backing boards and the board blank, and is put into a press machine together with the board blank and the backing board during the hot pressing.

3.2 Using a three-stage hot pressing method for the hot pressing: The first stage has a pressure of 4.0MPa, a temperature of 147°C, and time of 12 min.

The second stage has a balanced pressure of 1.0MPa, a temperature of 147°C, and time of 2 min; The third stage has a balanced pressure of 0.5MPa, a temperature of 147°C, and time of 30 s.

Preferably, the forgoing hot-pressed board is performed with preservation treatment, and artificial treatment is performed in a standard climate, so that the internal moisture content is moved until a balance is reached.

The forgoing straw recombined glulam is tested with a static bending strength, elastic modulus, compression resistance along grain, a screw holding force and impact toughness. A test method refers to requirements of an ordinary board used under a dry state based on the national standard GB/T

4897.2-2003 "Shaving Board". The followings are provided: Test results are shown in Table 1.

Table 1 Comparison table of test results of products prepared in Embodiments 1-6 and commercially available products Static bending Elastic Compression Screw Impact Serial numbers| strength modulus [resistance along [holding force| toughness (MPa) (Mpa) grain (MPa) (IN) (KJ/m?2) Erholen 1 wo ff [0 Embodiment 5 [72 8300 51 1300 156 pee pw wom Commercially [40 5000 35 130 available products It can be seen from Table 1 that the straw recombined glulam prepared in the embodiments of the present application is superior to the commercially available straw recombined glulam in many indicators, and has features of a high strength and a high hardness.

It can be understood that the forgoing implementations are merely exemplary implementations used to illustrate the principle of the present invention, but the present invention is not limited thereto. For the person skilled in the art, various modifications and improvements can be made without departing from the spirit and essence of the present invention, and these modifications and improvements are also regarded as the protection scope of the present invention.

Claims (12)

1. A method of preparing a straw recombined glulam, comprising the following steps: a step of pretreating straws of raw materials to form a core layer raw material and a surface layer raw material; a step of sizing the core layer raw material and the surface layer raw material, respectively; and a step of paving and hot pressing the core layer raw material and the surface layer raw material after sizing, to form the straw recombined glulam.

2. The method for preparing the straw recombined glulam according to claim 1, wherein the step of pretreating the straws of the raw materials to form the core layer raw material and the surface layer raw material comprises: removing the straws of the raw materials, as well as leaves and roots of the straws of the raw materials, cutting the straws into sections to form spare straws; for softening treatment, using a sodium hydroxide solution to spray or steam the spare straws; for combing treatment, rolling the softened straws until net-like straws are formed;

for a drying process, drying the combed straw to form a surface layer raw material with a moisture content of 8-10% and a core layer raw material with a moisture content of 5-7%.

3. The method for preparing the straw recombined glulam according to claim 2, wherein when spraying, the amount of the sodium hydroxide solution is 1.5-2.0% of a dry weight of the straws after the softening treatment, and the sodium hydroxide solution has a mass concentration of 1%; when steaming the straws under a temperature of 90-95°C for 2-2.5 h, the sodium hydroxide solution has a mass concentration of 1%.

4. The method for preparing the straw recombined glulam according to claim 1, wherein the step of sizing the core layer raw material and the surface layer raw material respectively comprises: mixing evenly the core layer raw material and the surface layer raw material with the adhesive, respectively, wherein the amount of the adhesive is 8-10% of the mass of the core layer raw material or the surface layer raw material.

5. The method for preparing the straw recombined glulam according to claim 4, wherein the adhesive is prepared by mixing corn starch-based API glue and non-blocked PMDI.

6. The method for preparing the straw recombined glulam according to claim 5, wherein the corn starch-based API glue and the non-blocked PMDI have a mass ratio of 100:15-20.

7. The method for preparing the straw recombined glulam according to claim 4, wherein the adhesive is a larch bark powder modified phenolic resin adhesive.

8. The method for preparing the straw recombined glulam according to claim 7, wherein preferably, the larch bark powder modified phenolic resin adhesive contains 2% by mass of a dimethyl silicone oil and 1% by mass of a silane coupling agent.

9. The method for preparing the straw recombined glulam according to claim 4, wherein the evenly mixing process uses a drum-type glue mixer and a ring-type glue mixer that are connected in series.

10. The method for preparing the straw recombined glulam according to claim 1, wherein the step of paving and hot pressing the core layer raw material and the surface layer raw material after sizing to form the straw recombined glulam comprises: paving the surface layer raw material in equal amounts on both sides of the core layer raw material, the surface layer raw material and the core layer raw material have a mass ratio of 0.75-0.85:1.

11. The method for preparing the straw recombined glulam according to claim 1, wherein the step of paving and hot pressing the core layer raw material and the surface layer raw material after sizing to form the straw recombined glulam comprises: using a three-stage hot pressing method for hot pressing: the first stage has a pressure of 4.0MPa, a temperature of 145-150°C, and time of 10-12 min; the second stage has a balanced pressure of 1.0MPa, a temperature of 145-150°C, and time of 2 min; the third stage has a balanced pressure of 0.5MPa, a temperature of 145-150°C, and time of 30 s.

12. A straw recombined glulam, which is prepared by using a method for preparing the straw recombined glulam according to any one of claims 1-11.